diff --git "a/P2P_astro-ph.json" "b/P2P_astro-ph.json" new file mode 100644--- /dev/null +++ "b/P2P_astro-ph.json" @@ -0,0 +1,4002 @@ +[ + { + "text": "Imprints of deviations from the gravitational inverse-square law on the\n power spectrum of mass fluctuations: Deviations from the gravitational inverse-square law would imprint\nscale-dependent features on the power spectrum of mass density fluctuations. We\nmodel such deviations as a Yukawa-like contribution to the gravitational\npotential and discuss the growth function in a mixed dark matter model with\nadiabatic initial conditions. Evolution of perturbations is considered in\ngeneral non-flat cosmological models with a cosmological constant, and an\nanalytical approximation for the growth function is provided. The coupling\nbetween baryons and cold dark matter across recombination is negligibly\naffected by modified gravity physics if the proper cutoff length of the\nlong-range Yukawa-like force is > 10 h^{-1} Mpc. Enhancement of gravity affects\nthe subsequent evolution, boosting large-scale power in a way that resembles\nthe effect of a lower matter density. This phenomenon is almost perfectly\ndegenerate in power-spectrum shape with the effect of a background of massive\nneutrinos. Back-reaction on density growth from a modified cosmic expansion\nrate should however also affect the normalization of the power spectrum, with a\nshape distortion similar to the case of a non-modified background.", + "category": "astro-ph" + }, + { + "text": "A New Weak Lensing Analysis of MS1224.7+2007: Galaxy cluster mass distributions are useful probes of Omega_0 and the nature\nof the dark matter. Large clusters will distort the observed shapes of\nbackground galaxies through gravitational lensing allowing the measurement of\nthe cluster mass distributions. For most cases, the agreement between weak\nlensing and radial velocity mass measurements of clusters is reasonably good.\nThere is, however, one significant exception, the z=0.32 cluster MS1224.7+2007,\nwhich has a lensing mass substantially larger than the virial mass and also a\nvery high mass-to-light ratio. Since this controversial object might be an\nunusually dark mass a follow-up study is definitely warranted. In this paper we\nstudy the mass and light distributions of MS1224+2007 out to a projected radius\nof 800/h kpc by measuring the gravitationally-induced distortions of background\ngalaxies. We detect a shear signal in the background galaxies in the radial\nrange 27.5 arcsec < r < 275 arcsec at the 5.5 sigma level. The resultant mass\nmap exhibits a peak centered on the dominant cluster galaxy and strong evidence\nfor substructure which is even more strongly seen in the galaxy distribution.\nAssuming all the detected shear is due to mass at z=0.32 we find cluster\nmass-to-light ratio of M/L_R = 640 +/- 150. The mass profile is quite flat\ncompared to other clusters, disagreeing with a pseudo-singular isothermal\nsphere at the 95% confidence level. Our mass and M/L estimates are consistent\nwith the previous weak lensing result. The discrepancy between the lensing and\nvirial mass remains although it might be partially explained by subclustering\nand infall perpendicular to the line-of-site. This cluster remains a candidate\ndark object deficient in baryons and as such severely tests cosmological\nmodels.", + "category": "astro-ph" + }, + { + "text": "Spherical Gravitational Collapse of Annihilating Dark Matter and the\n Minimum Mass of CDM Black Holes: Spherical gravitational collapse of a cold gas of annihilating particles\ninvolves a competition between the free-fall rate $\\propto\\sqrt{\\rho}$ and the\n(s-wave) annihilation rate $\\propto\\rho$. Thus, there is a critical density\n$\\rhoann$ above which annihilation proceeds faster than free fall.\nGravitational collapse of a cloud of (initial) mass $M$ to a black hole is only\npossible if $3/32\\pi G^3M^2\\lesssim\\rhoann$, or $M\\gtrsim\\Mann\\equiv (3/32\\pi\nG^3\\rhoann)^{1/2}$. For a particle mass $m$ and freeze-out temperature\n$T_f=m/x_f$, the minimum black hole mass is $\\Mann\\approx 10^{10}\\msun\n\\times(x_f\\sqrt{g_\\star}/100\\omcdm g_{\\star S}m({\\rm Gev}))$, where $g_{\\star\nS}$ and $g_\\star$ are degeneracy factors. The formation of a black hole of\ninitial mass $M_{BH}$ is accompanied by the annihilation of about $M_{ann}$\nreleased in a burst lasting a time $\\sim GM_{BH}$ that could reach a total\nannihilation luminosity $\\sim 10^{59} {\\rm erg s^{-1}}$. The absence of\nastronomical observations of such spectacular events suggests either: (i) the\nbranching ratio for CDM annihilation to $e^{+}e^{-}$ pairs or quarks $\\lesssim\n10^{-10}$, while the branching ratio to $\\nu{\\bar{\\nu}}$ is $\\lesssim 10^{-5}$;\nor (ii) CDM is not made of annihilating particles, but may be in some\nnon-annihilating form, such as axions; or (iii) CDM black holes never form.", + "category": "astro-ph" + }, + { + "text": "An outflow powers the optical rise of the nearby, fast-evolving tidal\n disruption event AT2019qiz: At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to\ndate, with a luminosity intermediate between the bulk of the population and\niPTF16fnl. Its proximity allowed a very early detection and triggering of\nmultiwavelength and spectroscopic follow-up well before maximum light. The\nvelocity dispersion of the host galaxy and fits to the TDE light curve indicate\na black hole mass $\\approx 10^6$ M$_\\odot$, disrupting a star of $\\approx 1$\nM$_\\odot$. Comprehensive UV, optical and X-ray data shows that the early\noptical emission is dominated by an outflow, with a luminosity evolution $L\n\\propto t^2$, consistent with a photosphere expanding at constant velocity\n($\\gtrsim 2000$ km s$^{-1}$), and a line-forming region producing initially\nblueshifted H and He II profiles with $v=3000-10000$ km s$^{-1}$. The fastest\noptical ejecta approach the velocity inferred from radio detections (modelled\nin a forthcoming companion paper from K.~D.~Alexander et al.), thus the same\noutflow may be responsible for both the fast optical rise and the radio\nemission -- the first time this connection has been observed in a TDE. The\nlight curve rise begins $29 \\pm 2$ days before maximum light, peaking when the\nphotosphere reaches the radius where optical photons can escape. The\nphotosphere then undergoes a sudden transition, first cooling at constant\nradius then contracting at constant temperature. At the same time, the\nblueshifts disappear from the spectrum and Bowen fluorescence lines (N III)\nbecome prominent, implying a source of far-UV photons, while the X-ray light\ncurve peaks at $\\approx 10^{41}$ erg s$^{-1}$. Assuming that these X-rays are\nfrom prompt accretion, the size and mass of the outflow are consistent with the\nreprocessing layer needed to explain the large optical to X-ray ratio in this\nand other optical TDEs, possibly favouring accretion-powered over\ncollision-powered outflow models.", + "category": "astro-ph" + }, + { + "text": "PyTransit: Fast and Easy Exoplanet Transit Modelling in Python: We present a fast and user friendly exoplanet transit light curve modelling\npackage PyTransit, implementing optimised versions of the Gimen\\'ez and the\nMandel & Agol transit models. The package offers an object-oriented Python\ninterface to access the two models implemented natively in Fortran with OpenMP\nparallelisation. A partial OpenCL version of the quadratic Mandel-Agol model is\nalso included for GPU-accelerated computations. The aim of PyTransit is to\nfacilitate the analysis of photometric time series of exoplanet transits\nconsisting of hundreds of thousands of datapoints, and of multi-passband\ntransit light curves from spectrophotometric observations, as a part of a\nresearcher's programming toolkit for building complex, problem-specific,\nanalyses.", + "category": "astro-ph" + }, + { + "text": "Formation of spiral structure from the violent relaxation of\n self-gravitating disks: We present the numerical study of the formation of spiral structure in the\ncontext of violent relaxation. Initial conditions are the out-of-equilibrium\ndisks of self-gravitating particles in rigid rotation. By that mechanism,\nrobust and non-stationary spiral arms can be formed within a few free-fall\ntimes by the shearing of the mass ejection following the collapse. With a\ncloser look, we find different properties of the arms in connection with the\ninitial configuration. The winding degree tends to increase with initial\nangular speed provided that a disk is thin. If disk surface is circular, both\nnumber and position of arms are governed by the Poissonian density fluctuations\nthat produce more arms as more particles are introduced. On the contrary, if\nthe surface ellipticity is imposed, the number of arms and their placement are\neffectively controlled. Otherwise, the increase of thickness leads to a\ncomplicated outcome since the number of arms and winding degree are less\neffectively controlled. We speculate that this complexity is caused by a strong\nnon-axisymmetric field during the violent relaxation that disorganizes the\npre-collapse motion and the concentration of particles.", + "category": "astro-ph" + }, + { + "text": "The Nature of Nearby Counterparts to Intermediate Redshift Luminous\n Compact Blue Galaxies II. CO Observations: We present the results of a single-dish beam-matched survey of the three\nlowest rotational transitions of CO in a sample of 20 local (D < 70 Mpc)\nLuminous Compact Blue Galaxies (LCBGs). These ~L*, blue, high surface\nbrightness, starbursting galaxies were selected with the same criteria used to\ndefine LCBGs at higher redshifts. Our detection rate was 70%, with those\ngalaxies having Lblue<7e9 Lsun no detected. We find the H2 masses of local\nLCBGs range from 6.6e6 to 2.7e9 Msun, assuming a Galactic CO-to-H2 conversion\nfactor. Combining these results with our earlier HI survey of the same sample,\nwe find that the ratio of molecular to atomic gas mass is low, typically 5-10%.\nUsing a Large Velocity Gradient model, we find that the average gas conditions\nof the entire ISM in local LCBGs are similar to those found in the centers of\nstar forming regions in our Galaxy, and nuclear regions of other galaxies. Star\nformation rates, determined from IRAS fluxes, are a few solar masses per year,\nmuch higher per unit dynamical mass than normal spirals. If this rate remains\nconstant, the molecular hydrogen depletion time scales are short, 10-200 Myr.", + "category": "astro-ph" + }, + { + "text": "Short gamma-ray burst jet propagation in binary neutron star merger\n environments: The multimessenger event GW170817/GRB 170817A confirmed that binary neutron\nstar (BNS) mergers can produce short gamma-ray burst (SGRB) jets. This evidence\npromoted new investigations on the mechanisms through which a BNS merger\nremnant can launch such a powerful relativistic outflow and on the propagation\nof the latter across the surrounding post-merger environment. In particular,\ngreat strides have been made in jet propagation models, establishing\nconnections between the initial jet launching conditions, including the\nincipient jet launching time (with respect to merger) and the injection\nparameters, and the observable SGRB prompt and afterglow emission. However,\npresent semi-analytical models and numerical simulations (with one notable\nexception) adopt simple hand-made prescriptions to account for the post-merger\nenvironment, lacking a direct association with any specific merging BNS system.\nHere, we present the first three-dimensional relativistic hydrodynamics\nsimulations of incipient SGRB jets propagating through a post-merger\nenvironment that is directly imported from the outcome of a previous general\nrelativistic BNS merger simulation. Our results show that the evolution and\nfinal properties of the jet can be largely affected by the anisotropies and the\ndeviations from axisymmetry and homologous expansion characterizing more\nrealistic BNS merger environments. In addition, we find that the inclusion of\nthe gravitational pull from the central compact object, often overlooked, can\nhave a major impact. Finally, we consider different jet launching times\nreferred to the same BNS merger model and discuss the consequences for the\nultimate jet properties.", + "category": "astro-ph" + }, + { + "text": "Long-term gamma-ray observations of the binary HESS J0632+057 with\n H.E.S.S., MAGIC and VERITAS: The gamma-ray binary HESS J0632+057 has been observed at very-high energies\n(E $>$ 100 GeV) for more than ten years by the major systems of imaging\natmospheric Cherenkov telescopes. We present a summary of results obtained with\nthe H.E.S.S., MAGIC, and VERITAS experiments based on roughly 440 h of\nobservations in total. This includes a discussion of an unusually bright TeV\noutburst of HESS J0632+057 in January 2018. The updated gamma-ray light curve\nnow covers all phases of the orbital period with significant detections in\nalmost all orbital phases. Results are discussed in context with simultaneous\nobservations with the X-ray Telescope onboard the Neil Gehrels Swift\nObservatory.", + "category": "astro-ph" + }, + { + "text": "The growth rate of cosmic structures in the local Universe with the\n ALFALFA survey: We investigate the growth rate of structures in the local Universe. For this,\nwe use as a cosmological tracer the HI line extra-galactic sources from the\nArecibo Legacy Fast ALFA (ALFALFA) survey to obtain a measurement of the\nnormalized growth rate parameter, $f \\sigma_{8}$, considered a powerful tool to\nconstrain alternative models of gravity. For these analyses, we calculate the\nLocal Group velocity due to the matter structures distribution in the ALFALFA\ncatalogue and compare it with the Local Group velocity relative to the Cosmic\nMicrowave Background frame to obtain the velocity scale parameter, $\\beta$.\nUsing Monte Carlo realizations and log-normal simulations, our methodology\nquantifies the errors introduced by shot-noise and partial sky coverage of the\nanalysed data. The measurement of the velocity scale parameter $\\beta$, and the\ncalculation of the matter fluctuation of the cosmological tracer,\n$\\sigma_{8}^{\\text{tr}}$, lead us to $f \\sigma_{8} = 0.46 \\pm 0.06$ at $\\bar{z}\n= 0.013$, in good agreement (at $1 \\sigma$ level) with the value expected in\nthe $\\Lambda$CDM concordance model. In addition, our analyses of the ALFALFA\nsample also provide a measurement of the growth rate of structures $f \\,=\\,\n0.56 \\pm 0.07$, at $\\bar{z} = 0.013$.", + "category": "astro-ph" + }, + { + "text": "Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the\n Class I Protostellar System TMC-1A: We have observed the Class I protostar TMC-1A in the Taurus molecular cloud\nusing the Submillimeter Array (SMA) and the Atacama Large\nMillimeter/submillimeter Array (ALMA) in the linearly polarized 1.3 mm\ncontinuum emission at angular resolutions of ~3\" and ~0.3\", respectively. The\nALMA observations also include CO, 13CO, and C18O J=2-1 spectral lines. The SMA\nobservations trace magnetic fields on the 1000-au scale, the directions of\nwhich are neither parallel nor perpendicular to the outflow direction. Applying\nthe Davis-Chandrasekhar-Fermi method to the SMA polarization angle dispersion,\nwe estimate a field strength in the TMC-1A envelope of 1-5 mG. It is consistent\nwith the field strength needed to reduce the radial infall velocity to the\nobserved value, which is substantially less than the local} free-fall velocity.\nThe ALMA polarization observations consist of two distinct components -- a\ncentral component and a north/south component. The central component shows\npolarization directions in the disk minor axis to be azimuthal, suggesting dust\nself-scattering in the TMC-1A disk. The north/south component is located along\nthe outflow axis and the polarization directions are aligned with the outflow\ndirection. We discuss possible origins of this polarization structure,\nincluding grain alignment by a toroidal magnetic field and mechanical alignment\nby the gaseous outflow. In addition, we discover a spiral-like residual in the\ntotal intensity (Stokes I) for the first time. The C18O emission suggests that\nmaterial in the spiral-like structure is infalling at a speed that is 20% of\nthe local Keplerian speed.", + "category": "astro-ph" + }, + { + "text": "Baseline correction for FAST radio recombination lines: a modified\n penalized least squares smoothing technique: A pilot project has been proceeded to map 1 deg$^2$ on the Galactic plane for\nradio recombination lines (RRLs) using the Five hundred meter Aperture\nSpherical Telescope (FAST). The motivation is to verify the techniques and\nreliabilities for a large-scale Galactic plane RRL survey with FAST aiming to\ninvestigate the ionized environment in the Galaxy. The data shows that the\nbandpass of the FAST 19 beam L-band is severely affected by radio frequency\ninterferences (RFIs) and standing wave ripples, which can hardly be corrected\nby traditional low order polynomials. In this paper, we investigate a series of\npenalized least square (PLS) based baseline correction methods for radio\nastronomical spectra that usually contain weak signals with high level of\nnoise. Three promising penalized least squares based methods, AsLS, arPLS, and\nasPLS are evaluated. Adopting their advantages, a modified method named rrlPLS\nis developed to optimize the baseline fitting to our RRL spectra. To check\ntheir effectiveness, the four methods are tested by simulations and further\nverified using observed data sets. It turns out that the rrlPLS method, with\noptimized parameter $\\lambda = 2 \\times 10^8$ , reveals the most sensitive and\nreliable emission features in the RRL map. By injecting artificial line\nprofiles into the real data cube, a further evaluation of profile distortion is\nconducted for rrlPLS. Comparing to simulated signals, the processed lines with\nlow signal-to-noise ratio are less affected, of which the uncertainties are\nmainly caused by the rms noise. The rrlPLS method will be applied for baseline\ncorrection in future data processing pipeline of FAST RRL survey. Configured\nwith proper parameters, the rrlPLS technique verified in this work may also be\nused for other spectroscopy projects.", + "category": "astro-ph" + }, + { + "text": "Outflowing disk formation in B[e] supergiants due to rotation and\n bi--stability in radiation driven winds: The effects of rapid rotation and bi-stability upon the density contrast\nbetween the equatorial and polar directions of a B[e] supergiant are\nre-investigated. Based upon a new slow solution for different high rotational\nradiation driven winds (Cur\\'e 2004) and the fact that bi--stability allows a\nchange in the line--force parameters ($\\alpha$, $k$, and $\\delta$), the\nequatorial densities are about $10^2$--$10^4$ times higher than the polar ones.\nThese values are in qualitative agreement with the observations.", + "category": "astro-ph" + }, + { + "text": "The ESO Nearby Abell Cluster Survey IX. The morphology-radius and\n morphology-density relations in rich galaxy clusters: We study the morphology-radius (MR-) and morphology-density (MD-) relations\nfor a sample of about 850 galaxies (with M <= -19.5) in 23 clusters from the\nENACS (ESO Nearby Abell Cluster Survey). On the basis of their radial\ndistributions we must distinguish: 1. brightest ellipticals (with M < -22), 2.\nlate spirals, and 3. the ensemble of less bright ellipticals, S0 galaxies and\nearly spirals. The latter have indistinguishable distributions of projected\nradial distance R. The brightest ellipticals are most centrally concentrated,\nthe late spirals are almost absent from the central regions and the other\nclasses are intermediate. Radial segregation of the ellipticals is due to the\nbrightest ellipticals only, that of the spirals to the late spirals only. We\nderive the MD-relation with two measures of projected density: one using the 10\nnearest neighbours (Sigma10) and another using only the nearest neighbour\n(Sigma1). The Sigma10 MD-relation only shows a significant difference between\nearly- and late-type galaxies, but the different galaxy types within those\nclasses are indistinguishable. However, The Sigma1 MD-relation shows that the\nnormal 'ellipticals' (with M >= -22), the S0 galaxies and the early spirals\nhave different Sigma1-distributions. The reason for this is that Sigma1 is much\nless correlated with R than is Sigma10, and thus has much less cross-talk from\nthe (MR-) relation. On average, the 'normal' ellipticals populate environments\nwith higher projected density than do the S0 galaxies while the early spirals\npopulate even less dense environments. The segregation of the brightest\nellipticals and the late spirals is driven mostly by global factors, while the\nsegregation between 'normal' ellipticals, S0 galaxies and early spirals is\ndriven primarily by local factors.", + "category": "astro-ph" + }, + { + "text": "Distances of Quasars and Quasar-Like Galaxies: Further Evidence that\n QSOs may be Ejected from Active Galaxies: If high-redshift QSOs are ejected from the nuclei of low-redshift galaxies,\nas some have claimed, a large portion of their redshift must be intrinsic\n(non-Doppler). If these intrinsic components have preferred values, redshifts\nwill tend to cluster around these preferred values and produce peaks in the\nredshift distribution. Doppler ejection and Hubble flow components will broaden\neach peak. Because ejection velocities are randomly directed and Hubble flow\ncomponents are always positive, in this model all peaks are expected to show an\nasymmetry, extending further out in the red wing. If peaks are present showing\nthis predicted asymmetry, it can lead directly to an estimate of quasar\ndistances. Using two quasar samples, one with high redshifts and one with low,\nit is shown here that not only do all peaks in these two redshift distributions\noccur at previously predicted preferred values, they also all show the\npredicted extra extension in the red wing. For the low and high redshift\nsamples the mean cosmological components are found to be z$_{c} \\sim 0.024$ and\n$\\sim 0.066$, respectively. The difference can be explained by the improved\ndetection limit of the high redshift sample. These results offer further\nevidence in favor of the model proposing that QSOs are ejected from active\ngalaxies.", + "category": "astro-ph" + }, + { + "text": "Probing the dynamical state of galaxy clusters: We show how hydrostatic equilibrium in galaxy clusters can be quantitatively\nprobed combining X-ray, SZ, and gravitational-lensing data. Our previously\npublished method for recovering three-dimensional cluster gas distributions\navoids the assumption of hydrostatic equilibrium. Independent reconstructions\nof cumulative total-mass profiles can then be obtained from the gas\ndistribution, assuming hydrostatic equilibrium, and from gravitational lensing,\nneglecting it. Hydrostatic equilibrium can then be quantified comparing the\ntwo. We describe this procedure in detail and show that it performs well on\nprogressively realistic synthetic data. An application to a cluster merger\ndemonstrates how hydrostatic equilibrium is violated and restored as the merger\nproceeds.", + "category": "astro-ph" + }, + { + "text": "Kilonova Light-Curve Interpolation with Neural Networks: Kilonovae are the electromagnetic transients created by the radioactive decay\nof freshly synthesized elements in the environment surrounding a neutron star\nmerger. To study the fundamental physics in these complex environments,\nkilonova modeling requires, in part, the use of radiative transfer simulations.\nThe microphysics involved in these simulations results in high computational\ncost, prompting the use of emulators for parameter inference applications.\nUtilizing a training set of 22248 high-fidelity simulations, we use a neural\nnetwork to efficiently train on existing radiative transfer simulations and\npredict light curves for new parameters in a fast and computationally efficient\nmanner. Our neural network can generate millions of new light curves in under a\nminute. We discuss our emulator's degree of off-sample reliability and\nparameter inference of the AT2017gfo observational data. Finally, we discuss\ntension introduced by multi-band inference in the parameter inference results,\nparticularly with regard to the neural network's recovery of viewing angle.", + "category": "astro-ph" + }, + { + "text": "Optical technologies for the observation of low Earth orbit objects: In order to avoid collisions with space debris, the near Earth orbit must be\ncontinuously scanned by either ground- or spaced-based facilities. For the low\nEarth orbit, radar telescopes are the workhorse for this task, especially due\nto their continuous availability. However, optical observation methods can\ndeliver complementary information, especially towards high accuracy\nmeasurements. Passive-optical observations are inexpensive and can yield very\nprecise information about the apparent position of the object in the sky via\ncomparison with background stars. However, the object's distance from the\nobserver is not readily accessible, which constitutes a major drawback of this\napproach for the precise calculation of the orbital elements. Two experimental\nmethods have been devised to overcome this problem: Using two observatories a\nfew kilometres apart, strictly simultaneous observations of the same object\nyield an accurate, instantaneous 3D position determination through measurement\nof the parallax. If only one observatory is available, a pulsed laser can be\nused in addition to the passive-optical channel to measure the distance to the\nobject, in a similar fashion as used by the satellite laser ranging community.\nHowever, compared to conventional laser ranging, a stronger laser and more\nelaborate tracking algorithms are necessary. The two approaches can also be\ncombined by illuminating the object with a pulsed laser from one observatory\nand measuring the return times at both observatories. These techniques are\nexplored by German Aerospace Center in Stuttgart using its orbital debris\nresearch observatory, in cooperation with the Satellite Laser Ranging station\nin Graz and the Geodetic Observatory in Wettzell. This contribution will\npresent some of the results and plans for further measurement campaigns.", + "category": "astro-ph" + }, + { + "text": "Hector - a new massively multiplexed IFS instrument for the\n Anglo-Australian Telescope: Hector will be the new massively-multiplexed integral field spectroscopy\n(IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the\nnext main dark-time instrument for the observatory. Based on the success of the\nSAMI instrument, which is undertaking a 3400-galaxy survey, the integral field\nunit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is\nbeing improved to a new innovative design for Hector. The distribution of\nhexabundle angular sizes is matched to the galaxy survey properties in order to\nimage 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging\nbundles will be positioned by 'starbug' robots across a new 3-degree field\ncorrector top end to be purpose-built for the AAT. Many thousand fibres will\nthen be fed into new replicable spectrographs. Fundamentally new science will\nbe achieved compared to existing instruments due to Hector's wider field of\nview (3 degrees), high positioning efficiency using starbugs, higher\nspectroscopic resolution (R~3000-5500 from 3727-7761A, with a possible redder\nextension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre\ncores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion\nand merger history and large-scale environment made every galaxy different in\nits morphology and star formation history. The high resolution, particularly in\nthe blue, will make Hector the only instrument to be able to measure\nhigher-order kinematics for galaxies down to much lower velocity dispersion\nthan in current large IFS galaxy surveys, opening up a wealth of new nearby\ngalaxy science.", + "category": "astro-ph" + }, + { + "text": "NBFTP: A Dedicated Data Transfer System for Remote Astronomical\n Observation at Dome A: Dome A, Antarctica has been thought to be one of the best astronomical sites\non the earth since decades ago. From it was first visited by astronomers in\n2008, dozens of facilities for astronomical observation and site testing were\ndeployed. Due to its special geographical location, the data and message\nexchange between Dome A and the domestic control center could only depend on\nIridium. Because the link bandwidth of Iridium is extremely limited, meanwhile\nthe network traffic cost is quite expensive and the network is rather unstable,\nthe commonly used data transfer tools, such as rsync and scp, are not suitable\nin this case. In this paper, we design and implement a data transfer tool\ncalled NBFTP (narrow bandwidth file transfer protocol) for the astronomical\nobservation of Dome A. NBFTP uses a uniform interface to arrange all types of\ndata and matches specific transmission schemes for different data types\naccording to rules. Break-point resuming and extensibility functions are also\nimplemented. Our experimental results show that NBFTP consumes 60% less network\ntraffic than rsync when detecting the data pending to be transferred. And when\ntransferring small files of 1KB, the network traffic consumption of NBFTP is\n40% less than rsync. However, as the file size increases, the network traffic\nconsumption of NBFTP tends to approach rsync, but it is still smaller than\nrsync.", + "category": "astro-ph" + }, + { + "text": "Rapid Dissipation of Protoplanetary Disks in Ophiuchus: We present the results of an age determination study for pre-main sequence\nstars in the Ophiuchus molecular cloud. The ages of eight pre-main sequence\nstars were estimated from surface gravities derived from high-resolution\nspectroscopy. The average age of the target stars was 0.7 Myr. By comparing the\nindividual age and the near-infrared color excess, we found that color excess\ndecreases gradually with a constant rate and the lifetime of the inner disk was\ndetermined to be 1.2 Myr. The estimated lifetime is nearly a half of the time\ncompared to that of the pre-main sequence stars in the Taurus molecular cloud\nestimated with the same method. This result indicates that the disk evolution\ntimescale depends on the environment of the star-forming region.", + "category": "astro-ph" + }, + { + "text": "Kinematics of OB Stars with Data from the LAMOST and Gaia Catalogues: We have analyzed the kinematics of OB stars from the list by Xiang et al.\n(2021) that contains $\\sim$13 000 single OB stars. For these stars there are\nphotometric distance estimates and proper motions from the Gaia catalogue and\nline-of-sight velocities from the LAMOST catalogue. Based on a sample of single\nOB stars and using the photometric distances and proper motions of stars from\nthe Gaia EDR3 catalogue, we have found the group velocity components\n$(U_\\odot,V_\\odot,W_\\odot)=(9.63,9.93,7.45)\\pm(0.27,0.34,0.10)$ km s$^{-1}$,\nand the following parameters of the angular velocity of Galactic rotation:\n$\\Omega_0=29.20\\pm0.18$ km s$^{-1}$ kpc$^{-1}$, $\\Omega^{'}_0=-4.150\\pm0.046$\nkm s$^{-1}$ kpc$^{-2}$ and $\\Omega^{''}_0=0.795\\pm0.018$ km s$^{-1}$\nkpc$^{-3}$, where the error per unit weight $\\sigma_0$ is 9.56 km s$^{-1}$ and\n$V_0=236.5\\pm3.3$ km s$^{-1}$ (for the adopted $R_0=8.1\\pm0.1$ kpc). Based on\nthe same OB stars, we have found the residual velocity dispersions\n$(\\sigma_1,\\sigma_2,\\sigma_3)=(15.13,9.69,7.98)\\pm(0.07,0.05,0.04)$ km\ns$^{-1}$. We show that using the line-of-sight velocities increases\nsignificantly the space velocity dispersion and leads to a biased estimate of\nthe velocity $U_\\odot$. A comparison of the distances scales used has shown\nthat the photometric distances from Xiang et al. (2021) should be lengthened\napproximately by 10%.", + "category": "astro-ph" + }, + { + "text": "Accretion-disc model spectra for dwarf-nova stars: Radiation from accretion discs in cataclysmic variable stars (CVs) provides\nfundamental information about the properties of these close binary systems and\nabout the physics of accretion in general. The detailed diagnostics of\naccretion disc structure can be achieved by including in its description all\nthe relevant heating and cooling physical mechanism, in particular the\nconvective energy transport that, although dominant at temperatures less than\nabout 10 000 K, is usually not taken into account when calculating spectra of\naccretion discs. We constructed a radiative transfer code coupled with a code\ndetermining the disc's hydrostatic vertical structure. We have obtained for the\nfirst time model spectra of cold, convective accretion discs. As expected,\nthese spectra are mostly flat in the optical wavelengths with no contribution\nfrom the UV, which in quiescence must be emitted by the white dwarf. The disc\nstructures obtained with our radiative-transfer code compare well with the\nsolutions of equations used to describe the dwarf-nova outburst cycle according\nto the thermal-viscous disc instability model thus allowing the two to be\ncombined. Our code allows calculating the spectral evolution of dwarf nova\nstars through their whole outburst cycle, providing a new tool for testing\nmodels of accretion discs in cataclysmic variables. We show that convection\nplays an important role in determining the vertical disc structure and\nsubstantially affects emitted spectra when, as often the case, it is effective\nat optical depths tau ~ 1. The emergent spectrum is independent of the\nparameters of the convection model.(Abstract shortened)", + "category": "astro-ph" + }, + { + "text": "Time-Variable Jet Ejections from RW Aur A, RY Tau and DG Tau: We present Gemini-NIFS, VLT-SINFONI and Keck-OSIRIS observations of\nnear-infrared [Fe II] emission associated with the well-studied jets from three\nactive T Tauri stars; RW Aur A, RY Tau and DG Tau taken from 2012-2021. We\nprimarily covered the redshifted jet from RW Aur A, and the blueshifted jets\nfrom RY Tau and DG Tau, to investigate long-term time variabilities potentially\nrelated to the activities of mass accretion and/or the stellar magnetic fields.\nAll of these jets consist of several moving knots with tangential velocities of\n70-240 km s-1, ejected from the star with different velocities and at irregular\ntime intervals. Via comparison with literature, we identify significant\ndifferences in tangential velocities for the DG Tau jet between 1985-2008 and\n2008-2021. The sizes of the individual knots appear to increase with time, and\nin turn, their peak brightnesses in the 1.644-micron emission decreased up to a\nfactor of ~30 during the epochs of our observations. A variety of the decay\ntimescales measured in the [Fe II] 1.644 micron emission can be attributed to\ndifferent pre-shock conditions if the moving knots are unresolved shocks.\nHowever, our data do not exclude the possibility that these knots are due to\nnon-uniform density/temperature distributions with another heating mechanism,\nor in some cases due to stationary shocks without proper motions. Spatially\nresolved observations of these knots with significantly higher angular\nresolutions are necessary to better understand their physical nature.", + "category": "astro-ph" + }, + { + "text": "Monte Carlo simulations of alternative sky observation modes with the\n Cherenkov Telescope Array: We investigate possible sky survey modes with the Middle Sized Telescopes\n(MST, aimed at covering the energy range from $\\sim$100 GeV to 10 TeV)\nsubsystem of the Cherenkov Telescope Array (CTA). We use the standard CTA\ntools, CORSIKA and sim_telarray, to simulate the development of gamma-ray\nshowers, proton background and the telescope response. We perform simulations\nfor the H.E.S.S.-site in Namibia, which is one of the candidate sites for the\nCTA experiment. We study two previously considered modes, parallel and\ndivergent, and we propose a new, convergent mode with telescopes tilted toward\nthe array center. For each mode we provide performance parameters crucial for\nchoosing the most efficient survey strategy. For the non-parallel modes we\nstudy the dependence on the telescope offset angle. We show that use of both\nthe divergent and convergent modes results in potential advantages in\ncomparison with use of the parallel mode. The fastest source detection can be\nachieved in the divergent mode with larger offset angles ($\\sim 6^{\\circ}$ from\nthe Field of View centre for the outermost telescopes), for which the time\nneeded to perform a scan at a given sensitivity level is shorter by a factor of\n$\\sim$2.3 than for the parallel mode. We note, however, the direction and\nenergy reconstruction accuracy for the divergent mode is even by a factor of\n$\\sim 2$ worse than for other modes. Furthermore, we find that at high energies\nand for observation directions close to the center of the array field of view,\nthe best performance parameters are achieved with the convergent mode, which\nfavors this mode for deep observations of sources with hard energy spectra.", + "category": "astro-ph" + }, + { + "text": "Radio Polarimetry Results for Young Southern Pulsars: We present radio polarimetry results for nine Southern pulsars. Six of the\nnine are young, with characteristic ages less than 100 kyr and high spin-down\nluminosities. All six show significant linear polarization, and we confirm a\npreviously noticed trend in which the degree of linear polarization increases\nwith spin-down luminosity. We have used the rotating vector model to fit the\nobserved position angle data for PSR J1513-5908 (B1509-58). We find that a\nmagnetic inclination angle alpha > 60 degrees is excluded at the 3-sigma level\nin the fit, and that the geometry suggested by the morphology of an apparent\nbipolar X-ray outflow is marginally inconsistent with a recent model of the\npulsar magnetosphere.", + "category": "astro-ph" + }, + { + "text": "Raytracing simulations of coupled dark energy models: Dark matter and dark energy are usually assumed to couple only\ngravitationally. An extension to this picture is to model dark energy as a\nscalar field coupled directly to cold dark matter. This coupling leads to new\nphysical effects, such as a fifth-force and a time-dependent dark matter\nparticle mass. In this work we examine the impact that coupling has on weak\nlensing statistics by constructing realistic simulated weak-lensing maps using\nraytracing techniques through N-body cosmological simulations. We construct\nmaps for different lensing quantities, covering a range of scales from a few\narcminutes to several degrees. The concordance $\\Lambda$CDM model is compared\nto different coupled dark energy models, described either by an exponential\nscalar field potential (standard coupled dark energy scenario) or by a SUGRA\npotential (bouncing model). We analyse several statistical quantities and our\nresults, with sources at low redshifts are largely consistent with previous\nwork on CMB lensing by Carbone et al., 2013. The most significant differences\nfrom the $\\Lambda$CDM model are due to the enhanced growth of the perturbations\nand to the effective friction term in non-linear dynamics. For the most extreme\nmodels, we see differences in the power spectra up to 40% compared to the\n$\\Lambda$CDM model. The different time evolution of the linear matter\noverdensity can account for most of the differences, but when controlling for\nthis using a $\\Lambda$CDM model having the same normalization, the overall\nsignal is smaller due to the effect of the friction term appearing in the\nequation of motion for dark matter particles.", + "category": "astro-ph" + }, + { + "text": "Discovery of a bright microlensing event with planetary features towards\n the Taurus region: a super Earth planet: The transient event labeled as TCP J05074264+2447555 recently discovered\ntowards the Taurus region was quickly recognized to be an ongoing microlensing\nevent on a source located at distance of only $700-800$ pc from Earth. Here, we\nshow that observations with high sampling rate close to the time of maximum\nmagnification revealed features that imply the presence of a binary lens system\nwith very low mass ratio components. We present a complete description of the\nbinary lens system which hosts an Earth-like planet with most likely mass of\n$9.2\\pm 6.6$ M$_{\\oplus}$. Furthermore, the source estimated location and\ndetailed Monte Carlo simulations allowed us to classify the event as due to the\nclosest lens system, being at a distance of $\\simeq 380$ pc and mass $\\simeq\n0.25$ M$_{\\odot}$.", + "category": "astro-ph" + }, + { + "text": "Cold dark matter heats up: One of the principal discoveries in modern cosmology is that standard model\nparticles (including baryons, leptons and photons) together comprise only 5% of\nthe mass-energy budget of the Universe. The remaining 95% consists of dark\nenergy and dark matter (DM). Consequently our picture of the universe is known\nas {\\Lambda}CDM, with {\\Lambda} denoting dark energy and CDM cold dark matter.\n{\\Lambda}CDM is being challenged by its apparent inability to explain the low\ndensity of DM measured at the centre of cosmological systems, ranging from\nfaint dwarf galaxies to massive clusters containing tens of galaxies the size\nof the Milky Way. But before making conclusions one should carefully include\nthe effect of gas and stars, which were historically seen as merely a passive\ncomponent during the assembly of galaxies. We now understand that these can in\nfact significantly alter the DM component, through a coupling based on rapid\ngravitational potential fluctuations.", + "category": "astro-ph" + }, + { + "text": "Estimating the impact of recombination uncertainties on the cosmological\n parameter constraints from cosmic microwave background experiments: [Abridged] We use our most recent training set for the RICO code to estimate\nthe impact of recombination uncertainties on the posterior probability\ndistributions which will be obtained from future CMB experiments, and in\nparticular the Planck satellite. Using a MCMC analysis to sample the posterior\ndistribution of the cosmological parameters, we find that Planck will have\nbiases of -0.7, -0.3 and -0.4 sigmas for n_S, Omega_b h2 and log(As),\nrespectively, in the minimal 6-parameter LCDM model, if the description of the\nrecombination history given by RICO is not used. The remaining parameters are\nnot significantly affected. We also show, that the cosmology dependence of the\ncorrections to the recombination history modeled with RICO has a negligible\nimpact on the posterior distributions obtained for the case of the Planck\nsatellite. In practice, this implies that the inclusion of additional\ncorrections to existing recombination codes can be achieved using simple\ncosmology-independent `fudge functions'. Finally, we also investigated the\nimpact of some recent improvements in the treatment of hydrogen recombination\nwhich are still not included in the current version of our training set for\nRico, by assuming that the cosmology dependence of those corrections can be\nneglected. In summary, with our current understanding of the complete\nrecombination process, the expected biases in the cosmological parameters\ninferred from Planck might be as large as -2.3, -1.7 and -1 sigmas for n_S,\nOmega_b h2 and log(As) respectively, if all those corrections are not taken\ninto account. We note that although the list of physical processes that could\nbe of importance for Planck seems to be nearly complete, still some effort has\nto be put in the validation of the results obtained by the different groups.", + "category": "astro-ph" + }, + { + "text": "The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and\n the demonstration of hybrid techniques: We are building a next-generation laser adaptive optics system, Robo-AO-2,\nfor the UH 2.2-m telescope that will deliver robotic, diffraction-limited\nobservations at visible and near-infrared wavelengths in unprecedented numbers.\nThe superior Maunakea observing site, expanded spectral range and rapid\nresponse to high-priority events represent a significant advance over the\nprototype. Robo-AO-2 will include a new reconfigurable natural guide star\nsensor for exquisite wavefront correction on bright targets and the\ndemonstration of potentially transformative hybrid AO techniques that promise\nto extend the faintness limit on current and future exoplanet adaptive optics\nsystems.", + "category": "astro-ph" + }, + { + "text": "Towards a multi-scale understanding of the gas-star formation cycle in\n the Central Molecular Zone: The Central Molecular Zone (CMZ, the central 500 pc of the Milky Way)\ncontains the largest reservoir of high-density molecular gas in the Galaxy, but\nforms stars at a rate 10-100 times below commonly-used star formation\nrelations. We discuss recent efforts in understanding how the nearest galactic\nnucleus forms its stars. The latest models of the gas inflow, star formation,\nand feedback duty cycle reproduce the main observable features of the CMZ,\nshowing that star formation is episodic and that the CMZ currently resides at a\nstar formation minimum. Using orbital modelling, we derive the\nthree-dimensional geometry of the CMZ and show how the orbital dynamics and the\nstar formation potential of the gas are closely coupled. We discuss how this\ncoupling reveals the physics of star formation and feedback under the\nconditions seen in high-redshift galaxies, and promotes the formation of the\ndensest stellar clusters in the Galaxy.", + "category": "astro-ph" + }, + { + "text": "Variability of VHE $\u03b3$-ray emission from the binary PSR B1259-63/LS\n 2883: We examine changes of the $\\gamma$-ray intensity observed from the direction\nof the binary system PSR B1259-63/LS 2883 during campaigns around its three\nperiastron passages. A simple and straightforward method is applied to the\npublished data obtained with the Imaging Atmospheric Cherenkov Technique.\nRegardless of many issues of the detection process, the method works only with\nnumbers of very high energetic photons registered in the specified regions.\nWithin the realm of this scheme, we recognized changes attributable to the\nvariations of the intrinsic source activity at high levels of significance.", + "category": "astro-ph" + }, + { + "text": "EMPRESS. IV. Extremely Metal-Poor Galaxies (EMPGs) Including Very\n Low-Mass Primordial Systems with M*=10^4--10^5 M_sun and 2--3% (O/H)_sun:\n High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-Instability\n Supernovae: We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of\nextremely metal poor galaxies (EMPGs) selected by a machine-learning technique\napplied to the deep (~26 AB mag) optical and wide-area (~500 deg^2) Subaru\nimaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs\nwith an oxygen abundance (O/H) less than ~10% solar value (O/H)_sun, and four\nsources are contaminants of moderately metal-rich galaxies or no emission-line\nobjects. Notably, two out of the nine EMPGs have extremely-low stellar masses\nand oxygen abundances of 5*10^4--7*10^5 M_sun and 2--3% (O/H)_sun,\nrespectively. With a sample of five EMPGs with (Fe/O) measurements, two (three)\nof which are taken from this study (the literature), we confirm that two EMPGs\nwith the lowest (O/H) ratios of ~2% (O/H)_sun show high (Fe/O) ratios of ~0.1,\nclose to the solar abundance ratio. Comparing galaxy chemical enrichment\nmodels, we find that the two EMPGs cannot be explained by a scenario of\nmetal-poor gas accretion/episodic star-formation history due to their low (N/O)\nratios. We conclude that the two EMPGs can be reproduced by an inclusion of\nbright hypernovae and/or hypothetical pair-instability supernovae (SNe)\npreferentially produced in a metal-poor environment. This conclusion implies\nthat primordial galaxies at z~10 could have a high abundance of Fe that is not\noriginated from Type Ia SNe with delays, and that Fe may not serve as a cosmic\nclock for primordial galaxies.", + "category": "astro-ph" + }, + { + "text": "The dust effects on galaxy scaling relations: Accurate galaxy scaling relations are essential for a successful model of\ngalaxy formation and evolution as they provide direct information about the\nphysical mechanisms of galaxy assembly over cosmic time. We present here a\ndetailed analysis of a sample of nearby spiral galaxies taken from the KINGFISH\nsurvey. The photometric parameters of the morphological components are obtained\nfrom bulge-disk decompositions using GALFIT data analysis algorithm, with\nsurface photometry of the sample done beforehand. Dust opacities are determined\nusing a previously discovered correlation between the central face-on dust\nopacity of the disk and the stellar mass surface density. The method and the\nlibrary of numerical results previously obtained are used to correct the\nmeasured photometric and structural parameteres for projection (inclination),\ndust and decomposition effects in order to derive their intrinsic values.\nGalaxy disk scaling relations are then presented, both the measured (observed)\nand the intrinsic (corrected) ones, in the optical regime, to show the scale of\nthe biases introduced by the aforementioned effects. The slopes of the\nsize-luminosity relations and the dust vs stellar mass are in agreement with\nvalues found in other works. We derive mean dust optical depth and dust/stellar\nmass ratios of the sample, which we find to be consistent with previous studies\nof nearby spiral galaxies. While our sample is rather small, it is sufficient\nto quantify the influence of galaxy environment (dust, in this case) when\nderiving scaling relations.", + "category": "astro-ph" + }, + { + "text": "Predicted Colors and Flux Densities of Protostars in the Herschel PACS\n and SPIRE Filters: Upcoming surveys with the Herschel Space Observatory will yield far-IR\nphotometry of large samples of young stellar objects, which will require\ncareful interpretation. We investigate the color and luminosity diagnostics\nbased on Herschel broad-band filters to identify and discern the properties of\nlow-mass protostars. We compute a grid of 2,016 protostars in various physical\ncongurations, present the expected flux densities and flux density ratios for\nthis grid of protostars, and compare Herschel observations of three protostars\nto the model results. These provide useful constraints on the range of colors\nand fluxes of protostar in the Herschel filters. We find that Herschel data\nalone is likely a useful diagnostic of the envelope properties of young stars", + "category": "astro-ph" + }, + { + "text": "Evidence for an X-ray Emitting Galactic Bulge: Shadows Cast by Distant\n Molecular Gas: A mosaic of 7 ROSAT PSPC pointed observations in the direction of (l,b ~ 10,0\ndeg) reveals deep X-ray shadows in the 0.5-2.0 keV band cast by dense molecular\ngas. The comparison between the observed on-cloud and off-cloud X-ray fluxes\nindicates that ~43% of the diffuse X-ray background in this direction in both\nthe 3/4 keV and 1.5 keV bands originates behind the molecular gas, which is\nlocated at 2-4 kpc from the Sun. Given the short mean free path of X-rays in\nthe 3/4 keV band in the Galactic plane (~1 kpc assuming an average space\ndensity of 1 cm^-3), this large percentage of the observed flux which\noriginates beyond the molecular gas most likely indicates a strong enhancement\nin the distribution of X-ray emitting gas in the Galactic center region,\npossibly associated with a Galactic X-ray bulge.", + "category": "astro-ph" + }, + { + "text": "Deep Learning for Gamma-Ray Bursts: A data driven event framework for\n X/Gamma-Ray analysis in space telescopes: This thesis comprises the first three chapters dedicated to providing an\noverview of Gamma Ray-Bursts (GRBs), their properties, the instrumentation used\nto detect them, and Artificial Intelligence (AI) applications in the context of\nGRBs, including a literature review and future prospects. Considering both the\ncurrent and the next generation of high X-ray monitors, such as Fermi-GBM and\nHERMES Pathfinder (an in-orbit demonstration of six 3U nano-satellites), the\nresearch question revolves around the detection of long and faint high-energy\ntransients, potentially GRBs, that might have been missed by previous detection\nalgorithms. To address this, two chapters introduce a new data-driven\nframework, DeepGRB.\n In Chapter 4, a Neural Network (NN) is described for background count rate\nestimation for X/gamma-ray detectors, providing a performance evaluation in\ndifferent periods, including both solar maxima, solar minima periods, and one\ncontaining an ultra-long GRB. The application of eXplainable Artificial\nIntelligence (XAI) is performed for global and local feature importance\nanalysis to better understand the behavior of the NN.\n Chapter 5 employs FOCuS-Poisson for anomaly detection in count rate\nobservations and estimation from the NN. DeepGRB demonstrates its capability to\nprocess Fermi-GBM data, confirming cataloged events and identifying new ones,\nproviding further analysis with estimates for localization, duration, and\nclassification. The chapter concludes with an automated classification method\nusing Machine Learning techniques that incorporates XAI for eventual bias\nidentification.", + "category": "astro-ph" + }, + { + "text": "Making the unmodulated Pyramid wavefront sensor smart. Closed-loop\n demonstration of neural network wavefront reconstruction with MagAO-X: Almost all current and future high-contrast imaging instruments will use a\nPyramid wavefront sensor (PWFS) as a primary or secondary wavefront sensor. The\nmain issue with the PWFS is its nonlinear response to large phase aberrations,\nespecially under strong atmospheric turbulence. Most instruments try to\nincrease its linearity range by using dynamic modulation, but this leads to\ndecreased sensitivity, most prominently for low-order modes, and makes it blind\nto petal-piston modes. In the push toward high-contrast imaging of fainter\nstars and deeper contrasts, there is a strong interest in using the PWFS in its\nunmodulated form. Here, we present closed-loop lab results of a nonlinear\nreconstructor for the unmodulated PWFS of the Magellan Adaptive Optics eXtreme\n(MagAO-X) system based on convolutional neural networks (CNNs). We show that\nour nonlinear reconstructor has a dynamic range of >600 nm root-mean-square\n(RMS), significantly outperforming the linear reconstructor that only has a 50\nnm RMS dynamic range. The reconstructor behaves well in closed loop and can\nobtain >80% Strehl at 875 nm under a large variety of conditions and reaches\nhigher Strehl ratios than the linear reconstructor under all simulated\nconditions. The CNN reconstructor also achieves the theoretical sensitivity\nlimit of a PWFS, showing that it does not lose its sensitivity in exchange for\ndynamic range. The current CNN's computational time is 690 microseconds, which\nenables loop speeds of >1 kHz. On-sky tests are foreseen soon and will be\nimportant for pushing future high-contrast imaging instruments toward their\nlimits.", + "category": "astro-ph" + }, + { + "text": "Relationship between the moment of inertia and the $k_2$ Love number of\n fluid extra-solar planets: Context: Tidal and rotational deformation of fluid giant extra-solar planets\nmay impact their transit light curves, making the $k_2$ Love number observable\nin the upcoming years. Studying the sensitivity of $k_2$ to mass concentration\nat depth is thus expected to provide new constraints on the internal structure\nof gaseous extra-solar planets. Aims: We investigate the link between the mean\npolar moment of inertia $N$ of a fluid, stably layered extra-solar planet and\nits $k_2$ Love number, aiming at obtaining analytical relationships valid, at\nleast, for some particular ranges of the model parameters. We also seek a\ngeneral, approximate relationship useful to constrain $N$ once observations of\n$k_2$ will become available. Methods: For two-layer fluid extra-solar planets,\nwe explore the relationship between $N$ and $k_2$ by analytical methods, for\nparticular values of the model parameters. We also explore approximate\nrelationships valid over all the possible range of two-layer models. More\ncomplex planetary structures are investigated by the semi-analytical propagator\ntechnique. Results: A unique relationship between $N$ and $k_2$ cannot be\nestablished. However, our numerical experiments show that a `rule of thumb' can\nbe inferred, valid for complex, randomly layered stable planetary structures.\nThe rule robustly defines the upper limit to the values of $N$ for a given\n$k_2$, and agrees with analytical results for a polytrope of index one and with\na realistic non-rotating model of the tidal equilibrium of Jupiter.", + "category": "astro-ph" + }, + { + "text": "The Completed SDSS-IV Extended Baryon Oscillation Spectroscopic Survey:\n N-body Mock Challenge for the Quasar Sample: The growth rate and expansion history of the Universe can be measured from\nlarge galaxy redshift surveys using the Alcock-Paczynski effect. We validate\nthe Redshift Space Distortion models used in the final analysis of the Sloan\nDigital Sky Survey (SDSS) extended Baryon Oscillation Spectroscopic Survey\n(eBOSS) Data Release 16 quasar clustering sample, in configuration and Fourier\nspace, using a series of HOD mock catalogues generated using the OuterRim\nN-body simulation. We test three models on a series of non-blind mocks, in the\nOuterRim cosmology, and blind mocks, which have been rescaled to new\ncosmologies, and investigate the effects of redshift smearing and catastrophic\nredshifts. We find that for the non-blind mocks, the models are able to recover\n$f\\sigma_8$ to within 3% and $\\alpha_\\parallel$ and $\\alpha_\\bot$ to within 1%.\nThe scatter in the measurements is larger for the blind mocks, due to the\nassumption of an incorrect fiducial cosmology. From this mock challenge, we\nfind that all three models perform well, with similar systematic errors on\n$f\\sigma_8$, $\\alpha_\\parallel$ and $\\alpha_\\bot$ at the level of\n$\\sigma_{f\\sigma_8}=0.013$, $\\sigma_{\\alpha_\\parallel}=0.012$ and\n$\\sigma_{\\alpha_\\bot}=0.008$. The systematic error on the combined consensus is\n$\\sigma_{f\\sigma_8}=0.011$, $\\sigma_{\\alpha_\\parallel}=0.008$ and\n$\\sigma_{\\alpha_\\bot}=0.005$, which is used in the final DR16 analysis. For BAO\nfits in configuration and Fourier space, we take conservative systematic errors\nof $\\sigma_{\\alpha_\\parallel}=0.010$ and $\\sigma_{\\alpha_\\bot}=0.007$.", + "category": "astro-ph" + }, + { + "text": "A Massive Millisecond Pulsar in an Eccentric Binary: The recent discovery of a population of eccentric (e ~ 0.1) millisecond\npulsar (MSP) binaries with low-mass white dwarf companions in the Galactic\nfield represents a challenge to evolutionary models that explain MSP formation\nas recycling: all such models predict that the orbits become highly\ncircularised during a long period of accretion. The members of this new\npopulation exhibit remarkably similar properties (orbital periods,\neccentricities, companion masses, spin periods) and several models have been\nput forward that suggest a common formation channel. In this work we present\nthe results of an extensive timing campaign focusing on one member of this new\npopulation, PSR J1946+3417. Through measurement of the both the advance of\nperiastron and Shapiro delay for this system, we determine the mass of the\npulsar, companion and the inclination of the orbit to be 1.828(22) Msun,\n0.2656(19) Msun and 76.4(6) , under the assumption that general relativity is\nthe true description of gravity. Notably, this is the third highest mass\nmeasured for any pulsar. Using these masses and the astrometric properties of\nPSR J1946+3417 we examine three proposed formation channels for eccentric MSP\nbinaries. While our results are consistent with eccentricity growth driven by a\ncircumbinary disk or neutron star to strange star phase transition, we rule out\nrotationally delayed accretion-induced collapse as the mechanism responsible\nfor the configuration of the PSR J1946+3417 system.", + "category": "astro-ph" + }, + { + "text": "Spatially Resolved Stellar Populations of $0.30.3 and/or\nunequal-mass companions (M_2/M_1<0.1) can decay by three-body interactions to\nthe gravitational wave emission regime in less than a Hubble time. The stellar\ncusp is significantly eroded, and cores as shallow as \\rho\\propto r^-0.7 may\ndevelop from a pre-existing singular isothermal density profile. A population\nof HVSs is ejected in the host galaxy halo, with a total mass ~M_2. We scale\nour results to the scattering of stars bound to Sgr A*, the massive black hole\nin the Galactic Center, by an inspiraling companion of intermediate mass.\nDepending on binary mass ratio, eccentricity, and initial slope of the stellar\ncusp, a core of radius ~0.1 pc typically forms in 1-10 Myr. On this timescale\nabout 500-2500 HVSs are expelled with speeds sufficiently large to escape the\ngravitational potential of the Milky Way.", + "category": "astro-ph" + }, + { + "text": "Wavelet analysis of MCG-6-30-15 and NGC 4051: a possible discovery of\n QPOs in 2:1 and 3:2 resonance: Following our previous work of Lachowicz & Czerny (2005), we explore further\nthe application of the continuous wavelet transform to X-ray astronomical\nsignals. Using the public archive of the XMM-Newton satellite, we analyze all\navailable EPIC-pn observations for nearby Seyfert 1 galaxies MCG-6-30-15 and\nNGC 4051. We confine our analysis to 0.002-0.007 Hz frequency band in which, on\nthe way of theoretically motivated premises, some quasi-periodic oscillations\n(QPOs) are expected to be found. We find that indeed wavelet power histogram\nanalysis reveals such QPOs centered at two frequencies of ~2.5E-3 Hz and 4-6E-3\nHz, respectively. We show that these quasi-periodic features can be\ndisentangled from the Poisson noise contamination level what is hardly to\nachieve with the standard Fourier analysis. Interestingly, we find some of them\nto be in 2:1 or 3:2 ratio. If real, our finding may be considered as a link\nbetween QPOs observed in AGN and kHz QPOs seen in X-ray binary systems.", + "category": "astro-ph" + }, + { + "text": "Alternating Direction Implicit Method for Two-Dimensional Fokker-Planck\n Equation of Dense Spherical Stellar Systems: The Fokker-Planck (FP) model is one of the commonly used methods for studies\nof the dynamical evolution of dense spherical stellar systems such as globular\nclusters and galactic nuclei. The FP model is numerically stable in most cases,\nbut we find that it encounters numerical difficulties rather often when the\neffects of tidal shocks are included in two-dimensional (energy and angular\nmomentum space) version of the FP model or when the initial condition is\nextreme (e.g., a very large cluster mass and a small cluster radius). To avoid\nsuch a problem, we have developed a new integration scheme for a\ntwo-dimensional FP equation by adopting an Alternating Direction Implicit (ADI)\nmethod given in the Douglas-Rachford split form. We find that our ADI method\nreduces the computing time by a factor of ~2 compared to the fully implicit\nmethod, and resolves problems of numerical instability.", + "category": "astro-ph" + }, + { + "text": "Optimal limits on f_{NL}^{local} from WMAP 5-year data: We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP\ndata. Marginalizing over the amplitude of foreground templates we get -4 <\nf_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses\nare roughly 40% larger than these. The probability that a Gaussian simulation,\nanalyzed using our estimator, gives a result larger in magnitude than the one\nwe find is 7%. Our pipeline gives consistent results when applied to the three\nand five year WMAP data releases and agrees well with the results from our own\nsub-optimal pipeline. We find no evidence of any residual foreground\ncontamination.", + "category": "astro-ph" + }, + { + "text": "Solution to the conflict between the resolved and unresolved galaxy\n stellar mass estimation from the perspective of JWST: By utilizing the spatially-resolved photometry of galaxies at $0.2 500 microJy, and that these faint polarized radio\nsources are more highly polarized than the strong source population. The median\nfractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I\nflux density between 1 and 30 mJy; approximately three times larger than\nsources with I > 100 mJy. The majority of the polarized sources have been\nidentified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey\n(SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC\n5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty\nAGNs, or with ellipticals with an aging stellar population. A few host galaxies\nhave colors that suggests significant PAH emission in the near-infrared. A\nsmall fraction, 12%, of the polarized sources are not detected in the SWIRE\ndata. None of the polarized sources in our sample appears to be associated with\nan actively star-forming galaxy.", + "category": "astro-ph" + }, + { + "text": "A Stellar Flare during the Transit of the Extrasolar Planet OGLE-TR-10b: We report a stellar flare occurring during a transit of the exoplanet\nOGLE-TR-10b, an event not previously reported in the literature. This reduces\nthe observed transit depth, particularly in the u'-band, but flaring could also\nbe significant in other bands and could lead to incorrect planetary parameters.\nWe suggest that OGLE-TR-10a is an active planet-hosting star and has an\nunusually high X-ray luminosity.", + "category": "astro-ph" + }, + { + "text": "Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies: We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of\nthe rare population of local galaxies that have properties that are very\nsimilar to distant Lyman Break Galaxies. Our six targets were specifically\nselected because they have optical emission-line properties that are\nintermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data\nprovide an important diagnostic of the presence of an AGN. We find X-ray\nluminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities\nthat are higher than values in pure starburst galaxies by factors ranging from\n~ 3 to 30. This strongly suggests the presence of an AGN in at least some of\nthe galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O\nIII]\\lambda 5007 emission-line are low by about an order-of-magnitude compared\nto Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN.\nEither the AGN hard X-rays are significantly obscured or the [O III] emission\nis dominated by the starburst. We searched for an iron emission line at ~ 6.4\nkeV, which is a key feature of obscured AGN, but only detected emission at the\n~ 2\\sigma level. Finally, we find that the ratios of the mid-infrared (24\\mu m)\ncontinuum to [O III]\\lambda 5007 luminosities in these LBAs are higher than the\nvalues for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we\nconclude that an AGN is likely to be present, but that the bolometric\nluminosity is produced primarily by an intense starburst. If these black holes\nare radiating at the Eddington limit, their masses would lie in the range of\n10^5 to 10^6 M_{sun}. These objects may offer ideal local laboratories to\ninvestigate the processes by which black holes grew in the early universe.", + "category": "astro-ph" + }, + { + "text": "Non-parametric Reconstruction of Photon Escape Fraction from\n Reionization: One of the most crucial yet poorly constrained parameters in modelling the\nionizing emissivity is the escape fraction of photons from star-forming\ngalaxies. Several theoretical and observational studies have been conducted\nover the past few years, but consensus regarding its redshift evolution has yet\nto be achieved. We present here the first non-parametric reconstruction of this\nparameter as a function of redshift from a data-driven reionization model using\na Gaussian Process Regression method. Our finding suggests a mild redshift\nevolution of escape fraction with a mean value of $4\\%,7\\%,\\sim10\\%$ at\n$z=2,6,12$. However, a constant escape fraction of $6-10\\%$ at $z\\gtrsim 6$ is\nstill allowed by current data and also matches other reionization-related\nobservations. With the detection of fainter high redshift galaxies from\nupcoming observations of JWST, the approach presented here will be a robust\ntool to put the most stringent constraint on escape fraction as well as\nreionization histories.", + "category": "astro-ph" + }, + { + "text": "Magnetized, Relativistic Jets: Extragalactic relativistic jets are composed by charged particles and\nmagnetic fields, as inferred from the synchrotron emission that we receive from\nthem. The Larmor radii of the particles propagating along the magnetic field\nare much smaller than the scales of the problem, providing the necessary\ncoherence to the system to treat is as a flow. We can thus study them using\nrelativistic magnetohydrodynamics. As a first step, we have studied the\nstructure of steady-state configurations of jets by using numerical\nsimulations. We have used a helical field configuration and have changed\ndifferent relevant parameters that control the way in which the energy flux is\ndistributed in jets (namely, the proportion of the energy flux carried by\ninternal, kinetic or magnetic energy). Our results show significant differences\namong the different kinds of jets. Finally, we also report on results based on\nsynthetic maps of our simulated jets.", + "category": "astro-ph" + }, + { + "text": "Thermal Convection in Stars and in Their Atmosphere: Thermal convection is one of the main mechanisms of heat transport and mixing\nin stars in general and also in the photospheric layers which emit the\nradiation that we observe with astronomical instruments. The present lecture\nnotes first introduce the role of convection in astrophysics and explain the\nbasic physics of convection. This is followed by an overview on the modelling\nof convection. Challenges and pitfalls in numerical simulation based modelling\nare discussed subsequently. Finally, a particular application for the\npreviously introduced concepts is described in more detail: the study of\nconvective overshooting into stably stratified layers around convection zones\nin stars.", + "category": "astro-ph" + }, + { + "text": "A Lagrangian Dynamical Theory for the Mass Function of Cosmic\n Structures: I Dynamics: A new theory for determining the mass function of cosmic structures is\npresented. It relies on a realistic treatment of collapse dynamics.\nGravitational collapse is analyzed in the Lagrangian perturbative framework.\nLagrangian perturbations provide an approximation of truncated type, i.e.\nsmall-scale structure is filtered out. The collapse time is suitably defined as\nthe instant at which orbit crossing takes place. The convergence of the\nLagrangian series in predicting the collapse time of a homogeneous ellipsoid is\ndemonstrated; it is also shown that third-order calculations are necessary in\npredicting collapse. Then, the Lagrangian prediction, with a correction for\nquasi-spherical perturbations, can be used to determine the collapse time of a\nhomogeneous ellipsoid in a fast and precise way. Furthermore, ellipsoidal\ncollapse can be considered as a particular truncation of the Lagrangian series.\nGaussian fields with scale-free power spectra are then considered. The\nLagrangian series for the collapse time is found to converge when the collapse\ntime is not large. In this case, ellipsoidal collapse gives a fast and accurate\napproximation of the collapse time; spherical collapse is found to poorly\nreproduce the collapse time, even in a statistical sense. Analytical fits of\nthe distribution functions of the inverse collapse times, as predicted by the\nellipsoid model and by third-order Lagrangian theory, are given. These will be\nnecessary for a determination of the mass function, which will be given in\npaper II.", + "category": "astro-ph" + }, + { + "text": "Equation of state description of the dark energy transition between\n quintessence and phantom regimes: The dark energy crossing of the cosmological constant boundary (the\ntransition between the quintessence and phantom regimes) is described in terms\nof the implicitly defined dark energy equation of state. The generalizations of\nthe models explicitly constructed to exhibit the crossing provide the insight\ninto the cancellation mechanism which makes the transition possible.", + "category": "astro-ph" + }, + { + "text": "Asteroids and Comets: Asteroids and comets are remnants from the era of Solar System formation over\n4.5 billion years ago, and therefore allow us to address two fundamental\nquestions in astronomy: what was the nature of our protoplanetary disk, and how\ndid the process of planetary accretion occur? The objects we see today have\nsuffered many geophysically-relevant processes in the intervening eons that\nhave altered their surfaces, interiors, and compositions. In this chapter we\nreview our understanding of the origins and evolution of these bodies, discuss\nthe wealth of science returned from spacecraft missions, and motivate important\nquestions to be addressed in the future.", + "category": "astro-ph" + }, + { + "text": "Radio continuum and far-infrared emission from the galaxies in the\n Eridanus group: The Eridanus galaxies follow the well-known radio-FIR correlation. Majority\n(70%) of these galaxies have their star formation rates below that of the Milky\nWay. The galaxies having a significant excess of radio emission are identified\nas low luminosity AGNs based on their radio morphologies obtained from the GMRT\nobservations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the\ngroup. The two most far-infrared and radio luminous galaxies in the group have\noptical and HI morphologies suggestive of recent tidal interactions. The\nEridanus group also has two far-infrared luminous but radio-deficient galaxies.\nIt is believed that these galaxies are observed within a few Myr of the onset\nof an intense star formation episode after being quiescent for at least a 100\nMyr. The upper end of the radio luminosity distribution of the Eridanus\ngalaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field\ngalaxies, other groups, and late-type galaxies in nearby clusters.", + "category": "astro-ph" + }, + { + "text": "AEGIS: The Morphologies of Green Galaxies at 0.4f}\n(F(x,v)-f) d^3x d^3v (with F(x,v) the coarse-grained distribution function)\nalways decreases on mixing. D(f) gives the excess mass from values of\nF(x,v))>f. This novel form of the mixing theorem extends the maximum\nphase-space density argument to all values of f. The excess-mass function can\nbe computed from N-body simulations and is additive: the excess mass of a\ncombination of non-overlapping systems is the sum of their individual D(f). I\npropose a novel interpretation for the coarse-grained distribution function,\nwhich avoids conceptual problems with the mixing theorem.\n As an example application, I show that for self-gravitating cusps (rho propto\nr^{-gamma} as r->0) the excess mass D propto f^{-2(3-gamma)/(6-gamma)} as\nf->oo, i.e. steeper cusps are less mixed than shallower ones, independent of\nthe shape of surfaces of constant density or details of the distribution\nfunction (e.g. anisotropy). This property, together with the additivity of D(f)\nand the mixing theorem, implies that a merger remnant cannot have a cusp\nsteeper than the steepest of its progenitors. Furthermore, I argue that the\nremnant's cusp should not be shallower either, implying that the steepest cusp\nalways survives.", + "category": "astro-ph" + }, + { + "text": "Multiple stellar populations in Schwarzschild modeling and the\n application to the Fornax dwarf: Dwarf spheroidal (dSph) galaxies are believed to be strongly dark matter\ndominated and thus are considered perfect objects to study dark matter\ndistribution and test theories of structure formation. They possess resolved,\nmultiple stellar populations that offer new possibilities for modeling. A\npromising tool for the dynamical modeling of these objects is the Schwarzschild\norbit superposition method. In this work we extend our previous implementation\nof the scheme to include more than one population of stars and a more general\nform of the mass-to-light ratio function. We tested the improved approach on a\nnearly spherical, gas-free galaxy formed in the cosmological context from the\nIllustris simulation. We modeled the binned velocity moments for stars split\ninto two populations by metallicity and demonstrate that in spite of larger\nsampling errors the increased number of constraints leads to significantly\ntighter confidence regions on the recovered density and velocity anisotropy\nprofiles. We then applied the method to the Fornax dSph galaxy with stars\nsimilarly divided into two populations. In comparison with our earlier work, we\nfind the anisotropy parameter to be slightly increasing, rather than\ndecreasing, with radius and more strongly constrained. We are also able to\ninfer anisotropy for each stellar population separately and find them to be\nsignificantly different.", + "category": "astro-ph" + }, + { + "text": "Sources of X-rays from galaxies: Galactic X-ray emission is a manifestation of various high-energy phenomena\nand processes. The brightest X-ray sources are typically accretion-powered\nobjects: active galactic nuclei and low- or high-mass X-ray binaries. Such\nobjects with X-ray luminosities of > 10^{37} ergs/s can now be detected\nindividually in nearby galaxies. The contributions from fainter discrete\nsources (including cataclysmic variables, active binaries, young stellar\nobjects, and supernova remnants) are well correlated with the star formation\nrate or stellar mass of galaxies. The study of discrete X-ray sources is\nessential to our understanding of stellar evolution, dynamics, and end-products\nas well as accretion physics. With the subtraction of the discrete source\ncontributions, one can further map out truly diffuse X-ray emission, which can\nbe used to trace the feedback from active galactic nuclei, as well as from\nstars, both young and old, in the form of stellar winds and supernovae. The\nX-ray emission efficiency, however, is only about 1% of the energy input rate\nof the stellar feedback alone. The bulk of the feedback energy is most likely\ngone with outflows into large-scale galactic halos. Much is yet to be\ninvestigated to comprehend the role of such outflows in regulating the\necosystem, hence the evolution of galaxies. Even the mechanism of the diffuse\nX-ray emission remains quite uncertain. A substantial fraction of the emission\ncannot arise directly from optically-thin thermal plasma, as commonly assumed,\nand most likely originates in its charge exchange with neutral gas. These\nuncertainties underscore our poor understanding of the feedback and its\ninterplay with the galaxy evolution.", + "category": "astro-ph" + }, + { + "text": "Massive black holes at high redshifts from superconducting cosmic\n strings: The observation of quasars at high redshifts presents a mystery in the theory\nof black hole formation. In order to source such objects, one often relies on\nthe presence of heavy seeds ($M \\approx 10^{4-6} \\, M_{\\odot}$) in place at\nearly times. Unfortunately, the formation of these heavy seeds are difficult to\nrealize within the standard astrophysical context. Here, we investigate whether\nsuperconducting cosmic string loops can source sufficiently strong\noverdensities in the early universe to address this mystery. We review a set of\ndirect collapse conditions under which a primordial gas cloud will undergo\nmonolithic collapse into a massive black hole (forming with a mass of $M_{BH}\n\\approx 10^5 \\, M_{\\odot}$ at $z \\approx 300$ in our scenario), and\nsystematically show how superconducting cosmic string loops can satisfy such\nconditions in regions of the $G\\mu-I$ parameter space.", + "category": "astro-ph" + }, + { + "text": "Bridging the Gap Between Simply Parametrized and Free-Form Pixelated\n Models of Galaxy Lenses: The Case of WFI 2033-4723 Quad: We study the radial and azimuthal mass distribution of the lensing galaxy in\nWFI2033-4723. Mindful of the fact that modeling results depend on modeling\nassumptions, we examine two very different recent models: simply parametrized\n(SP) models from the H0LiCOW collaboration, and pixelated free-form (FF) GLASS\nmodels. In addition, we fit our own models which are a compromise between the\nastrophysical grounding of SP, and the flexibility of FF approaches. Our models\nconsist of two offset parametric mass components, and generate many solutions,\nall fitting the quasar point image data. Among other results, we show that to\nreproduce point image properties the lensing mass must be lopsided, but the\norigin of this asymmetry can reside in the main lens plane or along the line of\nsight. We also show that there is a degeneracy between the slope of the density\nprofile and the magnitude of external shear, and that the models from various\nmodeling approaches are connected not by the mass sheet degeneracy, but by a\nmore generalized transformation. Finally, we discuss interpretation degeneracy\nwhich afflicts all mass modeling: inability to correctly assign mass to the\nmain lensing galaxy vs. nearby galaxies or line of sight structures. While this\nmay not be a problem for the determination of $H_0$, interpretation degeneracy\nmay become a major issue for the detailed study of galaxy structure.", + "category": "astro-ph" + }, + { + "text": "Synchrotron radiation from the fast tail of dynamical ejecta of neutron\n star mergers: We find, using high resolution numerical relativistic simulations, that the\ntail of the dynamical ejecta of neutron star mergers extends to mildly\nrelativistic velocities faster than $0.7c$. The kinetic energy of this fast\ntail is $\\sim 10^{47}$--$10^{49}$ erg, depending on the neutron star equation\nof state and on the binary masses. The synchrotron flare arising from the\ninteraction of this fast tail with the surrounding ISM can power the observed\nnon-thermal emission that followed GW170817, provided that the ISM density is\n$\\sim 10^{-2}\\,{\\rm cm^{-3}}$, the two neutron stars had roughly equal masses\nand the neutron star equation of state is soft (small neutron star radii). One\nof the generic predictions of this scenario is that the cooling frequency\ncrosses the X-ray band on a time scale of a few months to a year, leading to a\ncooling break in the X-ray light curve. If this dynamical ejecta scenario is\ncorrect, we expect that the synchrotron radio flare from the ejecta that have\nproduced the macronova/kilonova emission will be observable on time scales of\n$10^3$ to $10^5$ days. Further multi-frequency observations will confirm or\nrule out this dynamical ejecta scenario.", + "category": "astro-ph" + }, + { + "text": "Kinematics of Black Hole X-ray Binary GRS 1915+105: The space velocity of a stellar black hole encodes the history of its\nformation and evolution. Here we measure the 3-dimensional motion of the\nmicroquasar GRS 1915+105, using a decade of astrometry with the NRAO Very Long\nBaseline Array, together with the published radial velocity. The velocity in\nthe Galactic Plane deviates from circular rotation by 53-80 +_ 8 km/s, where\nthe range covers any specific distance from 6-12 kpc. Perpendicular to the\nplane, the velocity is only 10 +_ 4 km/s. The peculiar velocity is minimized at\na distance 9-10 kpc, and is then nearly in the radial direction towards the\nGalactic Center. We discuss mechanisms for the origin of the peculiar velocity,\nand conclude that it is most likely a consequence of Galactic velocity\ndiffusion on this old binary, rather than the result of a supernova kick during\nthe formation of the 14 Mo black hole. Finally, a brief comparison is made with\n4 other BH binaries whose kinematics are well determined.", + "category": "astro-ph" + }, + { + "text": "Inhomogeneous Big Bang Nucleosynthesis: Upper Limit on Omega_b and\n Production of Lithium, Beryllium, and Boron: We examine the Big Bang nucleosynthesis (BBN) process in the presence of\nsmall-scale baryon inhomogeneities. Primordial abundance yields for D, He4,\nLi6, Li7, Be9, and B11 are computed for wide ranges of parameters\ncharacterizing the inhomogeneities taking account of all relevant diffusive and\nhydrodynamic processes. These calculations may be of interest due to (a) recent\nobservations of the anisotropies in the cosmic microwave background radiation\nfavoring slightly larger baryonic contribution to the critical density,\nOmega_b, than allowed by a standard BBN scenario and (b) new observational\ndeterminations of Li6 and Be9 in metal-poor halo stars. We find considerable\nparameter space in which production of D and He4 is in agreement with\nobservational constraints even for Omega_b h^2 a factor 2-3 larger than the\nOmega_b inferred from standard BBN. Nevertheless, in this parameter space\nsynthesis of Li7 in excess of the inferred Li7 abundance on the Spite plateau\nresults. Production of Li6, Be9, and B11 in inhomogeneous BBN scenarios is\nstill typically well below the abundance of these isotopes observed in the most\nmetal-poor stars to date thus neither confirming nor rejecting inhomogeneous\nBBN. In an appendix we summarize results of a reevaluation of baryon diffusion\nconstants entering inhomogeneous BBN calculations.", + "category": "astro-ph" + }, + { + "text": "BST1047+1156: A (Failing) Ultradiffuse Tidal Dwarf in the Leo I Group: We use deep Hubble Space Telescope imaging to study the resolved stellar\npopulations in BST1047+1156, a gas-rich, ultradiffuse dwarf galaxy found in the\nintragroup environment of the Leo I galaxy group. While our imaging reaches\napproximately two magnitudes below the tip of the red giant branch at the Leo I\ndistance of 11 Mpc, we find no evidence for an old red giant sequence that\nwould signal an extended star formation history for the object. Instead, we\nclearly detect the red and blue helium burning sequences of its stellar\npopulations, as well as the fainter blue main sequence, all indicative of a\nrecent burst of star formation having taken place over the past 50--250 Myr.\nComparing to isochrones for young metal-poor stellar populations, we infer this\npost-starburst population to be moderately metal poor, with metallicity [M/H]\nin the range -1 to -1.5. The combination of a young, moderately metal-poor post\nstarburst population and no old stars motivates a scenario in which BST1047 was\nrecently formed during a weak burst of star formation in gas that was tidally\nstripped from the outskirts of the neighboring massive spiral M96. BST1047's\nextremely diffuse nature, lack of ongoing star formation, and disturbed HI\nmorphology all argue that it is a transitory object, a \"failing tidal dwarf\" in\nthe process of being disrupted by interactions within the Leo I group. Finally,\nin the environment surrounding BST1047, our imaging also reveals the old,\nmetal-poor ([M/H]=-1.3 +/- 0.2) stellar halo of M96 at a projected radius of 50\nkpc.", + "category": "astro-ph" + }, + { + "text": "Interstellar extinction in twenty open star clusters: The interstellar extinction law in twenty open star clusters namely Berkeley\n7, Collinder 69, Hogg 10, NGC 2362, Czernik 43, NGC 6530, NGC 6871, Bochum 10,\nHaffner 18, IC 4996, NGC 2384, NGC 6193, NGC 6618, NGC 7160, Collinder 232,\nHaffner 19, NGC 2401, NGC 6231, NGC 6823 and NGC 7380 have been studied in the\noptical and near-IR wavelength ranges. The difference between maximum and\nminimum values of E(B-V) indicates the presence of non-uniform extinction in\nall the clusters except Collinder 69, NGC 2362 and NGC 2384. The colour excess\nratios are consistent with a normal extinction law for the clusters NGC 6823,\nHaffner 18, Haffner 19, NGC 7160, NGC 6193, NGC 2401, NGC 2384, NGC 6871, NGC\n7380, Berkeley 7, Collinder 69 and IC 4996. We found that differential\ncolour-excess which may be due to the occurrence of dust and gas inside the\nclusters, decreases with age of the clusters. A spatial variation of colour\nexcess is found in NGC 6193 in sense that it decreases from east to west in\ncluster region. For cluster Berkeley 7, NGC 7380 and NGC 6871, a dependence of\ncolour excess with spectral class and luminosity is observed. Eight stars in\nCollinder 232, four stars in NGC 6530 and one star in NGC 6231 have colour\nexcess flux in near-IR. This indicates that these stars may have circumstellar\nmaterial around them.", + "category": "astro-ph" + }, + { + "text": "Dependence of the He/H8 emission ratio on brightness, temperature, and\n structuring of prominences: We investigate the dependence of the He/H8 emission ratio on kinetic\ntemperature and total Balmer brightness. The line pair He\\,{\\sc i}\\,3888\\,\\AA{}\nand H$_8$\\,3889 has been observed simultaneously with the Ca II 8498 line in a\nnumber of quiescent prominences. The He/H8 emission ratio R is found to cover\ndefined parts of a general anti-relation with the total H8 emission, depending\non the kinetic temperature, T_kin, of the individual prominence: High H8\nbrightness is related to small R and T_kin values, and preferably occurs in\nprominences with a less significant fine-structure.", + "category": "astro-ph" + }, + { + "text": "Clustered Massive Star Formation in Molecular Clouds: I review some important questions in the field of massive star formation:\nWhat are the initial conditions for proto star clusters and how do they arise?\nWhat are the initial conditions for individual massive star formation within\nstar clusters? How do massive protostars accumulate their mass? I compare the\nTurbulent Core Model (McKee & Tan 2003) to several nearby regions, including\nOrion KL. Here I also discuss the origin of BN's high proper motion.", + "category": "astro-ph" + }, + { + "text": "Prompt emission of GRB 121217A from gamma-rays to the NIR: The mechanism that causes the prompt-emission episode of gamma-ray bursts\n(GRBs) is still widely debated despite there being thousands of prompt\ndetections. The favoured internal shock model relates this emission to\nsynchrotron radiation. However, it does not always explain the spectral indices\nof the shape of the spectrum, often fit with empirical functions.\nMulti-wavelength observations are therefore required to help investigate the\npossible underlying mechanisms that causes the prompt emission. We present GRB\n121217A, for which we were able to observe its near-infrared (NIR) emission\nduring a secondary prompt-emission episode with the Gamma-Ray Burst Optical\nNear-infrared Detector (GROND) in combination with the Swift and Fermi\nsatellites, covering an energy range of 0.001 keV to 100 keV. We determine a\nphotometric redshift of z=3.1+/-0.1 with a line-of-sight extinction of A_V~0\nmag, utilising the optical/NIR SED. From the afterglow, we determine a bulk\nLorentz factor of Gamma~250 and an emission radius of R<10^18 cm. The\nprompt-emission broadband spectral energy distribution is well fit with a\nbroken power law with b1=-0.3+/-0.1, b2=0.6+/-0.1 that has a break at\nE=6.6+/-0.9 keV, which can be interpreted as the maximum injection frequency.\nSelf-absorption by the electron population below energies of E_a<6 keV suggest\na magnetic field strength of B~10^5 G. However, all the best fit models\nunderpredict the flux observed in the NIR wavelengths, which also only\nrebrightens by a factor of ~2 during the second prompt emission episode, in\nstark contrast to the X-ray emission, which rebrightens by a factor of ~100,\nsuggesting an afterglow component is dominating the emission. We present GRB\n121217A one of the few GRBs for which there are multi-wavelength observations\nof the prompt-emission period and show that it can be understood with a\nsynchrotron radiation model.", + "category": "astro-ph" + }, + { + "text": "Fast-varying time lags in the Quasi-periodic Oscillation in GRS 1915+105: The properties of sub-second time variability of the X-ray emission of the\nblack-hole binary GRS 1915+105 are very complex and strictly connected to its\npatterns of variability observed on long time scales. A key aspect for\ndetermining the geometry of the accretion flow is the study of time lags\nbetween emission at different energies, as they are associated to key time\nscales of the system. In particular, it is important to examine the lags\nassociated to the strong low-frequency Quasi-periodic Oscillations (QPOs), as\nthe QPOs provide unambiguous special frequencies to sample the variability. We\nhave analyzed data from an observation with the AstroSat satellite, in which\nthe frequency of the low-frequency QPO varies smoothly between 2.5 and 6.6 Hz\non a time scale of ~10 hours. The derived phase lags show the same properties\nand evolution of those observed on time scales of a few hundred days,\nindicating that changes in the system geometry can take place on times below\none day. We fit selected energy spectra of the source and rms and phase-lag\nspectra of the QPO with a time-variable Comptonization model, as done\npreviously to RossiXTE data of the same source, and find that indeed the\nderived parameters match those obtained for variations on much longer time\nscales.", + "category": "astro-ph" + }, + { + "text": "On the origin of X-ray spectra in luminous blazars: Gamma-ray luminosities of some quasar-associated blazars imply jet powers\nreaching values comparable to the accretion power even if assuming very strong\nDoppler boosting and very high efficiency of gamma-ray production. With much\nlower radiative efficiencies of protons than of electrons, and the recent\nreports of very strong coupling of electrons with shock-heated protons\nindicated by Particle-in-Cell (PIC) simulations, the leptonic models seem to be\nstrongly favored over the hadronic ones. However, the electron-proton coupling\ncombined with the ERC (External-Radiation-Compton) models of gamma-ray\nproduction in leptonic models predict extremely hard X-ray spectra, with energy\nindices about 0. This is inconsistent with the observed 2-10 keV slopes of\nblazars, which cluster around an index value of 0.6. This problem can be\nresolved by assuming that electrons can be cooled down radiatively to\nnon-relativistic energies, or that blazar spectra are entirely dominated by the\nSSC (Synchrotron-Self Compton) component up to at least 10 keV. Here, we show\nthat the required cooling can be sufficiently efficient only at distances r <\n0.03pc. SSC spectra, on the other hand, can be produced roughly co-spatially\nwith the observed synchrotron and ERC components, which are most likely located\nroughly at a parsec scale. We show that the dominant SSC component can also be\nproduced much further than the dominant synchrotron and ERC components, at\ndistances larger than 10 parsecs. Hence, depending on the spatial distribution\nof the energy dissipation along the jet, one may expect to see\ngamma-ray/optical events with either correlated or uncorrelated X-rays. In all\ncases the number of electron-positron pairs per proton is predicted to be very\nlow. The direct verification of the proposed SSC scenario requires sensitive\nobservations in the hard X-ray band which is now possible with the NuSTAR\nsatellite.", + "category": "astro-ph" + }, + { + "text": "The Radiative Efficiency of Hot Accretion Flows: Two significant progresses have been made in the past years on our\nunderstanding of hot accretion flows. One is that only a small fraction of\naccretion flow available at the outer boundary can finally falls onto the black\nhole while most of them is lost in outflow. Another one is that electrons may\ndirectly receive a large fraction of the viscously dissipated energy in the\naccretion flow, i.e, $\\delta\\sim 0.1-0.5$. The radiative efficiency of hot\naccretion flow when these two progresses are taken into account has not been\nsystematically studied and is the subject of the present paper. We consider two\nregimes of hot accretion model. One is the advection dominated accretion flows\n(ADAFs) which lie on low accretion rate regime, $\\la 10\\alpha^2\\ledd/c^2$;\nanother being the luminous hot accretion flows (LHAFs) which lie above this\naccretion rate. For the latter, we assume that the accretion flow will has a\ntwo-phase structure above a certain accretion rate, and a simplification is\nadopted in our calculation of the dynamics. Our results indicate that the\nradiative efficiency of hot accretion flow increases with the accretion rate\nand is highly enhanced by the direct viscous heating to electrons compared to\nthe previous case of $\\delta\\ll 1$. When the accretion rate is high, the\nradiative efficiency of hot accretion flow is comparable to that of the\nstandard thin disk. Fitting formulae of radiative efficiency as a function of\naccretion rate for various $\\delta$ values are presented.", + "category": "astro-ph" + }, + { + "text": "JWST high-z galaxy constraints on warm and cold dark matter models: We compare properties of high-redshift galaxies observed by JWST with\nhydrodynamical simulations, in the standard cold dark matter model and in warm\ndark matter models with a suppressed linear matter power spectrum. We find that\ncurrent data are not in tension with cold dark matter nor with warm dark matter\nmodels with mWDM > 2 keV, since they probe bright and rare objects whose\nphysical properties are similar in the different scenarios. We also show how\ntwo observables, the galaxy luminosity functions and the galaxy correlation\nfunction at small scales of faint objects, can be promising tools for\ndiscriminating between the different dark matter models. Further hints may come\nfrom early stellar-mass statistics and galaxy CO emission.", + "category": "astro-ph" + }, + { + "text": "A Fourier method for the determination of focus for telescopes with\n stars: We introduce a Fourier method (Fm) for the determination of best focus for\ntelescopes with stars. Our method fits a power function, that we will derive in\nthis paper, to a set of images taken as a function of focuser position. The\nbest focus position is where the power is maximum. Fm was first tested with\nsmall refractor and Schmidt-Cassegrain (SCT) telescopes. After the successful\nsmall telescope tests, we then tested Fm with a 2 m Ritchey-Chr\\'etien-Coud\\'e\n(RCC). Our tests show that Fm is immune to the problems inherent in the popular\nhalf-flux diameter method.", + "category": "astro-ph" + }, + { + "text": "The mean free path of ionizing photons at 5 < z < 6: evidence for rapid\n evolution near reionization: The mean free path of ionizing photons, $\\lambda_{\\rm mfp}$, is a key factor\nin the photoionization of the intergalactic medium (IGM). At $z \\gtrsim 5$,\nhowever, $\\lambda_{\\rm mfp}$ may be short enough that measurements towards QSOs\nare biased by the QSO proximity effect. We present new direct measurements of\n$\\lambda_{\\rm mfp}$ that address this bias and extend up to $z \\sim 6$ for the\nfirst time. Our measurements at $z \\sim 5$ are based on data from the Giant\nGemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At $z\n\\sim 6$ we use QSO spectra from Keck ESI and VLT X-Shooter. We measure\n$\\lambda_{\\rm mfp} = 9.09^{+1.62}_{-1.28}$ proper Mpc and\n$0.75^{+0.65}_{-0.45}$ proper Mpc (68% confidence) at $z = 5.1$ and 6.0,\nrespectively. The results at $z = 5.1$ are consistent with existing\nmeasurements, suggesting that bias from the proximity effect is minor at this\nredshift. At $z = 6.0$, however, we find that neglecting the proximity effect\nbiases the result high by a factor of two or more. Our measurement at $z = 6.0$\nfalls well below extrapolations from lower redshifts, indicating rapid\nevolution in $\\lambda_{\\rm mfp}$ over $5 < z < 6$. This evolution disfavors\nmodels in which reionization ended early enough that the IGM had time to fully\nrelax hydrodynamically by $z = 6$, but is qualitatively consistent with models\nwherein reionization completed at $z = 6$ or even significantly later. Our mean\nfree path results are most consistent with late reionization models wherein the\nIGM is still 20% neutral at $z=6$, although our measurement at $z = 6.0$ is\neven lower than these models prefer.", + "category": "astro-ph" + }, + { + "text": "On the origin of cosmic web: The emergence of one and two-dimensional configurations -- Zeldovich pancakes\n-- progenitors of the observed filaments and clusters and groups of galaxies,\nis predicted by means of a developed kinetic approach in analyzing the\nevolution of initial density perturbations. The self-consistent gravitational\ninteraction described by Vlasov-Poisson set of equations with branching\nconditions is shown to predict two-dimensional structures as of layers of\nincreased density and voids between them, i.e. the cellular macro-structure of\nthe Universe. The modified potential of weak-field General Relativity is\ninvolved, which enables one to explain the Hubble tension, revealing the\nconceptual discrepancy in the local galactic flows and the cosmological\nexpansion. This demonstrates the possible essential role of self-consistent\ngravity in the formation of the cosmic web.", + "category": "astro-ph" + }, + { + "text": "Mid-infrared spectra of T Tauri disks: Modeling the effects of a small\n inner cavity on CO2 and H2O emission: [Abridged] The inner few AU of disks around young stars are best probed in\nthe infrared. The James Webb Space Telescope (JWST) is now starting to\ncharacterize the chemistry of these regions in unprecedented detail. One\npeculiar subset of sources are the so-called ``CO2-only sources'', in which\nonly a strong 15 $\\mu$m CO2 feature was detected in the spectrum. One scenario\nthat could explain the weak emission from H2O is the presence of a small, inner\ncavity in the disk. If this cavity were to extend past the H2O snowline, but\nnot past the CO2 snowline, this could strongly suppress the H2O line flux\nw.r.t. that of CO2. In this work, we aim to test the validity of this\nstatement. Using the thermo-chemical code Dust And LInes (DALI), we created a\ngrid of T Tauri disk models with an inner cavity, meaning we fully depleted the\ninner region of the disk in gas and dust starting from the dust sublimation\nradius and ranging until a certain cavity radius. We present the evolution of\nthe CO2 and H2O spectra of a disk with inner cavity size, showing that, when a\nlarge-enough cavity is introduced, a spectrum that was initially dominated by\nH2O lines can become CO2-dominated instead. However, the cavity size needed for\nthis is around 4-5 AU, exceeding the nominal position of the CO2 snowline in a\nfull disk. The cause of this is most likely the alteration of the thermal\nstructure by the cavity, which pushes the snowlines outward. Alternative\nexplanations for bright CO2 emission are also briefly discussed. Our modeling\nwork shows that it is possible for the presence of a small inner cavity to\nexplain strong CO2 emission in a spectrum. However, the cavity needed to do so\nis larger than what was initially expected. As such, this scenario will be\neasier to test with sufficiently high angular resolution (millimeter)\nobservations.", + "category": "astro-ph" + }, + { + "text": "PAH and nbL Features Detection in Planetary Nebulae NGC 7027 and BD\n +303639 with TIRCAM2 Instrument on 3.6m DOT: High resolution infrared imaging observations of the young Planetary Nebulae\nNGC 7027 and BD +303639, taken with the newly installed TIFR Infrared Camera-II\n(TIRCAM2) on 3.6m Devasthal Optical Telescope (DOT), ARIES, Nainital, are being\nreported. The images are acquired in J, H, K, polycyclic aromatic hydrocarbon\n(PAH) and narrow-band L (nbL) filters. The observations show emission from warm\ndust and PAHs in the circumstellar shells. The imaging of the two objects are\namong the first observations in PAH and nbL bands using TIRCAM2 on DOT. The NGC\n7027 images in all bands show similar elliptical morphology with ~6\".7 and\n~4\".5 semi-major and semi-minor axes. Considering size up to 10% of peak value\nthe nebula extends upto 8\" from the central star revealing a multipolar\nevolution. The relatively cooler BD +303639 shows a rectangular-ring shaped\nnebula. In J and H bands it shows an angular diameter of ~8\", while a smaller\n~6\".9 size is observed in K, PAH and nbL bands. The 3.28 micron emission\nindicates presence of PAHs at about 6000 and 5000 AU from the central stars in\nNGC 7027 and BD +303639 respectively. Analysis suggests domination of neutral\nPAHs in BD+303639, while in NGC 7027 there is higher ionization and more\nprocessed PAH population.", + "category": "astro-ph" + }, + { + "text": "Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae: We present detailed NLTE synthetic spectra of hydrodynamic SNe Ia models. We\nmake no assumptions about the form of the spectrum at the inner boundary. We\ncalculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar\n``helium detonators.'' Gamma-ray deposition is handled in a simple, accurate\nmanner. We have parameterized the storage of energy that arises from the time\ndependent deposition of radioactive decay energy in a reasonable manner, that\nspans the expected range. We find that the Chandrasekhar-mass deflagration\nmodel W7 of Nomoto etal shows good agreement with the observed spectra of SN\n1992A and SN 1994D, particularly in the UV, where our models are expected to be\nmost accurate. The sub-Chandrasekhar models do not reproduce the UV deficit\nobserved in normal SNe Ia. They do bear some resemblance to sub-luminous SNe\nIa, but the shape of the spectra (i.e. the colors) are opposite to that of the\nobserved ones and the intermediate mass element lines such as Si II, and Ca II\nare extremely weak, which seems to be a generic difficulty of the models.\nAlthough the sub-Chandrasekhar models have a significant helium abundance\n(unlike Chandrasekhar-mass models), helium lines are not prominent in the\nspectra near maximum light and thus do not act as a spectral signature for the\nprogenitor.", + "category": "astro-ph" + }, + { + "text": "An External Shock Origin of GRB $\\textit{141028A}$: The prompt emission of the long, smooth, and single-pulsed gamma-ray burst,\nGRB $\\textit{141028A}$, is analyzed under the guise of an external shock model.\nFirst, we fit the $\\gamma$-ray spectrum with a two-component photon model,\nnamely synchrotron+blackbody, and then fit the recovered evolution of the\nsynchrotron $\\nu F_{\\nu}$ peak to an analytic model derived considering the\nemission of a relativistic blast-wave expanding into an external medium. The\nprediction of the model for the $\\nu F_{\\nu}$ peak evolution matches well with\nthe observations. We observe the blast-wave transitioning into the deceleration\nphase. Further we assume the expansion of the blast-wave to be nearly\nadiabatic, motivated by the low magnetic field deduced from the observations.\nThis allows us to recover within an order of magnitude the flux density at the\n$\\nu F_{\\nu}$ peak, which is remarkable considering the simplicity of the\nanalytic model. Across all wavelengths, synchrotron emission from a single\nforward shock provides a sufficient solution for the observations. Under this\nscenario we argue that the distinction between $\\textit{prompt}$ and $\\textit{\nafterglow}$ emission is superfluous as both early and late time emission\nemanate from the same source. While the external shock model is clearly not a\nuniversal solution, this analysis opens the possibility that at least some\nfraction of GRBs can be explained with an external shock origin of their prompt\nphase.", + "category": "astro-ph" + }, + { + "text": "Investigation of systematic effects in Kepler data: Seasonal variations\n in the light curve of HAT-P-7b: With years of Kepler data currently available, it can now be attempted to\nmeasure variations in planetary transit depths over time. To do so, it is of\nprimary importance to understand which systematic effects may affect the\nmeasurement of transits. We aim to measure the stability of Kepler measurements\nover years of observations. We present a study of the depth of about 500\ntransit events of the Hot Jupiter HAT-P-7b, using 14 quarters (Q0-Q13) of data\nfrom the Kepler Satellite. We find a systematic variation in the depth of the\nprimary transit, related to quarters of data and recurring yearly. These\nseasonal variations are about 1%. Within seasons, we find no evidence for\ntrends. We speculate that the cause of the seasonal variations could be unknown\nfield crowding or instrumental artifacts. Our results show that care must be\ntaken when combining transits throughout different quarters of Kepler data.\nMeasuring the relative planetary radius of HAT-P-7b without taking these\nsystematic effects into account leads to unrealistically low error estimates.\nThis effect could be present in all Kepler targets. If so, relative radius\nmeasurements of all Hot Jupiters to a precision much better than 1% are\nunrealistic.", + "category": "astro-ph" + }, + { + "text": "The F-CHROMA grid of 1D RADYN flare models: Context: Solar flares are the result of the sudden release of magnetic energy\nin the corona. Much of this energy goes into accelerating charged particles to\nhigh velocity. These particles travel along the magnetic field and the energy\nis dissipated when the density gets high enough, primarily in the solar\nchromosphere. Modelling this region is difficult because the radiation energy\nbalance is dominated by strong, optically thick spectral lines.\n Aims: Our aim is to provide the community with realistic simulations of a\nflaring loop with an emphasis on the detailed treatment of the chromospheric\nenergy balance. This will enable a detailed comparison of existing and upcoming\nobservations with synthetic observables from the simulations, thereby\nelucidating the complex interactions in a flaring chromosphere.\n Methods: We used the 1D radiation hydrodynamics code RADYN to perform\nsimulations of the effect of a beam of electrons injected at the apex of a\nsolar coronal loop. A grid of models was produced, varying the total energy\ninput, the steepness, and low-energy cutoff of the beam energy spectrum.\n Results: The full simulation results for a grid of models are made available\nonline. Some general properties of the simulations are discussed.", + "category": "astro-ph" + }, + { + "text": "Demystifying an unidentified EGRET source by VHE gamma-ray observations: In a novel approach in observational high-energy gamma-ray astronomy,\nobservations carried out by imaging atmospheric Cherenkov telescopes provide\nnecessary templates to pinpoint the nature of intriguing, yet unidentified\nEGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking\nadvantage of high spatial resolution images from H.E.S.S. observations, we were\nable to shed new light on the EGRET observed gamma-ray emission in the\nKookaburra complex, whose previous coverage in the literature is somewhat\ncontradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources\n(E>1 GeV), both in positional coincidence with the recently reported pulsar\nwind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations\nat VHE energies, supported by accumulating evidence from observations in the\nradio and X-ray band, are indicative for the PSR/plerionic origin of spatially\ncoincident, but still unidentified Galactic gamma-ray sources from EGRET. This\nnot only supports the already suggested connection between variable, but\nunidentified low-latitude gamma-ray sources with pulsar wind nebulae\n(3EGJ1420-6038 has been suggested as PWN candidate previoulsy), it also\ndocuments the ability of resolving apparently confused EGRET sources by\nconnecting the GeV emission as measured from a large-aperture space-based\ngamma-ray instrument with narrow field-of-view but superior spatial resolution\nobservations by ground-based atmospheric Cherenkov telescopes, a very promising\nidentification technique for achieving convincing individual source\nidentifications in the era of GLAST-LAT.", + "category": "astro-ph" + }, + { + "text": "Optical Outburst of the Gamma-Ray Blazar S4 0954+658 in March-April 2011: We present optical photopolarimetric observations of the BL Lac object S4\n0954+658 obtained with the 70-cm telescope in Crimea, 40-cm telescope in\nSt.Petersburg, and 1.8-m Perkins telescope at Lowell Observatory (Flagstaff,\nAz). After a faint state with a brightness level R ~17.6 mag registered in the\nfirst half of January 2011, the optical brightness of the source started to\nrise and reached ~14.8 mag during the middle of March, showing flare-like\nbehavior. The most spectacular case of intranight variability was observed\nduring the night of 2011 March 9, when the blazar brightened by ~0.7 mag within\n~7 hours. During the rise of the flux the position angle of optical\npolarization rotated smoothly over more than 200 degrees. S4 0954+658 is a\ngamma-ray blazar with gamma-ray flux of (5{\\pm}3)x10^{-10} phot/cm^2/s\naccording to the Fermi 11-month Catalog Extragalactic Sources. Our analysis of\ncontemporaneous Fermi LAT data does not show any sign of increased gamma-ray\nactivity above the detection threshold except for an elevated flux on 2011\nMarch 5, JD2455626, coincident with the local optical maximum.", + "category": "astro-ph" + }, + { + "text": "ExoMol line lists XXVIII: The rovibronic spectrum of AlH: A new line list for AlH is produced. The WYLLoT line list spans two\nelectronic states $X\\,{}^1\\Sigma^+$ and $A\\,{}^1\\Pi$. A diabatic model is used\nto model the shallow potential energy curve of the $A\\,{}^1\\Pi$ state, which\nhas a strong pre-dissociative character with only two bound vibrational states.\nBoth potential energy curves are empirical and were obtained by fitting to\nexperimentally derived energies of the $X\\,{}^1\\Sigma^+$ and $A\\,{}^1\\Pi$\nelectronic states using the diatomic nuclear motion codes Level and Duo. High\ntemperature line lists plus partition functions and lifetimes for three\nisotopologues $^{27}$AlH, $^{27}$AlD and $^{26}$AlH were generated using ab\ninitio dipole moments. The line lists cover both the $X$--$X$ and $A$--$X$\nsystems and are made available in electronic form at the CDS and ExoMol\ndatabases.", + "category": "astro-ph" + }, + { + "text": "Bright X-ray bursts from 1E 1724-3045 in Terzan 2: During about 3 years wide field monitoring of the Galactic Center region by\nthe WFC telescopes on board the BeppoSAX satellite, a total of 14 type-I X-ray\nbursts were detected from the burster 1E 1724-3045 located in the globular\ncluster Terzan 2. All the observed events showed evidence for photospheric\nradius expansion due to Eddington-limit burst luminosity, thus leading to an\nestimate of the source distance (~7.2 kpc). Preliminary results of the analysis\nof the bursts are presented.", + "category": "astro-ph" + }, + { + "text": "Statistical properties of local and intermediate z galaxies: Galaxy evolution during the last 9 Gyr is discussed. It can be traced back\nfrom well known present-day galaxies or directly observed for galaxies at\ndifferent look back times. This requires clear and consistently matched\nselection criteria for galaxy samples. There is a net decrease of rest-frame,\nUV luminosity density, at least since z = 1. It is interpreted as an important\ndecline of the star formation since the last ~9 Gyr. A similar trend is found\nfor the evolution of the IR luminosity density which accounts for heavily\nextincted starbursts. Interestingly the global star formation density, after\nincluding IR selected galaxies, is twice the value of estimates based on the UV\nluminosity density, and this holds from z=0 to z=1.\n Large disks are not contributing much to the observed decrease, which is\nmainly related to significant changes with the epoch in the distribution of\ngalaxy morphologies. A significant fraction of the global star formation occurs\nin luminous galaxies which are apparently small or in interacting galaxies\ndetected in the deepest IR or radio surveys.", + "category": "astro-ph" + }, + { + "text": "Asteroid Evolution: Role of Geotechnical Properties: This paper presents a brief review and latest results of the work that has\nbeen carried out by the Planetary Science community in order to understand that\nrole of the geotechnical properties of granular asteroids (commonly known as\n\"rubble-pile\" asteroids) in their formation, evolution and possible disruption.\nAs such, we will touch in aspects of the theoretical and numerical tools that\nhave been used with this objective and how the obtained results compare to the\nobserved asteroids.", + "category": "astro-ph" + }, + { + "text": "Can Gaia find planets around white dwarfs?: The Gaia spacecraft presents an unprecedented opportunity to reveal the\npopulation of long period (a>1\\,au) exoplanets orbiting stars across the H-R\ndiagram, including white dwarfs. White dwarf planetary systems have played an\nimportant role in the study of planetary compositions, from their unique\nability to provide bulk elemental abundances of planetary material in their\natmospheres. Yet, very little is known about the population of planets around\nwhite dwarfs. This paper predicts the population of planets that Gaia will\ndetect around white dwarfs, evolved from known planets orbiting main-sequence\nstars. We predict that Gaia will detect $8\\pm2$ planets around white dwarfs:\n$8\\pm\\,3\\%$ will lie inside 3\\,au and $40\\pm10\\,\\%$ will be less massive than\nJupiter. As surviving planets likely become dynamically detached from their\nouter systems, those white dwarfs with Gaia detected planets may not have\nplanetary material in their atmospheres. Comparison between the predicted\nplanet population and that found by Gaia will reveal the importance of\ndynamical instabilities and scattering of planets after the main-sequence, as\nwell as whether photoevaporation removes the envelopes of gas giants during\ntheir giant branch evolution.", + "category": "astro-ph" + }, + { + "text": "Evidence for ammonia-bearing species on the Uranian satellite Ariel\n supports recent geologic activity: We investigated whether ammonia-rich constituents are present on the surface\nof the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra\ncollected over a wide range of sub-observer longitudes and latitudes. We\nmeasured the band areas and depths of a 2.2-{\\micron} feature in these spectra,\nwhich has been attributed to ammonia-bearing species on other icy bodies. Ten\nspectra display prominent 2.2-{\\micron} features with band areas and depths >\n2{\\sigma}. We determined the longitudinal distribution of the 2.2-{\\micron}\nband, finding no statistically meaningful differences between Ariel's leading\nand trailing hemispheres, indicating that this band is distributed across\nAriel's surface. We compared the band centers and shapes of the five Ariel\nspectra displaying the strongest 2.2-{\\micron} bands to laboratory spectra of\nvarious ammonia-bearing and ammonium-bearing species, finding that the spectral\nsignatures of the Ariel spectra are best matched by ammonia-hydrates and flash\nfrozen ammonia-water solutions. Our analysis also revealed that four Ariel\nspectra display 2.24-{\\micron} bands (> 2{\\sigma} band areas and depths), with\nband centers and shapes that are best matched by ammonia ice. Because ammonia\nshould be efficiently removed over short timescales by ultraviolet photons,\ncosmic rays, and charged particles trapped in Uranus' magnetosphere, the\npossible presence of this constituent supports geologic activity in the recent\npast, such as emplacement of ammonia-rich cryolavas and exposure of\nammonia-rich deposits by tectonism, impact events, and mass wasting.", + "category": "astro-ph" + }, + { + "text": "The Properties of Fossil Groups of Galaxies: Numerical simulations as well as optical and X-ray observations over the last\nfew years have shown that poor groups of galaxies can evolve to what is called\na fossil group. Dynamical friction as the driving process leads to the\ncoalescence of individual galaxies in ordinary poor groups leaving behind\nnothing more than a central, massive elliptical galaxy supposed to contain the\nmerger history of the whole group. Due to merging timescales for less-massive\ngalaxies and gas cooling timescales of the X-ray intragroup medium exceeding a\nHubble time, a surrounding faint-galaxy population having survived this\ngalactic cannibalism as well as an extended X-ray halo similar to that found in\nordinary groups, is expected. Recent studies suggest that fossil groups are\nvery abundant and could be the progenitors of brightest cluster galaxies (BCGs)\nin the centers of rich galaxy clusters. However, only a few objects are known\nto the literature. This article aims to summarize the results of observational\nfossil group research over the last few years and presents ongoing work by the\nauthors. Complementary to previous research, the SDSS and RASS surveys have\nbeen cross-correlated to identify new fossil structures yielding 34 newly\ndetected fossil group candidates. Observations with ISIS at the 4.2m William\nHerschel Telescope on La Palma have been carried out to study the stellar\npopulations of the central ellipticals of 6 fossil groups. In addition\nmulti-object spectroscopy with VLTs VIMOS has been performed to study the shape\nof the OLF of one fossil system.", + "category": "astro-ph" + }, + { + "text": "A missing outskirts problem? Comparisons between stellar halos in the\n Dragonfly Nearby Galaxies Survey and the TNG100 simulation: Low surface brightness galactic stellar halos provide a challenging but\npromising path towards unraveling the past assembly histories of individual\ngalaxies. Here, we present detailed comparisons between the stellar halos of\nMilky Way-mass disk galaxies observed as part of the Dragonfly Nearby Galaxies\nSurvey (DNGS) and stellar mass-matched galaxies in the TNG100 run of the\nIllustrisTNG project. We produce stellar mass maps as well as mock $g$ and\n$r$-band images for randomly oriented simulated galaxies, convolving the latter\nwith the Dragonfly PSF and taking care to match the background noise, surface\nbrightness limits and spatial resolution of DNGS. We measure azimuthally\naveraged stellar mass density and surface brightness profiles, and find that\nthe DNGS galaxies generally have less stellar mass (or light) at large radii\n(>20 kpc) compared to their mass-matched TNG100 counterparts, and that\nsimulated galaxies with similar surface density profiles tend to have low\naccreted mass fractions for their stellar mass. We explore potential solutions\nto this apparent \"missing outskirts problem\" by implementing several ad-hoc\nadjustments within TNG100 at the stellar particle level. Although we are unable\nto identify any single adjustment that fully reconciles the differences between\nthe observed and simulated galaxy outskirts, we find that artificially delaying\nthe disruption of satellite galaxies and reducing the spatial extent of in-situ\nstellar populations result in improved matches between the outer profile shapes\nand stellar halo masses, respectively. Further insight can be achieved with\nhigher resolution simulations that are able to better resolve satellite\naccretion, and with larger samples of observed galaxies.", + "category": "astro-ph" + }, + { + "text": "A Propos Crossing the Hertzsprung Gap: The evolution of intermediate-mass and massive stars speeds up considerably\nafter they finish their hydrogen core-burning. Due to this accelerated\nevolution, the probability to observe stars during this episode is small. In\nsuitable stellar aggregates, in particular star clusters of appropriate ages,\nthe fast evolutionary phase causes a depopulated area~--~referred to as the\nHertzsprung gap~--~in color-magnitude diagrams and derivatives therefrom. The\nexplanation of the speed-up usually resorts to the star's Kelvin-Helmholtz\ntimescale and the Sch\\\"onberg-Chandrasekhar instability is called upon. This\nexposition challenges this viewpoint with counterexamples and argues that a\nsuitably defined nuclear timescale is enough to explain the fast evolution. A\nthermal instability, even though it develops in stars evolving through the\nHertzsprung gap, is not a necessary condition to trigger the phenomenon.", + "category": "astro-ph" + }, + { + "text": "First stars in Damped Lyman Alpha systems: In order to characterize Damped Lyman Alpha systems (DLAs) potentially\nhosting first stars, we present a novel approach to investigate DLAs in the\ncontext of Milky Way (MW) formation, along with their connection with the most\nmetal-poor stars and local dwarf spheroidal (dSph) galaxies. The merger tree\nmethod previously developed is extended to include inhomogeneous reionization\nand metal mixing, and it is validated by matching both the Metallicity\nDistribution Function of Galactic halo stars and the Fe-Luminosity relation of\ndSph galaxies. The model explains the observed NHI-Fe relation of DLAs along\nwith the chemical abundances of [Fe/H] < -2 systems. In this picture, the\nrecently discovered z_abs ~ 2.34 C-enhanced DLA (Cooke et al. 2011a), pertains\nto a new class of absorbers hosting first stars along with second-generation\nlong-living low-mass stars. These \"PopIII DLAs\" are the descendants of\nH2-cooling minihalos with Mh ~ 10^7 Msun, that virialize at z > 8 in neutral,\nprimordial regions of the MW environment and passively evolve after a short\ninitial period of star formation. The gas in these systems is warm Tg \\sim\n(40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars\nof total mass M* \\sim 10^{2-4} Msun.", + "category": "astro-ph" + }, + { + "text": "The DESI One-Percent Survey: Evidence for Assembly Bias from\n Low-Redshift Counts-in-Cylinders Measurements: We explore the galaxy-halo connection information that is available in\nlow-redshift samples from the early data release of the Dark Energy\nSpectroscopic Instrument (DESI). We model the halo occupation distribution\n(HOD) from z=0.1-0.3 using Survey Validation 3 (SV3; a.k.a., the One-Percent\nSurvey) data of the DESI Bright Galaxy Survey (BGS). In addition to more\ncommonly used metrics, we incorporate counts-in-cylinders (CiC) measurements,\nwhich drastically tighten HOD constraints. Our analysis is aided by the Python\npackage, galtab, which enables the rapid, precise prediction of CiC for any HOD\nmodel available in halotools. This methodology allows our Markov chains to\nconverge with much fewer trial points, and enables even more drastic speedups\ndue to its GPU portability. Our HOD fits constrain characteristic halo masses\ntightly and provide statistical evidence for assembly bias, especially at lower\nluminosity thresholds: the HOD of central galaxies in $z\\sim0.15$ samples with\nlimiting absolute magnitude $M_r < -20.0$ and $M_r < -20.5$ samples is\npositively correlated with halo concentration with a significance of 99.9% and\n99.5%, respectively. Our models also favor positive central assembly bias for\nthe brighter $M_r < -21.0$ sample at $z\\sim0.25$ (94.8% significance), but\nthere is no significant evidence for assembly bias with the same luminosity\nthreshold at $z\\sim0.15$. We provide our constraints for each threshold\nsample's characteristic halo masses, assembly bias, and other HOD parameters.\nThese constraints are expected to be significantly tightened with future DESI\ndata, which will span an area 100 times larger than that of SV3.", + "category": "astro-ph" + }, + { + "text": "Statistics in astronomy: Perhaps more than other physical sciences, astronomy is frequently\nstatistical in nature. The objects under study are inaccessible to direct\nmanipulation in the laboratory, so the astronomer is restricted to observing a\nfew external characteristics and inferring underlying properties and physics.\nAstronomy played a profound role in the historical development of statistics\nfrom the ancient Greeks through the 19th century. But the fields drifted apart\nin the 20th century as astronomy turned towards astrophysics and statistics\ntowards human affairs. Today we see a resurgence in astrostatistical activity\nwith the proliferation of survey mega-datasets and the need to link complicated\ndata to nonlinear astrophysical models. Several contemporary astrostatistical\nchallenges are outlined: heteroscedastic measurement errors, censoring and\ntruncation in multivariate databases; time series analysis of variable objects\nincluding dynamical models of extrasolar planetary systems; treatments of faint\nsources and other Poisson processes; the anisotropic spatial point process of\ngalaxy clustering; and model fitting and selection for the cosmic microwave\nbackground.", + "category": "astro-ph" + }, + { + "text": "The Initial Mass Functions in the Super-Star-Clusters NGC 1569A and NGC\n 1705-1: I use recent photometric and stellar velocity dispersion measurements of the\nsuper-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their\npresent-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/M\nratios, together with population synthesis models of evolving star-clusters, to\nconstrain the initial-mass-functions (IMFs) in these objects.\n I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. It\nfollows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFs\nwhich extend to 0.1 M_sun. This implies that most of the stellar mass in 1569A\nis contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF is\neither flat, with alpha<2$, or it is truncated at a lower mass-limit between 1\nand 3 M_sun.\n I compare the inferred IMFs with the mass functions (MFs) of Galactic\nglobular clusters. It appears that 1569A has a sufficient reservoir of low-mass\nstars for it to plausibly evolve into an object similar to Galactic globular\nclusters. However, the apparent deficiency of low-mass stars in 1705-1 may make\nit difficult for this SSC to become a globular cluster. If low-mass stars do\ndominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may be\nevidence that the most massive stars have formed close to the cluster cores.", + "category": "astro-ph" + }, + { + "text": "The detection of diffuse emission in HCG 16 with XMM-Newton: We report results obtained from analysis of the XMM-Newton observation of the\ncompact group of galaxies HCG 16. It is a peculiar system composed of 7\nspirals,\n 6 of which are active, and its nature as a bound system has been much\ndebated. The EPIC camera observations give new insights into the X-ray\nparameters describing the physical status of the group. We detect diffuse X-ray\nemission with a rather elliptical morphology which extends to at least a radius\nof 135 h^{-1}_{50} kpc from the group centre. The spectrum within this region\nis well modelled by a thermal plasma with a temperature of 0.49+/-0.17 keV, and\na non-zero metallicity. We measure a bolometric X-ray luminosity of 9.6 10{^40}\nh^{-2}_{50} erg/s which may be only a small fraction of the total luminosity\nbecause of the limit in spatial detection arising from the high background\nlevel. Despite its low temperature and luminosity, HCG 16 obeys the Lx-T\nrelation obtained for brighter galaxy groups even if it lies in a very extreme\nposition. The properties of the diffuse emission confirm the bound nature of\nHCG 16 even if the gas trapped in the potential well may not yet be virialized.\nThis reopens the debate about the real nature of spiral-dominated galaxy\ngroups, and on their role in a more general cosmological context.", + "category": "astro-ph" + }, + { + "text": "Long-term spectropolarimetric monitoring of the cool supergiant\n Betelgeuse: We report on a long-term monitoring of the cool supergiant Betelgeuse, using\nthe NARVAL and ESPaDOnS high-resolution spectropolarimeters, respectively\ninstalled at Telescope Bernard Lyot (Pic du Midi Observatory, France) and at\nthe Canada-France-Hawaii Telescope (Mauna Kea Observatory, Hawaii). The data\nset, constituted of circularly polarized (Stokes V) and intensity (Stokes I)\nspectra, was collected between 2010 and 2012. We investigate here the temporal\nevolution of magnetic field, convection and temperature at photospheric level,\nusing simultaneous measurements of the longitudinal magnetic field component,\nthe core emission of the Ca II infrared triplet, the line-depth ratio of\nselected photospheric lines and the radial velocity of the star.", + "category": "astro-ph" + }, + { + "text": "The Stellar Kinematics of Extragalactic Bulges: Galactic bulges are complex systems. Once thought to be small-scale versions\nof elliptical galaxies, advances in astronomical instrumentation (spectroscopy\nin particular) has revealed a wealth of photometric and kinematic substructure\nin otherwise simple-looking components. This review provides an overview of how\nour perspective on galactic bulges has changed over the years. While it is\nmainly focused on aspects related to the dynamical state of their stars, there\nwill be natural connections to other properties (e.g. morphology, stellar\npopulations) discussed in other reviews in this volume.", + "category": "astro-ph" + }, + { + "text": "Jet quenching in the neutron star low-mass X-ray binary 1RXS\n J180408.9$-$342058: We present quasi-simultaneous radio (VLA) and X-ray ($Swift$) observations of\nthe neutron star low-mass X-ray binary (NS-LMXB) 1RXS J180408.9$-$342058\n(J1804) during its 2015 outburst. We found that the radio jet of J1804 was\nbright ($232 \\pm 4 \\mu$Jy at $10$ GHz) during the initial hard X-ray state,\nbefore being quenched by more than an order of magnitude during the soft X-ray\nstate ($19 \\pm 4 \\mu$Jy). The source then was undetected in radio (< $13\n\\mu$Jy) as it faded to quiescence. In NS-LMXBs, possible jet quenching has been\nobserved in only three sources and the J1804 jet quenching we show here is the\ndeepest and clearest example to date. Radio observations when the source was\nfading towards quiescence ($L_X = 10^{34-35}$ erg s$^{-1}$) show that J1804\nmust follow a steep track in the radio/X-ray luminosity plane with $\\beta >\n0.7$ (where $L_R \\propto L_X^{\\beta}$). Few other sources have been studied in\nthis faint regime, but a steep track is inconsistent with the suggested\nbehaviour for the recently identified class of transitional millisecond\npulsars. J1804 also shows fainter radio emission at $L_X < 10^{35}$ erg\ns$^{-1}$ than what is typically observed for accreting millisecond pulsars.\nThis suggests that J1804 is likely not an accreting X-ray or transitional\nmillisecond pulsar.", + "category": "astro-ph" + }, + { + "text": "[O I] 6300 A Emission from Disks Around Herbig Ae/Be Stars: We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars\nin a search for the [O I] 6300.2 A line. The vast majority of the stars in our\nsample show narrow (FWHM < 100 km/s) emission lines, centered on the stellar\nradial velocity. Some stars in our sample show double-peaked lines profiles,\nwith peak-to-peak separations of about 10 km/s. The presence and strength of\nthe [O I] line emission appears to be well correlated with the far-infrared\nenergy distribution of each source: stars with a strong excess at 60 micron\nhave in general stronger [O I] emission than stars with weaker 60 micron\nexcesses. We interpret the observed [O I] 6300.2 A line profiles as arising in\nthe surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars.", + "category": "astro-ph" + }, + { + "text": "Cosmic Web & Caustic Skeleton: non-linear Constrained Realizations -- 2D\n case studies: The cosmic web consists of a complex configuration of voids, walls,\nfilaments, and clusters, which formed under the gravitational collapse of\nGaussian fluctuations. Understanding under what conditions these different\nstructures emerge from simple initial conditions, and how different\ncosmological models influence their evolution, is central to the study of the\nlarge-scale structure. Here, we present a general formalism for setting up\ninitial random density and velocity fields satisfying non-linear constraints\nfor specialized N-body simulations. These allow us to link the non-linear\nconditions on the eigenvalue and eigenvector fields of the deformation tensor,\nas specified by caustic skeleton theory, to the current-day cosmic web. By\nextending constrained Gaussian random field theory, and the corresponding\nHoffman-Ribak algorithm, to non-linear constraints, we probe the statistical\nproperties of the progenitors of the walls, filaments, and clusters of the\ncosmic web. Applied to cosmological N-body simulations, the proposed techniques\npave the way towards a systematic investigation of the evolution of the\nprogenitors of the present-day walls, filaments, and clusters, and the embedded\ngalaxies, putting flesh on the bones of the caustic skeleton. The developed\nnonlinear constrained random field theory is valid for generic cosmological\nconditions. For ease of visualization, the case study presented here probes the\ntwo-dimensional caustic skeleton.", + "category": "astro-ph" + }, + { + "text": "Mitigating Modal Noise in Multimode Circular Fibres by Optical Agitation\n using a Galvanometer: Modal noise appears due to the non-uniform and unstable distribution of light\nintensity among the finite number of modes in multimode fibres. It is an\nimportant limiting factor in measuring radial velocity precisely by fibre-fed\nhigh-resolution spectrographs. The problem can become particularly severe as\nthe fibre's core become smaller and the number of modes that can propagate\nreduces. Thus, mitigating modal noise in relatively small core fibres still\nremains a challenge. We present here a novel technique to suppress modal noise.\nTwo movable mirrors in the form of a galvanometer reimage the mode-pattern of\nan input fibre to an output fibre. The mixing of modes coupled to the output\nfibre can be controlled by the movement of mirrors applying two sinusoidal\nsignals through a voltage generator. We test the technique for four multimode\ncircular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a\ncombination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We\npresent the results of mode suppression both in terms of the direct image of\nthe output fibre and spectrum of white light obtained with the high-resolution\nspectrograph. We found that the galvanometer mitigated modal noise in all the\ntested fibres, but was most useful for smaller core fibres. However, there is a\ntrade-off between the modal noise reduction and light-loss. The GI50t provides\nthe best result with about 60% mitigation of modal noise at a cost of about 5%\noutput light-loss. Our solution is easy to use and can be implemented in\nfibre-fed spectrographs.", + "category": "astro-ph" + }, + { + "text": "Foraging with MUSHROOMS: A Mixed-Integer Linear Programming Scheduler\n for Multimessenger Target of Opportunity Searches with the Zwicky Transient\n Facility: Electromagnetic follow-up of gravitational wave detections is very resource\nintensive, taking up hours of limited observation time on dozens of telescopes.\nCreating more efficient schedules for follow-up will lead to a commensurate\nincrease in counterpart location efficiency without using more telescope time.\nWidely used in operations research and telescope scheduling, mixed integer\nlinear programming (MILP) is a strong candidate to produce these\nhigher-efficiency schedules, as it can make use of powerful commercial solvers\nthat find globally optimal solutions to provided problems . We detail a new\ntarget of opportunity scheduling algorithm designed with Zwicky Transient\nFacility in mind that uses mixed integer linear programming. We compare its\nperformance to \\texttt{gwemopt}, the tuned heuristic scheduler used by the\nZwicky Transient Facility and other facilities during the third LIGO-Virgo\ngravitational wave observing run. This new algorithm uses variable-length\nobserving blocks to enforce cadence requirements and ensure field\nobservability, along with having a secondary optimization step to minimize slew\ntime. \\blue{We show that by employing a hybrid method utilizing both this\nscheduler and \\texttt{gwemopt}, the previous scheduler used, in concert, we can\nachieve an average improvement in detection efficiency of 3\\%-11\\% over\n\\texttt{gwemopt} alone} for a simulated binary neutron star merger data set\nconsistent with LIGO-Virgo's third observing run, highlighting the potential of\nmixed integer target of opportunity schedulers for future multimessenger\nfollow-up surveys.", + "category": "astro-ph" + }, + { + "text": "Universal lateral distribution of energy deposit in air showers and its\n application to shower reconstruction: The light intensity distribution in a shower image and its implications to\nthe primary energy reconstructed by the fluorescence technique are studied.\nBased on detailed CORSIKA energy deposit simulations, a universal analytical\nformula is derived for the lateral distribution of light in the shower image\nand a correction factor is obtained to account for the fraction of shower light\nfalling into outlying pixels in the detector. The expected light profiles and\nthe corresponding correction of the primary shower energy are illustrated for\nseveral typical event geometries. This correction of the shower energy can\nexceed 10%, depending on shower geometry.", + "category": "astro-ph" + }, + { + "text": "The X-ray Luminosity Function of Nearby Rich and Poor Clusters of\n Galaxies: A Cosmological Probe: In this letter, we present a new determination of the local (z<0.09) X-ray\nluminosity function (XLF) using a large, statistical sample of 294 Abell\nclusters and the ROSAT All-Sky-Survey. Given our large sample size, we have\nreduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine\nour data with previous work in order to explore possible constraints imposed by\nthe shape of the XLF on cosmological models. A set of currently viable\ncosmologies is used to construct theoretical XLFs assuming Lx is proportional\nto M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the\nlocal X-ray temperature function. We fit these models to our observed XLF and\nverify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser\n1986) disagrees strongly with observations. If we assume that clusters can be\ndescribed by the pre-heated, constant core-entropy models of Evrard & Henry\n(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the\nenergy per unit mass in galaxies is roughly equal to the gas energy (ie if\nbeta=1). (abridged)", + "category": "astro-ph" + }, + { + "text": "Evidence for a Galactic Origin of Very Short Gamma Ray Bursts and\n Primordial Black Hole Sources: We systematically study the shortest time duration gamma ray bursts and find\nunique features that are best interpreted as sources of a galactic origin.\nThere is a significant angular asymmetry and the V/Vmax distribution provides\nevidence for a homogenous or Euclidean source distribution. We eview the\narguments that primordial black hole evaporation can give such GRBs. The rate\nof events is consistent with a PBH origin if we assume on enhanced local\ndensity, as are the other distributions. We suggest further tests of this\nhypothesis.", + "category": "astro-ph" + }, + { + "text": "Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron\n spectrum at young supernova remnants: Synchrotron X-rays can be a useful tool to investigate electron acceleration\nat young supernova remnants (SNRs). At present, since the magnetic field\nconfiguration around the shocks of SNRs is uncertain, it is not clear whether\nelectron acceleration is limited by SNR age, synchrotron cooling, or even\nescape from the acceleration region. We study whether the acceleration\nmechanism can be constrained by the cutoff shape of the electron spectrum\naround the maximum energy. We derive analytical formulae of the cutoff shape in\neach case where the maximum electron energy is determined by SNR age,\nsynchrotron cooling and escape from the shock. They are related to the energy\ndependence of the electron diffusion coefficient. Next, we discuss whether\ninformation on the cutoff shape can be provided by observations in the near\nfuture which will simply give the photon indices and the flux ratios in the\nsoft and hard X-ray bands. We find that if the power-law index of the electron\nspectrum is independently determined by other observations, then we can\nconstrain the cutoff shape by comparing theoretical predictions of the photon\nindices and/or the flux ratios with observed data which will be measured by\nNuSTAR and/or ASTRO-H. Such study is helpful in understanding the acceleration\nmechanism. In particular, it will supply another independent constraint on the\nmagnetic field strength around the shocks of SNRs.", + "category": "astro-ph" + }, + { + "text": "Spectral Analysis Code: PARAS SPEC: The light emitted from the stellar photosphere serves as a unique signature\nfor the nature of stars. The behaviour of these stellar lines depend upon the\nsurface temperature, mass, evolutionary status and chemical composition of the\nstar. With the advent of high-resolution spectrographs coupled with medium to\nlarge aperture telescopes around the globe, there is plenty of high-resolution\nand high signal-to-noise ratio data available to the astronomy community. Apart\nfrom radial velocity (RV) studies, such data offer us the unique opportunity to\nstudy chemical composition and atmospheric properties of the star. The\nprocedure used to derive these parameters must be automated and well adaptable\nto data available from any high-resolution spectrograph. We hereby present an\nIDL code, PARAS SPEC, which was primary designed to handle high-resolution\nspectroscopy data from PARAS spectrograph coupled with the 1.2~m telescope at\nMt. Abu, India. This code is designed to adapt with data from other\nspectrographs as well. The code PARAS SPEC estimates the stellar atmospheric\nparameters from the analysis of stellar spectra based on two primary methods,\nsynthetic spectral fitting and equivalent width method. Synthetic spectral\nfitting method involves fitting of the observed spectrum with different\nsynthetic spectra for a set of stellar parameters. The second method is based\non equivalent widths (EWs) that are used to derive abundances for a set of Fe~I\nand Fe~II lines from the observed spectra. The detailed methodology used to\ndesign this code and comparison of the results from literature values are\npresented in this paper.", + "category": "astro-ph" + }, + { + "text": "The physics of Lyman-alpha escape from disc-like galaxies: Hydrogen emission lines can provide extensive information about star-forming\ngalaxies in both the local and high-redshift Universe. We present a detailed\nLyman continuum (LyC), Lyman-alpha (Ly{\\alpha}), and Balmer line (H{\\alpha} and\nH\\b{eta}) radiative transfer study of a high-resolution isolated Milky-Way\nsimulation using the Arepo-RT radiation hydrodynamics code with the SMUGGLE\ngalaxy formation model. The realistic framework includes stellar feedback,\nnon-equilibrium thermochemistry, and dust grain evolution in the interstellar\nmedium (ISM). We extend our Cosmic Ly{\\alpha} Transfer (COLT) code with\nphotoionization equilibrium Monte Carlo radiative transfer for self-consistent\nend-to-end (non-)resonant line predictions. Accurate LyC reprocessing to\nrecombination emission requires modelling pre-absorption by dust (27.5%),\nhelium ionization (8.7%), and anisotropic escape fractions (7.9%), as these\nreduce the available budget for hydrogen line emission (55.9%). We investigate\nthe role of the multiphase dusty ISM, disc geometry, gas kinematics, and star\nformation activity in governing the physics of emission and escape, focusing on\nthe time variability, gas phase structure, and spatial, spectral, and viewing\nangle dependence of the emergent photons. Isolated disc simulations are\nwell-suited for comprehensive observational comparisons with local H{\\alpha}\nsurveys, but would require a proper cosmological circumgalactic medium (CGM)\nenvironment as well as less dust absorption and rotational broadening to serve\nas analogs for high-redshift Ly{\\alpha} emitting galaxies. Future applications\nof our framework to next-generation cosmological simulations of galaxy\nformation including radiation-hydrodynamics that resolve <10 pc multiphase ISM\nand <1 kpc CGM structures will provide crucial insights and predictions for\ncurrent and upcoming Ly{\\alpha} observations.", + "category": "astro-ph" + }, + { + "text": "Effects of the South Atlantic Anomaly on the muon flux at sea level: The goal of this study is to examine the response and changes of the muon\nintensity at ground, due to magnetic anomaly over south Atlantic. Based on the\ndata of two directional muon telescopes and located at 22S and 43W. These\ncoordinates are inside of the South Atlantic Anomaly (SAA) region, a dip in the\nmagnetosphere. This characteristic offers to the muon telescopes the lowest\nrigidity of response to cosmic protons and ions ($\\geq 0.4$ GV). The\nmagnetosphere's dip is responsible for several processes, such as the high\nconductivity of the atmospheric layers due to the precipitation of energetic\nparticles in this region and an zonal electric field known as the pre-reversal\nelectric field (PRE) with an enhancement at evening hours. In addition the open\nmagnetosphere, propitiate the magnetic reconnections of the IMF lines that will\ntake place in this site in the day side. These factors are responsible for an\nunusually large particle flux present in the SAA region, including particles\nwith energies above the pion production threshold. The main effect is an\nincrease of the muon intensity ($E_{\\mu}>0.2GeV$) at ground, in the day side,\nin up to ten times. We show that it is correlated with the pre-reversal\nelectric field, and propitiate the observation of muon enhancements due to\nsmall solar transient events, such as corotating interaction region (CIR) and\nmicro-flares. Details of these results are reported in this paper.", + "category": "astro-ph" + }, + { + "text": "The Star Formation Rates of Elliptical Galaxies from Core-Collapse\n Supernovae: The level of star formation in elliptical galaxies is poorly constrained, due\nto difficulties in quantifying the contamination of flux-based estimates of\nstar formation from unrelated phenomena, such as AGN and old stellar\npopulations. We here utilise core-collapse supernovae (CCSNe) as unambiguous\ntracers of recent star formation in ellipticals within a cosmic volume. We\nfirstly isolate a sample of 421 z < 0.2, r < 21.8 mag CCSNe from the SDSS-II\nSupernova Survey. We then introduce a Bayesian method of identifying\nellipticals via their colours and morphologies in a manner unbiased by redshift\nand yet consistent with manual classification from Galaxy Zoo 1. We find ~ 25 %\nof z < 0.2 r < 20 mag galaxies in the Stripe 82 region are ellipticals (~ 28000\ngalaxies). In total, 36 CCSNe are found to reside in ellipticals. We\ndemonstrate that such early-types contribute a non-negligible fraction of star\nformation to the present-day cosmic budget, at 11.2 $\\pm$ 3.1 (stat)\n$^{+3.0}_{-4.2}$ (sys) %. Coupling this result with the galaxy stellar mass\nfunction of ellipticals, the mean specific star formation rate (SSFR;\n$\\overline{S}$) of these systems is derived. The best-fit slope is given by log\n($\\overline{S}(M)$/yr) = - (0.80 $\\pm$ 0.59) log ($M/10^{10.5}\\rm{M}_{\\odot}$)\n- 10.83 $\\pm$ 0.18. The mean SSFR for all log ($M/\\rm{M}_{\\odot}$) > 10.0\nellipticals is found to be $\\overline{S} = 9.2 \\pm 2.4$ (stat) $^{+2.7}_{-2.3}$\n(sys) $\\times 10^{-12}$ yr$^{-1}$, which is consistent with recent estimates\nvia SED-fitting, and is 11.8 $\\pm$ 3.7 (stat) $^{+3.5}_{-2.9}$ (sys) % of the\nmean SSFR level on the main sequence as also derived from CCSNe. We find the\nmedian optical spectrum of elliptical CCSN hosts is statistically consistent\nwith that of a control sample of ellipticals that do not host CCSNe, implying\nthat these SN-derived results are well-representative of the total low-z\nelliptical population.", + "category": "astro-ph" + }, + { + "text": "Chlorine Abundances in Cool Stars: Chlorine abundances are reported in 15 evolved giants and one M dwarf in the\nsolar neighborhood. The Cl abundance was measured using the vibration-rotation\n1-0 P8 line of H$^{35}$Cl at 3.69851 $\\mu$m. The high resolution L-band spectra\nwere observed using the Phoenix infrared spectrometer on the Kitt Peak Mayall\n4m telescope. The average [$^{35}$Cl/Fe] abundance in stars with\n--0.72$<$[Fe/H]$<$0.20 is [$^{35}$Cl/Fe]=(--0.10$\\pm$0.15) dex. The mean\ndifference between the [$^{35}$Cl/Fe] ratios measured in our stars and chemical\nevolution model values is (0.16$\\pm$0.15) dex. The [$^{35}$Cl/Ca] ratio has an\noffset of $\\sim$0.35 dex above model predictions suggesting chemical evolution\nmodels are under producing Cl at the high metallicity range. Abundances of C,\nN, O, Si, and Ca were also measured in our spectral region and are consistent\nwith F and G dwarfs. The Cl versus O abundances from our sample match Cl\nabundances measured in planetary nebula and \\ion{H}{2} regions. In one star\nwhere both H$^{35}$Cl and H$^{37}$Cl could be measured, a $^{35}$Cl/$^{37}$Cl\nisotope ratio of 2.2$\\pm$0.4 was found, consistent with values found in the\nGalactic ISM and predicted chemical evolution models.", + "category": "astro-ph" + }, + { + "text": "A dynamical study on the habitability of terrestrial exoplanets I:\n Tidally evolved planet-satellite pairs: We investigate the obliquity and spin period of Earth-Moon like systems after\n4.5 Gyr of tidal evolution with various satellite masses and initial planetary\nobliquity and discuss their relations to the habitability of the planet. We\nfind three possible outcomes: either i) the system is still evolving, ii) the\nsystem is double synchronous or iii) the satellite has collided with the\nplanet. The transition between case i) and ii) is abrupt and occurs at slightly\nlarger satellite mass ($m_s \\sim 0.02m_p$) than the lunar mass. We suggest that\ncases ii) and iii) are less habitable than case i). Using results from models\nof giant impacts and satellite accretion, we found that the systems that mimic\nour own with rotation period $12 < P_p < 48$ h and current planetary obliquity\n$\\varepsilon_p < 40^\\circ$ or $\\varepsilon_p > 140^\\circ$ only represent 14% of\nthe possible outcomes. Elser et al. (2011) conclude that the probability of a\nterrestrial planet having a heavy satellite is 13%. Combining these results\nsuggests that the probability of ending up with a system such as our own is of\nthe order of 2%.", + "category": "astro-ph" + }, + { + "text": "The Cosmological Evolution of Self-interacting Dark Matter: We study the evolution of cosmological perturbations in dark-matter models\nwith elastic and velocity-independent self interactions. Such interactions are\nimprinted in the matter-power spectrum as dark acoustic oscillations, which can\nbe experimentally explored to determine the strength of the self scatterings.\nModels with self interactions have similarities to warm dark matter, as they\nlead to suppression of power on small scales when the dark-matter velocity\ndispersion is sizable. Nonetheless, both the physical origin and the extent of\nthe suppression differ for self-interacting dark matter from conventional warm\ndark matter, with a dark sound horizon controlling the reduction of power in\nthe former case, and a free-streaming length in the latter. We thoroughly\nanalyze these differences by performing computations of the linear power\nspectrum using a newly developed Boltzmann code. We find that while current\nLyman-$\\alpha$ data disfavor conventional warm dark matter with a mass less\nthan 5.3 keV, when self interactions are included at their maximal value\nconsistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4\nkeV. Finally, we make use of our analysis to set novel bounds on light scalar\nsinglet dark matter.", + "category": "astro-ph" + }, + { + "text": "Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma: We study the particle energy distribution in the cocoon surrounding Cygnus A,\nusing radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I\nimage. We show that the excess low frequency emission in the the lobe further\nfrom Earth cannot be explained by absorption or excess adiabatic expansion of\nthe lobe or a combination of both. We show that this excess emission is\nconsistent with emission from a relic counterlobe and a relic counterjet that\nare being re-energized by compression from the current lobe. We detect hints of\na relic hotspot at the end of the relic X-ray jet in the more distant lobe. We\ndo not detect relic emission in the lobe nearer to Earth as expected from light\ntravel-time effects assuming intrinsic symmetry. We determine that the duration\nof the previous jet activity phase was slightly less than that of the current\njet-active phase. Further, we explain some features observed at 5 and 15 GHz as\ndue to the presence of a relic jet.", + "category": "astro-ph" + }, + { + "text": "The temperature structure in the core of Sersic 159-03: We present results from a new 120 ks XMM-Newton observation of the cluster of\ngalaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray\nspectra obtained with the Reflection Grating Spectrometer (RGS). The spectra\nallow us to constrain the temperature structure in the core of the cluster and\ndetermine the emission measure distribution as a function of temperature. We\nalso fit the line widths of mainly oxygen and iron lines.", + "category": "astro-ph" + }, + { + "text": "Squeezing $f_{\\rm NL}$ out of the matter bispectrum with consistency\n relations: We show how consistency relations can be used to robustly extract the\namplitude of local primordial non-Gaussianity ($f_{\\rm NL}$) from the squeezed\nlimit of the matter bispectrum, well into the non-linear regime. First, we\nderive a non-perturbative relation between primordial non-Gaussianity and the\nleading term in the squeezed bispectrum, revising some results present in the\nliterature. This relation is then used to successfully measure $f_{\\rm NL}$\nfrom $N$-body simulations. We discuss the dependence of our results on\ndifferent scale cuts and redshifts. Specifically, the analysis is strongly\ndependent on the choice of the smallest soft momentum, $q_{\\rm min}$, which is\nthe most sensitive to primordial bispectrum contributions, but is largely\nindependent of the choice of the largest hard momentum, $k_{\\rm max}$, due to\nthe non-Gaussian nature of the covariance. We also show how the constraints on\n$f_{\\rm NL}$ improve at higher redshift, due to a reduced off-diagonal\ncovariance. In particular, for a simulation with $f_{\\rm NL} = 100$ and a\nvolume of $(2.4 \\text{ Gpc}/h)^3$, we measure $f_{\\rm NL} = 98 \\pm 12$ at\nredshift $z=0$ and $f_{\\rm NL} = 97 \\pm 8$ at $z=0.97$. Finally, we compare our\nresults with a Fisher forecast, showing that the current version of the\nanalysis is satisfactorily close to the Fisher error. We regard this as a first\nstep towards the realistic application of consistency relations to constrain\nprimordial non-Gaussianity using observations.", + "category": "astro-ph" + }, + { + "text": "Hubble Ultraviolet Spectroscopy of Jupiter Trojans: We present the first ultraviolet spectra of Jupiter Trojans. These\nobservations were carried out using the Space Telescope Imaging Spectrograph on\nthe Hubble Space Telescope and cover the wavelength range 200-550 nm at low\nresolution. The targets include objects from both of the Trojan color\nsubpopulations (less-red and red). We do not observe any discernible absorption\nfeatures in these spectra. Comparisons of the averaged UV spectra of less-red\nand red targets show that the subpopulations are spectrally distinct in the UV.\nLess-red objects display a steep UV slope and a rollover at around 450 nm to a\nshallower visible slope, whereas red objects show the opposite trend.\nLaboratory spectra of irradiated ices with and without H$_{2}$S exhibit\ndistinct UV absorption features; consequently, the featureless spectra observed\nhere suggest H$_{2}$S alone is not responsible for the observed color\nbimodality of Trojans, as has been previously hypothesized. We propose some\npossible explanations for the observed UV-visible spectra, including complex\norganics, space weathering of iron-bearing silicates, and masked features due\nto previous cometary activity.", + "category": "astro-ph" + }, + { + "text": "Supernova Remnants as a Probe of Dust Grains in the Interstellar Medium: Interstellar dust grains play a crucial role in the evolution of the galactic\ninterstellar medium (ISM). Despite its importance, however, dust remains poorly\nunderstood in terms of its origin, composition, and abundance throughout the\nuniverse. Supernova remnants (SNRs) provide a laboratory for studying the\nevolution of dust grains, as they are one of the only environments in the\nuniverse where it is possible to observe grains being both created and\ndestroyed. SNRs exhibit collisionally heated dust, allowing dust to serve as a\ndiagnostic both for grain physics and for the plasma conditions in the SNR. I\npresent theoretical models of collisionally heated dust which calculate grain\nemission as well as destruction rates. In these models, I incorporate physics\nsuch as nonthermal sputtering caused by grain motions through the gas, a more\nrealistic approach to sputtering for small grains, and arbitrary grain\ncompositions porous and composite grains. I apply these models to infrared and\nX-ray observations of Kepler's supernova and the Cygnus Loop in the galaxy, and\nSNRs 0509-67.5, 0519-69.0, and 0540-69.3 in the LMC. X-ray observations\ncharacterize the hot plasma while IR observations constrain grain properties\nand destruction rates. Such a multi-wavelength approach is crucial for a\ncomplete understanding of gas and dust interaction and evolution. Modeling of\nboth X-ray and IR spectra allows disentangling of parameters such as pre and\npostshock gas density, as well as swept-up masses of gas and dust, and can\nprovide constraints on the shock compression ratio. Observations also show that\nthe dust-to-gas mass ratio in the ISM is lower by a factor of several than what\nis inferred by extinction studies of starlight. Future observatories, such as\nthe James Webb Space Telescope and the International X-ray Observatory, will\nallow testing of models far beyond what is possible now.", + "category": "astro-ph" + }, + { + "text": "Bringing 2D Eclipse Mapping out of the Shadows with Leave-one-out\n Cross-validation: Eclipse mapping is a technique for inferring 2D brightness maps of transiting\nexoplanets from the shape of an eclipse light curve. With JWST's unmatched\nprecision, eclipse mapping is now possible for a large number of exoplanets.\nHowever, eclipse mapping has only been applied to two planets and the nuances\nof fitting eclipse maps are not yet fully understood. Here, we use\nLeave-one-out Cross- Validation (LOO-CV) to investigate eclipse mapping, with\napplication to a JWST NIRISS/SOSS observation of the ultra-hot Jupiter\nWASP-18b. LOO-CV is a technique that provides insight into the out-of-sample\npredictive power of models on a data-point-by-data-point basis. We show that\nconstraints on planetary brightness patterns behave as expected, with\nlarge-scale variations driven by the phase-curve variation in the light curve\nand smaller-scale structures constrained by the eclipse ingress and egress. For\nWASP-18b we show that the need for higher model complexity (smaller-scale\nfeatures) is driven exclusively by the shape of the eclipse ingress and egress.\nWe use LOO-CV to investigate the relationship between planetary brightness map\ncomponents when mapping under a positive-flux constraint to better understand\nthe need for complex models. Finally, we use LOO-CV to understand the\ndegeneracy between the competing ``hotspot'' and ``plateau'' brightness map\nmodels of WASP-18b, showing that the plateau model is driven by the ingress\nshape and the hotspot model is driven by the egress shape, but preference for\nneither model is due to outliers or unmodeled signals. Based on this analysis,\nwe make recommendations for the use of LOO-CV in future eclipse-mapping\nstudies.", + "category": "astro-ph" + }, + { + "text": "Multi-D Simulations of Ultra-Stripped Supernovae to Shock Breakout: The recent discoveries of many double neutron star systems and their\ndetection as LIGO-Virgo merger events call for a detailed understanding of\ntheir origin. Explosions of ultra-stripped stars in binary systems have been\nshown to play a key role in this context and have also generated interest as a\npotential explanation for rapidly evolving hydrogen-free transients. Here we\npresent the first attempt to model such explosions based on binary evolution\ncalculations that follow the mass transfer to the companion to obtain a\nconsistent core-envelope structure as needed for reliable predictions of the\nsupernova transient. We simulate the explosion in 2D and 3D, and confirm the\nmodest explosion energies ~10^50erg and small kick velocities reported earlier\nin 2D models based on bare carbon-oxygen cores. The spin-up of the neutron star\nby asymmetric accretion is small in 3D with no indication of spin-kick\nalignment. Simulations up to shock breakout show the mixing of sizeable amounts\nof iron group material into the helium envelope. In view of recent ideas for a\nmixing-length treatment (MLT) of Rayleigh-Taylor instabilities in supernovae,\nwe perform a detailed analysis of the mixing, which reveals evidence for\nbuoyancy-drag balance, but otherwise does not support the MLT approximation.\nThe mixing may have implications for the spectroscopic signatures of\nultra-stripped supernovae that need to be investigated in the future. Our\nstellar evolution calculation also predicts presupernova mass loss due to an\noff-centre silicon deflagration flash, which suggests that supernovae from\nextremely stripped cores may show signs of interactions with circumstellar\nmaterial.", + "category": "astro-ph" + }, + { + "text": "An Ultraviolet Spectrum of the Tidal Disruption Flare ASASSN-14li: We present a Hubble Space Telescope STIS spectrum of ASASSN-14li, the first\nrest-frame UV spectrum of a tidal disruption flare (TDF). The underlying\ncontinuum is well fit by a blackbody with $T_{\\mathrm{UV}} = 3.5 \\times 10^{4}$\nK, an order of magnitude smaller than the temperature inferred from X-ray\nspectra (and significantly more precise than previous efforts based on optical\nand near-UV photometry). Super-imposed on this blue continuum, we detect three\nclasses of features: narrow absorption from the Milky Way (probably a\nhigh-velocity cloud), and narrow absorption and broad (FWHM $\\approx 2000$-8000\nkm s$^{-1}$) emission lines at/near the systemic host velocity. The absorption\nlines are blueshifted with respect to the emission lines by $\\Delta v =\n-(250$-400) km s$^{-1}$. Due both to this velocity offset and the lack of\ncommon low-ionization features (Mg II, Fe II), we argue these arise from the\nsame absorbing material responsible for the low-velocity outflow discovered at\nX-ray wavelengths. The broad nuclear emission lines display a remarkable\nabundance pattern: N III], N IV], He II are quite prominent, while the common\nquasar emission lines of C III] and Mg II are weak or entirely absent. Detailed\nmodeling of this spectrum will help elucidate fundamental questions regarding\nthe nature of the emission process(es) at work in TDFs, while future UV\nspectroscopy of ASASSN-14li would help to confirm (or refute) the previously\nproposed connection between TDFs and \"N-rich\" quasars.", + "category": "astro-ph" + }, + { + "text": "Detection and Characterization of Exoplanets and Disks using Projections\n on Karhunen-Loeve Eigenimages: We describe a new method to achieve point spread function (PSF) subtractions\nfor high- contrast imaging using Principal Component Analysis (PCA) that is\napplicable to both point sources or extended objects (disks). Assuming a\nlibrary of reference PSFs, a Karhunen-Lo`eve transform of theses references is\nused to create an orthogonal basis of eigenimages, on which the science target\nis projected. For detection this approach provides comparable suppression to\nthe Locally Optimized Combination of Images (LOCI) algorithm, albeit with\nincreased robustness to the algorithm parameters and speed enhancement. For\ncharacterization of detected sources the method enables forward modeling of\nastrophysical sources. This alleviates the biases in the astrometry and\nphotometry of discovered faint sources, which are usually associated with LOCI-\nbased PSF subtractions schemes. We illustrate the algorithm performance using\narchival Hubble Space Telescope (HST) images, but the approach may also be\nconsidered for ground-based data acquired with Angular Differential Imaging\n(ADI) or integral-field spectrographs (IFS).", + "category": "astro-ph" + }, + { + "text": "Rotational broadening and conservation of angular momentum in\n post-extreme horizontal branch stars: We show that the recent realization that isolated post-extreme horizontal\nbranch (post-EHB) stars are generally characterized by rotational broadening\nwith values of $V_{\\rm rot} \\sin i$ between 25 and 30 km~s$^{-1}$ can be\nexplained as a natural consequence of the conservation of angular momentum from\nthe previous He-core burning phase on the EHB. The progenitors of these evolved\nobjects, the EHB stars, are known to be slow rotators with an average value of\n$V_{\\rm rot} \\sin i$ of $\\sim$7.7 km~s$^{-1}$. This implies significant spin-up\nbetween the EHB and post-EHB phases. Using representative evolutionary models\nof hot subdwarf stars, we demonstrate that angular momentum conservation in\nuniformly rotating strutures (rigid-body rotation) boosts that value of the\nprojected equatorial rotation speed by a factor $\\sim$3.6 by the time the model\nhas reached the region of the surface gravity-effective temperature plane where\nthe newly-studied post-EHB objects are found. This is exactly what is needed to\naccount for their observed atmospheric broadening. We note that the decrease of\nthe moment of inertia causing the spin-up is mostly due to the redistribution\nof matter that produces more centrally-condensed structures in the post-EHB\nphase of evolution, not to the decrease of the radius per se.", + "category": "astro-ph" + }, + { + "text": "Laboratory experiments and simulations on jets: Astrophysical jets have been studied with observations, theoretical models\nand numerical simulations for decades. Recently, supersonic magnetized jets\nhave been formed in laboratory experiments of high-energy density plasmas. I\nwill review these studies and discuss the experimental setup that has been used\nto form millimeter-scale jets driven by strong toroidal magnetic fields in a\nMAGPIE generator. The physical conditions of these experiments are such that\nthey can be scaled to astrophysical scenarios. These laboratory jets provide\ninsights on the underlying physics of magnetic tower jets and help constrain\nsome models of astrophysical jets. In this context, we also discuss the\nconnection between the laboratory jets and recent 3D-MHD numerical simulations\nof Poynting flux dominated jets. The simulations allow us to investigate the\neffects of thermal energy losses and base rotation on the growth rate of kink\nmode perturbations, and to compare the evolution of PFD jets with a\nhydrodynamic counterpart of the same energy flux.", + "category": "astro-ph" + }, + { + "text": "Time-Delayed transfer functions simulations for LMXBs: Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)\nhave demonstrated that Bowen flourescence is a very efficient tracer of the\ncompanion star in LMXBs. We present a numerical code to simulate time-delayed\ntransfer functions in LMXBs, specific to the case of reprocessing in emission\nlines. The code is also able to obtain geometrical and binary parameters by\nfitting observed (X-ray + optical) light curves using simulated annealing\nmethods. In this work we present the geometrical model for the companion star\nand the analytical model for the disc and show synthetic time-delay transfer\nfunctions for different orbital phases and system parameters.", + "category": "astro-ph" + }, + { + "text": "A New View of the Super Star Clusters in the Low-Metallicity Galaxy SBS\n 0335-052: We present a study of the individual super star clusters (SSCs) in the\nlow-metallicity galaxy SBS 0335-052 using new near-infrared and archival\noptical Hubble Space Telescope observations. The physical properties of the\nSSCs are derived from fitting model spectral energy distributions (SEDs) to the\noptical photometry, as well as from the H_alpha and Pa_alpha nebular emission.\nAmong the clusters, we find a significant age spread that is correlated with\nposition in the galaxy, suggesting successive cluster formation occurred in SBS\n0335-052 triggered by a large-scale disturbance traveling through the galaxy at\na speed of ~35 km/s. The SSCs exhibit I-band (~0.8 um) and near-IR (~1.6-2.1\num) excesses with respect to model SEDs fit to the optical data. We hypothesize\nthat the I-band excess is dominated by a photoluminescent process known as\nExtended Red Emission; however, this mechanism cannot account for the excesses\nobserved at longer near-IR wavelengths. From the cluster SEDs and colors, we\nfind that the primary origin of the near-IR excess observed in the youngest\nSSCs (<3 Myr) is hot dust emission, while evolved red supergiants dominate the\nnear-IR light in the older (>7 Myr) clusters. We also find evidence for a\nporous and clumpy interstellar medium (ISM) surrounding the youngest, embedded\nSSCs: the ionized gas emission underpredicts the expected ionizing luminosities\nfrom the optical stellar continuum, suggesting ionizing photons are leaking out\nof the immediate vicinity of the clusters before ionizing hydrogen. The\ncorrected, intrinsic ionizing luminosities of the two SSCs younger than ~3 Myr\nare each ~ 5x10^52 s^-1, which is equivalent to each cluster hosting ~5000 O7.5\nV stars. The inferred masses of these SSCs are ~10^6 M_sun.", + "category": "astro-ph" + }, + { + "text": "The role of electron heating physics in images and variability of the\n Galactic Centre black hole Sagittarius A*: The accretion flow around the Galactic Center black hole Sagittarius A* (Sgr\nA*) is expected to have an electron temperature that is distinct from the ion\ntemperature, due to weak Coulomb coupling in the low-density plasma. We present\nfour two-temperature general relativistic radiative magnetohydrodynamic\n(GRRMHD) simulations of Sgr A* performed with the code KORAL. These simulations\nuse different electron heating prescriptions, motivated by different models of\nthe underlying plasma microphysics. We compare the Landau-damped turbulent\ncascade model used in previous work with a new prescription we introduce based\non the results of particle-in-cell simulations of magnetic reconnection. With\nthe turbulent heating model, electrons are preferentially heated in the polar\noutflow, whereas with the reconnection model electrons are heated by nearly the\nsame fraction everywhere in the accretion flow. The spectra of the two models\nare similar around the submillimetre synchrotron peak, but the models heated by\nmagnetic reconnection produce variability more consistent with the level\nobserved from Sgr A*. All models produce 230~GHz images with distinct black\nhole shadows which are consistent with the image size measured by the Event\nHorizon Telescope, but only the turbulent heating produces an anisotropic\n`disc-jet' structure where the image is dominated by a polar outflow or jet at\nfrequencies below the synchrotron peak. None of our models can reproduce the\nobserved radio spectral slope, the large near-infrared and X-ray flares, or the\nnear-infrared spectral index, all of which suggest non-thermal electrons are\nneeded to fully explain the emission from Sgr A*.", + "category": "astro-ph" + }, + { + "text": "Comparative clustering analysis of Ca II 854.2 nm spectral profiles from\n simulations and observations: We aim to compare and contrast the typical shapes of synthetic Ca II 854.2 nm\nspectra found in Bifrost simulations having different magnetic activity with\nthe spectral shapes found in a quiet Sun observation from the Swedish 1-m Solar\nTelescope (SST). We use clustering techniques to extract the typical Ca II\n854.2 nm profile shapes synthesized from Bifrost simulations with varying\namounts of magnetic activity. We degrade the synthetic profiles to\nobservational conditions and repeat the clustering, and we compare our\nsynthetic results with actual observations. While the mean spectra for our high\nresolution simulations compare reasonably well with the observations, we find\nthat there are considerable differences between the clusters of observed and\nsynthetic intensity profiles, even after the synthetic profiles have been\ndegraded. The typical absorption profiles from the simulations are both\nnarrower and display a steeper transition from the inner wings to the line\ncore. Furthermore, even in our most quiescent simulation we find a far larger\nfraction of profiles with local emission around the core, or other exotic\nprofile shapes, than in the observations. Looking into the atmospheric\nstructure for a selected set of synthetic clusters, we find distinct\ndifferences in the temperature stratification for the clusters most and least\nsimilar to the observations. The narrow and steep profiles are associated with\neither weak gradients in temperature, or temperatures rising to a local maximum\nin the line wing forming region before sinking to a minimum in the line core\nforming region. The profiles that display less steep transitions show extended\ntemperature gradients that are steeper in the range $-3 \\lesssim \\log\n\\tau_{5000} \\lesssim -1$.", + "category": "astro-ph" + }, + { + "text": "Hydrogenation of small aromatic heterocycles at low temperatures: The recent wave of detections of interstellar aromatic molecules has sparked\ninterest in the chemical behavior of aromatic molecules under astrophysical\nconditions. In most cases, these detections have been made through chemically\nrelated molecules, called proxies, that implicitly indicate the presence of a\nparent molecule. In this study, we present the results of the theoretical\nevaluation of the hydrogenation reactions of different aromatic molecules\n(benzene, pyridine, pyrrole, furan, thiophene, silabenzene, and phosphorine).\nThe viability of these reactions allows us to evaluate the resilience of these\nmolecules to the most important reducing agent in the interstellar medium, the\nhydrogen atom (H). All significant reactions are exothermic and most of them\npresent activation barriers, which are, in several cases, overcome by quantum\ntunneling. Instanton reaction rate constants are provided between 50 K and 500\nK. For the most efficiently formed radicals, a second hydrogenation step has\nbeen studied. We propose that hydrogenated derivatives of furan, pyrrole, and\nspecially 2,3-dihydropyrrole, 2,5-dihydropyrrole, 2,3-dihydrofuran, and\n2,5-dihydrofuran are promising candidates for future interstellar detections.", + "category": "astro-ph" + }, + { + "text": "Parallax Results From URAT Epoch Data: We present 1103 trigonometric parallaxes and proper motions from the United\nStates Naval Observatory (USNO) Robotic Astrometric Telescope (URAT)\nobservations taken at the Naval Observatory Flagstaff Station (NOFS) over a 3\nyear period from April 2012 to June 2015 covering the entire sky north of about\nminus 10 deg declination. We selected 2 samples previously suspected nearby\nstars from known photometric distances and stars showing a large, significant\nparallax signature in URAT epoch data without any prior selection criteria. All\nsystems presented in this paper have an observed parallax greater than equal to\n40 mas with no previous published trigonometric parallax. The formal errors on\nthese weighted parallax solutions are mostly between 4 and 10 mas. This sample\ngives a significant (order 50%) increase to the number of known systems having\na trigonometric parallax to be within 25 pc of the Sun (without applying Lutz\nKelker bias corrections). A few of these are found to be within 10 pc. Many of\nthese new nearby stars display a total proper motion of less than 200 mas per\nyear. URAT parallax results have been verified against Hipparcos and Yale data\nfor stars in common. The publication of all significant parallax observations\nfrom URAT data is in preparation for CDS.", + "category": "astro-ph" + }, + { + "text": "A Quasar Wind Model: A quasar wind model is proposed to describe the spatial and velocity\nstructure of the broad line region. This model requires detailed\nphotoionization and magnetohydrodynamic simulation, as the broad line region it\ntoo small for direct spatial resolution. The emission lines are Doppler\nbroadened, since the gas is moving at high velocity. The high velocity is\nattained by the gas from a combination of radiative and magnetic driving\nforces. Once this model is complete, the model predictions will be tested\nagainst recent microlensing data in conjunction with diverse existing\nobservations.", + "category": "astro-ph" + }, + { + "text": "Relativistic effects in galaxy clustering in a parametrized\n post-Friedmann universe: We explore the signatures of quintessence and modified gravity theories in\nthe relativistic description of galaxy clustering within a parametrized\npost-Friedmann framework. For this purpose, we develop a calibration method to\nconsistently account for horizon-scale effects in the linear parametrized\nPost-Friedmann perturbations of minimally and nonminimally coupled\nscalar-tensor theories and test it against the full model-specific\nfluctuations. We further study the relativistic effects in galaxy clustering\nfor the normal and self-accelerating branches of the Dvali-Gabadadze-Porrati\nbraneworld model as well as for phenomenological modifications of gravity. We\nquantify the impact of modified gravity and dark energy models on galaxy\nclustering by computing the velocity-to-matter density ratio F, the velocity\ncontribution R, and the potential contribution P and give an estimate of their\ndetectability in future galaxy surveys. Our results show that, in general, the\nrelativistic correction contains additional information on gravity and dark\nenergy, which needs to be taken into account in consistent horizon-scale tests\nof departures from LCDM using the galaxy-density field.", + "category": "astro-ph" + }, + { + "text": "Core-collapse explosions of Wolf-Rayet stars and the connection to type\n IIb/Ib/Ic supernovae: We present non-LTE time-dependent radiative-transfer simulations of supernova\n(SN) IIb/Ib/Ic spectra and light curves, based on ~1B-energy piston-driven\nejecta, with and without 56Ni, produced from single and binary Wolf-Rayet (W-R)\nstars evolved at solar and sub-solar metallicities. Our bolometric light curves\nshow a 10-day long post-breakout plateau with a luminosity of 1-5x10^7Lsun. In\nour 56Ni-rich models, with ~3Msun ejecta masses, this plateau precedes a\n20-30-day long re-brightening phase initiated by the outward-diffusing heat\nwave powered by radioactive decay at depth. In low ejecta-mass models with\nmoderate mixing, Gamma-ray leakage starts as early as ~50d after explosion and\ncauses the nebular luminosity to steeply decline by ~0.02mag/d. Such\nsignatures, which are observed in standard SNe IIb/Ib/Ic, are consistent with\nlow-mass progenitors derived from a binary-star population. We propose that the\nmajority of stars with an initial mass ~<20Msun yield SNe II-P if 'effectively\"\nsingle, SNe IIb/Ib/Ic if part of a close binary system, and SN-less black holes\nif more massive. Our ejecta, with outer hydrogen mass fractions as low as\n~>0.01 and a total hydrogen mass of ~>0.001Msun, yield the characteristic SN\nIIb spectral morphology at early times. However, by ~15d after the explosion,\nonly Halpha may remain as a weak absorption feature. Our binary models,\ncharacterised by helium surface mass fractions of ~>0.85, systematically show\nHeI lines during the post-breakout plateau, irrespective of the 56Ni abundance.\nSynthetic spectra show a strong sensitivity to metallicity, which offers the\npossibility to constrain it directly from SN spectroscopic modelling.", + "category": "astro-ph" + }, + { + "text": "Multiple Populations in NGC 1851: Abundance Variations and UV\n Photometric Synthesis in the Washington and HST/WFC3 Systems: The analysis of multiple populations (MPs) in globular clusters, both\nspectroscopically and photometrically, is key in understanding their formation\nand evolution. The relatively narrow Johnson U, F336W, and Stromgren and Sloan\nu filters have been crucial in exhibiting these MPs photometrically, but in\nPaper I we showed that the broader Washington C filter can more efficiently\ndetect MPs in the test case globular cluster NGC 1851. In Paper I we also\ndetected a double MS that has not been detected in previous observations of NGC\n1851. We now match this photometry to NGC 1851's published RGB abundances and\nfind the two RGB branches observed in C generally exhibit different abundance\ncharacteristics in a variety of elements (e.g., Ba, Na, and O) and in CN band\nstrengths, but no single element can define the two RGB branches. However,\nsimultaneously considering [Ba/Fe] or CN strengths with either [Na/Fe], [O/Fe],\nor CN strengths can separate the two photometric RGB branches into two distinct\nabundance groups. Matches of NGC 1851's published SGB and HB abundances to the\nWashington photometry shows consistent characterizations of the MPs, which can\nbe defined as an O-rich/N-normal population and an O-poor/N-rich population.\nPhotometric synthesis for both the Washington C filter and the F336W filter\nfinds that these abundance characteristics, with appropriate variations in He,\ncan reproduce for both filters the photometric observations in both the RGB and\nthe MS. This photometric synthesis also confirms the throughput advantages that\nthe C filter has in detecting MPs.", + "category": "astro-ph" + }, + { + "text": "TOROS Optical follow-up of the Advanced LIGO-VIRGO O2 second\n observational campaign: We present the results of the optical follow-up, conducted by the TOROS\ncollaboration, of gravitational wave events detected during the Advanced\nLIGO-Virgo second observing run (Nov 2016 -- Aug 2017). Given the limited field\nof view ($\\sim100\\arcmin$) of our observational instrumentation we targeted\ngalaxies within the area of high localization probability that were observable\nfrom our sites. We analyzed the observations using difference imaging, followed\nby a Random Forest algorithm to discriminate between real and bogus transients.\nFor all three events that we respond to, except GW170817, we did not find any\nbona fide optical transient that was plausibly linked with the observed\ngravitational wave event. Our observations were conducted using telescopes at\nEstaci\\'{o}n Astrof\\'{\\i}sica de Bosque Alegre, Cerro Tololo Inter-American\nObservatory, and the Dr. Cristina V. Torres Memorial Astronomical Observatory.\nOur results are consistent with the LIGO-Virgo detections of a binary black\nhole merger (GW170104) for which no electromagnetic counterparts were expected,\nas well as a binary neutron star merger (GW170817) for which an optical\ntransient was found as expected.", + "category": "astro-ph" + }, + { + "text": "Short-lived Radio Bursts from the Crab Pulsar: Our high-time-resolution observations reveal that individual main pulses from\nthe Crab pulsar contain one or more short-lived microbursts. Both the energy\nand duration of bursts measured above 1 GHz can vary dramatically in less than\na millisecond. These fluctuations are too rapid to be caused by propagation\nthrough turbulence in the Crab Nebula or the interstellar medium; they must be\nintrinsic to the radio emission process in the pulsar. The mean duration of a\nburst varies with frequency as $\\nu^{-2}$, significantly different from the\nbroadening caused by interstellar scattering. We compare the properties of the\nbursts to some simple models of microstructure in the radio emission region.", + "category": "astro-ph" + }, + { + "text": "The Millennium Galaxy Catalogue: The luminosity functions of bulges and\n discs and their implied stellar mass densities: We derive the luminosity functions of elliptical galaxies, galaxy bulges,\ngalaxy pseudo-bulges and galaxy discs from our structural catalogue of 10,095\ngalaxies. In addition we compute their associated luminosity and stellar mass\ndensities. We show that spheroidal systems (elliptical galaxies and the bulges\nof disc galaxies) exhibit a strong color bimodality indicating two distinct\ntypes of spheroid which are separated by a core color of (u-r) ~ 2 mag. We\nargue that the similarity of the red elliptical and the red bulge luminosity\nfunctions supports our previous arguments that they share a common origin and\nsurprisingly find that the same follows for the blue ellipticals and blue\nbulges, the latter of which we refer to as pseudo-bulges. In terms of the\nstellar mass budget we find that $58\\pm6$ per cent is currently in the form of\ndiscs, 39+/-6 per cent in the form of red spheroids (13+/-4 per cent\nellipticals, 26+/-4 per cent bulges) and the remainder is in the form of blue\nspheroidal systems (~1.5 per cent blue ellipticals and ~1.5 per cent\npseudo-bulges). In terms of galaxy formation we argue that our data on galaxy\ncomponents strongly supports the notion of a two-stage formation process\n(spheroid first, disc later) but with the additional complexity of secular\nevolution occurring in quiescent discs giving rise to two distinct bulge types:\ngenuine 'classical' bulges and pseudo-bulges. We therefore advocate that there\nare three significant structures underpinning galaxy evolution: classical\nspheroids (old); pseudo-bulges (young) and discs (intermediate). The luminous\nnearby galaxy population is a mixture of these three structural types.\n[abridged].", + "category": "astro-ph" + }, + { + "text": "The effects of drift and winds on the propagation of Galactic cosmic\n rays: We study the effects of drift motions and the advection by a Galactic wind on\nthe propagation of cosmic rays in the Galaxy. We employ a simplified magnetic\nfield model, based on (and similar to) the Jansson-Farrar model for the\nGalactic magnetic field. Diffusion is allowed to be anisotropic. The relevant\nequations are solved numerically, using a set of stochastic differential\nequations. Inclusion of drift and a Galactic wind significantly shortens the\nresidence time of cosmic rays, even for moderate wind speeds", + "category": "astro-ph" + }, + { + "text": "A vestige low metallicity gas shell surrounding the radio galaxy\n 0943-242 at z=2.92: Observations are presented showing the doublet CIV 1550 absorption lines\nsuperimposed on the CIV emission in the radio galaxy 0943-242. Within the\nerrors, the redshift of the absorption system that has a column density of\nN_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha\nabsorption trough observed by Rottgering et al. (1995). The gas seen in\nabsorption has a resolved spatial extent of at least 13 kpc (the size of the\nextended emission line region). We first model the absorption and emission gas\nas co-spatial components with the same metallicity and degree of excitation.\nUsing the information provided by the emission and absorption line ratios of\nCIV and Ly-alpha, we find that the observed quantities are incompatible with\nphotoionization or collisional ionization of cloudlets with uniform properties.\nWe therefore reject the possibility that the absorption and emission phases are\nco-spatial and favour the explanation that the absorption gas has low\nmetallicity and is located further away from the host galaxy (than the emission\nline gas). The estimated low metallicity for the absorption gas in 0943-242 (Z\n\\~ 1% solar) and its proposed location -outer halo outside the radio cocoon-\nsuggest that its existence preceeds the observed AGN phase and is a vestige of\nthe initial starburst at the onset of formation of the parent galaxy.", + "category": "astro-ph" + }, + { + "text": "Isodensity Statistics on Clustering of High-z Objects in Cosmological\n Redshift-spaces: We discuss the systematic effects arising from the cosmological\nredshift-space (geometric) distortion on the statistical analysis of isodensity\ncontour using high-redshift catalogs. Especially, we present a simple\ntheoretical model for isodensity statistics in cosmological redshift-space, as\na generalization of the work by Matsubara (1996). The statistical quantities\nconsidered here are the two- and three-dimensional genus of isodensity contour,\nthe area of surface, the length of contour intersecting with a plane and the\nnumber of the crossing points of isodensity contour on a line. We give useful\nanalytic formulae for the isodensity statistics, which take into account the\ncorrections from the geometric distortion, the nonlinear clustering and the\nnonlinear velocity distortion phenomenologically. We then demonstrate how the\ngeometric distortion and the nonlinear corrections alter shapes of the\nstatistical quantities on the basis of plausible cosmological models. Our\nresults show that the nonlinear correction can be sensitive to a choice of the\nredshift-space coordinate as increasing the redshift. The low-dimensional\nquantities such as two-dimensional genus systematically yield anisotropy due to\nthe geometric and velocity distortions and their angle-dependence shows the\n$10\\sim20%$ difference of amplitude. Sensitivity for typical high-redshift\nsamples are estimated in an analytic manner, and the influence of the\nlight-cone effect for the isodensity statistics is also discussed.", + "category": "astro-ph" + }, + { + "text": "Evidence for Core Collapse in the Type Ib/c SN 1999ex: We present optical and infrared spectra of SN 1999ex that reveal a clear\nexample of an intermediate Type Ib/c case. This suggests a continuous\nspectroscopic sequence between Type Ib and Type Ic supernovae. We report UBVRIz\nphotometric observations of SN 1999ex that started only one day after\nexplosion, which permitted us to witness an elusive transient cooling phase\nthat lasted 4 days. The initial cooling and subsequent radioactive heating\nproduced a dip in the lightcurve which is consistent with explosion models\ninvolving core collapse of evolved massive helium stars, and inconsistent with\nlightcurves resulting from the thermonuclear runaway of compact white dwarfs.", + "category": "astro-ph" + }, + { + "text": "Abundances of lithium, oxygen, and sodium in the turn-off stars of\n Galactic globular cluster 47 Tuc: We aim to determine abundances of Li, O and Na in a sample of of 110 turn-off\n(TO) stars, in order to study the evolution of light elements in this cluster\nand to put our results in perspective with observations of other globular and\nopen clusters, as well as with field stars. We use medium resolution spectra\nobtained with the GIRAFFE spectrograph at the ESO 8.2m Kueyen VLT telescope and\nuse state of the art 1D model atmospheres and NLTE line transfer to determine\nthe abundances. We also employ CO5BOLD hydrodynamical simulations to assess the\nimpact of stellar granulation on the line formation and inferred abundances.\nOur results confirm the existence of Na-O abundance anti-correlation and hint\ntowards a possible Li-O anti-correlation in the TO stars of 47 Tuc. We find no\nconvincing evidence supporting the existence of Li-Na correlation. The obtained\n3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were\ndetected reliably, $\\langle A({\\rm Li})_{\\rm 3D~NLTE}\\rangle = 1.78 \\pm 0.18$\ndex, appears to be significantly lower than what is observed in other globular\nclusters. At the same time, star-to-star spread in Li abundance is also larger\nthan seen in other clusters. The highest Li abundance observed in 47 Tuc is\nabout 0.1 dex lower than the lowest Li abundance observed among the un-depleted\nstars of the metal-poor open cluster NGC 2243. The lithium abundances in 47\nTuc, when put into context with observations in other clusters and field stars,\nsuggest that stars that are more metal-rich than [FeH] \\sim -1.0 experience\nsignificant lithium depletion during their lifetime on the main sequence, while\nthe more metal-poor stars do not. Rather strikingly, our results suggest that\ninitial lithium abundance with which the star was created may only depend on\nits age (the younger the star, the higher its Li content) and not on its\nmetallicity.", + "category": "astro-ph" + }, + { + "text": "Missing Link Found? --- The ``runaway'' path to supermassive black holes: Observations of stellar kinematics, gas dynamics and masers around galactic\nnuclei have now firmly established that many galaxies host central supermassive\nblack holes (SMBHs) with masses in the range $10^6 \\sim 10^9$M$_{\\odot}$.\nHowever, how these SMBHs formed is not well understood. One reason for this\nsituation is the lack of observations of intermediate-mass BHs (IMBHs), which\ncould bridge the gap between stellar-mass BHs and SMBHs. Recently, this missing\nlink (i.e., an IMBH) has been found in observations made by the ASCA and the\nChandra of the central region of the starburst galaxy M82 \\citep{MT99, PG99,\nMT01, Ka01}. Subsequent observations by SUBARU have revealed that this IMBH\napparently coincides with a young compact star cluster. Based on these\nfindings, we suggest a new formation scenario for SMBHs. In this scenario,\nIMBHs first form in young compact star clusters through runaway merging of\nmassive stars. While these IMBHs are forming, the host star clusters sink\ntoward the galactic nucleus through dynamical friction, and upon evaporation\ndeposit their IMBHs near the galactic center. The IMBHs then form binaries and\neventually merge via gravitational radiation, forming an SMBH.", + "category": "astro-ph" + }, + { + "text": "The search for galactic dark matter clump candidates with Fermi and\n MAGIC: We present a systematic search for potential dark matter clumps in our Galaxy\namong the 630 unassociated sources included in the LAT 1-year Point Source\nCatalog. Assuming a dark matter particle that generates observable gamma-ray\nphotons beyond the Fermi energy range through self-annihilation, we compile a\nlist of reasonable targets for the MAGIC Imaging Atmospheric Cherenkov\nTelescopes. In order to narrow down the origin of these enigmatic sources, we\nsummarize ongoing multiwavelength studies including X-ray, radio, and optical\nspectroscopy. We report on observations of two of these candidates using the\nMAGIC Telescopes. We find that the synergy between Fermi and Cherenkov\ntelescopes, along with multiwavelength observations, could play a key role in\nindirect searches for dark matter.", + "category": "astro-ph" + }, + { + "text": "Early Solar System $r$-process Abundances Limit Collapsar Origin: Heavy elements produced exclusively through rapid neutron capture (the\n'$r$-process') originate from violent cosmic explosions. While neutron star\nmergers are the primary candidates, another plausible production site are\n'collapsars'---collapsing massive stars that form a black hole with an\naccretion disk. Here we show that collapsars are too rare to be the prime\norigin of $r$-process elements in the Solar System. By comparing numerical\nsimulations with the early Solar System abundances of actinides produced\nexclusively through the $r$-process, we exclude higher than 20% contribution\nfrom collapsars with 90% confidence. We additionally limit $r$-process ejecta\nmasses from collapsars to less than 10% of the ejecta mass from neutron star\nmergers, about $10^{-2}$M$_\\odot$.", + "category": "astro-ph" + }, + { + "text": "Opening the 21cm EoR Window: Measurements of Foreground Isolation with\n PAPER: We present new observations with the Precision Array for Probing the Epoch of\nReionization (PAPER) with the aim of measuring the properties of foreground\nemission for 21cm Epoch of Reionization experiments at 150 MHz. We focus on the\nfootprint of the foregrounds in cosmological Fourier space to understand which\nmodes of the 21cm power spectrum will most likely be compromised by foreground\nemission. These observations confirm predictions that foregrounds can be\nisolated to a \"wedge\"-like region of 2D (k-perpendicular, k-parallel)-space,\ncreating a window for cosmological studies at higher k-parallel values. We also\nfind that the emission extends past the nominal edge of this wedge due to\nspectral structure in the foregrounds, with this feature most prominent on the\nshortest baselines. Finally, we filter the data to retain only this \"unsmooth\"\nemission and image specific k-parallel modes of it. The resultant images show\nan excess of power at the lowest modes, but no emission can be clearly\nlocalized to any one region of the sky. This image is highly suggestive that\nthe most problematic foregrounds for 21cm EoR studies will not be easily\nidentifiable bright sources, but rather an aggregate of fainter emission.", + "category": "astro-ph" + }, + { + "text": "Calibration of photometry from the Gemini Multi-Object Spectrograph on\n Gemini North: All available observations of photometric standard stars obtained with the\nGemini Multi-Object Spectrograph at Gemini North in the period from August 2001\nto December 2003 have been used to establish the calibrations for photometry\nobtained with the instrument. The calibrations presented in this paper are\nbased on significantly more photometric standard star observations than usually\nused by the individual users. Nightly photometric zero points as well as color\nterms are determined. The color terms are expected to be valid for all\nobservations taken prior to UT 2004 November 21 at which time the Gemini North\nprimary mirror was coated with silver instead of aluminum. While the nightly\nzero points are accurate to 0.02 mag or better (random errors), the accuracy of\nthe calibrations is limited by systematic errors from so-called \"sky\nconcentration\", an effect seen in all focal reducer instruments. We conclude\nthat an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations\nderived in this paper. The color terms are strongest for very red objects, e.g.\nfor objects with (r'-z')=3.0 the resulting z' magnitudes will be ~0.35 mag too\nbright if the color term is ignored. The calibrations are of importance to the\nlarge Gemini user community with data obtained prior to UT 2004 November 21, as\nwell as future users of achive data from this period in time.", + "category": "astro-ph" + }, + { + "text": "Mid-infrared observations of the nucleus of comet P/2016 BA14\n (PANSTARRS): We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which\nwere obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of\n1.012 au and 0.026 au, respectively, approximately 30 hours before its closest\napproach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution\n($\\lambda$/$\\Delta \\lambda$~250) spectroscopic observations in the N-band and\nimaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7\nand 18.8 $\\mu$m) in the N- and Q-bands were obtained using the Cooled\nMid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru\ntelescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14\nat different wavelengths are consistent with a point-spread function. Owing to\nthe close approach of the comet to the Earth, the observed thermal emission\nfrom the comet is dominated by the thermal emission from its nucleus rather\nthan its dust coma. The observed spectral energy distribution of the nucleus at\nmid-infrared wavelengths is consistent with a Planck function at temperature\nT~350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by\nassuming an emissivity of 0.97). The normalized emissivity spectrum of the\ncomet exhibits absorption-like features that are not reproduced by the\nanhydrous minerals typically found in cometary dust coma, such as olivine and\npyroxene. Instead, the spectral features suggest the presence of large grains\nof phyllosilicate minerals and organic materials. Thus, our observations\nindicate that an inactive small body covered with these processed materials is\na possible end state of comets.", + "category": "astro-ph" + }, + { + "text": "On the cosmological mass function theory: This paper provides, from one side, a review of the theory of the\ncosmological mass function from a theoretical point of view, starting from the\nseminal paper of Press & Shechter (1974) to the last developments (Del Popolo &\nGambera (1998, 1999), Sheth & Tormen 1999 (ST), Sheth, Mo & Tormen 2001 (ST1),\nJenkins et al. 2001 (J01), Shet & Tormen 2002 (ST2), Del Popolo 2002a, Yagi et\nal. 2004 (YNY)), and from another side some improvements on the multiplicity\nfunction models in literature. ...", + "category": "astro-ph" + }, + { + "text": "Perturbations in Tachyon Dark Energy and their Effect on Matter\n Clustering: A non-canonical scalar tachyon field is a viable candidate for dark energy\nand has been found to be in good agreement with observational data. Background\ndata alone cannot completely rule out degeneracy between this model and others.\nTo further constrain the parameters, apart from the distance measurements, we\nstudy perturbations in the tachyon scalar field and how they affect matter\nclustering. We consider two tachyon potentials for this study, an inverse\nsquare potential and an exponential potential. We study the evolution of the\ngravitational potential, matter density contrast, and dark energy density\ncontrast, and compare them with the evolution in the $\\Lambda CDM $ model.\nAlthough perturbations in dark energy at sub-Hubble scales are negligible in\ncomparison with matter perturbations, they cannot be ignored at Hubble and\nsuper-Hubble scales ($\\lambda_p > 1000$ Mpc). We also study the evolution of\ngrowth function and growth rate of matter, and find that the growth rate is\nsignificantly suppressed in dark energy dominated era with respect to the\ngrowth rate for $\\Lambda CDM$ model. A comparison of these models with Redshift\nSpace Distortion growth rate data is presented by way of calculating\n$f\\sigma_8(z)$. There is a tension of $2.9\\sigma$ ($2.26\\sigma$ ) between\ngrowth rate data and Planck-2015 (Planck-2018) Cosmic Microwave Background\nRadiation data for $\\Lambda CDM$ model. We present constraints on free\nparameters of these models and show that perturbations in the tachyon scalar\nfield reduce this tension between different data sets.", + "category": "astro-ph" + }, + { + "text": "Determination of the Sun's Offset from the Galactic Plane Using Pulsars: We derive the Sun's offset from the local mean Galactic plane($z_\\odot$)\nusing the observed $z$ distribution of young pulsars. Pulsar distances are\nobtained from measurements of annual parallax, HI absorption spectra or\nassociations where available and otherwise from the observed pulsar dispersion\nand a model for the distribution of free electrons in the Galaxy. We fit the\ncumulative distribution function for a ${\\rm sech}^2(z)$ distribution function,\nrepresenting an isothermal self-gravitating disk, with uncertainties being\nestimated using the bootstrap method. We take pulsars having characteristic age\n$\\tau_c<10^{6.5}$~yr and located within 4.5~kpc of the Sun, omitting those\nwithin the local spiral arm and those significantly affected by the Galactic\nwarp, and solve for $z_\\odot$ and the scale height, $H$, for different cutoffs\nin $\\tau_c$. We compute these quantities using just the independently\ndetermined distances, and these together with DM-based distances separately\nusing the YMW16 and NE2001 Galactic electron density models. We find that an\nage cutoff at $10^{5.75}$~yr with YMW16 DM-distances gives the best results\nwith a minimum uncertainty in $z_\\odot$ and an asymptotically stable value for\n$H$ showing that, at this age and below, the observed pulsar $z$-distribution\nis dominated by the dispersion in their birth locations. From this sample of\n115 pulsars, we obtain $z_\\odot=13.4\\pm$4.4~pc and $H=56.9\\pm$6.5~pc, similar\nto estimated scale heights for OB stars and open clusters. Consistent results\nare obtained using the independent-only distances and using the NE2001 model\nfor the DM-based distances.", + "category": "astro-ph" + }, + { + "text": "Extra galactic sources of high energy neutrinos: The main goal of the construction of large volume, high energy neutrino\ntelescopes is the detection of extra-Galactic neutrino sources. The existence\nof such sources is implied by observations of ultra-high energy, >10^{19} eV,\ncosmic-rays (UHECRs), the origin of which is a mystery. The observed UHECR flux\nsets an upper bound to the extra-Galactic high energy neutrino intensity, which\nimplies that the detector size required to detect the signal in the energy\nrange of 1 TeV to 1 PeV is >=1 giga-ton, and much larger at higher energy.\nOptical Cerenkov neutrino detectors, currently being constructed under ice and\nwater, are expected to achieve 1 giga-ton effective volume for 1 TeV to 1 PeV\nneutrinos. Coherent radio Cerenkov detectors (and possibly large air-shower\ndetectors) will provide the >> 1 giga-ton effective volume required for\ndetection at ~10^{19} eV. Detection of high energy neutrinos associated with\nelectromagnetically identified sources will allow to identify the sources of\nUHECRs, will provide a unique probe of the sources, which may allow to resolve\nopen questions related to the underlying physics of models describing these\npowerful accelerators, and will provide information on fundamental neutrino\nproperties.", + "category": "astro-ph" + }, + { + "text": "Testing a Galactic Lensing Hypothesis with the Prompt Emission of GRB\n 221009A: Even at modest amplification, the optical depth to gravitational lensing\nthrough the Galaxy is $<10^{-5}$. However, the large apparent\nisotropic-equivalent energy of GRB 221009A coupled with a path through low\nGalactic latitude suggests that the conditional probability that this\nparticular GRB was lensed is greater than the very low a priori expectation.\nWith the extreme brightness of the prompt emission, this Galactic lensing\nhypothesis can be constrained by autocorrelation analysis of Fermi photons on\n0.1-1000 ms timescales. In relating lensing mass, magnification, and\nautocorrelation timescale, I show that a lensed-induced autocorrelation\nsignature by stellar lenses falls below the minimal variability timescale (MVT)\nexpected from a black hole central engine. However, lensing by Galactic dark\nmatter MACHOs ($M_l > 10-1000\\,M_\\odot$) could be confirmed with this approach.\nRegardless, at a peak $\\gamma$-ray photon rate of $>30$ ms$^{-1}$, GRB 221009A\nrepresents a prime opportunity to measure the smallest MVTs of GRBs.", + "category": "astro-ph" + }, + { + "text": "Potential of radio telescopes as high-frequency gravitational wave\n detectors: In the presence of magnetic fields, gravitational waves are converted into\nphotons and vice versa. We demonstrate that this conversion leads to a\ndistortion of the cosmic microwave background (CMB), which can serve as a\ndetector for MHz to GHz gravitational wave sources active before reionization.\nThe measurements of the radio telescope EDGES can be cast as a bound on the\ngravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the\nstrongest (weakest) cosmic magnetic fields allowed by current astrophysical and\ncosmological constraints. Similarly, the results of ARCADE 2 imply $h_c <\n10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these\nconstraints exceed current laboratory constraints by about seven orders of\nmagnitude. Future advances in 21cm astronomy may conceivably push these bounds\nbelow the sensitivity of cosmological constraints on the total energy density\nof gravitational waves.", + "category": "astro-ph" + }, + { + "text": "The Evolution of [OII] Emission from Cluster Galaxies: We investigate the evolution of the star formation rate in cluster galaxies.\nWe complement data from the CNOC1 cluster survey (0.15 1.\nThe total amount of observation time was about 60 hours and these observations\nare part of an ongoing programme, started in September 1990, to search for\nrapid variability in RQQSOs. No evidence for short-term variability greater\nthan about 0.1 magnitudes was detected in any of the 23 sources, however\nlong-term variability was recorded for the radio-quiet quasar PG 2112+059. The\nfinding charts are included here because they identify the RQQSO and the\nreference stars used in the photometry, and hence are available for use by\nother observers.", + "category": "astro-ph" + }, + { + "text": "H.E.S.S. observations of the supernova remnant RX J0852.0-4622:\n shell-type morphology and spectrum of a widely extended VHE gamma-ray source: The shell-type supernova remnant RX J0852.0-4622 was observed with the High\nEnergy Stereoscopic System (H.E.S.S.) of Atmospheric Cherenkov Telescopes\nbetween December 2004 and May 2005 for a total observation time of 33 hours,\nabove an average gamma-ray energy threshold of 250 GeV. The angular resolution\nof ~0.06 degree (for events triggering 3 or 4 telescopes) and the large field\nof view of H.E.S.S. ($5^{\\circ}$ diameter) are well adapted to studying the\nmorphology of the object in very high energy gamma-rays, which exhibits a\nremarkably thin shell very similar to the features observed in the radio range\nand in X-rays. The spectral analysis of the source from 300 GeV to 20 TeV is\nalso presented. Finally, the possible origins of the very high energy gamma-ray\nemission (Inverse Compton scattering by electrons or the decay of neutral pions\nproduced by proton interactions) are discussed, on the basis of morphological\nand spectral features obtained at different wavelengths.", + "category": "astro-ph" + }, + { + "text": "Dwarf Galaxies of Tidal Origin -- Relevant for Cosmology ?: Evolutionary synthesis models for Tidal Dwarf Galaxies (TDGs) are presented\nthat allow to have varying proportions of young stars formed in the\nmerger-induced starburst and of stars from the merging spirals' disks. The\nspecific metallicities as well as the gaseous emission of actively star forming\nTDGs are consistently accounted for. Comparison of models with observational\ndata (e.g. Duc, this volume) gives information on the present evolutionary\nstate and possible future luminosity evolution of TDGs. The redshift evolution\nof merger rates and of the gas content and metallicities of spiral galaxies are\nused to estimate the number of TDGs at various redshifts and to investigate\ntheir contribution to magnitude limited surveys.", + "category": "astro-ph" + }, + { + "text": "Mass Assembly of Stellar Systems and their Evolution with the SMA\n (MASSES) -- Full Data Release: We present and release the full dataset for the Mass Assembly of Stellar\nSystems and their Evolution with the SMA (MASSES) survey. This survey used the\nSubmillimeter Array (SMA) to image the 74 known protostars within the Perseus\nmolecular cloud. The SMA was used in two array configurations to capture\noutflows for scales $>$30$^{\\prime\\prime}$ ($>$9000 au) and to probe scales\ndown to $\\sim$1$^{\\prime\\prime}$ ($\\sim$300 au). The protostars were observed\nwith the 1.3 mm and 850 $\\mu$m receivers simultaneously to detect continuum at\nboth wavelengths and molecular line emission from CO(2-1), $^{13}$CO(2-1),\nC$^{18}$O(2-1), N$_2$D$^+$(3-2), CO(3-2), HCO$^+$(4-3), and\nH$^{13}$CO$^+$(4-3). Some of the observations also used the SMA's recently\nupgraded correlator, SWARM, whose broader bandwidth allowed for several more\nspectral lines to be observed (e.g., SO, H$_2$CO, DCO$^+$, DCN, CS, CN). Of the\nmain continuum and spectral tracers observed, 84% of the images and cubes had\nemission detected. The median C$^{18}$O(2-1) linewidth is $\\sim$1.0 km\ns$^{-1}$, which is slightly higher than those measured with single-dish\ntelescopes at scales of 3000-20000 au. Of the 74 targets, six are suggested to\nbe first hydrostatic core candidates, and we suggest that L1451-mm is the best\ncandidate. We question a previous continuum detection toward L1448 IRS2E. In\nthe SVS13 system, SVS13A certainly appears to be the most evolved source, while\nSVS13C appears to be hotter and more evolved than SVS13B. The MASSES survey is\nthe largest publicly available interferometric continuum and spectral line\nprotostellar survey to date, and is largely unbiased as it only targets\nprotostars in Perseus. All visibility ($uv$) data and imaged data are publicly\navailable at https://dataverse.harvard.edu/dataverse/full_MASSES/.", + "category": "astro-ph" + }, + { + "text": "Galaxy And Mass Assembly (GAMA): The absence of stellar mass segregation\n in galaxy groups and consistent predictions from GALFORM and EAGLE\n simulations: We investigate the contentious issue of the presence, or lack thereof, of\nsatellites mass segregation in galaxy groups using the Galaxy And Mass Assembly\n(GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological\nhydrodynamical simulation catalogues of galaxy groups. We select groups with\nhalo mass $12 \\leqslant \\log(M_{\\text{halo}}/h^{-1}M_\\odot) <14.5$ and redshift\n$z \\leqslant 0.32$ and probe the radial distribution of stellar mass out to\ntwice the group virial radius. All the samples are carefully constructed to be\ncomplete in stellar mass at each redshift range and efforts are made to\nregularise the analysis for all the data. Our study shows negligible mass\nsegregation in galaxy group environments with absolute gradients of\n$\\lesssim0.08$ dex and also shows a lack of any redshift evolution. Moreover,\nwe find that our results at least for the GAMA data are robust to different\nhalo mass and group centre estimates. Furthermore, the EAGLE data allows us to\nprobe much fainter luminosities ($r$-band magnitude of 22) as well as\ninvestigate the three-dimensional spatial distribution with intrinsic halo\nproperties, beyond what the current observational data can offer. In both cases\nwe find that the fainter EAGLE data show a very mild spatial mass segregation\nat $z \\leqslant 0.22$, which is again not apparent at higher redshift.\nInterestingly, our results are in contrast to some earlier findings using the\nSloan Digital Sky Survey. We investigate the source of the disagreement and\nsuggest that subtle differences between the group finding algorithms could be\nthe root cause.", + "category": "astro-ph" + }, + { + "text": "Structure and Evolution of the Envelopes of Deeply Embedded Massive\n Young Stars: The physical structure of the envelopes around a sample of fourteen massive\n(1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales\nusing maps and spectra in submillimeter continuum and lines of C17O, CS and\nH2CO. The total column densities and the temperature profiles are obtained by\nfitting self-consistent dust models to submillimeter photometry. Both the\nmolecular line and dust emission data indicate density gradients ~r^{-alpha},\nwith alpha=1.0-1.5, significantly flatter than the alpha=2.0 generally found\nfor low-mass objects. This flattening may indicate that in massive young\nstellar objects, nonthermal pressure is more important for the support against\ngravitational collapse, while thermal pressure dominates for low-mass sources.\nWe find alpha=2 for two hot core-type sources, but regard this as an upper\nlimit since in these objects, the CS abundance may be enhanced in the warm gas\nclose to the star.", + "category": "astro-ph" + }, + { + "text": "High-Precision Measurements of Brightness Variation of Nereid: Nereid, a satellite of Neptune, has a highly eccentric prograde orbit with a\nsemi-major axis larger than 200 Neptune radius and is classified as an\nirregular satellite. Although the capture origin of irregular satellites has\nbeen widely accepted, several previous studies suggest that Nereid was formed\nin the circumplanetary disk of Neptune and was ejected outward to the present\nlocation by Triton. Our time-series photometric observations confirm that the\nspin is stable and non-chaotic with a period of 11.5 hr as indicated by Grav et\nal. (2003). The optical colors of Nereid are indistinguishable from those of\ntrans-Neptunian objects and Centaurs, especially those with neutral colors. We\nalso find the consistency of Nereid's rotation with the size-rotation\ndistribution of small outer bodies. It is more likely that Nereid originates in\nan immigrant body captured from a heliocentric orbit which was 4-5 AU away from\nNeptune's orbit.", + "category": "astro-ph" + }, + { + "text": "Giant Metrewave Radio Telescope limits on cool HI in galaxy groups: We present Giant Metrewave Radio Telescope 21-cm HI observations towards a\nsample of compact radio sources behind galaxy groups, to search for cool HI.\nThe results -- from high dynamic range spectra for 8 lines-of-sight through 7\ngalaxy groups -- do not show any evidence for absorption by cool HI. At a\nresolution of 20 km/s, the optical depth upper limits obtained were between\n0.0075 and 0.035 (3sigma); these correspond to upper limits of a few times\n10**23 m**-2 for the column density of any cool HI along these lines of sight\n(assuming a spin temperature of 100 K).", + "category": "astro-ph" + }, + { + "text": "H\u03b1 and UV luminosities and star formation rates in a large sample\n of luminous compact galaxies: We present the results of a statistical study of the star formation rates\n(SFR) derived from the Galaxy Evolution Explorer (GALEX) observations in the\nultraviolet continuum and in the H\\alpha emission line for a sample of about\n800 luminous compact galaxies (LCGs). Galaxies in this sample have a compact\nstructure and include one or several regions of active star formation. Global\ngalaxy characteristics (metallicity, luminosity, stellar mass) are intermediate\nbetween ones of the nearby blue compact dwarf (BCD) galaxies and Lyman-break\ngalaxies (LBGs) at high redshifts z > 2 - 3. SFRs were corrected for\ninterstellar extinction which was derived from the optical Sloan Digital Sky\nSurvey (SDSS) spectra. We find that SFRs derived from the galaxy luminosities\nin the far ultraviolet (FUV) and near ultraviolet (NUV) ranges vary in a wide\nrange from 0.18 M_Sun/yr to 113 M_Sun/yr with median values of 3.8 M_Sun/yr and\n5.2 M_Sun/yr, respectively. Simple regression relations are found for\nluminosities L(H\\alpha) and L(UV) as functions of the mass of the young stellar\npopulation, the starburst age, and the galaxy metallicity. We consider the\nevolution of L(H\\alpha), L(FUV) and L(NUV) with a starburst age and introduce\nnew characteristics of star formation, namely the initial H\\alpha, FUV and NUV\nluminosities at zero starburst age.", + "category": "astro-ph" + }, + { + "text": "Recent Developments in Weak Lensing: Measurement of the gravitational distortion of images of distant galaxies is\nrapidly becoming established as a powerful probe of the dark mass distribution\nin clusters of galaxies. With the advent of large mosaics of CCD's these\nmethods should provide a composite total mass profile for galaxy haloes and\nalso measure the power spectrum of mass fluctuations on supercluster scales. We\ndescribe how HST observations have been used to place the observational\nmeasurement of the shear on a quantitative footing. By artifically stretching\nand then degrading WFPC2 images to simulate ground based observing it is now\npossible to directly calibrate the effect of atmospheric seeing. Similar\nexperiments show that one can remove the effect of artificial image anisotropy\narising in the atmosphere or telescope. There have also been important advances\nin the interpretation of the shear: reconstruction techniques have been\nextended to encompass the strong distortion regime of giant arcs etc., progress\nhas been made in removing a bias present in earlier reconstruction techniques,\nand we describe new techniques for `aperture densitometry'. We present some new\nresults on clusters of galaxies, and discuss the intimate connections between\nweak lensing and deep spectroscopy.", + "category": "astro-ph" + }, + { + "text": "Dust Reddened Quasars in FIRST and UKIDSS: Beyond the Tip of the Iceberg: We present the results of a pilot survey to find dust-reddened quasars by\nmatching the FIRST radio catalog to the UKIDSS near-infrared survey, and using\noptical data from SDSS to select objects with very red colors. The deep K-band\nlimit provided by UKIDSS allows for finding more heavily-reddened quasars at\nhigher redshifts as compared with previous work using FIRST and 2MASS. We\nselected 87 candidates with K<=17.0 from the UKIDSS Large Area Survey (LAS)\nFirst Data Release (DR1) which covers 190 deg2. These candidates reach up to\n~1.5 magnitudes below the 2MASS limit and obey the color criteria developed to\nidentify dust-reddened quasars. We have obtained 61 spectroscopic observations\nin the optical and/or near-infrared as well as classifications in the\nliterature and have identified 14 reddened quasars with E(B-V)>0.1, including\nthree at z>2. We study the infrared properties of the sample using photometry\nfrom the WISE Observatory and find that infrared colors improve the efficiency\nof red quasar selection, removing many contaminants in an infrared-to-optical\ncolor-selected sample alone. The highest-redshift quasars (z > 2) are only\nmoderately reddened, with E(B-V) ~ 0.2-0.3. We find that the surface density of\nred quasars rises sharply with faintness, comprising up to 17% of blue quasars\nat the same apparent K-band flux limit. We estimate that to reach more heavily\nreddened quasars (i.e., E(B-V) > 0.5) at z>2 and a depth of K=17 we would need\nto survey at least ~2.5 times more area.", + "category": "astro-ph" + }, + { + "text": "Are fulleranes responsible for the 21 micron feature?: Recent detections of C$_{60}$, C$_{70}$, and C$_{60}^+$ in space induced\nextensive studies of fullerene derivatives in circumstellar environments. As\nthe promising fullerene sources, protoplanetary nebulae (PPNe) show a number of\nunidentified bands in their infrared spectra, among which a small sample\nexhibits an enigmatic feature at $\\sim21$\\,$\\mu$m. Hydrogenation of fullerenes\ncan produce fulleranes emitting new infrared bands. In this paper, we\ninvestigate the possibility of fulleranes (C$_{60}$H$_m$) as the carrier of the\n21\\,$\\mu$m feature in terms of theoretical vibrational spectra of fulleranes.\nThe evidences favoring and disfavoring the fullerane hypothesis are presented.\nWe made an initial guess for the hydrogen coverage of C$_{60}$H$_m$ that may\ncontribute to the 21\\,$\\mu$m feature.", + "category": "astro-ph" + }, + { + "text": "Impact of SZ cluster residuals in CMB maps and CMB-LSS\n cross-correlations: Residual foreground contamination in cosmic microwave background (CMB) maps,\nsuch as the residual contamination from thermal Sunyaev-Zeldovich (SZ) effect\nin the direction of galaxy clusters, can bias the cross-correlation\nmeasurements between CMB and large-scale structure optical surveys. It is thus\nessential to quantify those residuals and, if possible, to null out SZ cluster\nresiduals in CMB maps. We quantify for the first time the amount of SZ cluster\ncontamination in the released Planck 2015 CMB maps through (i) the stacking of\nCMB maps in the direction of the clusters, and (ii) the computation of\ncross-correlation power spectra between CMB maps and the SDSS-IV large-scale\nstructure data. Our cross-power spectrum analysis yields a $30\\sigma$ detection\nat the cluster scale ($\\ell=1500-2500$) and a $39\\sigma$ detection on larger\nscales ($\\ell=500-1500$) due to clustering of SZ clusters, giving an overall\n$54\\sigma$ detection of SZ cluster residuals in the Planck CMB maps. The Planck\n2015 NILC CMB map is shown to have $44\\pm4\\%$ of thermal SZ foreground emission\nleft in it. Using the 'Constrained ILC' component separation technique, we\nconstruct an alternative Planck CMB map, the 2D-ILC map, which is shown to have\nnegligible SZ contamination, at the cost of being slightly more contaminated by\nGalactic foregrounds and noise. We also discuss the impact of the SZ residuals\nin CMB maps on the measurement of the ISW effect, which is shown to be\nnegligible based on our analysis.", + "category": "astro-ph" + }, + { + "text": "Optical Gravitational Lensing Experiment. Distance to the Magellanic\n Clouds with the Red Clump Stars: Are the Magellanic Clouds 15% Closer than\n Generally Accepted?: We present a new distance determination to the Large and Small Magellanic\nClouds using the newly developed red clump stars method (Paczynski and Stanek\n1998). This new, single-step, Hipparcos calibrated method seems to be one of\nthe most precise techniques of distance determination with very small\nstatistical error due to large number of red clump stars usually available. The\ndistances were determined independently along four lines-of-sight located at\nopposite sides of each Magellanic Cloud. The results for each line-of-sight are\nvery consistent. For the SMC we obtain the distance modulus:\nm-M=18.56+/-0.03+/-0.06 mag (statistical and systematic errors, respectively)\nand for the LMC: m-M=18.08+/-0.03+/-0.12} mag where systematic errors are\nmostly due to uncertainty in reddening estimates. Both distances will be\nrefined and systematic errors reduced when accurate reddening maps for our\nfields are available. Distance moduli to both Magellanic Clouds are ~0.4 mag\nsmaller than generally accepted values. The modulus to the LMC is in good\nagreement with the recent determinations from RR Lyrae type stars and upper\nlimit resulting from the SN1987A echo. We suspect that the distance to the LMC\nand SMC is shorter by about 15% than previously assumed: 42 kpc and 52 kpc,\nrespectively.\n We also present our color-magnitude diagrams around the red clump for the LMC\nand SMC. We identify vertical red clump, first noted by Zaritsky and Lin\n(1997), in the color-magnitude diagram of both Magellanic Clouds and we\ninterpret it as an evolutionary feature rather than unknown stellar population\nbetween the LMC and our Galaxy.", + "category": "astro-ph" + }, + { + "text": "Newly Identified Star Clusters in M33. I. Integrated Photometry and\n Color-Magnitude Diagrams: We present integrated photometry and color-magnitude diagrams (CMDs) for 24\nstar clusters in M33, of which 12 were previously uncataloged. These results\nare based on Advanced Camera for Surveys observations from the Hubble Space\nTelescope of two fields in M33. Our integrated V magnitudes and V-I colors for\nthe previously identified objects are in good agreement with published\nphotometry. We are able to estimate ages for 21 of these clusters using\nfeatures in the CMDs, including isochrone fitting to the main sequence turnoffs\nfor 17 of the clusters. Comparisons of these ages with the clusters' integrated\ncolors and magnitudes suggest that simple stellar population models perform\nreasonably well in predicting these properties.", + "category": "astro-ph" + }, + { + "text": "SuperAGILE: the hard X-ray Imager for the AGILE space mission: SuperAGILE is a coded mask experiment based on silicon microstrip detectors.\nIt operates in the 15-45 keV nominal energy range, providing crossed\none-dimensional images of the X-ray sky with an on-axis angular resolution of 6\narcmin, over a field of view in excess of 1 steradian. It was designed as the\nhard X-ray monitor of the AGILE space mission, a small satellite of the Italian\nSpace Agency devoted to image the gamma-ray sky in the 30 MeV - 50 GeV energy\nband. The AGILE mission was launched in a low-earth orbit on 23^{rd} April\n2007. In this paper we describe the SuperAGILE experiment, its construction and\ntest processes, and its performance before flight, based on the on-ground test\nand calibrations.", + "category": "astro-ph" + }, + { + "text": "Architectures of Planetary Systems and Implications for their Formation: Doppler planet searches revealed that many giant planets orbit close to their\nhost star or in highly eccentric orbits. These and subsequent observations\ninspired new theories of planet formation that invoke gravitation interactions\nin multiple planet systems to explain the excitation of orbital eccentricities\nand even short-period giant planets. Recently, NASA's Kepler mission has\nidentified over 300 systems with multiple transiting planet candidates,\nincluding many potentially rocky planets. Most of these systems include\nmultiple planets with closely-spaced orbits and sizes between that of Earth and\nNeptune. These systems represent yet another new and unexpected class of\nplanetary systems and provide an opportunity to test the theories developed to\nexplain the properties of giant exoplanets. Presently, we have limited\nknowledge about such planetary systems, mostly about their sizes and orbital\nperiods. With the advent of long-term, nearly continuous monitoring by Kepler,\nthe method of transit timing variations (TTVs) has blossomed as a new technique\nfor characterizing the gravitational effects of mutual planetary perturbations\nfor hundreds of planets. TTVs can provide precise (but complex) constraints on\nplanetary masses, densities and orbits, even for planetary systems with faint\nhost stars. In the coming years, astronomers will translate TTV observations\ninto increasingly powerful constraints on the formation and orbital evolution\nof planetary systems with low-mass planets. Between TTVs, improved Doppler\nsurveys, high-contrast imaging campaigns and microlensing surveys, astronomers\ncan look forward to a much better understanding of planet formation in the\ncoming decade.", + "category": "astro-ph" + }, + { + "text": "HR 62: A New Evolved Chemically Peculiar Late-B Star?: The spectrum of the evolved B8 III giant HR 62 exhibits weak He-lines and\nstrong Mn and P lines. HR 62 therefore resembles both a HgMn star (CP3) and a\nHe-weak PGa star (CP4).\n This study is a companion project to a high resolution survey of slowly\nrotationg late-B type stars aiming at finding new chemically peculiar stars. We\nhave analysed the spectra of HR 62 (B8 III) and the dwarf comparison star HR\n677 (B8 V) to derive their chemical abundances. Both stars have similar\neffective temperatures (12500 K) and projected rotational velocities ($\\sim$25\nkm s$^{-1}$).\n The medium resolution ($R$ $\\sim$14000) spectra covering the wavelength range\nof 4380-7350 \\AA{} of HR 62 and HR 677 have been obtained with the \\'{e}chelle\nspectrograph attached to the 40 cm telescope in Ankara University Kreiken\nObservatory (AUKR), Turkey. We have used SYNSPEC49/SYNPLOT written by I. Hubeny\nand T. Lanz to compute grids of synthetic spectra and derive elemental\nabundances by modeling selected unblended lines.\n We find that HR 62 exhibits underabundance of Si and remarkable overabundance\nof P and Mn with respect to the Sun. In contrast, HR 677 does not have\nabundances departing by more than $\\pm$ 0.25 dex from solar abundances. A mass\nof 5.4 $M_\\odot$ and an age of 90 Myr have been estimated for HR 62.\n We discuss the origin of the chemical peculiarities of HR 62 and its status\nas a CP star. The effective temperature of the star (12500 K) agrees well with\nthose of HgMn (CP3) stars. Furthermore, the main sequence end of its\nevolutionary track also intersects the domain of He-weak CP4 stars. Hence these\nfirst results suggest that HR 62 may be a transition object between the CP4 to\nCP3 subgroup. However, a more detailed analysis of higher resolution spectra at\nshorter wavelengths (< 4380 \\AA{}) is necessary to clearly address the nature\nof this interesting object.", + "category": "astro-ph" + }, + { + "text": "Modelling the radio to X-ray SED of galaxies: We present our model to interpret the SED of galaxies. The model for the UV\nto sub-mm SED is already well established (Silva et al 1998). We remind here\nits main features and show some applications. Recently we have extended the\nmodel to the radio range (Bressan et al 2001), and we have started to include\nthe X-ray emission from the stellar component.", + "category": "astro-ph" + }, + { + "text": "Chromospheric polarimetry through multi-line observations of the 850 nm\n spectral region III: Chromospheric jets driven by twisted magnetic fields: We investigate the diagnostic potential of the spectral lines at 850 nm for\nunderstanding the magnetism of the lower atmosphere. For that purpose, we use a\nnewly developed 3D simulation of a chromospheric jet to check the sensitivity\nof the spectral lines to this phenomenon as well as our ability to infer the\natmospheric information through spectropolarimetric inversions of noisy\nsynthetic data. We start comparing the benefits of inverting the entire\nspectrum at 850 nm versus only the Ca II 8542 A spectral line. We found a\nbetter match of the input atmosphere for the former case, mainly at lower\nheights. However, the results at higher layers were not accurate. After several\ntests, we determined that we need to weight more the chromospheric lines than\nthe photospheric ones in the computation of the goodness of the fit. The new\ninversion configuration allows us to obtain better fits and consequently more\naccurate physical parameters. Therefore, to extract the most from multi-line\ninversions, a proper set of weights needs to be estimated. Besides that, we\nconclude again that the lines at 850 nm, or a similar arrangement with Ca II\n8542 A plus Zeeman sensitive photospheric lines, poses the best observing\nconfiguration for examining the thermal and magnetic properties of the lower\nsolar atmosphere.", + "category": "astro-ph" + }, + { + "text": "Cosmological implications of the KATRIN experiment: The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put\nunprecedented constraints on the absolute mass of the electron neutrino,\n$\\mnue$. In this paper we investigate how this information on $\\mnue$ will\naffect our constraints on cosmological parameters. We consider two scenarios;\none where $\\mnue=0$ (i.e., no detection by KATRIN), and one where\n$\\mnue=0.3$eV. We find that the constraints on $\\mnue$ from KATRIN will affect\nestimates of some important cosmological parameters significantly. For example,\nthe significance of $n_s<1$ and the inferred value of $\\Omega_\\Lambda$ depend\non the results from the KATRIN experiment.", + "category": "astro-ph" + }, + { + "text": "Transiting Planets with LSST I: Potential for LSST Exoplanet Detection: The Large Synoptic Survey Telescope (LSST) has been designed in order to\nsatisfy several different scientific objectives that can be addressed by a\nten-year synoptic sky survey. However, LSST will also provide a large amount of\ndata that can then be exploited for additional science beyond its primary\ngoals. We demonstrate the potential of using LSST data to search for transiting\nexoplanets, and in particular to find planets orbiting host stars that are\nmembers of stellar populations that have been less thoroughly probed by current\nexoplanet surveys. We find that existing algorithms can detect in simulated\nLSST light curves the transits of Hot Jupiters around solar-type stars, Hot\nNeptunes around K dwarfs, and planets orbiting stars in the Large Magellanic\nCloud. We also show that LSST would have the sensitivity to potentially detect\nSuper-Earths orbiting red dwarfs, including those in habitable zone orbits, if\nthey are present in some fields that LSST will observe. From these results, we\nmake the case that LSST has the ability to provide a valuable contribution to\nexoplanet science.", + "category": "astro-ph" + }, + { + "text": "The High-Resolution Coronal Imager, Flight 2.1: The third flight of the High-Resolution Coronal Imager (Hi-C 2.1) occurred on\nMay 29, 2018, the Sounding Rocket was launched from White Sands Missile Range\nin New Mexico. The instrument has been modified from its original configuration\n(Hi-C 1) to observe the solar corona in a passband that peaks near 172 Angstrom\nand uses a new, custom-built low-noise camera. The instrument targeted Active\nRegion 12712, and captured 78 images at a cadence of 4.4 sec (18:56:22 -\n19:01:57 UT; 5 min and 35 sec observing time). The image spatial resolution\nvaries due to quasi-periodic motion blur from the rocket; sharp images contain\nresolved features of at least 0.47 arcsec. There are coordinated observations\nfrom multiple ground- and space-based telescopes providing an unprecedented\nopportunity to observe the mass and energy coupling between the chromosphere\nand the corona. Details of the instrument and the data set are presented in\nthis paper.", + "category": "astro-ph" + }, + { + "text": "A possible influence on standard model of quasars and active galactic\n nuclei in strong magnetic field: Recent observational evidence indicates that the center of our Milky Way\nharbours a super-massive object with ultra-strong radial magnetic field\n(Eatough et al., 2013). Here we demonstrate that the radiations observed in the\nvicinity of the Galactic Center (GC) (Falcke and Marko 2013) cannot be emitted\nby the gas of the accretion disk since the accreting plasma is prevented from\napproaching to the GC by the abnormally strong radial magnetic field. These\nfields obstruct the infalling accretion flow from the inner region of the disk\nand the central massive black hole in the standard model. It is expected that\nthe observed radiations near the Galactic Center cannot be generated by the\ncentral black hole.\n We also demonstrate that the observed ultra-strong radial magnetic field near\nthe Galactic Center ( Eatough et al., 2013) cannot be generated by the -\nturbulence dynamo mechanism of Parker since preliminary qualitative estimate in\nterms of this mechanism gives a magnetic field strength six orders of magnitude\nsmaller than the observed field strength at . However, both these difficulties\nor the dilemma of the standard model can be overcome if the central black hole\nin the standard model is replaced by a supper-massive stellar object containing\nmagnetic monopoles ( SMSOMM, Peng and Chou, 2001). The observed power peaking\nof the thermal radiation is essentially the same as our theoretical prediction.\nIn addition, the discovery of the ultra-strong radial magnetic field near the\nGalactic Center can be naturally explained and is consistent with the\nprediction of our model( Peng and Chou 2001). Furthermore, the observed\nultra-strong radial magnetic field in the vicinity of the Galactic Center may\nbe considered as the astronomical evidence for the existence of magnetic\nmonopoles as predicted by the Grand Unified Theory of particle physics.", + "category": "astro-ph" + }, + { + "text": "Kernel Selection for Gaussian Process in Cosmology: with Approximate\n Bayesian Computation Rejection and Nested Sampling: Gaussian Process (GP) has gained much attention in cosmology due to its\nability to reconstruct cosmological data in a model-independent manner. In this\nstudy, we compare two methods for GP kernel selection: Approximate Bayesian\nComputation (ABC) Rejection and nested sampling. We analyze three types of\ndata: cosmic Chronometer data (CC), Type Ia Supernovae (SNIa), and Gamma Ray\nBurst (GRB), using five kernel functions. To evaluate the differences between\nkernel functions, we assess the strength of evidence using Bayes factors. Our\nresults show that, for ABC Rejection, the Mat\\'ern kernel with $\\nu$=5/2 (M52\nkernel) outperformes the commonly used Radial Basis Function (RBF) kernel in\napproximating all three datasets. Bayes factors indicate that the M52 kernel\ntypically supports the observed data better than the RBF kernel, but with no\nclear advantage over other alternatives. However, nested sampling gives\ndifferent results, with the M52 kernel losing its advantage. Nevertheless,\nBayes factors indicate no significant dependence of the data on each kernel.", + "category": "astro-ph" + }, + { + "text": "Recovery from Giant Eruptions in Very Massive Stars: We use a hydro-and-radiative-transfer code to explore the behavior of a very\nmassive star (VMS) after a giant eruption -- i.e., following a supernova\nimpostor event. Beginning with reasonable models for evolved VMSs with masses\nof $80~M_\\odot$ and $120~M_\\odot$, we simulate the change of state caused by a\ngiant eruption via two methods that explicitly conserve total energy: 1.\nSynthetically removing outer layers of mass of a few $M_\\odot$ while reducing\nthe energy of the inner layers. 2. Synthetically transferring energy from the\ncore to the outer layers, an operation that automatically causes mass ejection.\nOur focus is on the aftermath, not the poorly-understood eruption itself. Then,\nusing a radiation-hydrodynamic code in 1D with realistic opacities and\nconvection, the interior disequilibrium state is followed for about 200 years.\nTypically the star develops a $\\sim 400 ~\\rm{km}~\\rm{s}^{-1}$ wind with a mass\nloss rate that begins around $0.1 ~M_\\odot~\\rm{yr^{-1}}$ and gradually\ndecreases. This outflow is driven by $\\kappa$-mechanism radial pulsations. The\n1D models have regular pulsations but 3D models will probably be more chaotic.\nIn some cases a plateau in the mass-loss rate may persist about 200 years,\nwhile other cases are more like $\\eta$ Car which lost $>10~M_\\odot$ and then\nhad an abnormal mass loss rate for more than a century after its eruption. In\nour model, the post-eruption outflow carried more mass than the initial\neruption. These simulations constitute a useful preliminary reconnaissance for\n3D models which will be far more difficult.", + "category": "astro-ph" + }, + { + "text": "The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave\n Event GW170817: The historic detection of gravitational waves from a binary neutron star\nmerger (GW170817) and its electromagnetic counterpart led to the first accurate\n(sub-arcsecond) localization of a gravitational-wave event. The transient was\nfound to be $\\sim$10\" from the nucleus of the S0 galaxy NGC 4993. We report\nhere the luminosity distance to this galaxy using two independent methods. (1)\nBased on our MUSE/VLT measurement of the heliocentric redshift ($z_{\\rm\nhelio}=0.009783\\pm0.000023$) we infer the systemic recession velocity of the\nNGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be\n$v_{\\rm CMB}=3231 \\pm 53$ km s$^{-1}$. Using constrained cosmological\nsimulations we estimate the line-of-sight peculiar velocity to be $v_{\\rm\npec}=307 \\pm 230$ km s$^{-1}$, resulting in a cosmic velocity of $v_{\\rm\ncosmic}=2924 \\pm 236$ km s$^{-1}$ ($z_{\\rm cosmic}=0.00980\\pm 0.00079$) and a\ndistance of $D_z=40.4\\pm 3.4$ Mpc assuming a local Hubble constant of\n$H_0=73.24\\pm 1.74$ km s$^{-1}$ Mpc$^{-1}$. (2) Using Hubble Space Telescope\nmeasurements of the effective radius (15.5\" $\\pm$ 1.5\") and contained intensity\nand MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the\nFundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10\nclusters containing 226 galaxies, this yields a distance estimate of $D_{\\rm\nFP}=44.0\\pm 7.5$ Mpc. The combined redshift and FP distance is $D_{\\rm NGC\n4993}= 41.0\\pm 3.1$ Mpc. This 'electromagnetic' distance estimate is consistent\nwith the independent measurement of the distance to GW170817 as obtained from\nthe gravitational-wave signal ($D_{\\rm GW}= 43.8^{+2.9}_{-6.9}$ Mpc) and\nconfirms that GW170817 occurred in NGC 4993.", + "category": "astro-ph" + }, + { + "text": "The Fluence Duration Bias: The fluence duration bias causes fluences and durations of faint gamma-ray\nbursts to be systematically underestimated relative to their peak fluxes. Using\nMonte Carlo analysis, we demonstrate how this effect explains characteristics\nof structure of the fluence vs. 1024 ms peak flux diagram. Evidence of this\nbias exists in the BATSE fluence duration database, and provides a partial\nexplanation for the existence of burst class properties.", + "category": "astro-ph" + }, + { + "text": "Testing the dark energy with gravitational lensing statistics: We study the redshift distribution of two samples of early-type gravitational\nlenses, extracted from a larger collection of 122 systems, to constrain the\ncosmological constant in the LCDM model and the parameters of a set of\nalternative dark energy models (XCDM, Dvali-Gabadadze-Porrati and Ricci dark\nenergy models), under a spatially flat universe. The likelihood is maximized\nfor $\\Omega_\\Lambda= 0.70 \\pm 0.09$ when considering the sample excluding the\nSLACS systems (known to be biased towards large image-separation lenses) and\nno-evolution, and $\\Omega_\\Lambda= 0.81\\pm 0.05$ when limiting to gravitational\nlenses with image separation larger than 2\" and no-evolution. In both cases,\nresults accounting for galaxy evolution are consistent within 1$\\sigma$. The\npresent test supports the accelerated expansion, by excluding the\nnull-hypothesis (i.e., $\\Omega_\\Lambda = 0 $) at more than 4$\\sigma$,\nregardless of the chosen sample and assumptions on the galaxy evolution. A\ncomparison between competitive world models is performed by means of the\nBayesian information criterion. This shows that the simplest cosmological\nconstant model - that has only one free parameter - is still preferred by the\navailable data on the redshift distribution of gravitational lenses. We perform\nan analysis of the possible systematic effects, finding that the systematic\nerrors due to sample incompleteness, galaxy evolution and model uncertainties\napproximately equal the statistical errors, with present-day data. We find that\nthe largest sources of systemic errors are the dynamical normalization and the\nhigh-velocity cut-off factor, followed by the faint-end slope of the velocity\ndispersion function.", + "category": "astro-ph" + }, + { + "text": "Formation of solar quiescent coronal loops through magnetic reconnection\n in an emerging active region: Coronal loops are building blocks of solar active regions. However, their\nformation mechanism is still not well understood. Here we present direct\nobservational evidence for the formation of coronal loops through magnetic\nreconnection as new magnetic fluxes emerge into the solar atmosphere.\nExtreme-ultraviolet observations of the Atmospheric Imaging Assembly (AIA)\nonboard the Solar Dynamics Observatory (SDO) clearly show the newly formed\nloops following magnetic reconnection within a plasma sheet. Formation of the\nloops is also seen in the h{\\alpha} line-core images taken by the New Vacuum\nSolar Telescope. Observations from the Helioseismic and Magnetic Imager onboard\nSDO show that a positive-polarity flux concentration moves towards a\nnegative-polarity one with a speed of ~0.4 km/s, before the formation of\ncoronal loops. During the loop formation process, we found signatures of flux\ncancellation and subsequent enhancement of the transverse field between the two\npolarities. The three-dimensional magnetic field structure reconstructed\nthrough a magnetohydrostatic model shows field lines consistent with the loops\nin AIA images. Numerous bright blobs with an average width of 1.37 Mm appear\nintermittently in the plasma sheet and move upward with a projected velocity of\n~114 km/s. The temperature, emission measure and density of these blobs are\nabout 3 MK, 2.0x10^(28) cm^(-5) and 1.2x10^(10) cm^(-3), respectively. A power\nspectral analysis of these blobs indicates that the observed reconnection is\nlikely not dominated by a turbulent process. We have also identified flows with\na velocity of 20 to 50 km/s towards the footpoints of the newly formed coronal\nloops.", + "category": "astro-ph" + }, + { + "text": "Interior properties of the inner Saturnian moons from space astrometry\n data: During the thirteen years in orbit around Saturn before its final plunge, the\nCassini spacecraft provided more than ten thousand astrometric measurements.\nSuch large amounts of accurate data enable the search for extremely faint\nsignals in the orbital motion of the saturnian moons. Among these, the\ndetection of the dynamical feedback of the rotation of the inner moons of\nSaturn on their respective orbits becomes possible. Using all the currently\navailable astrometric data associated with Atlas, Prometheus, Pandora, Janus\nand Epimetheus, we first provide a detailed analysis of the Cassini Imaging\nScience Subsystem (ISS) data, with special emphasis on their statistical\nbehavior and sources of bias. Then, we give updated estimates of the moons'\naveraged densities and try to infer more details about their interior\nproperties by estimating the physical librations for Prometheus, Pandora,\nEpimetheus and Janus from anomalies in their apsidal precession. Our results\nare compatible with a homogeneous interior for Janus and Epimetheus, within the\nuncertainty of the measurements. On the other hand, we found some inconsistency\nfor Pandora and Prometheus, which might result from a dynamical mismodeling of\nSaturn's gravity field. Last, we show how the synergistic introduction of\nlibration measurements directly derived from imaging should allow the moons'\nmoments of inertia to be better constrained.", + "category": "astro-ph" + }, + { + "text": "The first estimate of radio jet proper motion at z>5: The extremely high redshift (z=5.3) radio source SDSS J102623.61+254259.5\n(J1026+2542) is among the most distant and most luminous radio-loud active\ngalactic nuclei (AGN) known to date. Its one-sided radio jet structure on\nmilli-arcsecond (mas) and ~10-mas scales typical for blazars was first imaged\nat 5 GHz with very long baseline interferometry (VLBI) in 2006. Here we report\non our dual-frequency (1.7 and 5 GHz) imaging observations performed with the\nEuropean VLBI Network (EVN) in 2013. The prominent jet structure allows us to\nidentify individual components whose apparent displacement can be detected over\nthe time span of 7.33 yr. This is the first time when jet proper motions are\ndirectly derived in a blazar at z>5. The small values of up to ~0.1 mas/yr are\nconsistent with what is expected in a relativistic cosmological model if\nredshift is a measure of distance. The apparent superluminal jet speeds,\nconsidered tentative because derived from two epochs only, exceed 10c for three\ndifferent components along the jet. Based on modeling its spectral energy\ndistribution, J1026+2542 is known to have its X-ray jet oriented close to the\nline of sight, with significant Doppler boosting and a large bulk Lorentz\nfactor (Gamma~13). The new VLBI observations, indicating ~2.3 x 10^12 K lower\nlimit to the core brightness temperature, are consistent with this picture. The\nspectral index in the core region is -0.35.", + "category": "astro-ph" + }, + { + "text": "Spherical collapse and halo abundance in shift-symmetric Galileon theory: We present the nonlinear growth of bound cosmological structures using the\nspherical collapse approach in the shift-symmetric Galileon theories. In\nparticular, we focus on the class of models belonging to the Kinetic Gravity\nBraiding by adopting a general parametrization of the action encoding a large\nset of models by means of four free parameters: two defining the background\nevolution and two affecting the perturbations. For the latter we identify their\nspecific signatures on the linearised critical density contrast, nonlinear\neffective gravitational coupling and the virial overdensity and how they drive\ntheir predictions away from $\\Lambda$CDM. We then use the results of the\nspherical collapse model to predict the evolution of the halo mass function. We\nfind that the shift-symmetric model predicts a larger number of objects\ncompared to $\\Lambda$CDM for masses $M \\gtrsim 10^{14} h^{-1} \\mathrm{M}_\\odot$\nand such number increases for larger deviations from the standard model.\nTherefore, the shift-symmetric model shows detectable signatures which can be\nused to distinguish it from the standard scenario.", + "category": "astro-ph" + }, + { + "text": "Evolution of major sedimentary mounds on Mars: We present a new database of $>$300 layer-orientations from sedimentary\nmounds on Mars. These layer orientations, together with draped landslides, and\ndraping of rocks over differentially-eroded paleo-domes, indicate that for the\nstratigraphically-uppermost $\\sim$1 km, the mounds formed by the accretion of\ndraping strata in a mound-shape. The layer-orientation data further suggest\nthat layers lower down in the stratigraphy also formed by the accretion of\ndraping strata in a mound-shape. The data are consistent with\nterrain-influenced wind erosion, but inconsistent with tilting by flexure,\ndifferential compaction over basement, or viscoelastic rebound. We use a simple\nlandscape evolution model to show how the erosion and deposition of mound\nstrata can be modulated by shifts in obliquity. The model is driven by\nmulti-Gyr calculations of Mars' chaotic obliquity and a parameterization of\nterrain-influenced wind erosion that is derived from mesoscale modeling. Our\nresults suggest that mound-spanning unconformities with kilometers of relief\nemerge as the result of chaotic obliquity shifts. Our results support the\ninterpretation that Mars' rocks record intermittent liquid-water runoff during\na $>$10$^8$-yr interval of sedimentary rock emplacement.", + "category": "astro-ph" + }, + { + "text": "A high molecular fraction in a sub-damped absorber at z=0.56: Measuring rest-frame ultraviolet rotational transitions from the Lyman and\nWerner bands in absorption against a bright background continuum is one of the\nfew ways to directly measure molecular hydrogen (H2). Here we report the\ndetection of Lyman-Werner absorption from H2 at z=0.56 in a sub-damped Ly-alpha\nsystem with neutral hydrogen column density N(HI) = 10^(19.5 +/- 0.2) cm^-2.\nThis is the first H2 system analysed at a redshift < 1.5 beyond the Milky Way\nhalo. It has a surprisingly high molecular fraction: log f(H2) > -1.93 +/- 0.36\nbased on modelling the line profiles, with a robust model-independent lower\nlimit of f(H2) > 10^-3. This is higher than f(H2) values seen along sightlines\nwith similar N(HI) through the Milky Way disk and the Magellanic clouds. The\nmetallicity of the absorber is 0.19 +0.21 -0.10 solar, with a dust-to-gas ratio\n< 0.36 times the value in the solar neighbourhood. Absorption from associated\nlow-ionisation metal transitions such as OI and FeII is observed in addition to\nOVI. Using Cloudy models we show that there are three phases present; a ~100 K\nphase giving rise to H2, a ~10^4 K phase where most of the low-ionisation metal\nabsorption is produced; and a hotter phase associated with OVI. Based on\nsimilarities to high velocity clouds in the Milky Way halo showing H2 and the\npresence of two nearby galaxy candidates with impact parameters of ~10 kpc, we\nsuggest that the absorber may be produced by a tidally-stripped structure\nsimilar to the Magellanic Stream.", + "category": "astro-ph" + }, + { + "text": "The jet of Markarian 501 from the sub-parsec to the kpc scale: We have observed the BL Lac object Markarian 501 at 1.4 GHz with the High\nSensitivity Array and at 86 GHz with the global VLBI mm array. Thanks to the\ngreat resolution and sensitivity provided by these instruments, we probe\nregions of the radio jets never accessed before. The new data at 1.4 GHz allow\nus to map the one-sided jet at large distances from the core, and to constrain\njet properties thanks to the high jet to counter-jet brightness ratio. The 86\nGHz data give us a high resolution image of the nuclear region. Putting\ntogether these new results and available published data we discuss the\nproperties of this source from sub-parsec to kiloparsec scales.", + "category": "astro-ph" + }, + { + "text": "The ESO Imaging Survey: Status Report and Preliminary Results: The ESO Imaging Survey (EIS) presented in early issues of the Messenger, and\nwith up-to-date information on the ongoing observations available on the Web\n(http://www.eso.org/eis), is a concerted effort by ESO and the Member State\ncommunity to provide targets for the first year of operation of the VLT. It\nconsists of two parts: a relatively wide-angle survey (EIS-WIDE) to cover four\npre-selected patches of sky, 6 square degrees each, spread in right ascension\nto search for distant clusters and quasars and a deep, multicolor survey of\nfour optical (SUSI-2) and two infrared (SOFI) covering the HST/Hubble Deep\nField South (HDFS) and its flanking fields (EIS-DEEP). From the start, the main\nchallenge has been to carry out a public survey in a limited amount of time\nrequiring observations, software development and data reduction with the goal\nof distributing the survey data products before the call for proposal for the\nVLT. To cope with this one-year timetable, a novel type of collaboration\nbetween ESO and the community has been established which has allowed EIS to\ncombine the scientific and technical expertise fo the community with in-house\nknow-how and infrastructure. In spite of the adverse weather conditions in some\nof the earlier runs, EIS has already proved to be successful experiment\nachieving most of its scientific and technical goals, thereby laying the ground\nwork for future imaging surveys.", + "category": "astro-ph" + }, + { + "text": "Wolter-I-like X-ray telescope structure using one conical mirror and one\n quadric mirror: Nested multilayer mirrors are commonly used in X-ray telescope structures to\nincrease the collecting area. To balance the difficulty and cost of producing\nthese mirrors, the classical Wolter-I structure has previously been replaced\nwith a conical Wolter-I structure, but it can lead to significantly poorer\nangular resolution. In this paper, we consider changing one of the mirror\nshapes (paraboloid or hyperboloid) of the Wolter-I structure to a conical\nmirror shape, while the other mirror shape remains a quadric surface-type\nstructure, which could thus ensure the imaging quality. Based on a theoretical\nanalysis and the results of simulations, the cone-hyperboloid and\nparaboloid-cone structures are found to provide the best angular resolutions,\nand the cone-hyperboloid structure is shorter than the paraboloid-cone\nstructure at the focal length. The cone-hyperboloid structure is then nested to\nobtain the best on-axis angular resolution and off-axis images.", + "category": "astro-ph" + }, + { + "text": "Dust Processing in Disks around T Tauri Stars: The 8-14 micron emission spectra of 12 T Tauri stars in the Taurus/Auriga\ndark clouds and in the TW Hydrae association obtained with the Infrared\nSpectrograph (IRS; The IRS is a collaborative venture between Cornell\nUniversity and Ball Aerospace Corporation funded by NASA through the Jet\nPropulsion Laboratory and the Ames Research Center.) on board Spitzer are\nanalyzed. Assuming the 10 micron features originate from silicate grains in the\noptically thin surface layers of T Tauri disks, the 8-14 micron dust emissivity\nfor each object is derived from its Spitzer spectrum. The emissivities are fit\nwith the opacities of laboratory analogs of cosmic dust. The fits include small\nnonspherical grains of amorphous silicates (pyroxene and olivine), crystalline\nsilicates (forsterite and pyroxene), and quartz, together with large fluffy\namorphous silicate grains. A wide range in the fraction of crystalline silicate\ngrains as well as large silicate grains among these stars are found. The dust\nin the transitional-disk objects CoKu Tau/4, GM Aur, and DM Tau has the\nsimplest form of silicates, with almost no hint of crystalline components and\nmodest amounts of large grains. This indicates that the dust grains in these\nobjects have been modified little from their origin in the interstellar medium.\nOther stars show various amounts of crystalline silicates, similar to the wide\ndispersion of the degree of crystallinity reported for Herbig Ae/Be stars of\nmass <2.5 solar masses. Late spectral type, low-mass stars can have significant\nfractions of crystalline silicate grains. Higher quartz mass fractions often\naccompany low amorphous olivine-to-amorphous pyroxene ratios. It is also found\nthat lower contrast of the 10 micron feature accompanies greater crystallinity.", + "category": "astro-ph" + }, + { + "text": "Evolution Through the Post-Starburst Phase: Using Post-Starburst\n Galaxies as Laboratories for Understanding the Processes that Drive Galaxy\n Evolution: Post-starburst (or \"E+A\") galaxies trace the fastest and most dramatic\nprocesses in galaxy evolution. Recent work studying the evolution of galaxies\nthrough this phase have revealed insights on how galaxies undergo structural\nand stellar population changes as well as the role of various feedback\nmechanisms. In this review, I summarize recent work on identifying\npost-starburst galaxies; tracing the role of this phase through cosmic time;\nmeasuring stellar populations, on-going star formation, morphologies,\nkinematics, interstellar medium properties, and AGN activity; mechanisms to\ncause the recent starburst and its end; and the future evolution to quiescence\n(or not). The review concludes with a list of open questions and exciting\npossibilities for future facilities.", + "category": "astro-ph" + }, + { + "text": "A Comprehensive Consistency Check between Synchrotron radiation and the\n Observed Gamma-ray Burst Spectra: We performed a time-resolved spectral analysis of 53 bright gamma-ray bursts\n(GRBs) observed by \\textit{Fermi}/GBM. Our sample consists of 908 individual\nspectra extracted from the finest time slices in each GRB. We fitted them with\nthe synchrotron radiation model by considering the electron distributions in\nfive different cases: mono-energetic, single power-law, Maxwellian, traditional\nfast cooling, and broken power-law. Our results were further qualified through\nBayesian Information Criterion (BIC) by comparing with the fit by empirical\nmodels, namely the so-called Band function and cut-off power-law models. Our\nstudy showed that the synchrotron models, except for the fast-cooling case, can\nsuccessfully fit most observed spectra, with the single power-law case being\nthe most preferred. We also found that the electron distribution indices for\nthe single power-law synchrotron fit in more than half of our spectra exhibits\nflux-tracking behavior, i.e., the index increases/decreases with the flux\nincreasing/decreasing, implying that the distribution of the radiating\nelectrons is increasingly narrower with time before the flux peaks and becomes\nmore spreading afterward. Our results indicate that the synchrotron radiation\nis still feasible as a radiation mechanism of the GRB prompt emission phase.", + "category": "astro-ph" + }, + { + "text": "The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual\n Atomic and Molecular Data Centre, VAMDC: The CDMS was founded 1998 to provide in its catalog section line lists of\nmolecular species which may be observed in various astronomical sources using\nradio astronomy. The line lists contain transition frequencies with qualified\naccuracies, intensities, quantum numbers, as well as further auxilary\ninformation. They have been generated from critically evaluated experimental\nline lists, mostly from laboratory experiments, employing established\nHamiltonian models. Seperate entries exist for different isotopic species and\nusually also for different vibrational states. As of December 2015, the number\nof entries is 792. They are available online as ascii tables with additional\nfiles documenting information on the entries. The Virtual Atomic and Molecular\nData Centre was founded more than 5 years ago as a common platform for atomic\nand molecular data. This platform facilitates exchange not only between\nspectroscopic databases related to astrophysics or astrochemistry, but also\nwith collisional and kinetic databases. A dedicated infrastructure was\ndeveloped to provide a common data format in the various databases enabling\nqueries to a large variety of databases on atomic and molecular data at once.\nFor CDMS, the incorporation in VAMDC was combined with several modifications on\nthe generation of CDMS catalog entries. Here we introduce related changes to\nthe data structure and the data content in the CDMS. The new data scheme allows\nus to incorporate all previous data entries but in addition allows us also to\ninclude entries based on new theoretical descriptions. Moreover, the CDMS\nentries have been transferred into a mySQL database format. These developments\nwithin the VAMDC framework have been driven by the needs of the astronomical\ncommunity to be able to deal efficiently with large data sets obtained with the\nHerschel Space Telescope or, more recently, with the Atacama Large Millimeter\nArray.", + "category": "astro-ph" + }, + { + "text": "NH$_3$(3,3) and CH$_3$OH near Supernova Remnants: GBT and VLA\n Observations: We report on Green Bank Telescope 23.87 GHz NH$_3$(3,3), emission\nobservations in five supernova remnants interacting with molecular clouds\n(G1.4$-$0.1, IC443, W44, W51C, and G5.7$-$0.0). The observations show a clumpy\ngas density distribution, and in most cases the narrow line widths of\n$\\sim3-4$\\,km\\,s$^{-1}$ are suggestive of maser emission. Very Large Array\nobservations reveal 36~GHz and/or 44~GHz CH$_3$OH, maser emission in a majority\n(72\\%) of the NH$_3$, peak positions towards three of these SNRs. This good\npositional correlation is in agreement with the high densities required for the\nexcitation of each line. Through these observations we have shown that\nCH$_3$OH, and NH$_3$, maser emission can be used as indicators of high density\nclumps of gas shocked by supernova remnants, and provide density estimates\nthereof. Modeling of the optical depth of the NH$_3$(3,3) emission is compared\nto that of CH$_3$OH, constraining the densities of the clumps to a typical\ndensity of the order of $10^5$~cm$^{-3}$ for cospatial masers. Regions of gas\nwith this density are found to exist in the post-shocked gas quite close to the\nSNR shock front, and may be associated with sites where cosmic rays produce\ngamma-ray emission via neutral pion decay.", + "category": "astro-ph" + }, + { + "text": "Green's function of the cosmological thermalization problem II: effect\n of photon injection and constraints: The energy spectrum of the cosmic microwave background (CMB) provides a\npowerful tool for constraining standard and non-standard physics in the\nprimordial Universe. Previous studies mainly highlight spectral distortions\n(mu-, y- and r-type) created by episodes of early energy release; however,\nseveral processes also lead to copious photon production, which requires a\ndifferent treatment. Here, we carry out a first detailed study for the\nevolution of distortions caused by photon injection at different energies in\nthe CMB bands. We provide detailed analytical and numerical calculations\nillustrating the rich phenomenology of the associated distortion signals. We\nshow that photon injection at very high and very low frequencies creates\ndistortions that are similar to those from pure energy release. In the mu-era\n(z>3x10^5), a positive or negative chemical potential can be formed, depending\non the balance between added photon energy and number. At lower redshifts\n(z<3x10^5), partial information about the photon injection process (i.e.,\ninjection time and energy) can still be recovered, with the distortion being\nfound in a partially comptonized state. We briefly discuss current and future\nconstraints on scenarios with photon production. We also argue that more\ndetailed calculations for different scenarios with photon injection may be\nrequired to assess in which regimes these can be distinguished from pure energy\nrelease processes.", + "category": "astro-ph" + }, + { + "text": "The evolution of late-type galaxies from CASSOWARY lensing systems: We explore the properties of lensing galaxies and lensed faint sources at\nredshifts between 1.5 and 3.0. Our sample consists of 9 carefully selected\nstrongly-lensed galaxies discovered by the CASSOWARY survey in the Sloan\nDigital Sky Survey (SDSS) data. We find that, despite some limitations of the\noriginal SDSS data, the homogeneous sample of lensing systems can provide a\nuseful insight into lens and source properties. We also explore the limitations\nof using low-resolution data to model and analyse galaxy-galaxy lensing. We\nderive the relative alignment of mass and light in fitted lens profiles. The\nrange of magnification extends above 5, hence we are able to analyse\npotentially small and low-mass galaxies at high redshifts. We confirm the\nlikely evolution of the size-luminosity relation for blue star-forming galaxies\nas a function of redshift", + "category": "astro-ph" + }, + { + "text": "Chandra and Hubble Space Telescope Study of the Globular Cluster NGC 288: We report on the Chandra X-ray Observatory observations of the globular\ncluster NGC 288. We detect four X-ray sources within the core radius and seven\nadditional sources within the half-mass radius down to a limiting luminosity of\nLx=7e30 erg/s (assuming cluster membership) in the 0.3-7 keV band. We also\nobserved the cluster with the Hubble Space Telescope Advanced Camera for\nSurveys and identify optical counterparts to seven X-ray sources out of the\nnine sources within the HST field-of-view. Based on the X-ray and optical\nproperties, we find 2-5 candidates of cataclysmic variables (CVs) or\nchromospherically active binaries, and 2-5 background galaxies inside the\nhalf-mass radius. Since the core density of NGC 288 is very low, the faint\nX-ray sources of NGC 288 found in the Chandra and HST observations is higher\nthan the prediction on the basis of the collision frequency. We suggest that\nthe CVs and chromospherically active binaries are primordial in origin, in\nagreement with theoretical expectation.", + "category": "astro-ph" + }, + { + "text": "Astrometric Plate Reduction with Orthogonal Functions and\n Milli-Arcseconds Accuracy in Deep Proper Motion Surveys: We have been doing a sample survey in UBV photometry and proper motions as\npart of an investigation of galactic structure and evolution. The programme is\nbased on Schmidt plates (from OCA, Tautenburg, Palomar and ESO Schmidt\ntelescopes) digitized with the MAMA machine (CAI, Paris). The high astrometric\nquality of the MAMA gives access to micronic accuracy (leading to $<$ 2 mas per\nyear) on proper motions with a 35 years time base. The high proper motion\naccuracy for faint star probes in wide-areas give access to the properties of\nstar samples out of the solar neighborhood. We have analyzed components of the\nUVW galactic space motions resulting from the accurate proper motion surveys.\nThe kinematical distribution of F and G--type stars have been probed to\ndistances up to 2.5 kpc above the galactic plane. We have derived the constrain\non the structural parameters of the thin and thick disk components of the\nGalaxy.", + "category": "astro-ph" + }, + { + "text": "Comparison of modified black-body fits for the estimation of dust\n optical depths in interstellar clouds: When dust far-infrared spectral energy distributions (SEDs) are fitted with a\nsingle modified black body (MBB), the optical depths tend to be underestimated.\nThis is caused by temperature variations, and fits with several temperature\ncomponents could lead to smaller errors. We want to quantify the performance of\nthe standard model of a single MBB in comparison with some multi-component\nmodels. We are interested in both the accuracy and computational cost. We\nexamine some cloud models relevant for interstellar medium studies. Synthetic\nspectra are fitted with a single MBB, a sum of several MBBs, and a sum of fixed\nspectral templates, but keeping the dust opacity spectral index fixed. When\nobservations are used at their native resolution, the beam convolution becomes\npart of the fitting procedure. This increases the computational cost, but the\nanalysis of large maps is still feasible with direct optimisation or even with\nMarkov chain Monte Carlo methods. Compared to the single MBB fits,\nmulti-component models can show significantly smaller systematic errors, at the\ncost of more statistical noise. The $\\chi^2$ values of the fits are not a good\nindicator of the accuracy of the $\\tau$ estimates, due to the potentially\ndominant role of the model errors. The single-MBB model also remains a valid\nalternative if combined with empirical corrections to reduce its bias. It is\ntechnically feasible to fit multi-component models to maps of millions of\npixels. However, the SED model and the priors need to be selected carefully,\nand the model errors can only be estimated by comparing alternative models.", + "category": "astro-ph" + }, + { + "text": "Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IV.\n Discovery of 41 Quasars and Luminous Galaxies at 5.7 < z < 6.9: We report discovery of 41 new high-z quasars and luminous galaxies, which\nwere spectroscopically identified at 5.7 < z < 6.9. This is the fourth in a\nseries of papers from the Subaru High-z Exploration of Low-Luminosity Quasars\n(SHELLQs) project, based on the deep multi-band imaging data collected by the\nHyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the\nphotometric candidates by a Bayesian probabilistic algorithm, and then carried\nout follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru\nTelescope. Combined with the sample presented in the previous papers, we have\nnow spectroscopically identified 137 extremely-red HSC sources over about 650\ndeg2, which include 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III]\nemitters at z ~ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown\ndwarfs). The new quasars span the luminosity range from M1450 ~ -26 to -22 mag,\nand continue to populate a few magnitude lower luminosities than have been\nprobed by previous wide-field surveys. In a companion paper, we derive the\nquasar luminosity function at z ~ 6 over an unprecedentedly wide range of M1450\n~ -28 to -21 mag, exploiting the SHELLQs and other survey outcomes.", + "category": "astro-ph" + }, + { + "text": "Photometric Variability of the Disk Integrated Infrared Emission of the\n Earth: We present an analysis of the global-integrated mid-infrared emission flux of\nthe Earth based on data derived from satellite measurements. We have studied\nthe photometric annual, seasonal, and rotational variability of the thermal\nemission of the Earth to determine which properties can be inferred from the\npoint-like signal. We find that the analysis of the time series allows us to\ndetermine the 24 hr rotational period of the planet for most observing\ngeometries, due to large warm and cold areas, identified with geographic\nfeatures, which appear consecutively in the observer's planetary view. However,\nthe effects of global-scale meteorology can effectively mask the rotation for\nseveral days at a time. We also find that orbital time series exhibit a\nseasonal modulation, whose amplitude depends strongly on the latitude of the\nobserver but weakly on its ecliptic longitude. As no systematic difference of\nbrightness temperature is found between the dayside and nightside, the phase\nvariations of the Earth in the infrared range are negligible. Finally, we also\nconclude that the phase variation of a spatially unresolved Earth-Moon system\nis dominated by the lunar signal.", + "category": "astro-ph" + }, + { + "text": "The COS-Halos Survey: Physical Conditions and Baryonic Mass in the\n Low-Redshift Circumgalactic Medium: We analyze the physical conditions of the cool, photoionized (T $\\sim 10^4$\nK) circumgalactic medium (CGM) using the COS-Halos suite of gas column density\nmeasurements for 44 gaseous halos within 160 kpc of $L \\sim L^*$ galaxies at $z\n\\sim 0.2$. These data are well described by simple photoionization models, with\nthe gas highly ionized (n$_{\\rm HII}$/n$_{\\rm H} \\gtrsim 99\\%$) by the\nextragalactic ultraviolet background (EUVB). Scaling by estimates for the\nvirial radius, R$_{\\rm vir}$, we show that the ionization state (tracked by the\ndimensionless ionization parameter, U) increases with distance from the host\ngalaxy. The ionization parameters imply a decreasing volume density profile\nn$_{\\rm H}$ = (10$^{-4.2 \\pm 0.25}$)(R/R$_{\\rm vir})^{-0.8\\pm0.3}$. Our derived\ngas volume densities are several orders of magnitude lower than predictions\nfrom standard two-phase models with a cool medium in pressure equilibrium with\na hot, coronal medium expected in virialized halos at this mass scale. Applying\nthe ionization corrections to the HI column densities, we estimate a lower\nlimit to the cool gas mass M$_{\\rm CGM}^{\\rm cool} > 6.5 \\times 10^{10}$\nM$_{\\odot}$ for the volume within R $<$ R$_{\\rm vir}$. Allowing for an\nadditional warm-hot, OVI-traced phase, the CGM accounts for at least half of\nthe baryons purported to be missing from dark matter halos at the 10$^{12}$\nM$_{\\odot}$ scale.", + "category": "astro-ph" + }, + { + "text": "On the new short orbital period cataclysmic variable Halpha0242-2802: We present results from our phase-resolved spectroscopy of the newly\nidentified cataclysmic variable Halpha0242-2802. Halpha0242-2802 was identified\nfrom a deep UK Schmidt Halpha-R band survey as a candidate cataclysmic\nvariable. Although initial spectroscopy revealed an optical spectrum very\nsimilar to that of the famous short orbital period system WZ Sge, the analysis\nof our data shows that this is not the case. Halpha0242-28 differs from WZ Sge\nin both the accretion disk structure and the orbital period. In particular,\nHalpha0242-28 appears to be a system which has not reached the orbital period\nminimum, yet.", + "category": "astro-ph" + }, + { + "text": "Modelling the WMAP large-angle anomalies as an effect of a local density\n inhomogeneity: We investigate large-angle scale temperature anisotropy in the Cosmic\nMicrowave Background (CMB) with the Wilkinson Microwave Anisotropy Probe (WMAP)\ndata and model the large-angle anomalies as the effect of the CMB quadrupole\nanisotropies caused by the local density inhomogeneities. The quadrupole caused\nby the local density inhomogeneities is different from the special relativity\nkinematic quadrupole. If the observer inhabits a strong inhomogeneous region,\nthe local quadrupole should not be neglected. We calculate such local\nquadrupole under the assumption that there is a huge density fluctuation field\nin direction $(284^{\\circ},74^{\\circ})$, where the density fluctuation is\n$10^{-3}$, and its center is $\\sim 112h^{-1} \\rm {Mpc}$ away from us. After\nremoving such mock signals from WMAP data, the power in quadrupole, $C_2$,\nincreases from the range $(200\\sim260\\mu \\rm{K^2})$ to $\\sim1000\\mu \\rm{K^2}$.\nThe quantity S, which is used to estimate the alignment between the quadrupole\nand the octopole, decreases from $(0.7\\sim0.74)$ to $(0.31\\sim0.37)$, while the\nmodel predict that $C_2=1071.5\\mu \\rm{K^2}$, $S=0.412$. So our local density\ninhomogeneity model can, in part, explain the WMAP low-$\\ell$ anomalies.", + "category": "astro-ph" + }, + { + "text": "The Nature of LINER-like Emission in Red Galaxies: Passive red galaxies frequently contain warm ionized gas and have spectra\nsimilar to low-ionization nuclear emission-line regions (LINERs). Here we\ninvestigate the nature of the ionizing sources powering this emission, by\ncomparing nuclear spectroscopy from the Palomar survey with larger aperture\ndata from the Sloan Digital Sky Survey. We find the line emission in the\nmajority of passive red galaxies is spatially extended; the Halpha surface\nbrightness profile depends on radius (r) as r^(-1.28). We detect strong line\nratio gradients with radius in [N II]/Ha, [S II]/Ha, and [O III]/[S II],\nrequiring the ionization parameter to increase outwards. Combined with a\nrealistic gas density profile, this outward increasing ionization parameter\nconvincingly rules out AGN as the dominant ionizing source, and strongly favors\ndistributed ionizing sources. Sources that follow the stellar density profile\ncan additionally reproduce the observed luminosity-dependence of the line ratio\ngradient. Post-AGB stars provide a natural ionization source candidate, though\nthey have an ionization parameter deficit. Velocity width differences among\ndifferent emission lines disfavor shocks as the dominant ionization mechanism,\nand suggest that the interstellar medium in these galaxies contains multiple\ncomponents. We conclude that the line emission in most LINER-like galaxies\nfound in large aperture (>100pc) spectroscopy is not primarily powered by AGN\nactivity and thus does not trace the AGN bolometric luminosity. However, they\ncan be used to trace warm gas in these red galaxies.", + "category": "astro-ph" + }, + { + "text": "TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-Break\n Galaxies: Using integrated spectra for two gravitationally lensed galaxies from the\nJWST TEMPLATES Early Release Science program, we analyze faint auroral lines,\nwhich provide direct measurements of the gas-phase chemical abundance. For the\nbrighter galaxy, SGAS1723$+$34 ($z = 1.3293$), we detect the\n[OIII]$\\lambda4363$, [SIII]$\\lambda6312$, and [OII]$\\lambda\\lambda$7320,7330\nauroral emission lines, and set an upper limit for the [NII]$\\lambda5755$ line.\nFor the second galaxy, SGAS1226$+$21 ($z = 2.925$), we do not detect any\nauroral lines, and report upper limits. With these measurements and upper\nlimits, we constrain the electron temperatures in different ionization zones\nwithin both of these galaxies. For SGAS1723$+$34, where auroral lines are\ndetected, we calculate direct oxygen and nitrogen abundances, finding an N/O\nratio consistent with observations of nearby ($z\\sim 0$) galaxies. These\nobservations highlight the potent combination of JWST and gravitational lensing\nto measure faint emission lines in individual distant galaxies and to directly\nstudy the chemical abundance patterns in those galaxies.", + "category": "astro-ph" + }, + { + "text": "Microquasars: Progress made and open questions: In the last talk of the conference I summarized the main progress and\ncontributions to high energy astrophysics made by studies of microquasars in\nour Galaxy. To stimulate the general discussion I have underlined some of the\nquestions that will guide in the near future the research in this area of\nastrophysics. Here I present the viewgraphs and questions formulated during the\ngeneral discussion.", + "category": "astro-ph" + }, + { + "text": "Nested and Single Bars in Seyfert and Non-Seyfert Galaxies: We analyze the observed properties of nested and single stellar bar systems\nin disk galaxies. The 112 galaxies in our sample comprise the largest matched\nSeyfert vs. non-Seyfert sample of nearby galaxies with complete near-infrared\nor optical imaging sensitive to lengthscales ranging from tens of pc to tens of\nkpc. We find that a significant fraction of the sample galaxies, 17% +/- 4%,\nhas more than one bar, and that 28% +/- 5% of barred galaxies have nested bars.\nThe bar fractions appear to be stable according to reasonable changes in our\nadopted bar criteria. For these nested bars, we detect a clear division in\nlength between the large-scale (primary) bars and small-scale (secondary) bars,\nboth in absolute and normalized (to the size of the galaxy) length. We argue\nthat this bimodal distribution can be understood within the framework of the\ninner Lindblad resonances (ILRs), which are located where the gravitational\npotential of the innermost galaxy switches effectively from 3D to 2D. While\nprimary bars are found to correlate with the host galaxy sizes, no such\ncorrelation is observed for the secondary bars. Moreover, we find that\nsecondary bars differ morphologically from single bars. Overall, our matched\nSeyfert and non-Seyfert samples show a statistically significant excess of bars\namong the Seyfert galaxies at practically all lengthscales. We confirm our\nprevious result that Seyfert galaxies always show a preponderance of \"thick\"\nbars compared to the bars in non-Seyfert galaxies. Finally, no correlation is\nobserved between the presence of a bar and that of companion galaxies, even\nrelatively bright ones.", + "category": "astro-ph" + }, + { + "text": "The linear response of stellar systems does not diverge at marginal\n stability: The linear response of a stellar system's gravitational potential to a\nperturbing mass comprises two distinct contributions. Most famously, the system\nwill respond by forming a polarization 'wake' around the perturber. At the same\ntime, the perturber may also excite one or more 'Landau modes', i.e. coherent\noscillations of the entire stellar system which are either stable or unstable\ndepending on the system parameters. The amplitude of the first (wake)\ncontribution is known to diverge as a system approaches marginal stability. In\nthis paper we consider the linear response of a homogeneous stellar system to a\npoint mass moving on a straight line orbit. We prove analytically that the\ndivergence of the wake response is in fact cancelled by a corresponding\ndivergence in the Landau mode response, rendering the total response finite. We\ndemonstrate this cancellation explicitly for a box of stars with Maxwellian\nvelocity distribution. Our results imply that polarization wakes may be much\nless efficient drivers of secular evolution than previously thought. More\ngenerally, any prior calculation that accounted for wakes but ignored modes -\nsuch as those based on the Balescu-Lenard equation - may need to be revised.", + "category": "astro-ph" + }, + { + "text": "Cosmological constraints from 21cm surveys after reionization: 21cm emission from residual neutral hydrogen after the epoch of reionization\ncan be used to trace the cosmological power spectrum of density fluctuations.\nUsing a Fisher matrix formulation, we provide a detailed forecast of the\nconstraints on cosmological parameters that are achievable with this probe. We\nconsider two designs: a scaled-up version of the MWA observatory as well as a\nFast Fourier Transform Telescope. We find that 21cm observations dedicated to\npost-reionization redshifts may yield significantly better constraints than\nnext generation Cosmic Microwave Background (CMB) experiments. We find the\nconstraints on $\\Omega_\\Lambda$, $\\Omega_{\\rm m}h^2$, and $\\Omega_\\nu h^2$ to\nbe the strongest, each improved by at least an order of magnitude over the\nPlanck CMB satellite alone for both designs. Our results do not depend as\nstrongly on uncertainties in the astrophysics associated with the ionization of\nhydrogen as similar 21cm surveys during the epoch of reionization. However, we\nfind that modulation of the 21cm power spectrum from the ionizing background\ncould potentially degrade constraints on the spectral index of the primordial\npower spectrum and its running by more than an order of magnitude. Our results\nalso depend strongly on the maximum wavenumber of the power spectrum which can\nbe used due to non-linearities.", + "category": "astro-ph" + }, + { + "text": "The relation between 13CO(2-1) line width in molecular clouds and\n bolometric luminosity of associated IRAS sources: We search for evidence of a relation between properties of young stellar\nobjects (YSOs) and their parent molecular clouds to understand the initial\nconditions of high-mass star formation. A sample of 135 sources was selected\nfrom the Infrared Astronomical Satellite (IRAS) Point Source Catalog, on the\nbasis of their red color to enhance the possibility of discovering young\nsources. Using the Kolner Observatorium fur SubMillimeter Astronomie (KOSMA)\n3-m telescope, a single-point survey in 13CO(2-1) was carried out for the\nentire sample, and 14 sources were mapped further. Archival mid-infrared (MIR)\ndata were compared with the 13CO emissions to identify evolutionary stages of\nthe sources. A 13CO observed sample was assembled to investigate the\ncorrelation between 13CO line width of the clouds and the luminosity of the\nassociated YSOs. We identified 98 sources suitable for star formation analyses\nfor which relevant parameters were calculated. We detected 18 cores from 14\nmapped sources, which were identified with eight pre-UC HII regions and one UC\nHII region, two high-mass cores earlier than pre-UC HII phase, four possible\nstar forming clusters, and three sourceless cores. By compiling a large (360\nsources) 13CO observed sample, a good correlation was found between the 13CO\nline width of the clouds and the bolometric luminosity of the associated YSOs,\nwhich can be fitted as a power law: lg(dV13/km/s)=-0.023+0.135lg(Lbol/Lsolar).\nResults show that luminous (>10^3Lsolar) YSOs tend to be associated with both\nmore massive and more turbulent (dV13>2km/s) molecular cloud structures.", + "category": "astro-ph" + }, + { + "text": "A Comparative Analysis of Machine-learning Models for Solar Flare\n Forecasting: Identifying High-performing Active Region Flare Indicators: Solar flares create adverse space weather impacting space and Earth-based\ntechnologies. However, the difficulty of forecasting flares, and by extension\nsevere space weather, is accentuated by the lack of any unique flare trigger or\na single physical pathway. Studies indicate that multiple physical properties\ncontribute to active region flare potential, compounding the challenge. Recent\ndevelopments in machine learning (ML) have enabled analysis of\nhigher-dimensional data leading to increasingly better flare forecasting\ntechniques. However, consensus on high-performing flare predictors remains\nelusive. In the most comprehensive study to date, we conduct a comparative\nanalysis of four popular ML techniques (k-nearest neighbor, logistic\nregression, random forest classifier, and support vector machine) by training\nthese on magnetic parameters obtained from the Helioseismic and Magnetic Imager\n(HMI) on board the Solar Dynamics Observatory (SDO) for the entirety of solar\ncycle 24. We demonstrate that the logistic regression and support vector\nmachine algorithms perform extremely well in forecasting active region flaring\npotential. The logistic regression algorithm returns the highest true skill\nscore of $0.967 \\pm 0.018$, possibly the highest classification performance\nachieved with any strictly parametric study. From a comparative assessment, we\nestablish that the magnetic properties like total current helicity, total\nvertical current density, total unsigned flux, R_VALUE, and total absolute\ntwist are the top-performing flare indicators. We also introduce and analyze\ntwo new performance metrics, namely, severe and clear space weather indicators.\nOur analysis constrains the most successful ML algorithms and identifies\nphysical parameters that contribute most to active region flare productivity.", + "category": "astro-ph" + }, + { + "text": "Testing the accuracy of radiative cooling approximations in SPH\n simulations: Hydrodynamical simulations of star formation have stimulated a need to\ndevelop fast and robust algorithms for evaluating radiative cooling. Here we\nundertake a critical evaluation of what is currently a popular method for\nprescribing cooling in SPH simulations, i.e. the polytropic cooling due\noriginally to Stamatellos et al. This method uses the local density and\npotential to estimate the column density and optical depth to each particle and\nthen uses these quantities to evaluate an approximate expression for the net\nradiative cooling. We evaluate the algorithm by considering both spherical and\ndisc-like systems with analytic density and temperature structures. In\nspherical systems, the total cooling rate computed by the method is within\naround 20 for the astrophysically relevant case of opacity dominated by ice\ngrains and is correct to within a factor of order unity for a range of opacity\nlaws. In disc geometry, however, the method systematically under-estimates the\ncooling by a large factor at all heights in the disc. For the self-gravitating\ndisc studied, we find that the method under-estimates the total cooling rate by\na factor of 200. This discrepancy may be readily traced to the method's\nsystematic over-estimate of the disc column density and optical depth, since\n(being based only on the local density and potential) it does not take into\naccount the low column density route for photon escape normal to the disc\nplane. These results raise an obvious caution about the method's use in disc\ngeometry whenever an accurate cooling rate is required, although we note that\nthere are situations where the discrepancies highlighted above may not\nsignificantly affect the global outcome of simulations. Finally, we draw\nattention to our introduction of an analytic self-gravitating disc structure\nthat may be of use in the calibration of future cooling algorithms.", + "category": "astro-ph" + }, + { + "text": "Computation of atomic astrophysical opacities: The revision of the standard Los Alamos opacities in the 1980-1990s by a\ngroup from the Lawrence Livermore National Laboratory (OPAL) and the Opacity\nProject (OP) consortium was an early example of collaborative big-data science,\nleading to reliable data deliverables (atomic databases, monochromatic\nopacities, mean opacities, and radiative accelerations) widely used since then\nto solve a variety of important astrophysical problems. Nowadays the precision\nof the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is\na recurrent topic in a hot debate involving stringent comparisons between\ntheory, laboratory experiments, and solar and stellar observations in\nsophisticated research fields: the standard solar model (SSM), helio and\nasteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear\nreaction rates, solar neutrino observations, computational atomic physics, and\nplasma experiments. In this context, an unexpected downward revision of the\nsolar photospheric metal abundances in 2005 spoiled a very precise agreement\nbetween the helioseismic indicators (the radius of the convection zone\nboundary, the sound-speed profile, and helium surface abundance) and SSM\nbenchmarks, which could be somehow reestablished with a substantial opacity\nincrease. Recent laboratory measurements of the iron opacity in physical\nconditions similar to the boundary of the solar convection zone have indeed\npredicted significant increases (30-400%), although new systematic improvements\nand comparisons of the computed tables have not yet been able to reproduce\nthem. We give an overview of this controversy, and within the OP approach,\ndiscuss some of the theoretical shortcomings that could be impairing a more\ncomplete and accurate opacity accounting", + "category": "astro-ph" + }, + { + "text": "A rival for Babcock's star: the extreme 30-kG variable magnetic field in\n the Ap star HD 75049: The extraordinary magnetic Ap star HD75049 has been studied with data\nobtained with the ESO VLT and 2.2-m telescopes. Direct measurements reveal that\nthe magnetic field modulus at maximum reaches 30kG. The star shows photometric,\nspectral and magnetic variability with a rotation period of 4.049d. Variations\nof the mean longitudinal magnetic field can be described to first order by a\ncentred dipole model with an inclination i = 25 degrees, an obliquity beta = 60\ndegrees, and a polar field B_p = 42kG.\n The combination of the longitudinal and surface magnetic field measurements\nimply a radius of R = 1.7 R sun, suggesting the star is close to the zero-age\nmain sequence. HD75049 displays moderate overabundances of Si, Ti, Cr, Fe and\nlarge overabundances of rare earth elements. This star has the second strongest\nmagnetic field of any main sequence star after Babcock's star, HD215441, which\nit rivals.", + "category": "astro-ph" + }, + { + "text": "Theoretical aspects of asteroseismology: small steps towards a golden\n future: The current status of asteroseismic studies is here reviewed and the adequate\ntechniques of analysis available today for the study of the oscillation\nfrequencies are presented. Comments on prospects for future investigations\nthrough the possibility of getting ever more precise asteroseismic observations\nfrom ground and space are given.", + "category": "astro-ph" + }, + { + "text": "The Dilaton and Modified Gravity: We consider the dilaton in the strong string coupling limit and elaborate on\nthe original idea of Damour and Polyakov whereby the dilaton coupling to matter\nhas a minimum with a vanishing value at finite field-value. Combining this type\nof coupling with an exponential potential, the effective potential of the\ndilaton becomes matter density dependent. We study the background cosmology,\nshowing that the dilaton can play the role of dark energy. We also analyse the\nconstraints imposed by the absence of violation of the equivalence principle.\nImposing these constraints and assuming that the dilaton plays the role of dark\nenergy, we consider the consequences of the dilaton on large scale structures\nand in particular the behaviour of the slip functions and the growth index at\nlow redshift.", + "category": "astro-ph" + }, + { + "text": "Search for an annual modulation of dark-matter signals with a germanium\n spectrometer at the Sierra Grande Laboratory: Data collected during three years with a germanium spectrometer at the Sierra\nGrande underground laboratory have been analyzed for distinctive features of\nannual modulation of the signal induced by WIMP dark matter candidates. The\nmain motivation for this analysis was the recent suggestion by the DAMA/NaI\nCollaboration that a yearly modulation signal could not be rejected at the 90%\nconfidence level when analyzing data obtained with a high-mass low-background\nscintillator detector. We performed two different analyses of the data: First,\nthe statistical distribution of modulation-significance variables (expected\nfrom an experiment running under the conditions of Sierra Grande) was compared\nwith the same variables obtained from the data. Second, the data were analyzed\nin energy bins as an independent check of the first result and to allow for the\npossibility of a crossover in the expected signal. In both cases no\nstatistically significant deviation from the null result was found, which could\nsupport the hypothesis that the data contain a modulated component. A plot is\nalso presented to enable the comparison of these results to those of the DAMA\ncollaboration.", + "category": "astro-ph" + }, + { + "text": "The Early-time Optical Properties of Gamma-Ray Burst Afterglows: We present a multiwavelength analysis of 63 Gamma-Ray Bursts observed with\nthe world's three largest robotic optical telescopes, the Liverpool and Faulkes\nTelescopes (North and South). Optical emission was detected for 24 GRBs with\nbrightnesses ranging from R = 10 to 22 mag in the first 10 minutes after the\nburst. By comparing optical and X-ray light curves from t = 100 to about 10^6\nseconds, we introduce four main classes, defined by the presence or absence of\ntemporal breaks at optical and/or X-ray wavelengths. While 15/24 GRBs can be\nmodelled with the forward-shock model, explanation of the remaining nine is\nvery challenging in the standard framework even with the introduction of energy\ninjection or an ambient density gradient. Early X-ray afterglows, even segments\nof light curves described by a power-law, may be due to additional emission\nfrom the central engine. 39 GRBs in our sample were not detected and have deep\nupper limits (R < 22 mag) at early time. Of these, only ten were identified by\nother facilities, primarily at near infrared wavelengths, resulting in a dark\nburst fraction of about 50%. Additional emission in the early time X-ray\nafterglow due to late-time central engine activity may also explain some dark\nbursts by making the bursts brighter than expected in the X-ray band compared\nto the optical band.", + "category": "astro-ph" + }, + { + "text": "Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes). II. Expanded\n Survey Description and the Stripe 82 Catalog: We present 226 large ultra-diffuse galaxy (UDG) candidates ($r_e >\n5.3$\\arcsec, $\\mu_{0,g} > 24$ mag arcsec$^{-2}$) in the SDSS Stripe 82 region\nrecovered using our improved procedure developed in anticipation of processing\nthe entire Legacy Surveys footprint. The advancements include less constrained\nstructural parameter fitting, expanded wavelet filtering criteria,\nconsideration of Galactic dust, estimates of parameter uncertainties and\ncompleteness based on simulated sources, and refinements of our automated\ncandidate classification. We have a sensitivity $\\sim$1 mag fainter in\n$\\mu_{0,g}$ than the largest published catalog of this region. Using our\ncompleteness-corrected sample, we find that (1) there is no significant decline\nin the number of UDG candidates as a function of $\\mu_{0,g}$ to the limit of\nour survey ($\\sim$ 26.5 mag arcsec$^{-2}$); (2) bluer candidates have smaller\nS\\'ersic $n$; (3) most blue ($g-r < 0.45$ mag) candidates have $\\mu_{0,g}\n\\lesssim 25$ mag arcsec$^{-2}$ and will fade to populate the UDG red sequence\nwe observe to $\\sim 26.5$ mag arcsec$^{-2}$; (4) any red UDGs that exist\nsignificantly below our $\\mu_{0,g}$ sensitivity limit are not descended from\nblue UDGs in our sample; and (5) candidates with lower $\\mu_{0,g}$ tend to\nsmaller $n$. We anticipate that the final SMUDGes sample will contain $\\sim$\n30$\\times$ as many candidates.", + "category": "astro-ph" + }, + { + "text": "The First Two Years of Electromagnetic Follow-Up with Advanced LIGO and\n Virgo: We anticipate the first direct detections of gravitational waves (GWs) with\nAdvanced LIGO and Virgo later this decade. Though this groundbreaking technical\nachievement will be its own reward, a still greater prize could be observations\nof compact binary mergers in both gravitational and electromagnetic channels\nsimultaneously. During Advanced LIGO and Virgo's first two years of operation,\n2015 through 2016, we expect the global GW detector array to improve in\nsensitivity and livetime and expand from two to three detectors. We model the\ndetection rate and the sky localization accuracy for binary neutron star (BNS)\nmergers across this transition. We have analyzed a large, astrophysically\nmotivated source population using real-time detection and sky localization\ncodes and higher-latency parameter estimation codes that have been expressly\nbuilt for operation in the Advanced LIGO/Virgo era. We show that for most BNS\nevents the rapid sky localization, available about a minute after a detection,\nis as accurate as the full parameter estimation. We demonstrate that Advanced\nVirgo will play an important role in sky localization, even though it is\nanticipated to come online with only one-third as much sensitivity as the\nAdvanced LIGO detectors. We find that the median 90% confidence region shrinks\nfrom ~500 square degrees in 2015 to ~200 square degrees in 2016. A few distinct\nscenarios for the first LIGO/Virgo detections emerge from our simulations.", + "category": "astro-ph" + }, + { + "text": "COMPTEL observations of the quasar PKS 0528+134 during the first 3.5\n years of the CGRO mission: The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy\nrange 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have\nbeen analyzed. During the first two years PKS 0528+134 was most significantly\ndetected at energies above 3 MeV. During the last year there is only evidence\nfor the quasar at energies below 3 MeV indicating a spectral change. The\ntime-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well\nrepresented by a power-law shape. Spectra collected from different\nobservational periods reveal different power-law shapes: a hard state during\nflaring observations reported by EGRET, and a soft state otherwise. The\ncombined simultaneous EGRET and COMPTEL spectra indicate these two spectral\nstates as well. During low intensisty gamma-ray phases no spectral break is\nobvious from the combined COMPTEL and EGRET measurements. For the gamma-ray\nflaring phases however, the combined COMPTEL and EGRET data require a spectral\nbending at MeV-energies. By fitting broken power-law functions the best-fit\nvalues for the break in photon index range between 0.6 and 1.7, and for the\nbreak energy between ~5 MeV and ~20 MeV. Because the flux values measured by\nCOMPTEL below 3 MeV in both states are roughly equal, the observations would be\nconsistent with an additional spectral component showing up during gamma-ray\nflaring phases of PKS 0528+134. Such a component could be introduced by e.g. a\nhigh-energy electron-positron population with a low-energy cutoff in their bulk\nLorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for\ngamma-ray flaring phases shows that the major energy release across the entire\nelectro-magnetic spectrum is measured at MeV-energies.", + "category": "astro-ph" + }, + { + "text": "Temperature measurements with the relativistic Sunyaev-Zel'dovich effect: At temperatures above ~5 keV, the non-relativistic approximation used to\nderive the classical thermal Sunyaev-Zel'dovich effect spectrum begins to fail.\nWhen relativistic effects are included, the spectrum becomes\ntemperature-dependent. This leads to both a problem and an opportunity: a\nproblem, because when the temperature dependence is not accounted for the\nCompton-y estimate is biased; and an opportunity, because it represents a new\nway to measure the temperature of the intracluster medium independently of\nX-ray observations. This work presents current results from investigating the\nimpact of relativistic effects on Planck cluster observations, and projections\nfor future measurements of cluster temperatures using the Atacama Large\nAperture Sub-millimetre Telescope.", + "category": "astro-ph" + }, + { + "text": "Parameter estimation for coalescing massive binary black holes with LISA\n using the full 2-post-Newtonian gravitational waveform and spin-orbit\n precession: With one exception, previous analyses of the measurement accuracy of\ngravitational wave experiments for comparable-mass binary systems have\nneglected either spin-precession effects or subdominant harmonics and amplitude\nmodulations. Here we give the first explicit description of how these effects\ncombine to improve parameter estimation. We consider supermassive black hole\nbinaries as expected to be observed with the planned space-based interferometer\nLISA, and study the measurement accuracy for several astrophysically\ninteresting parameters obtainable taking into account the full 2PN waveform for\nspinning bodies, as well as spin-precession effects. We find that for binaries\nwith a total mass in the range 10^5 M_Sun < M < 10^7 M_Sun at a redshift of 1,\na factor ~1.5 is in general gained in accuracy, with the notable exception of\nthe determination of the individual masses in equal-mass systems, for which a\nfactor ~5 can be gained. We also find, as could be expected, that using the\nfull waveform helps increasing the upper mass limit for detection, which can be\nas high as M = 10^8 M_Sun at a redshift of 1, as well as the redshift limit\nwhere some information can be extracted from a system, which is roughly z = 10\nfor M < 10^7 M_Sun, 1.5-5 times higher than with the restricted waveform. We\ncomputed that the full waveform allows to use supermassive black hole binaries\nas standard sirens up to a redshift of z = 1.6, about 0.4 larger than what\nprevious studies allowed. We found that for lower unequal-mass binary systems,\nthe measurement accuracy is not as drastically improved as for other systems.\nThis suggests that for these systems, adding parameters such as eccentricity or\nalternative gravity parameters could be achieved without much loss in the\naccuracy.", + "category": "astro-ph" + }, + { + "text": "Observable tests of self-interacting dark matter in galaxy clusters: BCG\n wobbles in a constant density core: Models of Cold Dark Matter predict that the distribution of dark matter in\ngalaxy clusters should be cuspy, centrally concentrated. Constant density cores\nwould be strong evidence for beyond-CDM physics, such as Self-Interacting Dark\nMatter (SIDM). An observable consequence would be oscillations of the Brightest\nCluster Galaxy (BCG) in otherwise relaxed galaxy clusters. Offset BCGs have\nindeed been observed - but only interpreted via a simplified, analytic model of\noscillations. We compare these observations to the BAHAMAS-SIDM suite of\ncosmological simulations, which include SIDM and a fully hydrodynamical\ntreatment of star formation and feedback. We predict that the median offset of\nBCGs increases with the SIDM cross-section, cluster mass and the amount of\nstellar mass within 10kpc, while CDM exhibits no trend in mass. Interpolating\nbetween the simulated cross-sections, we find that the observations (of 10\nclusters) is consistent with CDM at the ~1.5$\\sigma$ level, and prefer\ncross-section $\\sigma$/m < 0.12(0.39)cm$^2$/g at 68% (95%) confidence level.\nThis is on the verge of ruling out velocity-independent dark matter\nself-interactions as the solution to discrepancies between the predicted and\nobserved behaviour of dwarf galaxies, and will be improved by larger surveys by\nEuclid or SuperBIT.", + "category": "astro-ph" + }, + { + "text": "Star formation history and environment of the dwarf galaxy UGCA 92: We present a quantitative star formation history of the nearby dwarf galaxy\nUGCA 92. This irregular dwarf is situated in the vicinity of the Local Group of\ngalaxies in a zone of strong Galactic extinction (IC 342 group of galaxies).\nThe galaxy was resolved into stars with HST/ACS including old red giant branch.\nWe have constructed a model of the resolved stellar populations and measured\nthe star formation rate and metallicity as function of time. The main star\nformation activity period occurred about 8 - 14 Gyr ago. These stars are mostly\nmetal-poor, with a mean metallicity [Fe/H] ~ -1.5 -- -2.0 dex. About 84 per\ncent of the total stellar mass was formed during this event. There are also\nindications of recent star formation starting about 1.5 Gyr ago and continuing\nto the present. The star formation in this event shows moderate enhancement\nfrom ~ 200 Myr to 300 Myr ago. It is very likely that the ongoing star\nformation period has higher metallicity of about -0.6 -- -0.3 dex. UGCA 92 is\noften considered to be the companion to the starburst galaxy NGC 1569.\nComparing our star formation history of UGCA 92 with that of NGC 1569 reveals\nno causal or temporal connection between recent star formation events in these\ntwo galaxies. We suggest that the starburst phenomenon in NGC 1569 is not\nrelated to the galaxy's closest dwarf neighbours and does not affect their star\nformation history.", + "category": "astro-ph" + }, + { + "text": "Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment: The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to\nthe flux of iron were measured by the ATIC-2 experiment. The ratios are\ndecreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as\nexpected. However, an unexpected sharp upturn in the ratios are observed for\nenergies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but\nwith lower amplitude was also discovered in the ATIC-2 data for the ratio of\nfluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.\nTherefore the spectrum of iron is significantly different from the spectra of\nother abundant even nuclei.", + "category": "astro-ph" + }, + { + "text": "Revisiting the Integrated Star Formation Law. Paper I: Non-Starbursting\n Galaxies: We use new and updated gas and dust-corrected SFR surface densities to\nrevisit the integrated star formation law for local \"quiescent\" spiral, dwarf,\nand low-surface-brightness galaxies. Using UV-based SFRs with individual\nIR-based dust corrections, we find that \"normal\" spiral galaxies alone define a\ntight $\\Sigma_{(\\textrm{HI}+\\textrm{H}_{2})}$-$\\Sigma_{\\textrm{SFR}}$ relation\ndescribed by a $n=1.41^{+0.07}_{-0.07}$ power law with a dispersion of\n$0.28^{+0.02}_{-0.02}$ (errors reflect fitting and statistical uncertainties).\nThe SFR surface densities are only weakly correlated with HI surface densities\nalone, but exhibit a stronger and roughly linear correlation with H$_{2}$\nsurface densities, similar to what is seen in spatially-resolved measurements\nof disks. However, many dwarf galaxies lie below the star formation law defined\nby spirals, suggesting a low-density threshold in the integrated star formation\nlaw. We consider alternative scaling laws that better describe both spirals and\ndwarfs. Our improved measurement precision also allows us to determine that\nmuch of the scatter in the star formation law is intrinsic, and we search for\ncorrelations between this intrinsic scatter and secondary physical parameters.\nWe find that dwarf galaxies exhibit second-order correlations with total gas\nfraction, stellar mass surface density, and dynamical time that may explain\nmuch of the scatter in the star formation law. Finally, we discuss various\nsystematic uncertainties that should be kept in mind when interpreting any\nstudy of the star formation law, particularly the $X(\\textrm{CO})$ conversion\nfactor and the diameter chosen to define the star-forming disk in a galaxy.", + "category": "astro-ph" + }, + { + "text": "The X-ray Telescope of the CAST Experiment: The CERN Axion Solar Telescope (CAST) searches for solar axions employing a 9\nTesla superconducting dipole magnet equipped with 3 independent detection\nsystems for X-rays from axion-photon conversions inside the 10 m long magnetic\nfield. Results of the first 6 months of data taking in 2003 imply a 95 % CL\nupper limit on the axion-photon coupling constant of 1.16x10(-10) GeV(-1) for\naxion masses < 0.02 eV. The most sensitive detector of CAST is a X-ray\ntelescope consisting of a Wolter I type mirror system and a fully depleted\npn-CCD as focal plane detector. Exploiting the full potential of background\nsuppression by focussing X-rays emerging from the magnet bore, the axion\nsensitivity obtained with telescope data taken in 2004, for the first time in a\ncontrolled laboratory experiment, will supersede axion constraints derived from\nstellar energy loss arguments.", + "category": "astro-ph" + }, + { + "text": "Differences between CO- and calcium triplet-derived velocity dispersions\n in spiral galaxies: evidence for central star formation?: We examine the stellar velocity dispersions (sigma) of a sample of 48\ngalaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is\nknown that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants\nthesigma derived from the near-infrared CO band-heads is smaller than that\nmeasured from optical lines, while no discrepancy between these measurements is\nfound for early-type galaxies. No such studies are available for spiral\ngalaxies - the subject of this paper. We used cross-dispersed spectroscopic\ndata obtained with the Gemini Near-Infrared Spectrograph (GNIRS), with spectral\ncoverage from 0.85 to 2.5um, to obtain sigma measurements from the 2.29 $\\mu$m\nCO band-heads (sigma_{CO}), and the 0.85 um calcium triplet (sigma_{CaT}). For\nthe spiral galaxies in the sample, we found that sigma_{CO} is smaller than\nsigma_{CaT}, with a mean fractional difference of 14.3%. The best fit to the\ndata is given by sigma_{opt} = (46.0+/-18.1) + (0.85+/-0.12)sigma_{CO}. This\n\"sigma discrepancy\" may be related to the presence of warm dust, as suggested\nby a slight correlation between the discrepancy and the infrared luminosity.\nThis is consistent with studies that have found no sigma-discrepancy in\ndust-poor early-type galaxies, and a much larger discrepancy in dusty merger\nremnants and ULIRGs. That sigma_{CO}$ is lower than sigma_{opt} may also\nindicate the presence of a dynamically cold stellar population component. This\nwould agree with the spatial correspondence between low sigma_{CO} and\nyoung/intermediate-age stellar populations that has been observed in\nspatially-resolved spectroscopy of a handful of galaxies.", + "category": "astro-ph" + }, + { + "text": "Minimal tau approximation and simulations of the alpha effect: The validity of a closure called the minimal tau approximation (MTA), is\ntested in the context of dynamo theory, wherein triple correlations are assumed\nto provide relaxation of the turbulent electromotive force. Under MTA, the\nalpha effect in mean field dynamo theory becomes proportional to a relaxation\ntime scale multiplied by the difference between kinetic and current helicities.\nIt is shown that the value of the relaxation time is positive and, in units of\nthe turnover time at the forcing wavenumber, it is of the order of unity. It is\nquenched by the magnetic field -- roughly independently of the magnetic\nReynolds number. However, this independence becomes uncertain at large magnetic\nReynolds number. Kinetic and current helicities are shown to be dominated by\nlarge scale properties of the flow.", + "category": "astro-ph" + }, + { + "text": "Accretion Flow Along a Dipolar Field: Application to Intermediate Polars: A hydrodynamic formulation for accretion flow channeled by a dipolar magnetic\nfield is constructed using a curvi-linear coordinate system natural to the\nfield structure. We solve the hydrodynamic equations and determine the\nvelocity, density and temperature profiles of the post-shock accretion flow.\nThe results are applied to accretion flows in intermediate polars. We have\nfound that for systems with massive white dwarfs (~1Msolar) the temperature\nprofiles in the flow can differ significantly to those obtained from models in\nwhich the accretion column is assumed to be cylindrical.", + "category": "astro-ph" + }, + { + "text": "All NIRspec needs is HST/WFC3 pre-imaging? The use of Milky Way Stars in\n WFC3 Imaging to Register NIRspec MSA Observations: The James Webb Space Telescope (JWST) will be an exquisite new near-infrared\nobservatory with imaging and multi-object spectroscopy through ESA's NIRspec\ninstrument with its unique Micro-Shutter Array (MSA), allowing for slits to be\npositioned on astronomical targets by opening specific 0.002\"-wide micro\nshutter doors.\n To ensure proper target acquisition, the on-sky position of the MSA needs to\nbe verified before spectroscopic observations start. An onboard centroiding\nprogram registers the position of pre-identified guide stars in a Target\nAcquisition (TA) image, a short pre-spectroscopy exposure without dispersion\n(image mode) through the MSA with all shutters open.\n The outstanding issue is the availability of Galactic stars in the right\nluminosity range for TA relative to typical high redshift targets. We explore\nthis here using the stars and $z\\sim8$ candidate galaxies identified in the\nsource extractor catalogs of Brightest of Reionizing Galaxies survey\n(BoRG[z8]), a pure-parallel program with Hubble Space Telescope Wide-Field\nCamera 3.\n We find that (a) a single WFC3 field contains enough Galactic stars to\nsatisfy the NIRspec astrometry requirement (20 milli-arcseconds), provided its\nand the NIRspec TA's are $m_{lim}>24.5$ AB in WFC3 F125W, (b) a single WFC3\nimage can therefore serve as the pre-image if need be, (c) a WFC3 mosaic and\naccompanying TA image satisfy the astrometry requirement at $\\sim23$ AB mag in\nWFC3 F125W, (d) no specific Galactic latitude requires deeper TA imaging due to\na lack of Galactic stars, and (e) a depth of $\\sim24$ AB mag in WFC3 F125W is\nneeded if a guide star in the same MSA quadrant as a target is required.\n We take the example of a BoRG identified $z\\sim8$ candidate galaxy and\nrequire a Galactic star within 20\" of it. In this case, a depth of 25.5 AB in\nF125W is required (with $\\sim$97% confidence).", + "category": "astro-ph" + }, + { + "text": "A Comparison of Semi-Analytic and Smoothed Particle Hydrodynamics Galaxy\n Formation: We compare the statistical properties of galaxies found in two different\nmodels of hierarchical galaxy formation: the semi-analytic model of Cole et al.\nand the smoothed particle hydrodynamics (SPH) simulations of Pearce et al.\nUsing a `stripped-down' version of the semi-analytic model which mimics the\nresolution of the SPH simulations and excludes physical processes not included\nin them, we find that the two models produce an ensemble of galaxies with\nremarkably similar properties, although there are some differences in the gas\ncooling rates and in the number of galaxies that populate halos of different\nmass. The full semi-analytic model, which has effectively no resolution limit\nand includes a treatment of star formation and supernovae feedback, produces\nsomewhat different (but readily understandable) results. Agreement is\nparticularly good for the present-day global fractions of hot gas, cold dense\n(i.e. galactic) gas and uncollapsed gas, for which the SPH and stripped-down\nsemi-analytic calculations differ by at most 25%. In the most massive halos,\nthe stripped-down semi-analytic model predicts, on the whole, up to 50% less\ngas in galaxies than is seen in the SPH simulations. The two techniques\napportion this cold gas somewhat differently amongst galaxies in a given halo.\nThis difference can be tracked down to the greater cooling rate in massive\nhalos in the SPH simulation compared to the semi-analytic model. (abridged)", + "category": "astro-ph" + }, + { + "text": "Modes of Accretion in X-ray Sources: Three classical modes of accretion are briefly discussed: wind-fed,\nspherical, and disk. The three modes are illustrated with the mass transfer\nonto black holes in high-mass X-ray binaries. Then a new regime of mini-disk\naccretion is described and it is argued that observed wind-fed X-ray sources\nare likely to accrete in this regime. Switching from one accretion mode to\nanother can cause the observed spectral state transitio ns.", + "category": "astro-ph" + }, + { + "text": "Is there a correlation between radio and gamma ray luminosities of AGN ?: The possibility of a correlation between the radio (cm)- and $\\gamma$-ray\nluminosity of variable AGN seen by EGRET is investigated. We performed\nMonte-Carlo simulations of typical data sets and applied different correlation\ntechniques (partial correlation analysis, $\\chi^2$-test applied on flux-flux\nrelations) in view of a truncation bias caused by sensitivity limits of the\nsurveys. For K-corrected flux densities, we find that with the least squares\nmethod only a linear correlation can be recovered. Partial correlation analysis\non the other side provides a robust tool to detect correlations even in\nflux-limited samples if intrinsic scatter does not exceed $\\sim 40$ \\% of the\noriginal $\\gamma$-ray luminosity. The analysis presented in this paper takes\ninto account redshift bias and truncation effects simultaneously which was\nnever considered in earlier papers.\n Applying this analysis to simultaneously observed radio- and $\\gamma$-ray\ndata, no correlation is found. However, an artificial correlation appears when\nusing the mean flux. This is probably due to the reduction of the dynamical\nrange in the flux-flux relation. Furthermore, we show that comparing the\nemission in both spectral bands at a high activity state leads to no convincing\ncorrelation.\n In conclusion, we can not confirm a correlation between radio and\n$\\gamma$-ray luminosities of AGN which is claimed in previous works.", + "category": "astro-ph" + }, + { + "text": "Glancing through the debris disk: Photometric analysis of DE Boo with\n CHEOPS: DE Boo is a unique system, with an edge-on view through the debris disk\naround the star. The disk, which is analogous to the Kuiper belt in the Solar\nSystem, was reported to extend from 74 to 84 AU from the central star. The high\nphotometric precision of the Characterising Exoplanet Satellite (CHEOPS)\nprovided an exceptional opportunity to observe small variations in the light\ncurve due to transiting material in the disk. This is a unique chance to\ninvestigate processes in the debris disk. Photometric observations of DE Boo of\na total of four days were carried out with CHEOPS. Photometric variations due\nto spots on the stellar surface were subtracted from the light curves by\napplying a two-spot model and a fourth-order polynomial. The photometric\nobservations were accompanied by spectroscopic measurements with the 1m RCC\ntelescope at Piszk\\'estet\\H{o} and with the SOPHIE spectrograph in order to\nrefine the astrophysical parameters of DE Boo. We present a detailed analysis\nof the photometric observation of DE Boo. We report the presence of nonperiodic\ntransient features in the residual light curves with a transit duration of\n0.3-0.8 days. We calculated the maximum distance of the material responsible\nfor these variations to be 2.47 AU from the central star, much closer than most\nof the mass of the debris disk. Furthermore, we report the first observation of\nflaring events in this system. We interpreted the transient features as the\nresult of scattering in an inner debris disk around DE Boo. The processes\nresponsible for these variations were investigated in the context of\ninteractions between planetesimals in the system.", + "category": "astro-ph" + }, + { + "text": "New approach to primary mass composition analysis with simultaneous use\n of ground and fluorescence detectors data: We study the possibility to reconstruct primary mass composition with the use\nof combinations of basic shower characteristics, measured in hybrid\nexperiments, such as depth of shower maximum from fluorescence side and signal\nin water Cherenkov tanks or in plastic scintillators from the ground side. To\noptimize discrimination performance of shower observables combinations we apply\nFisher's discriminant analysis and give statistical estimates of separation of\nthe obtained distributions on Fisher variables for proton and iron primaries.\nAt the final stage we apply Multiparametric Topological Analysis to these\ndistributions to extract composition from prepared mixtures with known\nfractions of showers from different primary particles. It is shown, that due to\nhigh sensitivity of water tanks to muons, combination of signal in them with\n$\\xmax$ looks especially promising for mass composition analysis, provided the\nenergy is determined from longitudinal shower profile.", + "category": "astro-ph" + }, + { + "text": "The metallicity dependence of WR wind models: With the advance of stellar atmosphere modelling during the last few years,\nlarge progress in the understanding of Wolf-Rayet (WR) mass loss has been\nachieved. In the present paper we review the most recent developments,\nincluding our own results from hydrodynamic non-LTE model atmospheres. In\nparticular, we address the important question of the Z-dependence of WR mass\nloss. We demonstrate that models for radiatively driven winds imply a rather\nstrong dependence on Z. Moreover, we point out the key role of the L/M-ratio\nfor WR-type mass loss.", + "category": "astro-ph" + }, + { + "text": "A numerical approach to stochastic inflation and primordial black holes: Certain models of cosmic inflation produce strong cosmological perturbations\nat short length scales, which may later collapse into primordial black holes.\nTo find the statistics of these strong perturbations and the ensuing black\nholes, it is necessary to go beyond linear perturbation theory. Stochastic\ninflation provides a way to take the leading non-linear effects into account.\nIn this contribution, I discuss recent progress in numerical computations of\nstochastic inflation. A numerical approach can include more of the\nnon-linearities than an analytical calculation, and can be applied to\nsingle-field inflationary models with any potential.", + "category": "astro-ph" + }, + { + "text": "CosTuuM: polarized thermal dust emission by magnetically oriented\n spheroidal grains: We present the new open source C++-based Python library CosTuuM that can be\nused to generate infrared absorption and emission coefficients for arbitrary\nmixtures of spheroidal dust grains that are (partially) aligned with a magnetic\nfield. We outline the algorithms underlying the software, demonstrate the\naccuracy of our results using benchmarks from literature, and use our tool to\ninvestigate some commonly used approximative recipes. We find that the linear\npolarization fraction for a partially aligned dust grain mixture can be\naccurately represented by an appropriate linear combination of perfectly\naligned grains and grains that are randomly oriented, but that the commonly\nused picket fence alignment breaks down for short wavelengths. We also find\nthat for a fixed dust grain size, the absorption coefficients and linear\npolarization fraction for a realistic mixture of grains with various shapes\ncannot both be accurately represented by a single representative grain with a\nfixed shape, but that instead an average over an appropriate shape distribution\nshould be used. Insufficient knowledge of an appropriate shape distribution is\nthe main obstacle in obtaining accurate optical properties. CosTuuM is\navailable as a standalone Python library and can be used to generate optical\nproperties to be used in radiative transfer applications.", + "category": "astro-ph" + }, + { + "text": "The smooth cyclotron line in Her X-1 as seen with NuSTAR: Her X-1, one of the brightest and best studied X-ray binaries, shows a\ncyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an\nideal target for detailed study with the Nuclear Spectroscopic Telescope Array\n(NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We\nobserved Her X-1 three times, coordinated with Suzaku, during one of the high\nflux intervals of its 35d super-orbital period. This paper focuses on the shape\nand evolution of the hard X-ray spectrum. The broad-band spectra can be fitted\nwith a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find\nthat the CRSF has a very smooth and symmetric shape, in all observations and at\nall pulse-phases. We compare the residuals of a line with a Gaussian optical\ndepth profile to a Lorentzian optical depth profile and find no significant\ndifferences, strongly constraining the very smooth shape of the line. Even\nthough the line energy changes dramatically with pulse phase, we find that its\nsmooth shape does not. Additionally, our data show that the continuum is only\nchanging marginally between the three observations. These changes can be\nexplained with varying amounts of Thomson scattering in the hot corona of the\naccretion disk. The average, luminosity-corrected CRSF energy is lower than in\npast observations and follows a secular decline. The excellent data quality of\nNuSTAR provides the best constraint on the CRSF energy to date.", + "category": "astro-ph" + }, + { + "text": "Flashes in a Star Stream: Automated Classification of Astronomical\n Transient Events: An automated, rapid classification of transient events detected in the modern\nsynoptic sky surveys is essential for their scientific utility and effective\nfollow-up using scarce resources. This presents some unusual challenges: the\ndata are sparse, heterogeneous and incomplete; evolving in time; and most of\nthe relevant information comes not from the data stream itself, but from a\nvariety of archival data and contextual information (spatial, temporal, and\nmulti-wavelength). We are exploring a variety of novel techniques, mostly\nBayesian, to respond to these challenges, using the ongoing CRTS sky survey as\na testbed. The current surveys are already overwhelming our ability to\neffectively follow all of the potentially interesting events, and these\nchallenges will grow by orders of magnitude over the next decade as the more\nambitious sky surveys get under way. While we focus on an application in a\nspecific domain (astrophysics), these challenges are more broadly relevant for\nevent or anomaly detection and knowledge discovery in massive data streams.", + "category": "astro-ph" + }, + { + "text": "A New 100-GHz Band Front-End System with a Waveguide-Type\n Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio\n Telescope: We developed a waveguide-type dual-polarization sideband-separating SIS\nreceiver system of the 100-GHz band for the 45-m radio telescope at the\nNobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode\ntransducer and two sideband-separating SIS mixers, which are both based on the\nwaveguide technique. The receiver has four intermediate frequency bands of\n4.0--8.0 GHz. Over the radio frequency range of 80--120 GHz, the\nsingle-sideband receiver noise temperatures are 50--100 K and the image\nrejection ratios are greater than 10 dB. We developed new matching optics for\nthe telescope beam as well as new IF chains for the four IF signals. The new\nreceiver system was installed in the telescope, and we successfully observed\nthe 12CO, 13CO and C18O emission lines simultaneously toward the Sagittarius B2\nregion to confirm the performance of the receiver system. The SSB noise\ntemperature of the system, including the atmosphere, became approximately half\nof that of the previous receiver system. The Image Rejection Ratios (IRRs) of\nthe two 2SB mixers were calculated from the 12CO and HCO+ spectra from the W51\ngiant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB\nfor the other polarization.", + "category": "astro-ph" + }, + { + "text": "A Complete Census of Circumgalactic MgII at Redshift z<~ 0.5: We present a survey of MgII absorbing gas in the vicinity of 380 random\ngalaxies, using 156 background quasi-stellar objects(QSOs) as absorption-line\nprobes. The sample comprises 211 isolated (73 quiescent and 138 star-forming\ngalaxies) and 43 non-isolated galaxies with sensitive constraints for both MgII\nabsorption and Ha emission. The projected distances span a range from d=9 to\n497 kpc, redshifts of the galaxies range from z=0.10 to 0.48, and rest-frame\nabsolute B-band magnitudes range from $M_{\\rm B}=-16.7$ to $-22.8$. Our\nanalysis shows that the rest-frame equivalent width of MgII, $W_r$(2796),\ndepends on halo radius($R_h$), $B$-band luminosity($L_{\\rm B}$) and stellar\nmass ($M_{\\rm star}$) of the host galaxies, and declines steeply with\nincreasing $d$ for isolated, star-forming galaxies. $W_r$(2796) exhibits no\nclear trend for either isolated, quiescent galaxies or non-isolated galaxies.\nThe covering fraction of MgII absorbing gas $\\langle \\kappa \\rangle$ is high\nwith $\\langle \\kappa \\rangle\\gtrsim 60$% at $<40$ kpc for isolated galaxies and\ndeclines rapidly to $\\langle \\kappa \\rangle\\approx 0$ at $d\\gtrsim100$ kpc.\nWithin the gaseous radius, $\\langle \\kappa \\rangle$ depends sensitively on both\n$M_{\\rm star}$ and the specific star formation rate inferred from Ha. Different\nfrom massive quiescent halos, the observed velocity dispersion of MgII gas\naround star-forming galaxies is consistent with expectations from virial\nmotion, which constrains individual clump mass to $m_{\\rm cl} \\gtrsim 10^5\n\\,\\rm M_\\odot$ and cool gas accretion rate of $\\sim 0.7-2 \\,M_\\odot\\,\\rm\nyr^{-1}$. We find no strong azimuthal dependence of MgII absorption for either\nstar-forming or quiescent galaxies. Our results highlight the need of a\nhomogeneous, absorption-blind sample for establishing a holistic description of\nchemically-enriched gas in the circumgalactic space.", + "category": "astro-ph" + }, + { + "text": "Quiescent Ultra-diffuse galaxies in the field originating from\n backsplash orbits: Ultra-diffuse galaxies (UDGs) are the lowest-surface brightness galaxies\nknown, with typical stellar masses of dwarf galaxies but sizes similar to\nlarger galaxies like the Milky Way. The reason for their extended sizes is\ndebated, with suggested internal processes like angular momentum, feedback or\nmergers versus external mechanisms or a combination of both. Observationally,\nwe know that UDGs are red and quiescent in groups and clusters while their\ncounterparts in the field are blue and star-forming. This dichotomy suggests\nenvironmental effects as main culprit. However, this scenario is challenged by\nrecent observations of isolated quiescent UDGs in the field. Here we use\n$\\Lambda$CDM cosmological hydrodynamical simulation to show that isolated\nquenched UDGs are formed as backsplash galaxies that were once satellites of\nanother galactic, group or cluster halo but are today a few Mpc away from them.\nThese interactions, albeit brief, remove the gas and tidally strip the\noutskirts of the dark matter haloes of the now quenched seemingly-isolated\nUDGs, which are born as star-forming field UDGs occupying dwarf-mass dark\nmatter haloes. Quiescent UDGs may therefore be found in non-negligible numbers\nin filaments and voids, bearing the mark of past interactions as stripped outer\nhaloes devoid of dark matter and gas compared to dwarfs with similar stellar\ncontent.", + "category": "astro-ph" + }, + { + "text": "Suzaku Metal Abundance Patterns in the Outflow Region of M82 and the\n Importance of Charge Exchange: We performed spectral analysis of Suzaku data of the galactic disk and\noutflow regions of the starburst galaxy M82. Thermal modeling of the central\ndisk regions requires at least three temperature components. The Ly$\\beta$ line\nfluxes of O VIII and Ne X exceed those expected from a plasma in collisional\nionization equilibrium. The ratios of Ly$\\beta$/Ly$\\alpha$ lines for O VIII and\nNe X are higher than those of collisional ionization equilibrium, which may be\ncaused by the process of charge exchange. In the outflow wind region, the\nspectra are well reproduced with two-temperature thermal models, and we have\nderived the metal abundances of O, Ne, Mg, and Fe in the outflow. The ratios of\nO/Fe, Ne/Fe, and Mg/Fe are about 2, 3, and 2, respectively, relative to the\nsolar value determined by Lodders (2003). Since there is no evidence of charge\nexchange in outflow region, the metal abundances should be more reliable than\nthose in the central region. This abundance pattern indicates that starburst\nactivity enriches the outflow through SN II metal ejection into intergalactic\nspace.", + "category": "astro-ph" + }, + { + "text": "The structure of steady, relativistic, magnetised jets with rotation: We present equilibrium models of relativistic magnetised, infinite,\naxisymmetric jets with rotation propagating through an homogeneous,\nunmagnetised ambient medium at rest. The jet models are characterised by six\nfunctions defining the radial profiles of density, pressure, and the toroidal\nand axial components of velocity and magnetic field. Fixing the ambient\npressure and the jet rest-mass density and axial components of the flow\nvelocity and magnetic field, we analyze the influence of the toroidal magnetic\nfield and several rotation laws on the structure of the equilibrium models. Our\napproach excludes by construction the analysis of the self-consistently\nmagnetically launched jet models or the force-free equilibrium solutions.\nSeveral forbidden regions in the magnetic pitch angle/magnetization plane are\nfound where models of the class considered in our study could not be settled.\nThese forbidden regions are associated with the existence of maximum axial and\ntoroidal magnetic field components compatible with the prescribed equilibrium\ncondition at the jet surface, and/or an excess of centrifugal force producing\ngaps with negative pressures in the jet. The present study can be easily\nextended to jet models with different transversal profiles and magnetic field\nconfigurations.\n In the last part of the paper, we test the ability of our RMHD code to\nmaintain steady equilibrium models of axisymmetric RMHD jets in one and two\nspatial dimensions. The one dimensional numerical simulations serve also as a\nconsistency proof of the fidelity of the analytical steady solutions discussed\nin the first part of the paper. The present study allows us to build initial\nequilibrium jet models with selected properties for dynamical (and emission)\nsimulations of magnetised relativistic jets with rotation.", + "category": "astro-ph" + }, + { + "text": "Core collapse supernovae as Cosmic Ray sources: Core collapse supernovae (CCSNe) produce fast shocks which pervade the dense\ncircum-stellar medium (CSM) of the stellar progenitor. Cosmic rays (CRs) if\naccelerated at these shocks can induce the growth of electromagnetic\nfluctuations in the foreshock medium. In this study, using a self-similar\ndescription of the shock evolution, we calculate the growth timescales of\nCR-driven instabilities. We select a sample of nearby core collapse radio\nsupernova of type II and Ib/Ic. From radio data we infer the parameters which\nenter in the calculation of the instability growth times. We find that extended\nIIb SNe shocks can trigger fast intra day instabilities, strong magnetic field\namplification and CR acceleration. In particular, the non-resonant streaming\ninstability can contribute to about 50\\% of the magnetic field intensity\ndeduced from radio data. This results in the acceleration of CRs in the range\n1-10 PeV within a few days after the shock breakout. In order to produce strong\nmagnetic field amplification and CR acceleration a fast shocks pervading a\ndense CSM is necessary. In that aspect IIn supernov\\ae~are also good\ncandidates. But a detailed modeling of the blast wave dynamics coupled with\nparticle acceleration is mandatory for this class of object before providing\nany firm conclusions. Finally, we find that the trans-relativistic object SN\n2009bb even if it produces more modest magnetic field amplification can\naccelerate CRs up to 2-3 PeV within 20 days after the outburst.", + "category": "astro-ph" + }, + { + "text": "Polarized QED Cascades over Pulsar Polar Caps: The formation of $e^\\pm$ plasmas within pulsar magnetospheres through quantum\nelectrodynamics (QED) cascades in vacuum gaps is widely acknowledged. This\npaper aims to investigate the effect of photon polarization during the QED\ncascade occurring over the polar cap of a pulsar. We employ a Monte Carlo-based\nQED algorithm that accurately accounts for both spin and polarization effects\nduring photon emission and pair production in both single-particle and\nparticle-in-cell (PIC) simulations. Our findings reveal distinctive properties\nin the photon polarization of curvature radiation (CR) and synchrotron\nradiation (SR). CR photons exhibit high linear polarization parallel to the\nplane of the curved magnetic field lines, whereas SR photons, on average,\ndemonstrate weak polarization. As the QED cascade progresses, SR photons\ngradually dominate over CR photons, thus reducing the average degree of photon\npolarization. Additionally, our study highlights an intriguing observation: the\npolarization of CR photons enhances $e^\\pm$ pair production by approximately\n5%, in contrast to the inhibition observed in laser-plasma interactions. Our\nself-consistent QED PIC simulations in the corotating frame reproduce the\nessential results obtained from single-particle simulations.", + "category": "astro-ph" + }, + { + "text": "Analyzing spatial coherence using a single mobile field sensor: According to the Van Citter-Zernike theorem the intensity distribution of a\nspatially incoherent source and the mutual coherence function of the light\nimpinging on two wave sensors are related. It is the comparable relationship\nusing a single mobile sensor moving at a certain velocity relative to the\nsource which is calculated in this article. The autocorelation function of the\nelectric field at the sensor contains information about the intensity\ndistribution. This expression could be employed in aperture synthesis.", + "category": "astro-ph" + }, + { + "text": "Radiation-Dominated Disks Are Thermally Stable: When the accretion rate is more than a small fraction of Eddington, the inner\nregions of accretion disks around black holes are expected to be\nradiation-dominated. However, in the alpha-model, these regions are also\nexpected to be thermally unstable. In this paper, we report two 3-d radiation\nMHD simulations of a vertically-stratified shearing box in which the ratio of\nradiation to gas pressure is ~ 10, and yet no thermal runaway occurs over a\ntimespan ~ 40 cooling times. Where the time-averaged dissipation rate is\ngreater than the critical dissipation rate that creates hydrostatic equilibrium\nby diffusive radiation flux, the time-averaged radiation flux is held to the\ncritical value, with the excess dissipated energy transported by radiative\nadvection. Although the stress and total pressure are well-correlated as\npredicted by the alpha-model, we show that stress fluctuations precede pressure\nfluctuations, contrary to the usual supposition that the pressure controls the\nsaturation level of the magnetic energy. This fact explains the thermal\nstability. Using a simple toy-model, we show that independently-generated\nmagnetic fluctuations can drive radiation pressure fluctuations, creating a\ncorrelation between the two while maintaining thermal stability.", + "category": "astro-ph" + }, + { + "text": "Velocity-dependent J-factors for annihilation radiation from\n cosmological simulations: We determine the dark matter pair-wise relative velocity distribution in a\nset of Milky Way-like halos in the Auriga and APOSTLE simulations. Focusing on\nthe smooth halo component, the relative velocity distribution is well-described\nby a Maxwell-Boltzmann distribution over nearly all radii in the halo. We\nexplore the implications for velocity-dependent dark matter annihilation,\nfocusing on four models which scale as different powers of the relative\nvelocity: Sommerfeld, s-wave, p-wave, and d-wave models. We show that the\nJ-factors scale as the moments of the relative velocity distribution, and that\nthe halo-to-halo scatter is largest for d-wave, and smallest for Sommerfeld\nmodels. The J-factor is strongly correlated with the dark matter density in the\nhalo, and is very weakly correlated with the velocity dispersion. This implies\nthat if the dark matter density in the Milky Way can be robustly determined,\none can accurately predict the dark matter annihilation signal, without the\nneed to identify the dark matter velocity distribution in the Galaxy.", + "category": "astro-ph" + }, + { + "text": "Radiation Magnetohydrodynamics Simulation of Proto-Stellar Collapse:\n Two-Component Molecular Outflow: We perform a three-dimensional nested-grid radiation magneto-hydrodynamics\n(RMHD) simulation with self-gravity to study the early phase of the low-mass\nstar formation process from a rotating molecular cloud core to a first\nadiabatic core just before the second collapse begins. Radiation transfer is\nhandled with the flux-limited diffusion approximation, operator-splitting and\nimplicit time-integrator. In the RMHD simulation, the outer region of the first\ncore attains a higher entropy and the size of first core is larger than that in\nthe magnetohydrodynamics simulations with the barotropic approximation. Bipolar\nmolecular outflow consisting of two components is driven by magnetic Lorentz\nforce via different mechanisms, and shock heating by the outflow is observed.\nUsing the RMHD simulation we can predict and interpret the observed properties\nof star-forming clouds, first cores and outflows with millimeter/submillimeter\nradio interferometers, especially the Atacama Large Millimeter/submillimeter\nArray (ALMA).", + "category": "astro-ph" + }, + { + "text": "Balmer line shifts in quasars: We offer a broad review of Balmer line phenomenology in type 1 active\ngalactic nuclei, briefly sum- marising luminosity and radio loudness effects,\nand discussing interpretation in terms of nebular physics along the 4D\neigenvector 1 sequence of quasars. We stress that relatively rare, peculiar\nBalmer line profiles (i.e., with large shifts with respect to the rest frame or\ndouble and multiple peaked) that start attracted attentions since the 1970s are\nstill passable of multiple dynamical interpretation. More mainstream objects\nare still not fully understood as well, since competing dynamical models and\ngeometries are possible. Further progress may come from inter-line comparison\nacross the 4D Eigenvector 1 sequence.", + "category": "astro-ph" + }, + { + "text": "The velocity dispersion and mass-to-light ratio of the remote halo\n globular cluster NGC 2419: Precise radial velocity measurements from HIRES on the Keck I telescope are\npresented for 40 stars in the outer halo globular cluster NGC 2419. These data\nare used to probe the cluster's stellar mass function and search for the\npresence of dark matter in this cluster. NGC 2419 is one of the best Galactic\nglobular clusters for such a study due to its long relaxation time (T_{r0} ~\n10^{10} yr) and large Galactocentric distance (R_{GC} ~ 90 kpc) -- properties\nthat make significant evolutionary changes in the low-mass end of the cluster\nmass function unlikely. We find a mean cluster velocity of =-20.3 +- 0.7\nkm/sec and an internal velocity dispersion of \\sigma = 4.14 +- 0.48 km/sec,\nleading to a total mass of (9.0 +- 2.2) * 10^5 Msun and a global mass-to-light\nratio of M/L_V = 2.05 +- 0.50 in solar units. This mass-to-light ratio is in\ngood agreement with what one would expect for a pure stellar system following a\nstandard mass function at the metallicity of NGC 2419. In addition, the\nmass-to-light ratio does not appear to rise towards the outer parts of the\ncluster. Our measurements therefore rule out the presence of a dark matter halo\nwith mass larger than ~10^7 Msun inside the central 500 pc, which is lower than\nwhat is found for the central dark matter densities of dSph galaxies. We also\ndiscuss the relevance of our measurements for alternative gravitational\ntheories such as MOND, and for possible formation scenarios of ultra-compact\ndwarf galaxies.", + "category": "astro-ph" + }, + { + "text": "The JCMT Gould Belt Survey: Evidence for Dust Grain Evolution in Perseus\n Star-forming Clumps: The dust emissivity spectral index, $\\beta$, is a critical parameter for\nderiving the mass and temperature of star-forming structures, and consequently\ntheir gravitational stability. The $\\beta$ value is dependent on various dust\ngrain properties, such as size, porosity, and surface composition, and is\nexpected to vary as dust grains evolve. Here we present $\\beta$, dust\ntemperature, and optical depth maps of the star-forming clumps in the Perseus\nMolecular Cloud determined from fitting SEDs to combined Herschel and JCMT\nobservations in the 160 $\\mu$m, 250 $\\mu$m, 350 $\\mu$m, 500 $\\mu$m, and 850\n$\\mu$m bands. Most of the derived $\\beta$, and dust temperature values fall\nwithin the ranges of 1.0 - 2.7 and 8 - 20 K, respectively. In Perseus, we find\nthe $\\beta$ distribution differs significantly from clump to clump, indicative\nof grain growth. Furthermore, we also see significant, localized $\\beta$\nvariations within individual clumps and find low $\\beta$ regions correlate with\nlocal temperature peaks, hinting at the possible origins of low $\\beta$ grains.\nThroughout Perseus, we also see indications of heating from B stars and\nembedded protostars, as well evidence of outflows shaping the local landscape.", + "category": "astro-ph" + }, + { + "text": "Galaxy and Mass Assembly (GAMA): Optimal Tiling of Dense Surveys with a\n Multi-Object Spectrograph: A heuristic greedy algorithm is developed for efficiently tiling spatially\ndense redshift surveys. In its first application to the Galaxy and Mass\nAssembly (GAMA) redshift survey we find it rapidly improves the spatial\nuniformity of our data, and naturally corrects for any spatial bias introduced\nby the 2dF multi object spectrograph. We make conservative predictions for the\nfinal state of the GAMA redshift survey after our final allocation of time, and\ncan be confident that even if worse than typical weather affects our\nobservations, all of our main survey requirements will be met.", + "category": "astro-ph" + }, + { + "text": "Exploring the Properties of the M31 Halo Globular Cluster System: Following on from our discovery of a significant population of M31 outer halo\nglobular clusters (GCs), and updates to the Revised Bologna Catalogue of M31\nGCs, we investigate the GC system of M31 out to an unprecedented radius\n(~120kpc). We derive various ensemble properties, including the magnitude,\ncolour and metallicity distributions, as well as the GC number density profile.\nOne of our most significant findings is evidence for a flattening in the radial\nGC number density profile in the outer halo. Intriguingly, this occurs at a\ngalactocentric radius of ~2 degrees (~30 kpc) which is the radius at which the\nunderlying stellar halo surface density has also been shown to flatten. The GCs\nwhich lie beyond this radius are remarkably uniform in terms of their blue\n(V-I)o colours, consistent with them belonging to an ancient population with\nlittle to no metallicity gradient. Structural parameters are also derived for a\nsample of 13 newly-discovered extended clusters (ECs) and we find the lowest\nluminosity ECs have magnitudes and sizes similar to Palomar-type GCs in the\nMilky Way halo. We argue that our findings provide strong support for a\nscenario in which a significant fraction of the outer halo GC population of M31\nhas been accreted.", + "category": "astro-ph" + }, + { + "text": "Large-amplitude rapid X-ray variability in the narrow-line Seyfert 1\n galaxy PG 1404$+$226: We present the first results from a detailed analysis of a new, long\n($\\sim100$ ks) XMM-Newton observation of the narrow-line Seyfert 1 galaxy PG\n1404$+$226 which showed a large-amplitude, rapid X-ray variability by a factor\nof $\\sim7$ in $\\sim10$ ks with an exponential rise and a sharp fall in the\ncount rate. We investigate the origin of the soft X-ray excess emission and\nrapid X-ray variability in the source through time-resolved spectroscopy and\nfractional root-mean-squared (rms) spectral modeling. The strong soft X-ray\nexcess below 1 keV observed both in the time-averaged and time-resolved spectra\nis described by the intrinsic disk Comptonization model as well as the\nrelativistic reflection model where the emission is intensive merely in the\ninner regions ($r_{\\rm in}<1.7 r_{\\rm g}$) of an ionized accretion disk. We\ndetected no significant UV variability while the soft X-ray excess flux varies\ntogether with the primary power-law emission (as $F_{{\\rm primary}}\\propto\nF_{{\\rm excess}}^{1.54}$), although with a smaller amplitude, as expected in\nthe reflection scenario. The observed X-ray fractional rms spectrum is\napproximately constant with a drop at $\\sim0.6$ keV and is described by a\nnon-variable emission line component with the observed energy of $\\sim0.6$ keV\nand two variable spectral components: a more variable primary power-law\nemission and a less variable soft excess emission. Our results suggest the\n`lamppost geometry' for the primary X-ray emitting hot corona which illuminates\nthe innermost accretion disk due to strong gravity and gives rise to the soft\nX-ray excess emission.", + "category": "astro-ph" + }, + { + "text": "Spitzer observations of NGC2264: The nature of the disk population: NGC2264 is a young cluster with a rich circumstellar disk population which\nmakes it an ideal target for studying the evolution of stellar clusters. Our\ngoal is to study its star formation history and to analyse the primordial disk\nevolution of its members. The study presented is based on data obtained with\nSpitzer IRAC and MIPS, combined with deep NIR ground-based FLAMINGOS imaging\nand previously published optical data. We build NIR dust extinction maps of the\nmolecular cloud associated with the cluster, and determine it to have a mass of\n2.1x10^3Msun above an Av of 7mag. Using a differential K_s-band luminosity\nfunction of the cluster, we estimate the size of its population to be\n1436$\\pm$242 members. The star formation efficiency is ~25%. We identify the\ndisk population: (i) optically thick inner disks, (ii) anaemic inner disks, and\n(iii) disks with inner holes, or transition disks. We analyse the spatial\ndistribution of these sources and find that sources with thick disks segregate\ninto sub-clusterings, whereas sources with anaemic disks do not. Furthermore,\nsources with anaemic disks are found to be unembedded (Av<3mag), whereas the\nclustered sources with thick disks are still embedded within the parental\ncloud. NGC2264 has undergone more than one star-forming event, where the\nanaemic and extincted thick disk population appear to have formed in separate\nepisodes. We also find tentative evidence of triggered star-formation in the\nFox Fur Nebula. In terms of disk evolution, our findings support the emerging\ndisk evolution paradigm of two distinct evolutionary paths for primordial\noptically thick disks: a homologous one where the disk emission decreases\nuniformly at NIR and MIR wavelengths, and a radially differential one where the\nemission from the inner region of the disk decreases more rapidly than from the\nouter region (forming transition disks).", + "category": "astro-ph" + }, + { + "text": "Quantum sensor networks as exotic field telescopes for multi-messenger\n astronomy: Multi-messenger astronomy, the coordinated observation of different classes\nof signals originating from the same astrophysical event, provides a wealth of\ninformation about astrophysical processes with far-reaching implications. So\nfar, the focus of multi-messenger astronomy has been the search for\nconventional signals from known fundamental forces and standard model\nparticles, like gravitational waves (GW). In addition to these known effects,\nquantum sensor networks could be used to search for astrophysical signals\npredicted by beyond-standard-model (BSM) theories. Exotic bosonic fields are\nubiquitous features of BSM theories and appear while seeking to understand the\nnature of dark matter and dark energy and solve the hierarchy and strong CP\nproblems. We consider the case where high-energy astrophysical events could\nproduce intense bursts of exotic low-mass fields (ELFs). We propose to expand\nthe toolbox of multi-messenger astronomy to include networks of precision\nquantum sensors that by design are shielded from or insensitive to conventional\nstandard-model physics signals. We estimate ELF signal amplitudes, delays,\nrates, and distances of GW sources to which global networks of atomic\nmagnetometers and atomic clocks could be sensitive. We find that, indeed, such\nprecision quantum sensor networks can function as ELF telescopes to detect\nsignals from sources generating ELF bursts of sufficient intensity. Thus ELFs,\nif they exist, could act as additional messengers for astrophysical events.", + "category": "astro-ph" + }, + { + "text": "Perspectives for multi-messenger astronomy with the next generation of\n gravitational-wave detectors and high-energy satellites: The Einstein Telescope (ET) is going to bring a revolution for the future of\nmulti-messenger astrophysics. In order to detect the counterparts of binary\nneutron star (BNS) mergers at high redshift, the high-energy observations will\nplay a crucial role. Here, we explore the perspectives of ET, as single\nobservatory and in a network of gravitational-wave (GW) detectors, operating in\nsynergy with future $\\gamma$-ray and X-ray satellites. We predict the\nhigh-energy emission of BNS mergers and its detectability in a theoretical\nframework which is able to reproduce the properties of the current sample of\nobserved short GRBs (SGRB). We estimate the joint GW and high-energy detection\nrate for both the prompt and afterglow emissions, testing several combinations\nof instruments and observational strategies. We find that the vast majority of\nSGRBs detected in $\\gamma$-rays will have a detectable GW counterpart; the\njoint detection efficiency approaches $100\\%$ considering a network of third\ngeneration GW observatories. The probability of identifying the electromagnetic\ncounterpart of BNS mergers is significantly enhanced if the sky localisation\nprovided by GW instruments is observed by wide field X-ray monitors. We\nemphasize that the role of the future X-ray observatories will be very crucial\nfor the detection of the fainter emission outside the jet core, which will\nallow us to probe the yet unexplored population of low-luminosity SGRBs in the\nnearby Universe, as well as to unveil the nature of the jet structure and the\nconnections with the progenitor properties.", + "category": "astro-ph" + }, + { + "text": "Accuracy of Mesh Based Cosmological Hydrocodes: Tests and Corrections: We perform a variety of tests to determine the numerical resolution of the\ncosmological TVD eulerian code developed by Ryu et al (1993). Tests include\n512^3 and 256^3 simulations of a Pk=k^{-1} spectrum to check for\nself-similarity and comparison of results with those from higher resolution SPH\nand grid-based calculations (Frenk et al 1998). We conclude that in regions\nwhere density gradients are not produced by shocks the code degrades resolution\nwith a Gaussian smoothing (radius) length of 1.7 cells. At shock caused\ngradients (for which the code was designed) the smoothing length is 1.1 cells.\nFinally, for \\beta model fit clusters, we can approximately correct numerical\nresolution by the transformation R^2_{core}\\to R^2_{core}-(C\\Delta l)^2, where\n\\Delta l is the cell size and C=1.1-1.7. When we use these corrections on our\npreviously published computations for the SCDM and \\Lambda CDM models we find\nluminosity weighted, zero redshift, X-ray cluster core radii of (210\\pm 86,\n280\\pm 67)h^{-1}kpc, respectively, which are marginally consistent with\nobserved (Jones & Forman 1992) values of 50-200h^{-1}kpc. Using the corrected\ncore radii, the COBE normalized SCDM model predicts the number of bright\nL_x>10^{43}erg/s clusters too high by a factor of \\sim 20 and the \\Lambda CDM\nmodel is consistent with observations.", + "category": "astro-ph" + }, + { + "text": "Extreme Jet Ejections from the Black Hole X-ray Binary V404 Cygni: We present simultaneous radio through sub-mm observations of the black hole\nX-ray binary (BHXB) V404 Cygni during the most active phase of its June 2015\noutburst. Our $4$ hour long set of overlapping observations with the Very Large\nArray, the Sub-millimeter Array, and the James Clerk Maxwell Telescope\n(SCUBA-2), covers 8 different frequency bands (including the first detection of\na BHXB jet at $666 \\,{\\rm GHz}/450\\mu m$), providing an unprecedented\nmulti-frequency view of the extraordinary flaring activity seen during this\nperiod of the outburst. In particular, we detect multiple rapidly evolving\nflares, which reach Jy-level fluxes across all of our frequency bands. With\nthis rich data set we performed detailed MCMC modeling of the repeated flaring\nevents. Our custom model adapts the van der Laan synchrotron bubble model to\ninclude twin bi-polar ejections, propagating away from the black hole at bulk\nrelativistic velocities, along a jet axis that is inclined to the line of\nsight. The emission predicted by our model accounts for projection effects,\nrelativistic beaming, and the geometric time delay between the approaching and\nreceding ejecta in each ejection event. We find that a total of 8 bi-polar,\ndiscrete jet ejection events can reproduce the emission that we observe in all\nof our frequency bands remarkably well. With our best fit model, we provide\ndetailed probes of jet speed, structure, energetics, and geometry. Our analysis\ndemonstrates the paramount importance of the mm/sub-mm bands, which offer a\nunique, more detailed view of the jet than can be provided by radio frequencies\nalone.", + "category": "astro-ph" + }, + { + "text": "Broad-Band Imaging of a Large Sample of Irregular Galaxies: We present the results of UBV imaging of a large sample of irregular\ngalaxies: 94 Im systems, 24 Blue Compact Dwarfs (BCDs), and 18 Sm galaxies. We\nalso include JHK imaging of 41 of these galaxies. The sample spans a large\nrange in galactic parameters. Ellipse fit axial ratios, inclinations, and\nposition angles are derived, integrated photometry and azimuthally-averaged\nsurface photometry profiles are determined, and exponential fits give the\ncentral surface brightnesses, scale lengths, and isophotal and half-power\nradii. These data are used to address the shapes of Im galaxies, look for clues\nto past interactions in large-scale peculiarities, examine the nature and\nconsequences of bars, study color gradients and large-scale color variations,\nand compare the exponential disk profiles of the young and old stellar\ncomponents. For example, color gradients exhibit a great variety and not all\npassbands are correlated. Bars are associated with higher star formation rates.\nMany irregulars show a double exponential radial light profile that is steeper\nin the outer parts, and these are reproduced by a new model of star formation\nthat is discussed in a companion paper. Some galaxies, primarily BCDs, have\ndouble exponentials that are steeper (and bluer) in the inner parts, presumably\nfrom centralized star formation. Im-types have thicker, less-prominent dust\nlayers than spiral galaxies because of their lower average surface densities\nand midplane extinctions.", + "category": "astro-ph" + }, + { + "text": "Lyman-Werner UV Escape Fractions from Primordial Halos: Population III stars can regulate star formation in the primordial Universe\nin several ways. They can ionize nearby halos, and even if their ionizing\nphotons are trapped by their own halos, their Lyman-Werner (LW) photons can\nstill escape and destroy H$_2$ in other halos, preventing them from cooling and\nforming stars. LW escape fractions are thus a key parameter in cosmological\nsimulations of early reionization and star formation but have not yet been\nparametrized for realistic halos by halo or stellar mass. To do so, we perform\nradiation hydrodynamical simulations of LW UV escape from 9--120 M$_{\\odot}$\nPop III stars in $10^5$ to $10^7$ M$_{\\odot}$ halos with ZEUS-MP. We find that\nphotons in the LW lines (i.e. those responsible for destroying H$_{2}$ in\nnearby systems) have escape fractions ranging from 0% to 85%. No LW photons\nescape the most massive halo in our sample, even from the most massive star.\nEscape fractions for photons elsewhere in the 11.18--13.6~eV energy range,\nwhich can be redshifted into the LW lines at cosmological distances, are\ngenerally much higher, being above 60% for all but the least massive stars in\nthe most massive halos. We find that shielding of H$_2$ by neutral hydrogen,\nwhich has been neglected in most studies to date, produces escape fractions\nthat are up to a factor of three smaller than those predicted by H$_2$\nself-shielding alone.", + "category": "astro-ph" + }, + { + "text": "Search for Outbursts in the Narrow 511-keV Line from Compact Sources\n Based on INTEGRAL Data: We present the results of a systematic search for outbursts in the narrow\npositron annihilation line on various time scales (5x10^4 - 10^6 s) based on\nthe SPI/INTEGRAL data obtained from 2003 to 2008. We show that no outbursts\nwere detected with a statistical significance higher than ~6 sigma for any of\nthe time scales considered over the entire period of observations. We also show\nthat, given the large number of independent trials, all of the observed spikes\ncould be associated with purely statistical flux fluctuations and, in part,\nwith a small systematic prediction error of the telescope's instrumental\nbackground. Based on the exposure achieved in ~6 yr of INTEGRAL operation, we\nprovide conservative upper limits on the rate of outbursts with a given\nduration and flux in different parts of the sky.", + "category": "astro-ph" + }, + { + "text": "Testing the Frozen-Flow Approximation: We investigate the accuracy of the frozen--flow approximation (FFA), recently\nproposed by Matarrese \\etal (1992), for following the nonlinear evolution of\ncosmological density fluctuations under gravitational instability. We compare a\nnumber of statistics between results of the FFA and nbody simulations,\nincluding those used by Melott, Pellman \\& Shandarin (1993) to test the\nZel'dovich approximation. The FFA performs reasonably well in a statistical\nsense, e.g. in reproducing the counts--in--cell distribution, at small scales,\nbut it does poorly in the crosscorrelation with nbody which means it is\ngenerally not moving mass to the right place, especially in models with high\nsmall--scale power.", + "category": "astro-ph" + }, + { + "text": "Full Monte Carlo simulations of radio emission from extensive air\n showers with CoREAS: CoREAS is a Monte Carlo simulation code for the calculation of radio emission\nfrom extensive air showers. It is based on the \"endpoint formalism\" for\nradiation from moving charges implemented directly in CORSIKA. Consequently,\nthe full complexity of the air-shower physics is taken into account without the\nneed for approximations or assumptions on the emission mechanism. We present\nresults of simulations for an unthinned shower performed with CoREAS for both\nMHz and GHz frequencies. At MHz frequencies, the simulations predict the\nwell-known mixture of geomagnetic and charge excess radiation. At GHz\nfrequencies, the emission is strongly influenced by Cherenkov effects arising\nfrom the varying refractive index in the atmosphere. In addition, a qualitative\ndifference in the symmetry of the GHz radiation pattern is observed when\ncompared to the ones at lower frequencies. We also discuss the strong increase\nin the ground area subtended by the radio emission when going from\nnear-vertical to very inclined geometries, making very inclined air showers the\nmost promising ones for cosmic ray radio detection.", + "category": "astro-ph" + }, + { + "text": "Rest-frame UV single-epoch black hole mass estimates of low-luminosity\n AGN at intermediate redshifts: The ability to accurately derive black hole (BH) masses at progressively\nhigher redshifts and over a wide range of continuum luminosities has become\nindispensable in the era of large-area extragalactic spectroscopic surveys. In\nthis paper we present an extension of existing comparisons between rest-frame\nUV and optical virial BH mass estimators to intermediate redshifts and\nluminosities comparable to the local H$\\beta$ reverberation mapped active\ngalactic nuclei (AGN). We focus on the MgII, CIV, and CIII] broad emission\nlines and compare them to both H$\\alpha$ and H$\\beta$. We use newly acquired\nnear-infrared spectra from the FMOS instrument on the Subaru telescope for 89\nbroad-lined AGN at redshifts between 0.3 and 3.5, complemented by data from the\nAGES survey. We employ two different prescriptions for measuring the emission\nline widths and compare the results. We confirm that MgII shows a tight\ncorrelation with H$\\alpha$ and H$\\beta$, with a scatter of ~0.25 dex. The CIV\nand CIII] estimators, while showing larger scatter, are viable virial mass\nestimators after accounting for a trend with the UV-to-optical luminosity\nratio. We find an intrinsic scatter of ~0.37 dex between Balmer and carbon\nvirial estimators by combining our dataset with previous high redshift\nmeasurements. This updated comparison spans a total of 3 decades in BH mass. We\ncalculate a virial factor for CIV/CIII] logf(CIV/CIII])=0.87 with an estimated\nsystematic uncertainty of ~0.4 dex and find excellent agreement between the\nlocal reverberation mapped AGN sample and our high-z sample.", + "category": "astro-ph" + }, + { + "text": "Detrending algorithms in large time-series: Application to TFRM-PSES\n data: Certain instrumental effects and data reduction anomalies introduce\nsystematic errors in photometric time-series. Detrending algorithms such as the\nTrend Filtering Algorithm (TFA) (Kov\\'{a}cs et al. 2004) have played a key role\nin minimizing the effects caused by these systematics. Here we present the\nresults obtained after applying the TFA, Savitszky-Golay (Savitzky & Golay\n1964) detrending algorithms and the Box Least Square phase folding algorithm\n(Kov\\'{a}cs et al. 2002) to the TFRM-PSES data (Fors et al. 2013). Tests\nperformed on this data show that by applying these two filtering methods\ntogether, the photometric RMS is on average improved by a factor of 3-4, with\nbetter efficiency towards brighter magnitudes, while applying TFA alone yields\nan improvement of a factor 1-2. As a result of this improvement, we are able to\ndetect and analyze a large number of stars per TFRM-PSES field which present\nsome kind of variability. Also, after porting these algorithms to Python and\nparallelizing them, we have improved, even for large data samples, the\ncomputing performance of the overall detrending+BLS algorithm by a factor of\n$\\sim$10 with respect to Kov\\'{a}cs et al. (2004).", + "category": "astro-ph" + }, + { + "text": "Proper Motions of H2O Masers in the Water Fountain Source IRAS\n 19190+1102: We report on the results of two epochs of Very Long Baseline Array (VLBA)\nobservations of the 22 GHz water masers toward IRAS 19190+1102. The water maser\nemission from this object shows two main arc-shaped formations perpendicular to\ntheir NE-SW separation axis. The arcs are separated by ~280 mas in position,\nand are expanding outwards at an angular rate of 2.35 mas/yr. We detect maser\nemission at velocities between -53.3 km/s to +78.0 km/s and there is a distinct\nvelocity pattern where the NE masers are blueshifted and the SW masers are\nredshifted. The outflow has a three-dimensional outflow velocity of 99.8 km/s\nand a dynamical age of about 59 yr. A group of blueshifted masers not located\nalong the arcs shows a change in velocity of more than 35 km/s between epochs,\nand may be indicative of the formation of a new lobe. These observations show\nthat IRAS 19190+1102 is a member of the class of \"water fountain\"'\npre-planetary nebulae displaying bipolar structure", + "category": "astro-ph" + }, + { + "text": "Radio Relics in Clusters of Galaxies: In this paper we review the observational results on Relic radio sources in\nclusters of galaxies. We discuss their observational properties, structures and\nradio spectra. We will show that Relics can be divided according to their size,\nmorphology, and location in the galaxy cluster. These differences could be\nrelated to physical properties of Relic sources. The comparison with cluster\nconditions suggests that Relics could be related to shock waves originated by\ncluster mergers.", + "category": "astro-ph" + }, + { + "text": "Energy balance and Alfv\u00e9n Mach numbers in compressible\n magnetohydrodynamic turbulence with a large-scale magnetic field: Energy equipartition is a powerful theoretical tool for understanding\nastrophysical plasmas. It is invoked, for example, to measure magnetic fields\nin the interstellar medium (ISM), as evidence for small-scale turbulent dynamo\naction, and, in general, to estimate the energy budget of star-forming\nmolecular clouds. In this study we motivate and explore the role of the\nvolume-averaged root-mean-squared (rms) magnetic coupling term between the\nturbulent, $\\delta\\mathbf{B}$ and large-scale, $\\mathbf{B}_0$ fields, $\\left<\n(\\delta\\mathbf{B}\\cdot\\mathbf{B}_0)^{2} \\right>^{1/2}_{\\mathcal{V}}$. By\nconsidering the second moments of the energy balance equations we show that the\nrms coupling term is in energy equipartition with the volume-averaged turbulent\nkinetic energy for turbulence with a sub-Alfv\\'enic large-scale field. Under\nthe assumption of exact energy equipartition between these terms, we derive\nrelations for the magnetic and coupling term fluctuations, which provide\nexcellent, parameter-free agreement with time-averaged data from 280 numerical\nsimulations of compressible MHD turbulence. Furthermore, we explore the\nrelation between the turbulent, mean-field and total Alfv\\'en Mach numbers, and\ndemonstrate that sub-Alfv\\'enic turbulence can only be developed through a\nstrong, large-scale magnetic field, which supports an extremely\nsuper-Alfv\\'enic turbulent magnetic field. This means that the magnetic field\nfluctuations are significantly subdominant to the velocity fluctuations in the\nsub-Alfv\\'enic large-scale field regime. Throughout our study, we broadly\ndiscuss the implications for observations of magnetic fields and understanding\nthe dynamics in the magnetised ISM.", + "category": "astro-ph" + }, + { + "text": "Radio Emission from UV Cet: Auroral Emission from a Stellar\n Magnetosphere: The archetypical flare star UV Cet was observed by MeerKAT on 5-6 October\n2021. A large radio outburst with a duration of $\\sim\\!2$ hr was observed\nbetween 886-1682 MHz with a time resolution of 8s and a frequency resolution of\n0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is\ncharacterized by three peaks containing a multitude of broadband arcs or\npartial arcs in the time-frequency domain. In general, the arcs are highly\nright-hand circularly polarized. During end of the third peak, brief bursts\noccur that are significantly elliptically polarized. We present a simple model\nthat appears to be broadly consistent with the characteristics of the radio\nemission from UV Cet. Briefly, the stellar magnetic field is modeled as a\ndipole aligned with the rotational axis of the star. The radio emission\nmechanism is assumed to be due to the cyclotron maser instability where x-mode\nradiation near the electron gyrofrequency is amplified. While the elliptically\npolarized bursts may be intrinsic to the source, rather stringent limits are\nimposed on the plasma density in the source and along the propagation path. We\nsuggest that the elliptically polarized radiation may instead be the result of\nreflection on an over-dense plasma structure at some distance from the source.\nRadio emission from UV~Cet shares both stellar and planetary attributes.", + "category": "astro-ph" + }, + { + "text": "A multidimensional hydrodynamic code for structure evolution in\n cosmology: A cosmological multidimensional hydrodynamic code is described and tested.\nThis code is based on modern high-resolution shock-capturing techniques. It can\nmake use of a linear or a parabolic cell reconstruction as well as an\napproximate Riemann solver. The code has been specifically designed for\ncosmological applications. Two tests including shocks have been considered: the\nfirst one is a standard shock tube and the second test involves a spherically\nsymmetric shock. Various additional cosmological tests are also presented. In\nthis way, the performance of the code is proved. The usefulness of the code is\ndiscussed; in particular, this powerful tool is expected to be useful in order\nto study the evolution of the hot gas component located inside nonsymmetric\ncosmological structures.", + "category": "astro-ph" + }, + { + "text": "Statistical Analysis of Soft X-Ray Solar Flares During Solar Cycles 21,\n 22 and 23: This paper presents a statistical analysis of Soft X-ray (SXR) flares during\nthe period January 1976 to December 2007 covering solar cycles (SCs) 21, 22,\nand 23. We have analysed north-south (N-S) and east-west (E-W) asymmetry of SXR\nat low (less than equal to 40 degree), high (greater than equal to 50 degree)\nand total latitudes and center meridian distances (CMDs) respectively. We have\nalso presented the N-S and E-W asymmetry of different intensity classes (B, C,\nM, and X) during the period of investigation. A slight southern and eastern\nexcess is found after analysis during SC 21, 22, and 23. We found that the\nannual N-S and E-W hemispheric asymmetry at low latitudes and CMDs is the same\nas total latitudes and CMDs respectively. E-W asymmetry is different at low and\nhigh CMDs. Our statistical result shows that N-S asymmetry is statistically\nmore significant than E-W asymmetry. Total SXR flare activity during SC 23 is\nhigh compared to SC 21 and 22. The B class flare activity is higher for SC 23\nwhere as C, M and X class activities are higher for SC 21. We have also\nanalysied the flare evolution parameters, i.e. duration, rise time, decay time\nand event asymmetry for total SXR as well as for different classes for last\nthree SCs. The duration, rise time and decay time increase with increasing\nintensity class. On analysing event asymmetry indices, we found more positive\nvalues during SC 21 (64.86 per cent) and SC 22 (54.31 per cent), but for SC 23\nwe have more negative values (48.08 per cent). Our study shows that during SC\n23 we have more SXR flare events having shorter decay time as compared to SC 21\nand SC 22.", + "category": "astro-ph" + }, + { + "text": "Search for sub-millimeter H2O masers in active galaxies - the detection\n of a 321 GHz H2O maser in NGC4945: We present further results of a search for extragalactic submillimeter H2O\nmasers using the Atacama Large Millimeter/Submillimeter Array (ALMA). The\ndetection of a 321 GHz H2O maser in the nearby Type 2 Seyfert galaxy, the\nCircinus galaxy, has previously been reported, and here the spectral analysis\nof four other galaxies is described. We have discovered H2O maser emission at\n321 GHz toward the center of NGC 4945, a nearby Type 2 Seyfert. The maser\nemission shows Doppler-shifted velocity features with velocity ranges similar\nto those of the previously reported 22 GHz H2O masers, however the\nnon-contemporaneous observations also show differences in velocity offsets. The\nsub-parsec-scale distribution of the 22 GHz H2O masers revealed by earlier VLBI\n(Very Long Baseline Interferometry) observations suggests that the\nsubmillimeter masers could arise in an edge-on rotating disk. The maser\nfeatures remain unresolved by the synthesized beam of ~ 0.54 (~30 pc) and are\nlocated toward the 321 GHz continuum peak within errors. A marginally detected\n(3 sigma) high-velocity feature is redshifted by 579 km/s with respect to the\nsystemic velocity of the galaxy. Assuming that this feature is real and arises\nfrom a Keplerian rotating disk in this galaxy, it is located at a radius of\n~0.020 pc (~1.5 x 10^5 Schwarzschild radii), which would enable molecular\nmaterial closer to the central engine to be probed than the 22 GHz H2O masers.\nThis detection confirms that submillimeter H2O masers are a potential tracer of\nthe circumnuclear regions of active galaxies, which will benefit from higher\nangular resolution studies with ALMA.", + "category": "astro-ph" + }, + { + "text": "The effects of relativistic bulk motion of X-ray flares in the corona on\n the iron Kalpha line in Seyfert 1 galaxies: We study the effects of the bulk motion of X-ray flares on the shape and\nequivalent width of the iron Kalpha line from an untruncated cold disk around a\nKerr black hole using fully relativistic calculations. The flares are located\nabove a cold accretion disk -- either on or off the rotation axis. For on- or\noff-axis flares, the upward/outward bulk motion causes a reduction of the iron\nKalpha line width. To a distant observer with a low inclination angle (\\theta_o\n\\simlt 30deg.), larger upward/outward bulk velocities decrease the extension of\nthe red wing, with little change in the location of the blue `edge'. In\ncontrast, an observer at a large inclination angle (e.g. \\theta_o=60deg.) sees\nboth the red wing and the blue `edge' change with the bulk velocity. The\nequivalent width of the iron Kalpha line decreases rapidly with increasing bulk\nvelocity of flares. However, the `narrower' line profiles observed in some\nobjects (e.g. IC4329A and NGC4593) are difficult to produce using the\nout-flowing magnetic flare model with an appropriate equivalent width unless\nthe X-ray emission is concentrated in an outer region with a radius of several\ntens of r_g=GM/c^2 or more. An important result is that the iron Kalpha line\nintensity is found to be constant even though the continuum flux varies\nsignificantly, which is true for out-flowing magnetic flares with different\nbulk velocities but similar intrinsic luminosities when located close to the\ncentral black hole. We find that fluctuations in the bulk velocities of\nout-flowing low-height flares located at the inner region (r\\simlt 15r_g) can\naccount for a constant iron Kalpha line and significant continuum variation as\nobservered in MCG-6-30-15 and NGC5548. (Abridged)", + "category": "astro-ph" + }, + { + "text": "Statistical properties of flares and sunspots over the solar cycle: The present paper reviews results derived from statistical studies on solar\nactivity indices. The prolonged minimum phase of cycle 23 raised the question\nof peculiarities inherent in cycle 23. The most important solar activity index\nis the relative sunspot number and though most of other indices are closely\nrelated, shifts are obtained between their peak activity of the order of 1-2\nyears. These shifts reveal a 22-yr pattern which can be attributed to solar\ninterior or dynamo related processes. The minimum phase of cycle 23 is not\nfound to be exceptional. Investigating the relative sunspot numbers over the\npast 150 years, solar cycles of more prolonged minima are observed. Since 1920\nsolar activity is quite high ('modern maximum') and cycle 23 might be the\nherald of the end of this phase.", + "category": "astro-ph" + }, + { + "text": "Radiative and dynamic stability of a dilute plasma: We analyze the linear stability of a dilute, hot plasma, taking into account\nthe effects of stratification and anisotropic thermal conduction. The work is\nmotivated by attempts to understand the dynamics of the intracluster medium in\ngalaxy clusters. We show that magnetic field configurations that nominally\nstabilize either the heat-flux driven buoyancy instability (associated with a\npositive thermal gradient) or the magnetothermal instability (negative thermal\ngradient) can lead to previously unrecognized g-mode overstabilities. The\ndriving source of the overstability is either radiative cooling (positive\ntemperature gradient) or the heat flux itself (negative temperature gradient).\nWhile the implications of these overstabilities have yet to be explored, we\nspeculate that the cold fronts observed in many relaxed galaxy clusters may be\nrelated to their non-linear evolution.", + "category": "astro-ph" + }, + { + "text": "Intrinsic Instrumental Polarization and High-Precision Pulsar Timing: Radio telescopes are used to accurately measure the time of arrival (ToA) of\nradio pulses in pulsar timing experiments that target mostly millisecond\npulsars (MSPs) due to their high rotational stability. This allows for detailed\nstudy of MSPs and forms the basis of experiments to detect gravitational waves.\nApart from intrinsic and propagation effects, such as pulse-to-pulse jitter and\ndispersion variations in the interstellar medium, timing precision is limited\nin part by the following: polarization purity of the telescope's orthogonally\npolarized receptors, the signal-to-noise ratio (S/N) of the pulsar profile, and\nthe polarization fidelity of the system. Using simulations, we present how\nfundamental limitations in recovering the true polarization reduce the\nprecision of ToA measurements. Any real system will respond differently to each\nsource observed depending on the unique pulsar polarization profile. Using the\nprofiles of known MSPs we quantify the limits of observing system\nspecifications that yield satisfactory ToA measurements, and we place a\npractical design limit beyond which improvement of the system results in\ndiminishing returns. Our aim is to justify limits for the front-end\npolarization characteristics of next generation radio telescopes, leading to\nthe Square Kilometre Array (SKA).", + "category": "astro-ph" + }, + { + "text": "WIMP decay as a possible Warm Dark Matter model: The Weakly Interacting Massive Particles(WIMPs) have long been the favored\nCDM candidate in the standard $\\Lambda$CDM model. However, owing to great\nimprovement in the experimental sensitivity in the past decade, some parameter\nspace of the SUSY-based WIMP model is ruled out. In addition, WIMP as the CDM\nparticle is also at variance with other astrophysical observables at small\nscales. We consider a model that addresses both these issues. In the model, the\nWIMP decays into a massive particle and radiation. We study the background\nevolution and the first order perturbation theory (coupled Einstein-Boltzmann\nequations) for this model and show that the dynamics can be captured by a\nsingle parameter $r=m_L/q$, which is the ratio of the lighter mass and the\ncomoving momentum of the decay particle. We incorporate the relevant equations\nin the existing Boltzmann code CLASS to compute the matter power spectra and\nCMB angular power spectra. The decaying WIMP model is akin to a non-thermal\nWarm Dark Matter(WDM) model and suppresses matter power at small scales, which\ncould alleviate several issues that plague the CDM model. We compare the\npredictions of the model with CMB, galaxy clustering, and high-z HI data. Both\nthese data sets yield $r\\gtrsim 10^6$, which can be translated into the bounds\non other parameters. In particular, we obtain the following lower bounds on the\nthermally-averaged self-annihilation cross-section of WIMPs $\\langle \\sigma v\n\\rangle$, and the lighter mass $m_L$: $\\langle \\sigma v \\rangle \\gtrsim\n4.9\\times 10^{-34} \\, \\rm cm^3 \\, sec^{-1}$ and $m_L \\gtrsim 2.4 \\, \\rm keV$.\nThe lower limit on $m_L$ is comparable to constraints on the mass of\nthermally-produced WDM particle. The limit on the self-annihilation\ncross-section greatly expands the available parameter space as compared to the\nstable WIMP scenario.", + "category": "astro-ph" + }, + { + "text": "WMAP2006: Cosmological Parameters and Large-scale Structure of the\n Universe: The parameters of cosmological model with cold dark matter and cosmological\nconstant (Lambda CDM) have been determined on a basis of three-year cosmic\nmicrowave background observations by space mission WMAP, as well as the data on\nthe large-scale structure of the Universe. The data cover scales from 1 up to\n10000 Mpc. The best-fit values of LambdaCDM model parameters were found by\nminimization of chi^2 using the Levenberg-Markquardt approach\n(Omega_Lambda=0.736+-0.065, Omega_m=0.238+-0.080, Omega_b=0.05+-0.011, h=0.68+-\n0.09, sigma_8=0.73+-0.08 and n_s=0.96+-0.015). It is shown that the LambdaCDM\nmodel with these values of the parameters agrees well with the angular power\nspectrum of cosmic microwave background and with power spectra of the density\nperturbations, estimated from spatial distributions of galaxies, rich galaxy\nclusters and from statistics of Ly_alpha absorption lines in spectra of distant\nquasars as well. The accordance of modeled characteristics of the large-scale\nstructure with observable ones was analyzed, and possible reasons of\nsignificant discrepancies between some of them were considered.", + "category": "astro-ph" + }, + { + "text": "Numerical and analytical studies on model gravitating systems: In this thesis we study the evolution of systems of concentric shells\ninteracting gravitationally and in the process (1) propose and implement a\nnearly energy-conserving numerical integration scheme for evolving the\nconcentric spherical shells systems with 1024 particles or less; (2) look at\nthe possibility of chaos in few shell systems; and (3) study the evolution of\nmany shell systems in the Vlasov limit.\n The proposed numerical integration scheme is a nearly energy conserving\nhybrid of the Verlet and modified Euler-Cromer integration schemes.\n The rotational 2-shell spherical system is investigated in detail using the\nhybrid numerical integration scheme. Plots of time-series, phase space\nprojections, Poincare sections, power spectra, and Lyapunov exponents are\nobtained for the system. These diagnostic tools, taken together, clearly show\nthe chaotic nature of the rotational 2-shell system. Three types of periodic\norbits are observed: collapsed, one-point, and three-point periodic orbits. We\nbelieve that the three-point periodic orbits result from a rotation-induced\nbifurcation. Four types of quasiperiodic orbits are also observed. Three of\nthese are a result of slight changes in the initial conditions corresponding to\nthe three types of periodic orbits. The fourth type of quasiperiodic orbit\nseparates the chaotic region from the non-chaotic regions in phase space.\n The short-time evolution of collisionless spherical shells system is studied\nusing both numerical and analytical methods. Approximate expressions for the\nshort-time evolution of the collisionless rotational shells system are obtained\nusing Vlasov-Poisson perturbation theory in the high-virial limit. The\nagreement between the analytical results and numerical results for finite\nshells systems improves as the number of shells in the system increases.", + "category": "astro-ph" + }, + { + "text": "Spectral Survey of X-Ray Bright Active Galactic Nuclei from the Rossi\n X-ray Timing Explorer: Using long-term monitoring data from the Rossi X-ray Timing Explorer (RXTE),\nwe have selected 23 active galactic nuclei (AGN) with sufficient brightness and\noverall observation time to derive broadband X-ray spectra from 3 to >100 keV.\nOur sample includes mainly radio-quiet Seyferts, as well as seven radio-loud\nsources. Given the longevity of the RXTE mission, the greater part of our data\nis spread out over more than a decade, providing truly long-term average\nspectra and eliminating inconsistencies arising from variability. We present\nlong-term average values of absorption, Fe line parameters, Compton reflection\nstrengths and photon indices, as well as fluxes and luminosities for the hard\nand very hard energy bands, 2-10 keV and 20-100 keV respectively. We find\ntentative evidence for high-energy rollovers in three of our objects. We\nimprove upon previous surveys of the very hard X-ray energy band in terms of\naccuracy and sensitivity, particularly with respect to confirming and\nquantifying the Compton reflection component. This survey is meant to provide a\nbaseline for future analysis with respect to the long-term averages for these\nsources and to cement the legacy of RXTE, and especially its High Energy X-ray\nTiming Experiment, as a contributor to AGN spectral science.", + "category": "astro-ph" + }, + { + "text": "The Temporal Analysis of Light Pollution in Turkey using VIIRS data: Artificial Light pollution (AL) in Turkey and in Turkish observatories\nbetween 2012--2020 have been studied using the archival data of Visible\nInfrared Imaging Radiometer Suite (VIIRS) instrument. The astroGIS database has\nbeen used in processing the data (https://www.astrogis.org)\n\\cite{2020MNRAS.493.1204A}. The total energy released to space from Turkey\nincreased by 80\\% in 2019 with respect to 2012. In the span of the dataset, a\nsteady and continuous increase has been observed throughout all cities of the\ncountry. On the other hand, Dark Sky Park locations, East and Southeast\nAnatolian regions and mostly rural areas around the cities kept their AL level\nconstant. Four demographic parameters have been studied and they were found to\nbe correlated very well with AL: Population ($R \\simeq 0.90$); GDP ($R \\simeq\n0.87$); Total Power Consumption ($R \\simeq 0.66$) and Outdoor Lightening ($R\n\\simeq 0.67$). Contrary to countries acting to prevent AL increases, Turkey\nseems to be at the beginning of an era where AL will arithmetically increase\nthroughout the country and enormous amount of energy will continuously escape\nto space and therefore will be wasted. Therefore, a preventive legislation,\nespecially for invaluable astronomical site locations such as TURAG, TUG, DAG\nand \\c{C}AAM where each is counted as a truly dark site due to their SQM\nvalues, has to be enacted in Turkey, in very near future.", + "category": "astro-ph" + }, + { + "text": "The Imprint of Presupernova Winds on Supernova Remnant Evolution:\n Towards More Realistic Models for Type Ia Supernova Remnants and their\n Spectra: Supernova remnants are usually analysed in the light of hydrodynamical models\nof the interaction of supernova ejecta with either a constant density ambient\nmedium or a circumstellar medium produced by a constant presupernova wind.\nHowever, the ejection of energetic wind during the presupernova phase changes\nthe ambient medium structure and, consequently, the early supernova remnant\nevolution. We have analysed the evolution of young remnants of type Ia\nsupernovae, focusing on the imprint of the presupernova wind history on the\nsupernova remnant structure and on the influence of the explosion mechanism. We\nhave found that the remnant evolution is most sensitive to the explosion\nmechanism at ages not larger than a few hundred years, while the presupernova\nhistory shows its influence at later epochs, before the Sedov phase sets in.", + "category": "astro-ph" + }, + { + "text": "Formation of the Musca filament: Evidence for asymmetries in the\n accretion flow due to a cloud-cloud collision: Context. Dense molecular filaments are ubiquituous in the interstellar\nmedium, yet their internal physical conditions and formation mechanism remain\ndebated. Aims. We study the kinematics and physical conditions in the Musca\nfilament and the Chamaeleon-Musca complex to constrain the physics of filament\nformation. Methods. We produced CO(2-1) isotopologue maps with the APEX\ntelescope that cut through the Musca filament. We further study a NANTEN2\n$^{12}$CO(1-0) map of the Musca cloud and the HI emission of the\nChamaeleon-Musca complex. Results. The Musca cloud contains multiple velocity\ncomponents. Radiative transfer modelling of the CO emission indicates that the\nMusca filament consists of a cold ($\\sim$10 K), dense (n$_{H_2}\\sim$10$^4$\ncm$^{-3}$) crest, which is best described with a cylindrical geometry.\nConnected to the crest, a separate gas component at T$\\sim$15 K and\nn$_{H_2}\\sim$10$^3$ cm$^{-3}$ is found, the so-called strands. The filament\ncrest has a transverse velocity gradient that is linked to the kinematics of\nthe nearby ambient cloud. Studying the large scale kinematics, we find\ncoherence of the asymmetric kinematics from the 50 pc HI cloud down to the\nMusca filament. We also report a strong [C$^{18}$O]/[$^{13}$CO] abundance drop\nby an order of magnitude from the filament crest to the strands over a distance\n$<$ 0.2 pc in a weak far-ultraviolet (FUV) field. Conclusions. The dense Musca\nfilament crest is a long-lived (several crossing times), dynamic structure that\ncan form stars in the near future because of continuous mass accretion. This\nmass accretion appears to be triggered by a HI cloud-cloud collision, which\nbends the magnetic field around dense filaments. This bending of the magnetic\nfield is then responsible for the observed asymmetric accretion scenario of the\nMusca filament, which is, for instance, seen as a V-shape in the\nposition-velocity (PV) diagram.", + "category": "astro-ph" + }, + { + "text": "Joint analysis of EDGES $21$-cm line observations with standard candles\n and rulers in $\u039b$CDM and non-adiabatic gCg models: A decomposed generalised Chaplygin gas (gCg) with energy flux from dark\nenergy to dark matter, represented by a negative value for the gas parameter\n$\\alpha$, is shown to alleviate the tension between EDGES data and the\ncosmological standard model. Using EDGES data and employing a Bayesian\nstatistical analysis, the agreement with the standard model is only marginal.\nHowever, if $\\alpha$ is negative enough the gCg fits remarkably well the data,\neven in combination with SNe Ia datasets. On the other hand, when the CMB and\nBAO acoustic scales are included the preferred value for $\\alpha$ is near zero,\nimplying that a small deviation from $\\Lambda$CDM is predicted.", + "category": "astro-ph" + }, + { + "text": "Bisymmetric normal modes in soft-centred and realistic galactic discs: We test methods for the determination of unstable modes in stellar discs: a\npoint collocation scheme in the action sub-space, a scheme based on expansion\nof the density and potential on the biorthonormal basis, and a finite element\nmethod. Using models of galaxies with low and high mass concentration to the\ncenter, the existence of two different kinds of spectra of unstable modes is\ndemonstrated. Characteristic features of methods and obtained spectra are\ndiscussed.\n Despite ignoring any constraint on the continuity or differentiability of the\nperturbed DF, the collocation scheme is reliable for obtaining spectra and\npatterns in both kinds of models. The method based on the expansion of the\nperturbed potential and surface density over a biorthogonal basis was not\napplicable to a model with high mass concentration. The finite element method\nsuccessfully used in various fields of science and engineering is currently\nsensitive to the presence of resonant orbits due to the choice of interpolation\nfunctions for the distribution function.", + "category": "astro-ph" + }, + { + "text": "Cosmology with Modified Newtonian Dynamics (MOND): It is well-known that the application of Newtonian dynamics to an expanding\nspherical region leads to the correct relativistic expression (the Friedmann\nequation) for the evolution of the cosmic scale factor. Here, the cosmological\nimplications of Milgrom's modified Newtonian dynamics (MOND) are considered by\nmeans of a similar procedure. Earlier work by Felten demonstrated that in a\nregion dominated by modified dynamics, the expansion cannot be uniform\n(separations cannot be expressed in terms of a scale factor) and that any such\nregion will eventually re-collapse regardless of the initial expansion velocity\nand mean density. Here I show that, because of the acceleration threshold for\nthe MOND phenomenology, a region dominated by MOND will have a finite size\nwhich, in the early Universe ($z > 3$), is smaller than the horizon scale.\nTherefore, uniform expansion and homogeneity on horizon scale are consistent\nwith MOND-dominated non-uniform expansion and the development of\ninhomogeneities on smaller scale. In the radiation-dominated era, the amplitude\nof MOND-induced inhomogeneities is much smaller than that implied by\nobservations of the cosmic background radiation, and the thermal and dynamical\nhistory of the Universe is identical to that of the standard Big Bang. When\nmatter first dominates the energy density of the Universe, the cosmology\ndiverges from that of the standard model. Objects of galaxy mass are the first\nvirialized objects to form (by z=10) and larger structure develops rapidly. At\nthe present epoch, the Universe would be inhomogeneous out to a substantial\nfraction of the Hubble radius.", + "category": "astro-ph" + }, + { + "text": "Multi-wavelength observation of cosmic-ray air-showers with\n CODALEMA/EXTASIS: Since 2003, significant efforts have been devoted to the understanding of the\nradio emission of extensive air shower in the range [20-200] MHz. Despite some\nstudies led until the early nineties, the [1-10] MHz band has remained unused\nfor 20 years. However, it has been measured by some pioneering experiments that\nextensive air shower emit a strong electric field in this band and that there\nis evidence of a large increase in the amplitude of the radio pulse at lower\nfrequencies. The EXTASIS experiment, located within the Nan\\c{c}ay\nRadioastronomy Observatory and supported by the CODALEMA experiment, aims to\nreinvestigate the [1-10] MHz band, and especially to study the so-called\n\"Sudden Death\" contribution, the expected electric field emitted by shower\nfront when hitting the ground level. Currently, EXTASIS has confirmed some\nresults obtained by the pioneering experiments, and tends to bring explanations\nto the other ones, for instance the role of the underlying atmospheric electric\nfield. Moreover, CODALEMA has demonstrated that in the most commonly used\nfrequency band ([20-80] MHz) the electric field profile of EAS can be well\nsampled, and contains all the information needed for the reconstruction of EAS:\nan automatic comparison between the SELFAS3 simulations and data has been\ndeveloped, allowing us to reconstruct in an almost real time the primary cosmic\nray characteristics.", + "category": "astro-ph" + }, + { + "text": "Origin of the long-term modulation of radio emission of LS I +61 303: One of the most unusual aspects of the X-ray binary LSI +61 303 is that at\neach orbit (P1=26.4960 \\pm 0.0028 d) one radio outburst occurs whose amplitude\nis modulated with Plong, a long-term period of more than 4 yr. It is still not\nclear whether the compact object of the system or the companion Be star is\nresponsible for the long-term modulation. We study here the stability of Plong.\nSuch a stability is expected if Plong is due to periodic (P2) Doppler boosting\nof periodic (P1) ejections from the accreting compact object of the system. On\nthe contrary it is not expected if Plong is related to variations in the mass\nloss of the companion Be star. We built a database of 36.8 yr of radio\nobservations of LSI +61 303 covering more than 8 long-term cycles. We performed\ntiming and correlation analysis. In addition to the two dominant features at P1\nand P2, the timing analysis gives a feature at Plong=1628 \\pm 48 days. The\ndetermined value of Plong agrees with the beat of the two dominant features,\ni.e. Pbeat=1/(\\nu1 -\\nu2)=1626 \\pm 68 d. The correlation coefficient of the\nradio data oscillates at multiples of Pbeat. Cycles in varying Be stars change\nin length and disappear after 2-3 cycles following the well-studied case of the\nbinary system zeta Tau. On the contrary, in LSI +61 303 the long-term period is\nquite stable and repeats itself over the available 8 cycles. The long-term\nmodulation in LSI +61 303 accurately reflects the beat of periodical Doppler\nboosting (induced by precession) with the periodicity of the ejecta. The peak\nof the long-term modulation occurs at the coincidence of the maximum number of\nejected particles with the maximum Doppler boosting of their emission; this\ncoincidence occurs every 1/(\\nu1 - \\nu2) and creates the long-term modulation\nobserved in LSI +61 303.", + "category": "astro-ph" + }, + { + "text": "Fossil Signatures of Main-sequence Convective Core Overshoot Estimated\n through Asteroseismic Analyses: Some physical processes that occur during a star's main-sequence evolution\nalso affect its post main-sequence evolution. It is well known that stars with\nmasses above approximately 1.1 $M_{\\odot}$ have well-mixed convective cores on\nthe main sequence, however, the structure of the star in the neighborhood of\nthe convective core regions is currently underconstrained. We use\nasteroseismology to study the properties of the stellar core, in particular,\nconvective boundary mixing through convective overshoot, in such intermediate\nmass stars. These core regions are poorly constrained by the acoustic (p) mode\noscillations observed for cool main sequence stars. Consequently, we seek\nfossil signatures of main sequence core properties during the subgiant and\nearly first-ascent red giant phases of evolution. During these stages of\nstellar evolution, modes of mixed character that sample the deep interior, can\nbe observed. These modes sample the regions of the stars that are affected by\nthe main-sequence structure of these regions. We model the global and near-core\nproperties of 62 subgiant and early first-ascent red giant branch stars\nobserved by the \\textit{Kepler}, K2, and TESS space missions. We find that the\neffective overshoot parameter, $\\alpha_{\\text{ov, eff}}$, increases from $M =\n1.0M_{\\odot}$ to $M = 1.2 M_{\\odot}$ before flattening out, although we note\nthat the relationship between $\\alpha_{\\text{ov, eff}}$ and mass will depend on\nthe incorporated modelling choices of internal physics and nuclear reaction\nnetwork. We also situate these results within existing studies of main-sequence\nconvective core boundaries.", + "category": "astro-ph" + }, + { + "text": "Generation of High-Energy Photons at Ultra-Relativistic Shock Breakout\n in Supernovae: We present theoretical expectations for non-thermal emission due to the bulk\nComptonization at the ultra-relativistic shock breakout. We calculate the\ntransfer of photons emitted from the shocked matter with a Monte Carlo code\nfully taking into account special relativity. As a hydrodynamical model, we use\na self-similar solution of Nakayama & Shigeyama (2005). Our calculations reveal\nthat the spectral shape exhibits a double peak or a single peak depending on\nthe shock temperature at the shock breakout. If it is significantly smaller\nthan the rest energy of an electron, the spectrum has a double peak. We also\ndisplay a few example of light curves, and estimate the total radiation energy.\nIn comparison with observations of gamma-ray bursts, a part of the higher\nenergy component in the spectra and the total energy can be reproduced by some\nparameter sets. Meanwhile, the lower energy counterpart in the Band function is\nnot reproduced by our results and the duration time seems too short to\nrepresent the entire event of a gamma-ray burst. Therefore the subsequent phase\nwill constitute the lower energy part in the spectrum.", + "category": "astro-ph" + }, + { + "text": "A new class of pulsating hot subdwarfs: Using high-cadence observations from the Zwicky Transient Facility at low\nGalactic latitudes, we have discovered a new class of pulsating, hot, compact\nstars. We have found four candidates, exhibiting blue colors ($g-r\\leq-0.1$\nmag), pulsation amplitudes of $>5\\%$, and pulsation periods of $200 - 475$ sec.\nFourier transforms of the lightcurves show only one dominant frequency.\nPhase-resolved spectroscopy for three objects reveals significant radial\nvelocity, T$_{\\rm eff}$ and log(g) variations over the pulsation cycle,\nconsistent with large amplitude radial oscillations. The mean T$_{\\rm eff}$ and\nlog(g) for these stars are consistent with hot subdwarf B (sdB) effective\ntemperatures and surface gravities. We calculate evolutionary tracks using MESA\nand adiabatic pulsations using GYRE for low-mass helium-core pre-white dwarfs\nand low mass helium-burning stars. Comparison of low-order radial oscillation\nmode periods with the observed pulsation periods show better agreement with the\npre-white dwarf models. Therefore, we suggest that these new pulsators and Blue\nLarge-Amplitude Pulsators (BLAPs) could be members of the same class of\npulsators, composed of young $\\approx0.25-0.35$ M$_\\odot$ helium-core pre-white\ndwarfs.", + "category": "astro-ph" + }, + { + "text": "Understanding Radio-Selected Thermal Sources in M 33: Ultraviolet,\n Optical, Near-Infrared, Spitzer Mid-Infrared, and Radio Observations: We present ultraviolet, optical, near-infrared, Spitzer mid-infrared, and\nradio images of 14 radio-selected objects in M 33. These objects are thought to\nrepresent the youngest phase of star cluster formation. We have detected the\nmajority of cluster candidates in M 33 at all wavelengths. From the near-IR\nimages, we derived ages 2-10 Myr, K_S-band extinctions (A_K_S) of 0-1 mag, and\nstellar masses of 10^3-10^4 M_solar. We have generated spectral energy\ndistributions (SEDs) of each cluster from 0.1 micron to 160 microns. From these\nSEDs, we have modeled the dust emission around these star clusters to determine\nthe dust masses (1-10^3 M_solar) and temperatures (40-90 K) of the clusters'\nlocal interstellar medium. Extinctions derived from the JHK_S, Halpha, and UV\nimages are similar to within a factor of 2 or 3. These results suggest that\neleven of the fourteen radio-selected objects are optically-visible young star\nclusters with a surrounding H II region, that two are background objects,\npossibly AGN, and that one is a Wolf-Rayet star with a surrounding H II region.", + "category": "astro-ph" + }, + { + "text": "A star disrupted by a stellar black hole as the origin of the cloud\n falling toward the Galactic center: We propose that the cloud moving on a highly eccentric orbit near the central\nblack hole in our Galaxy, reported by Gillessen et al., is formed by a\nphotoevaporation wind originating in a disk around a star that is tidally\nperturbed and shocked at every peribothron passage. The disk is proposed to\nhave formed when a stellar black hole flew by the star, tidally disrupted its\nenvelope, and placed the star on its present orbit with some of the tidal\ndebris forming a disk. A disrupting encounter at the location of the observed\ncloud is most likely to be caused by a stellar black hole because of the\nexpected dynamical mass segregation; the rate of these disk-forming encounters\nmay be as high as $\\sim 10^{-6}$ per year. The star should also be spun up by\nthe encounter, so the disk may subsequently expand by absorbing angular\nmomentum from the star. Once the disk expands up to the tidal truncation\nradius, the tidal perturbation of the outer disk edge at every peribothron may\nplace gas streams on larger orbits which can give rise to a photoevaporation\nwind that forms the cloud at every orbit. This model predicts that, after the\ncloud is disrupted at the next peribothron passage in 2013, a smaller\nunresolved cloud will gradually grow around the star on the same present orbit.\nAn increased infrared luminosity from the disk may also be detectable when the\nperibothron is reached. We also note that this model revives the encounter\ntheory for planet formation.", + "category": "astro-ph" + }, + { + "text": "Coronal Polarization: We present an overview of the physical mechanisms responsible for the coronal\npolarization at different wavelength regimes. We also review different\ntechniques using coronal polarization to determine various quantities necessary\nfor understanding the thermodynamic properties of the solar coronal plasma.\nThis includes the coronal magnetic field, electronic densities, temperatures,\nvelocities, etc. The future needs to acquire better information on the solar\ncorona using polarization will be outlined.", + "category": "astro-ph" + }, + { + "text": "Improving convergence in smoothed particle hydrodynamics simulations\n without pairing instability: The numerical convergence of smoothed particle hydrodynamics (SPH) can be\nseverely restricted by random force errors induced by particle disorder,\nespecially in shear flows, which are ubiquitous in astrophysics. The increase\nin the number NH of neighbours when switching to more extended smoothing\nkernels at fixed resolution (using an appropriate definition for the SPH\nresolution scale) is insufficient to combat these errors. Consequently, trading\nresolution for better convergence is necessary, but for traditional smoothing\nkernels this option is limited by the pairing (or clumping) instability.\nTherefore, we investigate the suitability of the Wendland functions as\nsmoothing kernels and compare them with the traditional B-splines. Linear\nstability analysis in three dimensions and test simulations demonstrate that\nthe Wendland kernels avoid the pairing instability for all NH, despite having\nvanishing derivative at the origin (disproving traditional ideas about the\norigin of this instability; instead, we uncover a relation with the kernel\nFourier transform and give an explanation in terms of the SPH density\nestimator). The Wendland kernels are computationally more convenient than the\nhigher-order B-splines, allowing large NH and hence better numerical\nconvergence (note that computational costs rise sub-linear with NH). Our\nanalysis also shows that at low NH the quartic spline kernel with NH ~= 60\nobtains much better convergence then the standard cubic spline.", + "category": "astro-ph" + }, + { + "text": "Large Inverse Transient Phase Response of Titanium-nitride-based\n Microwave Kinetic Inductance Detectors: Following optical pulses ($\\lambda=405~\\text{nm}$) on titanium nitride (TiN)\nMicrowave Kinetic Inductance Detectors (MKIDs) cooled down at temperatures $T\n\\le T_c / 20$ ($T_c \\simeq 4.6~\\text{K}$), we observe a large phase-response\nhighlighting two different modes simultaneously that are nevertheless related.\nThe first corresponds to the well-known transition of cooper-pair breaking into\nquasi-particles which produces a known phase response. This is immediately\nfollowed by a large inverse response lasting several hundreds of microseconds\nto several milliseconds depending on the temperature. We propose to model this\ninverse pulse as the thermal perturbation of the superconductor and interaction\nwith two level system (TLS) that reduces the dielectric constant which in turns\nmodify the capacitance and therefore the resonance frequency. The ratio of the\nTLS responding to the illumination is on the order of that of the area of the\ninductor to the whole resonator", + "category": "astro-ph" + }, + { + "text": "Hydrodynamics of Embedded Planets' First Atmospheres. I. A Centrifugal\n Growth Barrier for 2D Flows: In the core accretion paradigm of planet formation, gas giants only form a\nmassive atmosphere after their progenitors exceeded a threshold mass: the\ncritical core mass. Most (exo)planets, being smaller and rock/ice-dominated,\nnever crossed this line. Nevertheless, they were massive enough to attract\nsubstantial amounts of gas from the disc, while their atmospheres remained in\npressure-equilibrium with the disc. Our goal is to characterise the\nhydrodynamical properties of the atmospheres of such embedded planets and their\nimplication for their (long-term) evolution. In this paper -- the first in\nseries -- we start to investigate the properties of an isothermal and inviscid\nflow past a small, embedded planet by conducting local, 2D hydrodynamical\nsimulations. Using the PLUTO code we confirm that the flow is steady and bound.\nThis steady outcome is most apparent for the log-polar grid (with the grid\nspacing proportional to the distance from the planet). For low-mass planets,\nCartesian grids are somewhat less efficient as they have difficulty to follow\nthe circular, large speeds in the deep atmosphere. Relating the amount of\nrotation to the gas fraction of the atmosphere, we find that more massive\natmospheres rotate faster -- a finding consistent with Kelvin's circulation\ntheorem. Rotation therefore limits the amount of gas that planets can acquire\nfrom the nebula. Dependent on the Toomre-Q parameter of the circumstellar disc,\nthe planet's atmosphere will reach Keplerian rotation before self-gravity\nstarts to become important.", + "category": "astro-ph" + }, + { + "text": "Stellar collisions in galactic centers: black hole growth and color\n gradients: We study the effects of stellar collisions, particularly on feeding massive\nblack holes (BHs) and color gradients, in realistic galactic centers. We find\nthat the mass released by stellar collisions is not sufficient to account for\nthe present BH mass in galactic centers, especially in bright galaxies. This\nstudy, together with the study by Magorrian & Tremaine (1999) on tidal\ndisruption of stars by massive BHs, implies that the material for BH growth\n(especially in galaxies brighter than ~10^9 Lsun) can only come from other\nsources, for example, the mass released by stellar evolution in the initial ~1\nGyr of the galaxy's lifetime, or the gas that sinks to the galactic center in a\ngalaxy merger. We also analyze how the color of a stellar system is affected by\ncollisions of stars. We find that collisions between main-sequence stars cannot\ncause observable color gradients in the visible bands at projected radius\nR>0.1\" in M31, M32 and other nearby galactic centers. This result is consistent\nwith the lack of an observable color gradient in M32 at R>0.1\". At even smaller\nradii, the color differences caused by collisions between main-sequence stars\nare at most 0.08 mag at R=0.02\". The averaged blueing due to stellar collisions\nin the region R<0.1\" of M32 should not be larger than 0.06 mag in color index\nU-V and 0.02 mag in V-I. The observed blueing in the center of the galaxy M31\n(in a 0.14\"x0.14\" box) must be caused by some mechanism other than collisions\nbetween main-sequence stars.", + "category": "astro-ph" + }, + { + "text": "Decaying dark matter search with NuSTAR deep sky observations: We present the results of the search for decaying dark matter with particle\nmass in the 6-40 keV range with NuSTAR deep observations of COSMOS and ECDFS\nempty sky fields. We show that main contribution to the decaying dark matter\nsignal from the Milky Way galaxy comes through the aperture of the NuSTAR\ndetector, rather than through the focusing optics. High sensitivity of the\nNuSTAR detector, combined with the large aperture and large exposure times of\nthe two observation fields allow us to improve previously existing constraints\non the dark matter decay time by up to an order of magnitude in the mass range\n10-30 keV. In the particular case of the nuMSM sterile neutrino dark matter,\nour constraints impose an upper bound m<20 keV on the dark matter particle\nmass. We report detection of four unidentified spectral lines in our data set.\nThese line detections are either due to the systematic effects (uncertainties\nof calibrations of the NuSTAR detectors) or have an astrophysical origin. We\ndiscuss different possibilities for testing the nature of the detected lines.", + "category": "astro-ph" + }, + { + "text": "HST Imaging in the Chandra Deep Field South: I. Multiple AGN Populations: We present preliminary results from imaging three HST/WFPC2 fields in V and I\nwithin the Chandra Deep Field South (CDFS). HST's sensitivity and resolution\nare sufficient to reveal optical counterparts for 24 of the 26 CDFS X-ray\nsources detected in the 300 ksec X-ray catalog and to determine the\nmorphologies of most of these. We find that the X-ray sources comprise two\napparently distinct populations of optical candidates: one optically faint (I >\n24) with V - I colors consistent with the I > 24 field population; the other\nsignificantly brighter (I < 22) with colors redder than the I < 22 field\npopulation. More than 2/3 of the X-ray source counterparts are resolved\ngalaxies. The brighter sources are mostly AGN, based on their high X-ray\nluminosity. The optically resolved sources in the brighter population have a\nvery narrow range of V - I color and appear to be a mix of both late and early\ntype morphologies at low to moderate redshift. We show that the second\npopulation, with fainter optical counterparts, can be explained as higher\nredshift Type 2 AGN.", + "category": "astro-ph" + }, + { + "text": "Modelling extragalactic extinction through gamma-ray burst afterglows: We analyze extragalactic extinction profiles derived through gamma-ray burst\nafterglows, using a dust model specifically constructed on the assumption that\ndust grains are not immutable but respond time-dependently to the local\nphysics. Such a model includes core-mantle spherical particles of mixed\nchemical composition (silicate core, sp2 and sp3 carbonaceous layers), and an\nadditional molecular component, in the form of free-flying polycyclic aromatic\nhydrocarbons. We fit most of the observed extinction profiles. Failures occur\nfor lines of sight presenting remarkable rises blueward the bump. We find a\ntendency in the carbon chemical structure to become more aliphatic with the\ngalactic activity, and to some extent with increasing redshifts. Moreover, the\ncontribution of the moleclar component to the total extinction is more\nimportant in younger objects. The results of the fitting procedure (either\nsuccesses and failures) may be naturally interpreted through an evolutionary\nprescription based on the carbon cycle in the interstellar medium of galaxies.", + "category": "astro-ph" + }, + { + "text": "Likelihood Methods for the Detection and Characterization of Gamma-ray\n Pulsars with the Fermi Large Area Telescope: The sensitivity of the Large Area Telescope (LAT) aboard the Fermi Gamma-ray\nSpace Telescope allows detection of thousands of new gamma-ray sources and\ndetailed characterization of the spectra and variability of bright sources.\nUnsurprisingly, this increased capability leads to increased complexity in data\nanalysis. Likelihood methods are ideal for connecting models with data, but the\ncomputational cost of folding the model input through the multi-scale\ninstrument response function is appreciable. Both interactive analysis and\nlarge projects---such as analysis of the full gamma-ray sky---can be\nprohibitive or impossible, reducing the scope of the science possible with the\nLAT. To improve on this situation, we have developed pointlike, a software\npackage for fast maximum likelihood analysis of LAT data. It is interactive by\ndesign and its rapid evaluation of the likelihood facilitates exploratory and\nlarge-scale, all-sky analysis. We detail its implementation and validate its\nperformance on simulated data. We demonstrate its capability for interactive\nanalysis and present several all-sky analyses. These include a search for new\ngamma-ray sources and the selection of LAT sources with pulsar-like\ncharacteristics for targeted radio pulsation searches. We conclude by\ndeveloping sensitive periodicity tests incorporating spectral information\nobtained from pointlike.", + "category": "astro-ph" + }, + { + "text": "Astroinformatics based search for globular clusters in the Fornax Deep\n Survey: In the last years, Astroinformatics has become a well defined paradigm for\nmany fields of Astronomy. In this work we demonstrate the potential of a\nmultidisciplinary approach to identify globular clusters (GCs) in the Fornax\ncluster of galaxies taking advantage of multi-band photometry produced by the\nVLT Survey Telescope using automatic self-adaptive methodologies. The data\nanalyzed in this work consist of deep, multi-band, partially overlapping images\ncentered on the core of the Fornax cluster. In this work we use a Neural-Gas\nmodel, a pure clustering machine learning methodology, to approach the GC\ndetection, while a novel feature selection method ($\\Phi$LAB) is exploited to\nperform the parameter space analysis and optimization. We demonstrate that the\nuse of an Astroinformatics based methodology is able to provide GC samples that\nare comparable, in terms of purity and completeness with those obtained using\nsingle band HST data (Brescia et al. 2012) and two approaches based\nrespectively on a morpho-photometric (Cantiello et al. 2018b) and a PCA\nanalysis (D'Abrusco et al. 2015) using the same data discussed in this work.", + "category": "astro-ph" + }, + { + "text": "Significance for signal changes in gamma-ray astronomy: We describe a straightforward modification of frequently invoked methods for\nthe determination of the statistical significance of a gamma-ray signal\nobserved in a counting process. A simple criterion is proposed to decide\nwhether a set of measurements of the numbers of photons registered in the\nsource and background regions is consistent with the assumption of a constant\nsource activity. This method is particularly suitable for immediate evaluation\nof the stability of the observed gamma-ray signal. It is independent of the\nexposure estimates, reducing thus the impact of systematic inaccuracies, and\nproperly accounts for the fluctuations in the number of detected photons. The\nusefulness of the method is demonstrated on several examples. We discuss\nintensity changes for gamma-ray emitters detected at very high energies by the\ncurrent gamma-ray telescopes (e.g. 1ES 0229+200, 1ES 1959+650 and PG 1553+113).\nSome of the measurements are quantified to be exceptional with large\nstatistical significances.", + "category": "astro-ph" + }, + { + "text": "Evidence of residual Doppler shift on three pulsars, PSR B1259-63,\n 4U1627-67 and PSR J2051-0827: The huge derivative of orbital period observed in binary pulsar PSR B1259-63,\nthe torque reversal displaying on low mass X-ray binary, 4U1627-67 and the long\nterm change of orbital period of PSR J2051-0827, seem totally unrelated\nphenomena occurring at totally different pulsar systems. In this paper, they\nare simply interpreted by the same mechanism, residual Doppler shift. In a\nbinary system with periodic signals sending to an observer, the drift of the\nsignal frequency actually changes with the varying orbital velocity, projected\nto line of sight at different phases of orbit. And it has been taken for\ngranted that the net red-shift and blue-shift of an full orbit circle be\ncancelled out, so that the effect of Doppler shift to the signal in binary\nmotion cannot be accumulated over the orbital period. However, taking the\npropagation time at each velocity state into account, the symmetry of the\nvelocity distribution over the orbital phase is broken. Consequently, the net\nDoppler shift left in an orbit is non-zero. Understanding this Newtonian second\nDoppler effect not only makes pulsars better laboratory in the test of\ngravitational effects, but also allows us to extract the angular momentum of\nthe pulsar of PSR J2051-0827, $\\leq 2\\times 10^{43}gcm^2$; and the accretion\ndisc of 4U 1627-67, $7\\times 10^{50} gcm^2/s$, respectively, which are of\nimportance in the study of structure of neutron stars and the physics of\naccretion disc of X-ray binaries.", + "category": "astro-ph" + }, + { + "text": "The small observed scale of AGN--driven outflows, and inside--out disc\n quenching: Observations of massive outflows with detectable central AGN typically find\nthem within radii $\\lesssim 10$ kpc. We show that this apparent size\nrestriction is a natural result of AGN driving if this process injects total\nenergy only of order the gas binding energy to the outflow, and the AGN varies\nover time (`flickers') as suggested in recent work. After the end of all AGN\nactivity the outflow continues to expand to larger radii, powered by the\nthermal expansion of the remnant shocked AGN wind. We suggest that on average,\noutflows should be detected further from the nucleus in more massive galaxies.\nIn massive gas--rich galaxies these could be several tens of kpc in radius. We\nalso consider the effect that pressure of such outflows has on a galaxy disc.\nIn moderately gas--rich discs, with gas-to-baryon fraction $< 0.2$, the outflow\nmay induce star formation significant enough to be distinguished from quiescent\nby an apparently different normalisation of the Kennicutt-Schmidt law. The star\nformation enhancement is probably stronger in the outskirts of galaxy discs, so\ncoasting outflows might be detected by their effects upon the disc even after\nthe driving AGN has shut off. We compare our results to the recent inference of\ninside--out quenching of star formation in galaxy discs.", + "category": "astro-ph" + }, + { + "text": "The state of globular clusters at birth II: primordial binaries: (abridged) In this paper, we constrain the properties of primordial binary\npopulations in Galactic globular clusters using the MOCCA Monte Carlo code for\ncluster evolution. Our results are compared to the observations of Milone et\nal. (2012) using the photometric binary populations as proxies for the true\nunderlying distributions, in order to test the hypothesis that the data are\nconsistent with an universal initial binary fraction near unity and the binary\norbital parameter distributions of Kroupa (1995). With the exception of a few\npossible outliers, we find that the data are to first-order consistent with the\nuniversality hypothesis. Specifically, the present-day binary fractions inside\nthe half-mass radius r$_{\\rm h}$ can be reproduced assuming either high initial\nbinary fractions near unity with a dominant soft binary component as in the\nKroupa distribution combined with high initial densities (10$^4$-10$^6$\nM$_{\\odot}$ pc$^{-3}$), or low initial binary fractions ($\\sim$ 5-10%) with a\ndominant hard binary component combined with moderate initial densities near\ntheir present-day values (10$^2$-10$^3$ M$_{\\odot}$ pc$^{-3}$). This apparent\ndegeneracy can be broken using the binary fractions outside r$_{\\rm h}$- only\nhigh initial binary fractions with a significant soft component combined with\nhigh initial densities can contribute to reproducing the observed\nanti-correlation between the binary fractions outside r$_{\\rm h}$ and the total\ncluster mass. We further illustrate using the simulated present-day binary\norbital parameter distributions and the technique introduced in Leigh et al.\n(2012) that the relative fractions of hard and soft binaries can be used to\nfurther constrain the initial cluster density and mass-density relation. Our\nresults favour an initial mass-density relation of the form r$_{\\rm h} \\propto$\nM$_{\\rm clus}^{\\alpha}$ with $\\alpha <$ 1/3.", + "category": "astro-ph" + }, + { + "text": "Kinematic evolution of the young local associations and the Sco-Cen\n complex: In this work we propose a scenario for the history of the recent star\nformation (during the last 20-30 Myr) in the nearest solar neighbourhood (~150\npc), from the study of the spatial and kinematic properties of the members of\nthe so-called young local associations, the Sco-Cen complex and the Local\nBubble, the most important structure observed in the local interstellar medium\n(ISM).", + "category": "astro-ph" + }, + { + "text": "Science Highlights from VERITAS: The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a\nground-based array located at the Fred Lawrence Whipple Observatory in southern\nArizona and is one of the world's most sensitive gamma-ray instruments at\nenergies of 85 GeV to $>$30 TeV. VERITAS has a wide scientific reach that\nincludes the study of extragalactic and Galactic objects as well as the search\nfor astrophysical signatures of dark matter and the measurement of cosmic rays.\nIn this paper, we will summarize the current status of the VERITAS observatory\nand present some of the scientific highlights from the last two years, focusing\nin particular on those results shown at the 2015 ICRC in The Hague,\nNetherlands.", + "category": "astro-ph" + }, + { + "text": "CMB Polarization can constrain cosmology better than CMB temperature: We demonstrate that for a cosmic variance limited experiment, CMB E\npolarization alone places stronger constraints on cosmological parameters than\nCMB temperature. For example, we show that EE can constrain parameters better\nthan TT by up to a factor 2.8 when a multipole range of l=30-2500 is\nconsidered. We expose the physical effects at play behind this remarkable\nresult and study how it depends on the multipole range included in the\nanalysis. In most relevant cases, TE or EE surpass the TT based cosmological\nconstraints. This result is important as the small scale astrophysical\nforegrounds are expected to have a much reduced impact on polarization, thus\nopening the possibility of building cleaner and more stringent constraints of\nthe LCDM model. This is relevant specially for proposed future CMB satellite\nmissions, such as CORE or PRISM, that are designed to be cosmic variance\nlimited in polarization till very large multipoles. We perform the same\nanalysis for a Planck-like experiment, and conclude that even in this case TE\nalone should determine the constraint on $\\Omega_ch^2$ better than TT by 15%,\nwhile determining $\\Omega_bh^2$, $n_s$ and $\\theta$ with comparable accuracy.\nFinally, we explore a few classical extensions of the LCDM model and show again\nthat CMB polarization alone provides more stringent constraints than CMB\ntemperature in case of a cosmic variance limited experiment.", + "category": "astro-ph" + }, + { + "text": "Intra Cluster Light properties in the CLASH-VLT cluster MACS\n J1206.2-0847: We aim at constraining the assembly history of clusters by studying the intra\ncluster light (ICL) properties, estimating its contribution to the fraction of\nbaryons in stars, f*, and understanding possible systematics/bias using\ndifferent ICL detection techniques. We developed an automated method, GALtoICL,\nbased on the software GALAPAGOS to obtain a refined version of typical BCG+ICL\nmaps. We applied this method to our test case MACS J1206.2-0847, a massive\ncluster located at z=0.44, that is part of the CLASH sample. Using deep\nmulti-band SUBARU images, we extracted the surface brightness (SB) profile of\nthe BCG+ICL and we studied the ICL morphology, color, and contribution to f*\nout to R500. We repeated the same analysis using a different definition of the\nICL, SBlimit method, i.e. a SB cut-off level, to compare the results. The most\npeculiar feature of the ICL in MACS1206 is its asymmetric radial distribution,\nwith an excess in the SE direction and extending towards the 2nd brightest\ncluster galaxy which is a Post Starburst galaxy. This suggests an interaction\nbetween the BCG and this galaxy that dates back to t <= 1.5 Gyr. The BCG+ICL\nstellar content is 8% of M_(*,500) and the (de-) projected baryon fraction in\nstars is f*=0.0177 (0.0116), in excellent agreement with recent results. The\nSBlimit method provides systematically higher ICL fractions and this effect is\nlarger at lower SB limits. This is due to the light from the outer envelopes of\nmember galaxies that contaminate the ICL. Though more time consuming, the\nGALtoICL method provides safer ICL detections that are almost free of this\ncontamination. This is one of the few ICL study at redshift z > 0.3. At\ncompletion, the CLASH/VLT program will allow us to extend this analysis to a\nstatistically significant cluster sample spanning a wide redshift range:\n0.2 0.02 in virtually all blue HB stars. Using\nhigh-precision Stroemgren photometry and spectroscopic gravities for blue HB\nstars, we find that any helium enhancement among most of the cluster's blue HB\nstars is very likely less than 0.01, thus ruling out the much higher helium\nenhancements that have been proposed in the literature.", + "category": "astro-ph" + }, + { + "text": "Is there a polarization horizon?: Modern radio spectrometers make measurement of polarized intensity as a\nfunction of Faraday depth possible. I investigate the effect of depolarization\nalong a model line of sight. I model sightlines with two components informed by\nobservations: a diffuse interstellar medium with a lognormal electron density\ndistribution and a narrow, denser component simulating a spiral arm or H~{\\sc\nii} region, all with synchrotron-emitting gas mixed in. I then calculate the\npolarized intensity from 300-1800~MHz and calculate the resulting Faraday depth\nspectrum. The idealized synthetic observations show far more Faraday complexity\nthan is observed in Global Magneto-Ionic Medium Survey observations. In a model\nwith a very nearby H~{\\sc ii} region observed at low frequencies, most of the\neffects of a \"depolarization wall\" are evident: the H~{\\sc ii} region\ndepolarizes background emission and less (but not zero) information from beyond\nthe H~{\\sc ii} region reaches the observer. In other cases, the effects are not\nso clear, as significant amounts of information reach the observer even through\nsignificant depolarization, and it is not clear that low-frequency observations\nsample largely different volumes of the interstellar medium than high-frequency\nobservations. The observed Faraday depth can be randomized such that it does\nnot always have any correlation with the true Faraday depth.", + "category": "astro-ph" + }, + { + "text": "Asteroseismic modeling of gravity modes in slowly rotating A/F stars\n with radiative levitation: It has been known for several decades that transport of chemical elements is\ninduced by the process of microscopic atomic diffusion. Yet, the effect of\natomic diffusion, including radiative levitation, has hardly been studied in\nthe context of gravity mode pulsations of core-hydrogen burning stars. In this\npaper, we study the difference in the properties of such modes for models with\nand without atomic diffusion. We perform asteroseismic modeling of two slowly\nrotating A- and F-type pulsators, KIC11145123 ($f_{\\rm rot} \\approx0.010~{\\rm\nd}^{-1}$) and KIC9751996 ($f_{\\rm rot} \\approx0.0696~{\\rm d}^{-1}$),\nrespectively, based on the periods of individual gravity modes. For both stars,\nwe find models whose g-mode periods are in very good agreement with the {\\it\nKepler\\/} asteroseismic data, keeping in mind that the theoretical/numerical\nprecision of present-day stellar evolution models is typically about two orders\nof magnitude lower than the measurement errors. Using the Akaike Information\nCriterion (AIC) we have made a comparison between our best models with and\nwithout diffusion, and found very strong evidence for signatures of atomic\ndiffusion in the pulsations of KIC11145123. In the case of KIC9751996 the\nmodels with atomic diffusion are not able to explain the data as well as the\nmodels without it. Furthermore, we compare the observed surface abundances with\nthose predicted by the best fitting models. The observed abundances are\ninconclusive for KIC9751996, while those of KIC11145123 from the literature can\nbetter be explained by a model with atomic diffusion.", + "category": "astro-ph" + }, + { + "text": "The Mexican Million Models Database: a virtual observatory for gaseous\n nebulae: The 3MdB (Mexican Million Models database) is a large database of\nphotoionization models for H II regions. The number of free parameters for the\nmodels is close to 15, including the description of the ionizing Spectral\nEnergy Distribution (effective temperature, luminosity, surface gravity, for\ndifferent type of stellar atmosphere models) and the description of the ionized\ngas (distance to the ionizing source, density, abundances of the most common\nelements, dust). The outputs of the models are more than 70 emission line\nintensities, the ionic fractions and temperatures. All the parameters and\noutputs are included in the MySQL database, giving the possibility to the user\nto search into the database for example for all the models that reproduce a\ngiven set of observations.", + "category": "astro-ph" + }, + { + "text": "Probing the magnetosphere of the M8.5 dwarf TVLM513-46546 by modelling\n its auroral radio emission. Hint of star exoplanet interaction?: In this paper we simulate the cyclic circularly-polarised pulses of the\nultra-cool dwarf TVLM513-46546, observed with the VLA at 4.88 and 8.44 GHz on\nMay 2006, by using a 3D model of the auroral radio emission from the stellar\nmagnetosphere. During this epoch, the radio light curves are characterised by\ntwo pulses left-hand polarised at 4.88 GHz, and one doubly-peaked (of opposite\npolarisations) pulse at 8.44 GHz. To take into account the possible deviation\nfrom the dipolar symmetry of the stellar magnetic field topology, the model\ndescribed in this paper is also able to simulate the auroral radio emission\nfrom a magnetosphere shaped like an offset-dipole. To reproduce the timing and\npattern of the observed pulses, we explored the space of parameters controlling\nthe auroral beaming pattern and the geometry of the magnetosphere. Through the\nanalysis of the TVLM513-46546 auroral radio emission, we derive some\nindications on the magnetospheric field topology that is able to simultaneously\nreproduce the timing and patterns of the auroral pulses measured at 4.88 and\n8.44 GHz. Each set of model solutions simulates two auroral pulses (singly or\ndoubly peaked) per period. To explain the presence of only one 8.44 GHz pulse\nper period, we analyse the case of auroral radio emission limited only to a\nmagnetospheric sector activated by an external body, like the case of the\ninteraction of Jupiter with its moons.", + "category": "astro-ph" + }, + { + "text": "Magnetic flux emergence in fast rotating stars: Fast rotating cool stars are characterised by high magnetic activity levels\nand frequently show dark spots up to polar latitudes. Their distinctive surface\ndistributions of magnetic flux are investigated in the context of the\nsolar-stellar connection by applying the solar flux eruption and surface flux\ntransport models to stars with different rotation rates, mass, and evolutionary\nstage. The rise of magnetic flux tubes through the convection zone is primarily\nbuoyancy-driven, though their evolution can be strongly affected by the\nCoriolis force. The poleward deflection of the tube's trajectory increases with\nthe stellar rotation rate, which provides an explanation for magnetic flux\neruption at high latitudes. The formation of proper polar spots likely requires\nthe assistance of meridional flows both before and after the eruption of\nmagnetic flux on the stellar surface. Since small radiative cores support the\neruption of flux tubes at high latitudes, low-mass pre-main sequence stars are\npredicted to show high mean latitudes of flux emergence. In addition to flux\neruption at high latitudes, main sequence components of close binary systems\nshow spot distributions which are non-uniform in longitude. Yet these\n`preferred longitudes' of flux eruption are expected to vanish beyond a certain\npost-main sequence evolutionary stage.", + "category": "astro-ph" + }, + { + "text": "Gemini Near-Infrared Field Spectrograph Observations of the Seyfert 2\n Galaxy Mrk 3: Feeding and Feedback on Galactic and Nuclear Scales: We explore the kinematics of the stars, ionized gas, and warm molecular gas\nin the Seyfert 2 galaxy Mrk~3 (UGC~3426) on nuclear and galactic scales with\n{\\it Gemini} Near-Infrared Field Spectrograph (NIFS) observations, previous\n{\\it Hubble Space Telescope} data, and new long-slit spectra from the {\\it\nApache Point Observatory} ({\\it APO}) 3.5 m telescope. The {\\it APO} spectra\nare consistent with our previous suggestion that a galactic-scale gas/dust disk\nat PA $=$ 129\\arcdeg, offset from the major axis of the host S0 galaxy at PA\n$=$ 28\\arcdeg, is responsible for the orientation of the extended narrow-line\nregion (ENLR). The disk is fed by an H~I tidal stream from a gas-rich spiral\ngalaxy (UGC~3422) $\\sim$100 kpc to the NW of Mrk 3, and is ionized by the AGN\nto a distance of at least $\\sim$20\\arcsec\\ ($\\sim$5.4 kpc) from the central\nsupermassive black hole (SMBH). The kinematics within at least 320 pc of the\nSMBH are dominated by outflows with radial (line of sight) velocities up to\n1500 km s$^{-1}$ in the ionized gas and 500 km s$^{-1}$ in the warm molecular\ngas, consistent with in situ heating, ionization, and acceleration of ambient\ngas to produce the narrow-line region (NLR) outflows. There is a disk of\nionized and warm molecular gas within $\\sim$400 pc of the SMBH that has\nre-oriented close to the stellar major axis but is counter-rotating, consistent\nwith claims of external fueling of AGN in S0 galaxies.", + "category": "astro-ph" + }, + { + "text": "Inverse Compton cooling in Klein-Nishina regime and GRB prompt spectrum: Synchrotron radiation mechanism, when electrons are accelerated in a\nrelativistic shock, is known to have serious problems to explain the observed\ngamma-ray spectrum below the peak for most Gamma-Ray Bursts (GRBs); the\nsynchrotron spectrum below the peak is much softer than observed spectra.\nRecently, the possibility that electrons responsible for the radiation cool via\nInverse Compton, but in the Klein-Nishina regime, has been proposed as a\nsolution to this problem. We provide an analytical study of this effect and\nshow that it leads to a hardening of the low energy spectrum but not by enough\nto make it consistent with the observed spectra for most GRBs (this is assuming\nthat electrons are injected continuously over a time scale comparable to the\ndynamical time scale, as is expected for internal shocks of GRBs). In\nparticular, we find that it is not possible to obtain a spectrum with\n\\alpha>-0.1 (f_{\\nu} \\propto \\nu^{\\alpha}) whereas the typical observed value\nis \\alpha\\sim0. Moreover, extreme values for a number of parameters are\nrequired in order that \\alpha\\sim-0.1: the energy fraction in magnetic field\nneeds to be less than about 10^{-4}, the thermal Lorentz factor of electrons\nshould be larger than 10^6, and the radius where gamma-rays are produced should\nbe not too far away from the deceleration radius. These difficulties suggest\nthat the synchrotron radiation mechanism in internal shocks does not provide a\nself-consistent solution when \\alpha>-0.2.", + "category": "astro-ph" + }, + { + "text": "Photometric Study on Stellar Magnetic Activity: I. Flare Variability of\n Red Dwarf Stars in the Open Cluster M37: Based on one-month long MMT time-series observations of the open cluster M37,\nwe monitored light variations of nearly 2500 red dwarfs and successfully\nidentified 420 flare events from 312 cluster M dwarf stars. For each flare\nlight curve, we derived observational and physical parameters, such as flare\nshape, peak amplitude, duration, energy, and peak luminosity. We show that cool\nstars produce serendipitous flares energetic enough to be observed in the\n$r$-band, and their temporal and peak characteristics are almost the same as\nthose in traditional $U$-band observations. We also found many large-amplitude\nflares with inferred $\\Delta u > 6$ mag in the cluster sample which had been\nrarely reported in previous ground-based observations. Following the ergodic\nhypothesis, we investigate in detail statistical properties of flare parameters\nover a range of energy ($E_{r}$ $\\simeq$ $10^{31}-10^{34}$ erg). As expected,\nthere are no statistical differences in the distributions of flare timescales,\nenergies, and frequencies among stars of the same age and mass group. We note\nthat our sample tend to have longer rise and decay timescales compared to those\nseen in field flare stars of the same spectral type and be more energetic.\nFlare frequency distributions follow power-law distributions with slopes $\\beta\n\\sim0.62-1.21$ for all flare stars and $\\beta \\sim0.52-0.97$ for stars with\nmembership information ($P_{mem} \\geq 0.2$). These are in general agreement\nwith previous works on flare statistics of young open clusters and nearby field\nstars. Our results give further support to the classical age-activity\nrelations.", + "category": "astro-ph" + }, + { + "text": "On the early chemical evolution of the Milky Way: A few topics concerning the early chemical evolution of the Milky Way are\ncritically discussed. In particular, it is argued that: 1) Observed abundance\npatterns of extremely metal poor stars (of Pop. II) do not constrain the mass\nrange of the first generation (Pop. III) stars; the latter may well be normal\nmassive stars (10-50 Msun) or very massive ones (140-1000 Msun) or a\ncombination of the two classes. 2) The discrepancy between primordial Li\nabundance (after WMAP) and the observed ``Spite plateau'' cannot be due to\nastration by a generation of massive Pop. III stars, as recently suggested,\nunless if such stars eject negligible amounts of metals. 3) The observed halo\nmetallicity disribution may well be understood in the framework of hierarchical\ngalaxy formation, as shown here with a simple semi-analytical model. 4)\nFormation of the Milky Way's halo from a myriad of smaller sub-haloes may have\nimportant implications for our understanding of the abundance patterns of\nr-elements, the origin of which remains still unclear.", + "category": "astro-ph" + }, + { + "text": "Shedding Light on the Isolation of Luminous Blue Variables: In the standard view of massive star evolution, luminous blue variables\n(LBVs) are transitional objects between the most massive O-type stars and\nWolf-Rayet (WR) stars. With short lifetimes, these stars should all be found\nnear one another. A recent study of LBVs in the Large Magellanic Cloud (LMC)\nfound instead that LBVs are considerably more isolated than either O-type stars\nor WRs, with a distribution intermediate between that of the WRs and red\nsupergiants (RSGs). A similar study, using a more restricted sample of LBVs,\nreached the opposite conclusion. Both studies relied upon the distance to the\nnearest spectroscopically identified O-type star to define the degree of\nisolation. However, our knowledge of the spectroscopic content of the LMC is\nquite spotty. Here we re-examine the issue using carefully defined photometric\ncriteria to select the highest mass unevolved stars (\"bright blue stars,\" or\nBBSs), using spatially complete photometric catalogs of the LMC, M31, and M33.\nOur study finds that the LBVs are no more isolated than BBSs or WRs. This\nresult holds no matter which sample of LBVs we employ. A statistical test shows\nthat we can rule out the LBVs having the same distribution as the RSGs, which\nare about 2x more isolated. We demonstrate the robustness of our results using\nthe second-closest neighbor. Furthermore, the majority of LBVs in the LMC are\nfound in or near OB associations as are the BBS and WRs; the RSGs are not. We\nconclude that the spatial distribution of LBVs therefore is consistent with the\nstandard picture of massive star evolution.", + "category": "astro-ph" + }, + { + "text": "Luminosity effect of O I 7771-5 triplet and atmospheric microturbulence\n in evolved A-, F-, and G-type stars: It is known that the strength of neutral oxygen triplet lines at 7771-5 A\nshows a luminosity effect in evolved A through G stars. However, its general\nbehavior across the HR diagram is not yet well understood, since the\napplicability limit of the relations proposed by various previous work (tending\nto be biased toward supergiants) still remains unclear. Besides, our\nunderstanding on the nature of atmospheric micro-scale turbulence, which is\nconsidered to play a significant role (along with the non-LTE line\nintensification) for the cause of this effect, is still insufficient. Towards\nclarifying these problems, we carried out an extensive non-LTE spectrum-fitting\nanalysis of O I 7771--5 lines for unbiased sample of 75 evolved A-, F,- and\nG-type stars over wide luminosity classes (from subgiants through supergiants)\nincluding rapid rotators, from which the total equivalent width (W_77) was\nderived and the microturbulence (xi) was determined by two different (profile-\nand abundance-based) methods for each star. While we confirmed that W_77 tends\nto increase in the global sense as a star's absolute magnitude (M_V) becomes\nmore luminous, distinctly different trends were found between lower-gravity\n(log g <~ 2.5) and higher-gravity (log g >~ 2.5) stars, in the sense that the\nM_V vs. W_77 formulas proposed by past studies are applicable only to the\nformer supergiant group. In case of using W_77 for empirical M_V evaluation by\nsuch simple formulas, it is recommended to confine only to supergiants of -5 >\nM_V > -10. Regarding the microturbulence significantly controlling W_77, it\nroughly shows an increasing tendency with a decrease in surface gravity.\nHowever, the trend is not monotonic but rather intricate (e.g., hump,\nstagnation, or discontinuously large increase) depending on the stellar type\nand evolutionary stage.", + "category": "astro-ph" + }, + { + "text": "HST/ACS color-magnitude diagrams of candidate intermediate-age M 31\n globular clusters. The role of blue horizontal branches: We present deep (V ~ 28.0) BV photometry obtained with the wide field channel\nof the Advanced Camera for Surveys on board HST for four M31 globular clusters\nthat were identified as candidate intermediate-age (age ~ 1-9 Gyr) by various\nauthors, based on their integrated spectra and/or broad/intermediate-band\ncolors. Two of them (B292 and B350) display an obvious blue horizontal branch,\nindicating that they are as old as the oldest Galactic globulars. On the other\nhand, for the other two (B058 and B337), which display red horizontal branches,\nit was not possible either to confirm or disconfirm the age estimate from\nintegrated spectra. The analysis of the distribution in the spectral indices\nMg2 and H_beta of the M31 and Milky Way clusters whose horizontal branch can be\nclassified as red or blue based on existing CMDs, strongly suggests that\nclassical age diagnostics from integrated spectra may be significantly\ninfluenced by the HB morphology of the clusters and can lead to erroneous\nage-classifications. We also provide the CMD for another two clusters that fall\ninto the field of the main targets, B336, an old and metal-poor globular with a\nsignificant population of RR-Lyrae variables, and the newly discovered B531, a\ncluster with a very red red giant branch.", + "category": "astro-ph" + }, + { + "text": "Dissipative dark matter explains rotation curves: Dissipative dark matter, where dark matter particles interact with a massless\n(or very light) boson, is studied. Such dark matter can arise in simple hidden\nsector gauge models, including those featuring an unbroken $U(1)'$ gauge\nsymmetry, leading to a dark photon. Previous work has shown that such models\ncan not only explain the LSS and CMB, but potentially also dark matter\nphenomena on small scales, such as the inferred cored structure of dark matter\nhalos. In this picture, dark matter halos of disk galaxies not only cool via\ndissipative interactions but are also heated via ordinary supernovae\n(facilitated by an assumed photon - dark photon kinetic mixing interaction).\nThis interaction between the dark matter halo and ordinary baryons, a very\nspecial feature of these types of models, plays a critical role in governing\nthe physical properties of the dark matter halo. Here, we further study the\nimplications of this type of dissipative dark matter for disk galaxies.\nBuilding on earlier work, we develop a simple formalism which aims to describe\nthe effects of dissipative dark matter in a fairly model independent way. This\nformalism is then applied to generic disk galaxies. We also consider specific\nexamples, including NGC 1560 and a sample of dwarf galaxies from the LITTLE\nTHINGS survey. We find that dissipative dark matter, as developed here, does a\nfairly good job accounting for the rotation curves of the galaxies considered.\nNot only does dissipative dark matter explain the linear rise of the rotational\nvelocity of dwarf galaxies at small radii, but it can also explain the observed\nwiggles in rotation curves which are known to be correlated with corresponding\nfeatures in the disk gas distribution.", + "category": "astro-ph" + }, + { + "text": "Investigating the Effects of Finite Resolution on Observed Transverse\n Jet Profiles: Both the emission properties and evolution of Active Galactic Nuclei (AGN)\nradio jets are dependent on the magnetic fields that thread them. Faraday\nRotation gradients are a very important way of investigating these magnetic\nfields, and can provide information on the orientation and structure of the\nmagnetic field in the immediate vicinity of the jet; for example, a toroidal or\nhelical field component should give rise to a systematic gradient in the\nobserved Faraday rotation across the jet, as well as characteristic intensity\nand polarization profiles. However, real observed radio images have finite\nresolution, usually expressed via convolution with a Gaussian beam whose size\ncorresponds to the central lobe of the point source response function. This\nwill tend to blur transverse structure in the jet profile, raising the question\nof how well resolved a jet must be in the transverse direction in order to\nreliably detect transverse structure associated with a helical jet magnetic\nfield. We present results of simulated intensity, polarization and Faraday\nrotation images designed to directly and empirically investigate the effect of\nfinite resolution on observed transverse jet structures.", + "category": "astro-ph" + }, + { + "text": "The Bright Rim Prominences according to 2.5D Radiative Transfer: Solar prominences observed close to the limb commonly include a bright\nfeature that, from the perspective of the observer, runs along the interface\nbetween itself and the underlying chromosphere. Despite several idealised\nmodels being proposed to explain the underlying physics, a more general\napproach remains outstanding. In this manuscript we demonstrate as a\nproof-of-concept the first steps in applying the Lightweaver radiative transfer\nframework's 2.5D extension to a `toy' model prominence + VAL3C chromosphere,\ninspired by recent 1.5D experiments that demonstrated a significant radiative\nchromosphere--prominence interaction. We find the radiative connection to be\nsignificant enough to enhance both the electron number density within the\nchromosphere, as well as its emergent intensity across a range of spectral\nlines in the vicinity of the filament absorption signature. Inclining the\nviewing angle from the vertical, we find these enhancements to become\nincreasingly asymmetric and merge with a larger secondary enhancement sourced\ndirectly from the prominence underside. In wavelength, the enhancements are\nthen found to be the largest in both magnitude and horizontal extent for the\nspectral line cores, decreasing into the line wings. Similar behaviour is found\nwithin new Chinese H$\\alpha$ Solar Explorer (CHASE)/H$\\alpha$ Imaging\nSpectrograph (HIS) observations, opening the door for subsequent statistical\nconfirmations of the theoretical basis we develop here.", + "category": "astro-ph" + }, + { + "text": "Methoxymethanol Formation Starting from CO-Hydrogenation: Methoxymethanol (CH3OCH2OH, MM) has been identified through gas-phase\nsignatures in both high- and low-mass star-forming regions. This molecule is\nexpected to form upon hydrogen addition and abstraction reactions in CO-rich\nice through radical recombination of CO hydrogenation products. The goal of\nthis work is to investigate experimentally and theoretically the most likely\nsolid-state MM reaction channel -- the recombination of CH2OH and CH3O radicals\n-- for dark interstellar cloud conditions and to compare the formation\nefficiency with that of other species that were shown to form along the\nCO-hydrogenation line. Hydrogen atoms and CO or H2CO molecules are co-deposited\non top of the predeposited H2O ice to mimic the conditions associated with the\nbeginning of 'rapid' CO freeze-out. Quadrupole mass spectrometry is used to\nanalyze the gas-phase COM composition following a temperature programmed\ndesorption. Monte Carlo simulations are used for an astrochemical model\ncomparing the MM formation efficiency with that of other COMs. Unambiguous\ndetection of newly formed MM has been possible both in CO+H and H2CO+H\nexperiments. The resulting abundance of MM with respect to CH3OH is about 0.05,\nwhich is about 6 times less than the value observed toward NGC 6334I and about\n3 times less than the value reported for IRAS 16293B. The results of\nastrochemical simulations predict a similar value for the MM abundance with\nrespect to CH3OH factors ranging between 0.06 to 0.03. We find that MM is\nformed by co-deposition of CO and H2CO with H atoms through the recombination\nof CH2OH and CH3O radicals. In both the experimental and modeling studies, the\nefficiency of this channel alone is not sufficient to explain the observed\nabundance of MM. These results indicate an incomplete knowledge of the reaction\nnetwork or the presence of alternative solid-state or gas-phase formation\nmechanisms.", + "category": "astro-ph" + }, + { + "text": "Ram Pressure Stripping in the Low Luminosity Virgo Cluster Elliptical\n Galaxy NGC 4476: We present a deep VLA search for HI emission from the low-luminosity Virgo\nCluster elliptical galaxy NGC 4476, which contains 1.1 x 10^8 M_sun of\nmolecular gas in an undisturbed disk in regular rotation. No HI was detected.\nThe rms noise in the final image corresponds to a 3 sigma column density\nsensitivity of 1.2 x 10^20 cm^{-2} at the position of NGC 4476, averaged over\nthe 4 kpc beam. The total HI mass is less than 1.5 x 10^7 M_sun. If we compare\nour HI upper limit to the H_2 content, we find that NGC 4476 is extremely\ndeficient in HI compared to other galaxies detected in these two species. The\nH_2/HI mass ratio for NGC 4476 is > 7, whereas typical H_2/HI ratios for\nelliptical galaxies detected in both HI and H_2 are <~2. Based on this extreme\nHI deficiency and the intra-cluster medium (ICM) density at the projected\ndistance from M87 we argue that either NGC 4476 has undergone ram-pressure\nstripping while traveling through the Virgo cluster core or its average\nmolecular gas density is larger and its interstellar UV field is smaller than\nin typical spiral galaxies. NGC 4476 is located 12' in projection from M87,\nwhich causes extreme continuum confusion problems. We also discuss in detail\nthe techniques used for continuum subtraction. The spectral dynamic range of\nour final image is 50,000 to 1.", + "category": "astro-ph" + }, + { + "text": "The Crab Pulsar at Centimeter Wavelengths II: Single Pulses: We have carried out new, high-frequency, high-time-resolution observations of\nthe Crab pulsar. Combining these with our previous data, we characterize bright\nsingle pulses associated with the Main Pulse, both the Low-Frequency and\nHigh-Frequency Interpulses, and the two High-Frequency Components. Our data\ninclude observations at frequencies ranging from 1 to 43 GHz with time\nresolution down to a fraction of a nanosecond. We find at least two types of\nemission physics are operating in this pulsar. Both Main Pulses and\nLow-Frequency Interpulses, up to about 10 GHz, are characterized by nanoshot\nemission - overlapping clumps of narrow-band nanoshots, each with its own\npolarization signature. High-Frequency Interpulses, between 5 and 30 GHz, are\ncharacterized by spectral band emission - linearly polarized emission\ncontaining about 30 proportionately spaced spectral bands. We cannot say\nwhether the longer-duration High-Frequency Component pulses are due to a\nscattering process, or if they come from yet another type of emission physics.", + "category": "astro-ph" + }, + { + "text": "The Role for the Inner Disk in Mass Accretion to the Star in the Early\n Phase of Star Formation: A physical mechanism that drives FU Orionis-type outbursts is reconsidered.\nWe study the effect of inner part of a circumstellar disk covering a region\nfrom near the central star to the radius of approximately $5$ AU (hereafter,\nthe inner disk). Using the fluctuated mass accretion rate onto the inner disk\n$\\dot{M}_{\\rm out}$, we consider the viscous evolution of the inner disk and\nthe time variability of the mass accretion rate onto the central star\n$\\dot{M}_{\\rm in}$ by means of numerical calculation of an unsteady viscous\naccretion disk in a one-dimensional axisymmetric model. First, we calculate the\nevolution of the inner disk assuming an oscillating $\\dot{M}_{\\rm out}$. It is\nshown that the time variability of $\\dot{M}_{\\rm in}$ does not coincide with\n$\\dot{M}_{\\rm out}$ due to viscous diffusion. Second, we investigate the\nproperties of spontaneous outbursts with temporally constant $\\dot{M}_{\\rm\nout}$. Outburst occur only in a limited range of mass accretion rates onto the\ninner disk $10^{-10}<\\dot{M}_{\\rm out}< 3\\times 10^{-6}~{\\rm M}_{\\odot} {\\rm\nyr}^{-1}$ due to gravo-magneto limit cycle (GML). Finally, we discuss the case\nwith a combination of episodic $\\dot{M}_{\\rm out}$ and accretion outbursts\ncause by the GML in the inner disk. The GML can drive accretion outbursts onto\nthe star even for the case of fluctuating $\\dot{M}_{\\rm out}$, although\nfluctuations of $\\dot{M}$ decay during transmitting the inner disk inwards. We\nnewly identified two modes of outburst which are spontaneous one and stimulated\none. In a stimulated mode of outburst, $\\dot{M}_{\\rm out}$ does appear directly\nin $\\dot{M}_{\\rm in}$ (the latter defining the stellar accretion luminosity).\nIn a spontaneous mode of outburst, $\\dot{M}_{\\rm out}$ appears as the interval\nbetween outbursts.", + "category": "astro-ph" + }, + { + "text": "Kinetic \"jets\" from fast moving pulsars: Some fast-moving pulsars, like the Guitar and the Lighthouse, exhibit\nasymmetric non-thermal emission features that extend well beyond their ram\npressure confined pulsar wind nebulae (PWNe). Using 3D relativistic simulations\nwe explain these features as kinetically streaming pulsar wind particles that\nescaped into the interstellar medium (ISM) due to reconnection between the PWN\nand ISM magnetic fields. The structure of the reconnecting magnetic fields at\nthe incoming and outgoing regions produce highly asymmetric magnetic bottles,\nand result in asymmetric extended features. For the features to become visible,\nthe ISM magnetic field should be sufficiently high, $B_{\\rm ISM}>10$~$\\mu$G. We\nalso discuss archival observations of PWNe displaying evidence of kinetic jets:\nthe Dragonfly PWN (PSR J2021+3651), G327.1--1.1, and MSH 11--62, the latter two\nof which exhibit \"snail eyes\" morphologies. We suggest that in those cases the\npulsar is moving along the ambient magnetic field in a frisbee-type\nconfiguration.", + "category": "astro-ph" + }, + { + "text": "The Spitzer ice legacy: Ice evolution from cores to protostars: Ices regulate much of the chemistry during star formation and account for up\nto 80% of the available oxygen and carbon. In this paper, we use the Spitzer\nc2d ice survey, complimented with data sets on ices in cloud cores and\nhigh-mass protostars, to determine standard ice abundances and to present a\ncoherent picture of the evolution of ices during low- and high-mass star\nformation. The median ice composition H2O:CO:CO2:CH3OH:NH3:CH4:XCN is\n100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass\nprotostars, respectively, and 100:31:38:4:-:-:- in cloud cores. In the low-mass\nsample, the ice abundances with respect to H2O of CH4, NH3, and the component\nof CO2 mixed with H2O typically vary by <25%, indicative of co-formation with\nH2O. In contrast, some CO and CO2 ice components, XCN and CH3OH vary by factors\n2-10 between the lower and upper quartile. The XCN band correlates with CO,\nconsistent with its OCN- identification. The origin(s) of the different levels\nof ice abundance variations are constrained by comparing ice inventories toward\ndifferent types of protostars and background stars, through ice mapping,\nanalysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on\nthe analysis, the first ice formation phase is driven by hydrogenation of\natoms, which results in a H2O-dominated ice. At later prestellar times, CO\nfreezes out and variations in CO freeze-out levels and the subsequent CO-based\nchemistry can explain most of the observed ice abundance variations. The last\nimportant ice evolution stage is thermal and UV processing around protostars,\nresulting in CO desorption, ice segregation and formation of complex organic\nmolecules. The distribution of cometary ice abundances are consistent with with\nthe idea that most cometary ices have a protostellar origin.", + "category": "astro-ph" + }, + { + "text": "X-ray properties of early-type stars in the Tarantula Nebula from T-ReX: We reassess the historical $L_{X}/L_{Bol}$ relation for early-type stars from\na comparison between T-ReX, the Chandra ACIS X-ray survey of the Tarantula\nNebula in the LMC, and contemporary spectroscopic analysis of massive stars\nobtained primarily from VLT/FLAMES, VLT/MUSE and HST/STIS surveys. For 107\nsources in common (some host to multiple stars), the majority of which are\nbolometrically luminous (40% exceed $10^6 L_{\\odot}$), we find an average $\\log\nL_{X} /L_{Bol} = -6.90 \\pm 0.65$. Excluding extreme systems Mk 34 (WN5h+WN5h),\nR140a (WC4+WN6+) and VFTS 399 (O9 IIIn+?), plus four WR sources with\nanomalously hard X-ray components (R130, R134, R135, Mk 53) and 10 multiple\nsources within the spatially crowded core of R136a, $\\log L_{X}/L_{Bol} = -7.00\n\\pm 0.49$, in good agreement with Galactic OB stars. No difference is found\nbetween single and binary systems, nor between O, Of/WN and WR stars, although\nthere does appear to be a trend towards harder X-ray emission from O dwarfs,\nthrough O (super)giants, Of/WN stars and WR stars. The majority of known OB\nstars in the Tarantula are not detected in the T-ReX point source catalogue, so\nwe have derived upper limits for all undetected OB stars for which log\n$L_{Bol}/L_{\\odot} \\geq 5.0$. A survival analysis using detected and\nupper-limit log $L_{X}/L_{Bol}$ values indicates no significant difference\nbetween luminous O stars in the LMC and the Carina Nebula. This analysis\nsuggests that metallicity does not strongly influence $L_{X}/L_{Bol}$. Plasma\ntemperatures for single, luminous O stars in the Tarantula\n($\\overline{kT_{m}}=1.0$ keV) are higher than counterparts in Carina\n($\\overline{kT_{m}}=0.5$ keV).", + "category": "astro-ph" + }, + { + "text": "Extreme chemical abundance ratio suggesting an exotic origin for an\n ultra-diffuse galaxy: Ultra diffuse galaxies are a population of extended galaxies but with\nrelatively low luminosities. The origin of these objects remains unclear,\nlargely due to the observational challenges of the low surface brightness\nUniverse. We present here a detailed stellar population analysis of a\nrelatively isolated UDG, DGSAT I, based on spectroscopic data from the Keck\nCosmic Web Imager integral field unit. The star formation history of DGSAT I\nseems to be extended, with a mean luminosity-weighted age of ~3 Gyr, in\nagreement with previous photometric studies. However, we find a very high\n[Mg/Fe] abundance ratio, which is extreme even in the context of the highly\nalpha-enhanced massive ellipticals and ultra-faint dwarfs. The\n[Mg/Fe]-enhancement of DGSAT I appears to be 10 times higher than the most\nmagnesium-enhanced stellar systems discovered to date, and suggests that the\nchemical enrichment of this object was dominated by core-collapse supernovae.\nIntriguingly, this breaks the canonical relation between [Mg/Fe] and star\nformation time-scale. With a measured velocity dispersion of 56 +/- 10 km/s,\nDGSAT I also shows a high mass-to-light ratio, which indicates that it is\nhighly dark matter-dominated. The metal-poor conditions of DGSAT I may have\nenhanced the formation of massive stars, while at the same time, additional\nmechanisms are needed to prevent iron-rich yields from being recycled into\nstars. These results suggest that some ultra-diffuse galaxies could have\nexperienced chemical enrichment episodes similar to the first building blocks\nof galaxies.", + "category": "astro-ph" + }, + { + "text": "Discerning Exoplanet Migration Models Using Spin-Orbit Measurements: We investigate the current sample of exoplanet spin-orbit measurements to\ndetermine whether a dominant planet migration channel can be identified, and at\nwhat confidence. We use the predictions of Kozai migration plus tidal friction\n(Fabrycky and Tremaine 2007) and planet-planet scattering (Nagasawa et al.\n2008) as our misalignment models, and we allow for a fraction of intrinsically\naligned systems, explainable by disk migration. Bayesian model comparison\ndemonstrates that the current sample of 32 spin-orbit measurements strongly\nfavors a two-mode migration scenario combining planet-planet scattering and\ndisk migration over a single-mode Kozai migration scenario. Our analysis\nindicates that between 34% and 76% of close-in planets (95% confidence)\nmigrated via planet-planet scattering. Separately analyzing the subsample of 12\nstars with T_eff > 6250 K---which Winn et al. (2010) predict to be the only\ntype of stars to maintain their primordial misalignments---we find that the\ndata favor a single-mode scattering model over Kozai with 81% confidence. We\nalso assess the number of additional hot star spin-orbit measurements that will\nlikely be necessary to provide a more confident model selection, finding that\nan additional 20-30 measurements has a >50% chance of resulting in a\n95%-confident model selection, if the current model selection is correct. While\nwe test only the predictions of particular Kozai and scattering migration\nmodels in this work, our methods may be used to test the predictions of any\nother spin-orbit misaligning mechanism.", + "category": "astro-ph" + }, + { + "text": "Laboratory Observations and Simulations of Phase Reddening: The visible reflectance spectrum of many solar system bodies changes with\nchanging viewing geometry for reasons not fully understood. It is often\nobserved to redden (increasing spectral slope) with increasing solar phase\nangle, an effect known as phase reddening. Only once, in an observation of the\nMartian surface by the Viking 1 lander, was reddening observed up to a certain\nphase angle with bluing beyond, making the reflectance ratio as a function of\nphase angle shaped like an arch. However, in laboratory experiments this\narch-shape is frequently encountered. To investigate this, we measured the\nbidirectional reflectance of particulate samples of several common rock types\nin the 400-1000 nm wavelength range and performed ray-tracing simulations. We\nconfirm the occurrence of the arch for surfaces that are forward scattering,\ni.e. are composed of semi-transparent particles and are smooth on the scale of\nthe particles, and for which the reflectance increases from the lower to the\nhigher wavelength in the reflectance ratio. The arch shape is reproduced by the\nsimulations, which assume a smooth surface. However, surface roughness on the\nscale of the particles, such as the Hapke and van Horn (1963) fairy castles\nthat can spontaneously form when sprinkling a fine powder, leads to monotonic\nreddening. A further consequence of this form of microscopic roughness (being\nindistinct without the use of a microscope) is a flattening of the disk\nfunction at visible wavelengths, i.e. Lommel-Seeliger-type scattering. The\nexperiments further reveal monotonic reddening for reflectance ratios at\nnear-IR wavelengths. The simulations fail to reproduce this particular\nreddening, and we suspect that it results from roughness on the surface of the\nparticles. Given that the regolith of atmosphereless solar system bodies is\ncomposed of small particles, our results indicate that the prevalence of\nmonotonic (...)", + "category": "astro-ph" + }, + { + "text": "The COS CGM Compendium. III: Metallicity and Physical Properties of the\n Cool Circumgalactic Medium at z<1: We characterize the metallicities and physical properties of cool,\nphotoionized gas in a sample of 152 z<1 strong Lya forest systems (SLFSs,\nabsorbers with 15 100 cone are 5-10 degrees, corresponding to\nabout 0.4-1.5% of the hemisphere and apparent isotropized energies (kinetic\nplus internal) up to ~1e51 erg. 10-30% of the deposited energy are transferred\nto the outflow with Gamma > 100. Our models confirm the viability of\npost-merger BH-torus systems as engines of short, hard GRBs and can explain the\ndurations of all observed short GRBs, because different propagation velocities\nof the front and rear ends lead to a radial stretching of the ultrarelativistic\nfireball before transparency is reached. The ultrarelativistic flow reveals a\nhighly non-uniform structure with Lorentz factor variations up to factors of a\nfew, caused by the action of Kelvin-Helmholtz instabilities that originate at\nthe fireball-torus interface (abbreviated).", + "category": "astro-ph" + }, + { + "text": "Distance measurements as a probe of cosmic acceleration: A major recent evelopment in observational cosmology has been an accurate\nmeasurement of the luminosity distance-redshift relation out to redshifts z=0.8\nfrom Type Ia supernova standard candles. The results have been argued as\nevidence for cosmic acceleration. It is well known that this assertion depends\non the assumption that we know the equation of state for all mass-energy other\nthan normal pressureless matter; popular models are based on either the\ncosmological constant or on the more general quintessence formulation. But this\nassertion also depends on a number of other assumptions, implicit in the\nderivation of the standard cosmological field equations: large-scale isotropy\nand homogeneity, the flatness of the Universe, and the validity of general\nrelativity on cosmological scales (where it has not been tested). A detailed\nexamination of the effects of these assumptions on the interplay between the\nluminosity distance-redshift relation and the acceleration of the Universe is\nnot possible unless one can define the precise nature of the failure of any\nparticular assumption. However a simple quantitative investigation is possible\nand reveals a number of considerations about the relative importance of the\ndifferent assumptions. In this paper we present such an investigation. We find\nthat the relationship between the distant-redshift relation and the sign of the\ndeceleration parameter is fairly robust and is unaffected if only one of the\nassumptions that we investigate is invalid so long as the deceleration\nparameter is not close to zero (it would not be close to zero in the\ncurrently-favored Omega_Lambda = 1 - Omega_matter = 0.7 or 0.8 Universe, for\nexample). Failures of two or more assumptions in concordance may have stronger\neffects.", + "category": "astro-ph" + }, + { + "text": "Light Nuclei solving Auger puzzles. The Cen-A imprint: Ultra High Energy Cosmic Rays (UHECR) map at 60 EeV have been found recently\nby AUGER group spreading anisotropy signatures in the sky. The result have been\ninterpreted as a manifestation of AGN sources ejecting protons at GZK edges\nmostly from Super-galactic Plane. The result is surprising due to the absence\nof much nearer Virgo cluster. Moreover, early GZK cut off in the spectra may be\nbetter reconcile with light nuclei (than with protons). In addition a large\ngroup (nearly a dozen) of events cluster suspiciously along Cen-A. Finally,\nproton UHECR composition nature is in sharp disagreement with earlier AUGER\nclaim of a heavy nuclei dominance at 40 EeV. Therefore we interpret here the\nsignals as mostly UHECR light nuclei (He, Be, B, C, O), very possibly mostly\nthe lightest (He,Be) ones, ejected from nearest AGN Cen-A, UHECR smeared by\ngalactic magnetic fields, whose random vertical bending is overlapping with\nsuper-galactic arm. The eventual AUGER misunderstanding took place because of\nsuch a rare coincidence between the Super Galactic Plane (arm) and the smeared\n(randomized) signals from Cen-A, bent orthogonally to the Galactic fields. Our\nderivation verify the consistence of the random smearing angles for He, Be and\nB, C, O, in reasonable agreement with the AUGER main group events around Cen-A.\nOnly few other rare events are spread elsewhere. The most collimated from Cen-A\nare the lightest. The most spread the heavier. Consequently Cen-A is the best\ncandidate UHE neutrino tau observable by HEAT and AMIGA as enhanced AUGER array\nat tens-hundred PeV energy. This model maybe soon tested by new events\nclustering around the Cen-A and by composition imprint study.", + "category": "astro-ph" + }, + { + "text": "Selecting Quasar Candidates by a SVM Classification System: We develop and demonstrate a classification system constituted by several\nSupport Vector Machines (SVM) classifiers, which can be applied to select\nquasar candidates from large sky survey projects, such as SDSS, UKIDSS, GALEX.\nHow to construct this SVM classification system is presented in detail. When\nthe SVM classification system works on the test set to predict quasar\ncandidates, it acquires the efficiency of 93.21% and the completeness of\n97.49%. In order to further prove the reliability and feasibility of this\nsystem, two chunks are randomly chosen to compare its performance with that of\nthe XDQSO method used for SDSS-III's BOSS. The experimental results show that\nthe high faction of overlap exists between the quasar candidates selected by\nthis system and those extracted by the XDQSO technique in the dereddened i-band\nmagnitude range between 17.75 and 22.45, especially in the interval of\ndereddened i-band magnitude < 20.0. In the two test areas, 57.38% and 87.15% of\nthe quasar candidates predicted by the system are also targeted by the XDQSO\nmethod. Similarly, the prediction of subcategories of quasars according to\nredshift achieves a high level of overlap with these two approaches. Depending\non the effectiveness of this system, the SVM classification system can be used\nto create the input catalog of quasars for the GuoShouJing Telescope (LAMOST)\nor other spectroscopic sky survey projects. In order to get higher confidence\nof quasar candidates, cross-result from the candidates selected by this SVM\nsystem with that by XDQSO method is applicable.", + "category": "astro-ph" + }, + { + "text": "Broadband Observations of the Compton-thick Nucleus of NGC 3393: We present new NuSTAR and Chandra observations of NGC 3393, a galaxy reported\nto host the smallest separation dual AGN resolved in the X-rays. While past\nresults suggested a 150 pc separation dual AGN, three times deeper Chandra\nimaging, combined with adaptive optics and radio imaging suggest a single,\nheavily obscured, radio-bright AGN. Using VLA and VLBA data, we find an AGN\nwith a two-sided jet rather than a dual AGN and that the hard X-ray, UV,\noptical, NIR, and radio emission are all from a single point source with a\nradius <0.2\". We find that the previously reported dual AGN is most likely a\nspurious detection resulting from the low number of X-ray counts (<160) at 6-7\nkeV and Gaussian smoothing of the data on scales much smaller than the PSF\n(0.25\" vs. 0.80\" FWHM). We show that statistical noise in a single Chandra PSF\ngenerates spurious dual peaks of the same separation (0.55$\\pm$0.07\" vs. 0.6\")\nand flux ratio (39$\\pm$9% vs. 32% of counts) as the purported dual AGN. With\nNuSTAR, we measure a Compton-thick source (NH=$2.2\\pm0.4\\times10^{24}$\ncm$^{-2}$) with a large torus half-opening angle, {\\theta}=79 which we\npostulate results from feedback from strong radio jets. This AGN shows a 2-10\nkeV intrinsic to observed flux ratio of 150. Using simulations, we find that\neven the deepest Chandra observations would severely underestimate the\nintrinsic luminosity of NGC 3393 above z>0.2, but would detect an unobscured\nAGN of this luminosity out to high redshift (z=5).", + "category": "astro-ph" + }, + { + "text": "Estimation of the XUV radiation onto close planets and their evaporation: Context: The current distribution of planet mass vs. incident stellar X-ray\nflux supports the idea that photoevaporation of the atmosphere may take place\nin close-in planets. Integrated effects have to be accounted for. A proper\ncalculation of the mass loss rate due to photoevaporation requires to estimate\nthe total irradiation from the whole XUV range. Aims: The purpose of this paper\nis to extend the analysis of the photoevaporation in planetary atmospheres from\nthe accessible X-rays to the mostly unobserved EUV range by using the coronal\nmodels of stars to calculate the EUV contribution to the stellar spectra. The\nmass evolution of planets can be traced assuming that thermal losses dominate\nthe mass loss of their atmospheres. Methods: We determine coronal models for 82\nstars with exoplanets that have X-ray observations available. Then a synthetic\nspectrum is produced for the whole XUV range (~1-912 {\\AA}). The determination\nof the EUV stellar flux, calibrated with real EUV data, allows us to calculate\nthe accumulated effects of the XUV irradiation on the planet atmosphere with\ntime, as well as the mass evolution for planets with known density. Results: We\ncalibrate for the first time a relation of the EUV luminosity with stellar age\nvalid for late-type stars. In a sample of 109 exoplanets, few planets with\nmasses larger than ~1.5 Mj receive high XUV flux, suggesting that intense\nphotoevaporation takes place in a short period of time, as previously found in\nX-rays. The scenario is also consistent with the observed distribution of\nplanet masses with density. The accumulated effects of photoevaporation over\ntime indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr.\nConclusions: Coronal radiation produces rapid photoevaporation of the\natmospheres of planets close to young late-type stars. More complex models are\nneeded to explain fully the observations.", + "category": "astro-ph" + }, + { + "text": "Twenty Years of Searching for (and Finding) Globular Cluster Pulsars: Globular clusters produce orders of magnitude more millisecond pulsars per\nunit mass than the Galactic disk. Since the first cluster pulsar was uncovered\ntwenty years ago, at least 138 have been identified - most of which are binary\nmillisecond pulsars. Because of their origins involving stellar encounters,\nmany of these systems are exotic objects that would never be observed in the\nGalactic disk. Examples include pulsar-main sequence binaries, extremely rapid\nrotators (including the current record holder), and millisecond pulsars in\nhighly eccentric orbits. These systems are allowing new probes of the\ninterstellar medium, the equation of state of material at supra-nuclear\ndensity, the mass distribution of neutron stars, and the dynamics of globular\nclusters.", + "category": "astro-ph" + }, + { + "text": "Survey of Li-rich giants among Kepler and LAMOST fields: Determination\n of Li-rich giants Evolutionary Phase: In this letter, we report the discovery of 24 new super Li-rich (A(Li) $\\ge$\n3.2) giants of He-core burning phase at red clump region. Results are based on\nsystematic search of a large sample of about 12,500 giants common to the LAMOST\nspectroscopic and Kepler time resolved photometric surveys. The two key\nparameters derived from Kepler data; average period spacing ($\\Delta p$)\nbetween $l=1$ mixed gravity dominated g-modes and average large frequency\nseparation ($\\Delta \\nu$) $l=0$ acoustic p-modes, suggest all the Li-rich\ngiants are in He-core burning phase. This is the first unbiased survey\nsubjected to a robust technique of asteroseismic analysis to unambiguously\ndetermine evolutionary phase of Li-rich giants. The results provide a strong\nevidence that Li enhancement phenomenon is associated with giants of He-core\nburning phase, post He-flash, rather than any other phase on RGB with inert\nHe-core surrounded by H-burning shell.", + "category": "astro-ph" + }, + { + "text": "Planet formation via pebble accretion in externally photoevaporating\n discs: We demonstrate that planet formation via pebble accretion is sensitive to\nexternal photoevaporation of the outer disc. In pebble accretion, planets grow\nby accreting from a flux of solids (pebbles) that radially drift inwards from\nthe pebble production front. If external photoevaporation truncates the outer\ndisc fast enough, it can shorten the time before the pebble production front\nreaches the disc outer edge, cutting off the supply of pebble flux for\naccretion, hence limiting the pebble mass reservoir for planet growth.\nConversely, cloud shielding can protect the disc from strong external\nphotoevaporation and preserve the pebble reservoir. Because grain growth and\ndrift can occur quickly, shielding even on a short time-scale (<1 Myr) can have\na non-linear impact on the properties of planets growing by pebble accretion.\nFor example a $10^{-3} M_\\oplus$ planetary seed at 25 au stays at 25 au with a\nlunar mass if the disc is immediately irradiated by a $10^3$ G$_0$ field, but\ngrows and migrates to be approximately Earth-like in both mass and orbital\nradius if the disc is shielded for just 1 Myr. In NGC 2024, external\nphotoevaporation is thought to happen to discs that are <0.5 Myr old, which\ncoupled with the results here suggests that the exact planetary parameters can\nbe very sensitive to the star forming environment. Universal shielding for\ntime-scales of at least $\\sim1.5$ Myr would be required to completely nullify\nthe environmental impact on planetary architectures.", + "category": "astro-ph" + }, + { + "text": "Galaxies behind the Milky Way and the Great Attractor: Dust and stars in the plane of the Milky Way create a \"Zone of Avoidance\" in\nthe extragalactic sky. Galaxies are distributed in gigantic labyrinth\nformations, filaments and great walls with occasional dense clusters. They can\nbe traced all over the sky, except where the dust within our own galaxy becomes\ntoo thick - leaving about 25% of the extragalactic sky unaccounted for. Our\nGalaxy is a natural barrier which constrains the studies of large-scale\nstructures in the Universe, the peculiar motion of our Local Group of galaxies\nand other streaming motions (cosmic flows) which are important for\nunderstanding formation processes in the Early Universe and for cosmological\nmodels. Only in recent years have astronomers developed the techniques to peer\nthrough the disk and uncover the galaxy distribution in the Zone of Avoidance.\nI present the various observational multi-wavelength procedures (optical, far\ninfrared, near infrared, radio and X-ray) that are currently being pursued to\nmap the galaxy distribution behind our Milky Way. Particular emphasis is given\nto discoveries in the Great Attractor region -- a from streaming motions\npredicted huge overdensity centered behind the Galactic Plane. The recently\nunveiled massive rich cluster A3627 seems to constitute the previously\nunidentified core of the Great Attractor.", + "category": "astro-ph" + }, + { + "text": "Dark energy with rigid voids versus relativistic voids alone: The standard model of cosmology is dominated - at the present epoch - by dark\nenergy. Its voids are rigid and Newtonian within a relativistic background. The\nmodel prevents them from becoming hyperbolic. Observations of rapid velocity\nflows out of voids are normally interpreted within the standard model that is\nrigid in comoving coordinates, instead of allowing the voids' density parameter\nto drop below critical and their curvature to become negative. Isn't it time to\nadvance beyond nineteenth century physics and relegate dark energy back to the\n\"no significant evidence\" box?", + "category": "astro-ph" + }, + { + "text": "Serendipitous discovery of a cluster of galaxies with a peculiar central\n galaxy: We report the serendipitous discovery of a cluster of galaxies at z=0.369.\nThirty-eight candidate members were identified based on rough broad-band\nphotometric redshifts, and three members were confirmed spectroscopically. The\nbrightest cluster galaxy (BCG) is exceptionally blue, with B-V=0.12 and\nV-I=1.02. The surface-brightness profile of the BCG follows an r^(1/4)-law\nprofile out to 3\" in all three bands. The effective radius is significantly\nsmaller in bluer bandpasses, resulting in a blue core and a color gradient\nopposite to the metallicity-induced color gradient observed in typical\nelliptical galaxies. Beyond 3\" an extended envelope of emission in excess of\nthe r^(1/4)-law profile is observed, the position angle of which coincides with\nthe major axis of the galaxy cluster. The spectrum of the BCG contains strong\nBalmer absorption, a minimal 4000 A break, and a broad Mg II emission line,\nsuggesting that the galaxy has undergone recent star formation and may harbor a\ncentral AGN. The presence of numerous nearby bright stars makes this cluster an\ninteresting target for next-generation adaptive optics using natural guide\nstars.", + "category": "astro-ph" + }, + { + "text": "A deterministic model for forecasting long-term solar activity: A phenomenological model is presented for the quantitative description of\nindividual solar cycles' features, such as onset, intensity, evolution, in\nterms of the number of M and X-class solar flares. The main elements of the\nmodel are the relative ecliptic motion of the planets Jupiter and Saturn, and\nits synergy with a quasi-periodic component of solar activity. Using as input\nthe temporal distribution of flares during cycle 21, the general evolution of\ncycles 22-24 is reproduced in notable agreement with the observations,\nincluding the resurgence of activity in the last months of 2017, and further\npredictions are provided for cycle 25. This deterministic description could\ncontribute to elucidating the responsible physical mechanisms and forecasting\nspace weather.", + "category": "astro-ph" + }, + { + "text": "NGC 5128 globular cluster candidates out to 150 kpc: a comprehensive\n catalog from Gaia and ground based data: We present a new catalog of 40502 globular cluster (GC) candidates in NGC\n5128 out to a projected radius of $\\sim$150 kpc, based on data from the\nPanoramic Imaging Survey of Centaurus and Sculptor (PISCeS), Gaia Data Release\n2, and the NOAO Source Catalog. Ranking these candidates based on the\nlikelihood that they are true GCs, we find that approximately 1900 belong to\nour top two ranking categories and should be the highest priority for\nspectroscopic follow-up for confirmation. Taking into account our new data and\na vetting of previous GC catalogs, we estimate a total GC population of $1450\n\\pm 160$ GCs. We show that a substantial number of sources previously argued to\nbe low-velocity GCs are instead foreground stars, reducing the inferred GC\nvelocity dispersion. This work showcases the power of Gaia to identify slightly\nextended sources at the $\\sim 4$ Mpc distance of NGC 5128, enabling accurate\nidentification of GCs throughout the entire extended halo, not just the inner\nregions that have been the focus of most previous work.", + "category": "astro-ph" + }, + { + "text": "Probing Flavor Structure of Cosmic Ray $e^\\mp$ Spectrum and Implications\n for Dark Matter Indirect Searches: Measuring high energy cosmic ray electrons/positrons (CRE) provides important\nmeans for the dark matter (DM) indirect detection and for probing the nearby\ngalactic sources. In this work, we perform a systematic analysis of the flavor\nstructure of DM annihilations into charged leptons based on the cosmic ray CRE\nspectra measured by DAMPE, Fermi-LAT, AMS-02, and CALET experiments. We study\nthe annihilations of possible TeV scale DM particles in a nearby subhalo, which\nis proposed to explain the possible peak-like structure of the DAMPE CRE data.\nWe pay special attention to the possible non-resonant excess (besides the\npossible peak-like structure) and demonstrate that such non-resonant excess can\nmainly arise from the decay of muons produced by the DM annihilations in the\nsubhalo. With these we study the flavor composition of the lepton final states\nfrom DM annihilations $\\chi\\chi\\to e^+e^-, \\mu^+\\mu^-, \\tau^+\\tau^-$ by fitting\nthe CRE data. We demonstrate that decays of the final states $\\mu^+ \\mu^-$ and\n$\\tau^+ \\tau^-$ can provide the non-resonant excess, while the peak excess\narises from the $e^+ e^-$ final state. We further analyze the constraints on\nthe lepton flavor composition using the Fermi-LAT $\\gamma$-ray measurements. We\nfind that the flavor composition is consistent with the Fermi-LAT data at\nrelatively low Galactic latitudes, while the fraction of the final state\n$\\tau^\\pm$ is severely bounded.", + "category": "astro-ph" + }, + { + "text": "Constraining the equation of state of neutron stars using multimessenger\n observations: Neutron stars are the densest objects known in our visible universe.\nProperties of matter inside a neutron star are encoded in its equation of\nstate, which has wide-ranging uncertainty from a theoretical perspective. With\nthe current understanding of quantum chromodynamics, it is hard to determine\nthe interactions of neutron star matter at such high densities. Also performing\nmany body calculations is computationally intractable. Besides the constitution\nof the neutron star core is highly speculative -- it is not ruled out that it\ncontains exotic matter like strange baryons, meson condensates, quark matter,\netc. Although the matter inside the neutron star is extremely dense, but the\ntemperature of this object is very cold in most of its life span. We cannot\nproduce such dense but rather cold material in our laboratory. Since probing\nthe physics of neutron star matter is inaccessible by our earth based\nexperiments, we look for astrophysical observations of neutron stars. This\nthesis deals with the theoretical and computational techniques required to\ntranslate neutron star observables from astrophysical observations to its\nequation of state.", + "category": "astro-ph" + }, + { + "text": "Timing calibration of the APOLLO experiment: The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) began\nmillimeter-precision ranging to the Moon in 2006. Until now, a comprehensive\nvalidation of APOLLO system range accuracy has not been possible because of\ncentimeter-scale deficiencies in computational models of the Earth-Moon range,\nand because APOLLO lacked an internal timing calibration system. Here, we\nreport on the development of a system that enables in-situ calibration of the\ntiming response of the APOLLO apparatus, simultaneous with lunar range\nmeasurements. The system was installed in August 2016. Preliminary results show\nthat the APOLLO system can provide lunar range measurements with millimeter\naccuracy.", + "category": "astro-ph" + }, + { + "text": "Mass measurements and 3D orbital geometry of PSR J1933$-$6211: PSR J1933$-$6211 is a 3.5-ms pulsar in a 12.8-d orbit with a white dwarf\n(WD). Its high proper motion and low dispersion measure result in such\nsignificant interstellar scintillation that high signal-to-noise detections\nrequire long observing durations or fortuitous timing. We turn to the sensitive\nMeerKAT telescope and, combined with historic Parkes data, leverage PSR\nJ1933$-$6211's kinematic and relativistic effects to constrain its 3D orbital\ngeometry and the component masses. We obtain precise proper motion and parallax\nestimates, and measure their effects as secular changes in the Keplerian\norbital parameters: a variation in orbital period of $7(1) \\times 10^{-13}$ s\ns$^{-1}$ and a change in projected semi-major axis of $1.60(5) \\times 10^{-14}$\ns s$^{-1}$. A self-consistent analysis of all kinematic and relativistic\neffects yields a distance of $1.6^{+0.2}_{-0.3}$ kpc, an orbital inclination,\n$i = 55(1)$ deg and a longitude of the ascending node, $\\Omega =\n255^{+8}_{-14}$ deg. The probability densities for $\\Omega$ and $i$ and their\nsymmetric counterparts, ($180-i$, $360-\\Omega$), are seen to depend on the\nfiducial orbit used to measure the time of periastron passage. We investigate\nthis unexpected dependence and rule out software-related causes using\nsimulations. Nevertheless, we constrain the pulsar and WD masses to\n$1.4^{+0.3}_{-0.2}$ M$_\\odot$ and $0.43(5)$ M$_\\odot$ respectively. These\nstrongly disfavour a helium-dominated WD. The orbital similarities between PSRs\nJ1933$-$6211 and J1614$-$2230 suggest they underwent Case A Roche lobe\noverflow, an extended evolution while the companion star is still on the Main\nSequence. However, with a mass of $\\sim 1.4$ M$_\\odot$, PSR J1933$-$6211 has\nnot accreted significant matter. This highlights the low accretion efficiency\nof the spin-up process and suggests that observed neutron star masses are\nmostly a result of supernova physics.", + "category": "astro-ph" + }, + { + "text": "Searching for Low-mass Population III Stars Disguised as White Dwarfs: It is uncertain whether or not low-mass Population III stars ever existed.\nWhile limits on the number density of Population III stars with $M_{\\ast}\n\\approx 0.8~M_{\\odot}$ have been derived using Sloan Digital Sky Survey (SDSS)\ndata, little is known about the occurrence of Population III stars at lower\nmasses. In the absence of reliable parallaxes, the spectra of metal-poor main\nsequence (MPMS) stars with $M_{\\ast} \\lesssim 0.8~M_{\\odot}$ can easily be\nconfused with cool white dwarfs. To resolve this ambiguity, we present a\nclassifier that differentiates between MPMS stars and white dwarfs based on\nphotometry and/or spectroscopy without the use of parallax information. We\nbuild and train our classifier using state-of-the-art theoretical spectra and\nevaluate it on existing SDSS-based classifications for objects with reliable\nGaia DR2 parallaxes. We then apply our classifier to a large catalog of objects\nwith SDSS photometry and spectroscopy to search for MPMS candidates. We\ndiscover several previously unknown candidate extremely metal-poor (EMP) stars\nand recover numerous confirmed EMP stars already in the literature. We conclude\nthat archival SDSS spectroscopy has already been exhaustively searched for EMP\nstars. We predict that the lowest-mass primordial-composition stars will have\nredder optical-to-infrared colors than cool white dwarfs at constant effective\ntemperature due to surface gravity-dependent collision-induced absorption from\nmolecular hydrogen. We suggest that the application of our classifier to data\nproduced by next-generation spectroscopic surveys will set stronger constraints\non the number density of low-mass Population III stars in the Milky Way.", + "category": "astro-ph" + }, + { + "text": "Applicability of the linearly perturbed FRW metric and Newtonian\n cosmology: It has been argued that the effect of cosmological structure formation on the\naverage expansion rate is negligible, because the linear approximation to the\nmetric remains applicable in the regime of non-linear density perturbations. We\ndiscuss why the arguments based on the linear theory are not valid. We\nemphasise the difference between Newtonian gravity and the weak field, small\nvelocity limit of general relativity in the cosmological setting.", + "category": "astro-ph" + }, + { + "text": "Forward Modeling of Solar Coronal Magnetic Field Measurements Based on a\n Magnetic-field-induced Transition in Fe X: It was recently proposed that the intensity ratios of several extreme\nultraviolet spectral lines from the Fe X ion can be used to measure the solar\ncoronal magnetic field based on the magnetic-field-inducedtransition (MIT)\ntheory. To verify the suitability of this method, we performed forward\nmodelingwith a three-dimensional radiation magnetohydrodynamic model of a solar\nactive region. Intensities of several spectral lines from Fe X were synthesized\nfrom the model. Based on the MIT theory, intensity ratios of the MIT line Fe X\n257 A to several other Fe X lines were used to derive the magnetic field\nstrengths, which were then compared with the field strengths in the model. We\nalso developed a new method to simultaneously estimate the coronal density and\ntemperature from the Fe X 174/175 and 184/345 A line ratios. Using these\nestimates, we demonstrated that the MIT technique can provide reasonably\naccurate measurements of the coronal magnetic field in both on-disk and\noff-limb solar observations. Our investigation suggests that a spectrometer\nthat can simultaneously observe the Fe X 174, 175, 184, 257, and 345 A lines\nand allow an accurate radiometric calibration for these lines is highly desired\nto achieve reliable measurements of the coronal magnetic field. We have also\nevaluatedthe impact of the uncertainty in the Fe X 3p4 3d 4D5/2 and 4D7/2\nenergy difference on the magnetic field measurements.", + "category": "astro-ph" + }, + { + "text": "Microlensing by gas filaments: Gas in the interstellar matter is generally organized in filamentary\nstructures, which may be also relevant for a complementary explanation of the\ndark matter in the Galactic halo. We examine the possibility that such\nstructures may act as gravitational microlenses on background sources. To this\npurpose, we derive the general properties of a cylindrical lens and compare the\nlight curves produced by such microlensing events with those generated by\nspherically symmetric clouds. We find that the establishment of the symmetry of\nthe lens through the sole analysis of the light curve may be problematic, while\nthe analysis of the astrometric shift of the centroid of the image can\ndiscriminate between the two classes of clouds. On the basis of our analysis,\nwe find that only gas filaments with a very high density could be detectable.\nSuch clouds are unlikely to exist in a long-lived state. Therefore,\nmicrolensing cannot discriminate on the existence and the relevance of gas\nfilaments in the Halo, which could well be present and escape detection by\nordinary microlensing surveys.", + "category": "astro-ph" + }, + { + "text": "Shock formation around planets orbiting M-dwarf stars: Bow shocks can be formed around planets due to their interaction with the\ncoronal medium of the host stars. The net velocity of the particles impacting\non the planet determines the orientation of the shock. At the Earth's orbit,\nthe (mainly radial) solar wind is primarily responsible for the formation of a\nshock facing towards the Sun. However, for close-in planets that possess high\nKeplerian velocities and are frequently located at regions where the host\nstar's wind is still accelerating, a shock may develop ahead of the planet. If\nthe compressed material is able to absorb stellar radiation, then the signature\nof bow shocks may be observed during transits. Bow-shock models have been\ninvestigated in a series of papers (Vidotto et al. 2010, 2011,a,b; Llama et al.\n2011) for known transiting systems. Once the signature of a bow-shock is\nobserved, one can infer the magnetic field intensity of the transiting planet.\nHere, we investigate the potential to use this model to detect magnetic fields\nof (hypothetical) planets orbiting inside the habitable zone of M-dwarf stars.\nFor these cases, we show, by means of radiative transfer simulations, that the\ndetection of bow-shocks of planets surrounding M-dwarf stars may be more\ndifficult than for the case of close-in giant planets orbiting solar-type\nstars.", + "category": "astro-ph" + }, + { + "text": "Performance and energy footprint assessment of FPGAs and GPUs on HPC\n systems using Astrophysics application: New challenges in Astronomy and Astrophysics (AA) are urging the need for a\nlarge number of exceptionally computationally intensive simulations. \"Exascale\"\n(and beyond) computational facilities are mandatory to address the size of\ntheoretical problems and data coming from the new generation of observational\nfacilities in AA. Currently, the High Performance Computing (HPC) sector is\nundergoing a profound phase of innovation, in which the primary challenge to\nthe achievement of the \"Exascale\" is the power-consumption. The goal of this\nwork is to give some insights about performance and energy footprint of\ncontemporary architectures for a real astrophysical application in an HPC\ncontext. We use a state-of-the-art N-body application that we re-engineered and\noptimized to exploit the heterogeneous underlying hardware fully. We\nquantitatively evaluate the impact of computation on energy consumption when\nrunning on four different platforms. Two of them represent the current HPC\nsystems (Intel-based and equipped with NVIDIA GPUs), one is a micro-cluster\nbased on ARM-MPSoC, and one is a \"prototype towards Exascale\" equipped with\nARM-MPSoCs tightly coupled with FPGAs. We investigate the behavior of the\ndifferent devices where the high-end GPUs excel in terms of time-to-solution\nwhile MPSoC-FPGA systems outperform GPUs in power consumption. Our experience\nreveals that considering FPGAs for computationally intensive application seems\nvery promising, as their performance is improving to meet the requirements of\nscientific applications. This work can be a reference for future platforms\ndevelopment for astrophysics applications where computationally intensive\ncalculations are required.", + "category": "astro-ph" + }, + { + "text": "Investigating the damping rate of phase-mixed Alfven waves: Context: This paper investigates the effectiveness of phase mixing as a\ncoronal heating mechanism. A key quantity is the wave damping rate, $\\gamma$,\ndefined as the ratio of the heating rate to the wave energy.\n Aims: We investigate whether or not laminar phase-mixed Alfv\\'en waves can\nhave a large enough value of $\\gamma$ to heat the corona. We also investigate\nthe degree to which the $\\gamma$ of standing Alfv\\'en waves which have reached\nsteady-state can be approximated with a relatively simple equation. Further\nfoci of this study are the cause of the reduction of $\\gamma$ in response to\nleakage of waves out of a loop, the quantity of this reduction, and how\nincreasing the number of excited harmonics affects $\\gamma$.\n Results: We find that at observed frequencies $\\gamma$ is too small to heat\nthe corona by approximately three orders of magnitude. Therefore, we believe\nthat laminar phase mixing is not a viable stand-alone heating mechanism for\ncoronal loops. We show that $\\gamma$ is largest at resonance. We find our\nsimple equation provides a good estimate for the damping rate (within\napproximately 10% accuracy) for resonant field lines. However, away from\nresonance, the equation provides a poor estimate, predicting $\\gamma$ to be\norders of magnitude too large. We find that leakage acts to reduce $\\gamma$ but\nplays a negligible role if $\\gamma$ is of the order required to heat the\ncorona. If the wave energy follows a power spectrum with slope -5/3 then\n$\\gamma$ grows logarithmically with the number of excited harmonics. If the\nnumber of excited harmonics is increased by much more than 100, then the\nheating is mainly caused by gradients that are parallel to the field rather\nthan perpendicular to it. Therefore, in this case, the system is not heated\nmainly by phase mixing.", + "category": "astro-ph" + }, + { + "text": "K2 Ultracool Dwarfs Survey. V. High superflare rates on rapidly rotating\n late-M dwarfs: We observed strong superflares (defined as flares with energy in excess of\n10^33 erg) on three late-M dwarfs: 2MASS J08315742+2042213 (hereafter\n2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter 2M0837+2050; M8 V) and\n2MASS J08312608+2244586 (hereafter 2M0831+2244; M9 V). 2M0831+2042 and\n2M0837+2050 are members of the young (~700 Myr) open cluster Praesepe. The\nstrong superflare on 2M0831+2042 has an equivalent duration (ED) of 13.7 hr and\nan estimated energy of 1.3 X 10^35 erg. We observed five superflares on\n2M0837+2050, on which the strongest superflare has an ED of 46.4 hr and an\nestimated energy of 3.5 X 10^35 erg. This energy is larger by 2.7 orders of\nmagnitude than the largest flare observed on the older (7.6 Gyr) planet-hosting\nM8 dwarf TRAPPIST-1. Furthermore, we also observed five superflares on\n2M0831+2244 which is probably a field star. The estimated energy of the\nstrongest superflare on 2M0831+2244 is 6.1 X 10^34 erg. 2M0831+2042,\n2M0837+2050 and 2MASS J0831+2244 have rotation periods of 0.556\\pm0.002,\n0.193\\pm0.000 and 0.292\\pm0.001 d respectively, which are measured by using K2\nlight curves. We compare the flares of younger targets with those of TRAPPIST-1\nand discuss the possible impacts of such flares on planets in the habitable\nzone of late-M dwarfs.", + "category": "astro-ph" + }, + { + "text": "The Decrease of Specific Angular Momentum and the Hot Toroid Formation:\n The Massive Clump G10.6-0.4: This is the first paper of our series of high resolution (1\") studies of the\nmassive star forming region G10.6--0.4. We present the emission line\nobservations of the hot core type tracers (O$^{13}$CS, OCS, SO$_{2}$) with\n$\\sim$0$\"$.5 resolution. By comparing the results to the high--resolution\nNH$_{3}$ absorption line observation, we confirm for the first time the\nrotationally flattened hot toroid in the central $<$0.1 pc region, which has a\nrotational axis perpendicular to its geometrical major axis.\n In addition, we present the observations of NH$_{3}$, $^{13}$CS, and\nCH$_{3}$CN with $\\sim$1$\"$ resolution, and follow the dynamics of the molecular\naccretion flow from the 0.3 pc radius to the inner 0.03 pc radius. With\nreference to the rotational axis of the hot toroid, we measure the rotational\nvelocity from the molecular emission in the region. The results are consistent\nwith an envelope with a rapid decrease of the specific angular momentum from\nthe outer to the inner region. These new results improve the current\nunderstanding of the molecular accretion flow in an ultracompact (UC)\nH\\textsc{ii} region created by the embedded O-type cluster.", + "category": "astro-ph" + }, + { + "text": "2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the\n CHIMERA Code: Much progress in realistic modeling of core-collapse supernovae has occurred\nrecently through the availability of multi-teraflop machines and the increasing\nsophistication of supernova codes. These improvements are enabling simulations\nwith enough realism that the explosion mechanism, long a mystery, may soon be\ndelineated. We briefly describe the CHIMERA code, a supernova code we have\ndeveloped to simulate core-collapse supernovae in 1, 2, and 3 spatial\ndimensions. We then describe the results of an ongoing suite of 2D simulations\ninitiated from a 12, 15, 20, and 25 solar mass progenitor. These have all\nexhibited explosions and are currently in the expanding phase with the shock at\nbetween 5,000 and 20,000 km. We also briefly describe an ongoing simulation in\n3 spatial dimensions initiated from the 15 solar mass progenitor.", + "category": "astro-ph" + }, + { + "text": "Large-Scale Structure and Future Surveys: As the 2dF Galaxy Redshift Survey and Sloan Digital Sky Survey move toward\ncompletion, it is time to ask what the next generation of survey of large-scale\nstructure should be. I discuss some of the cosmological justifications for such\nsurveys and conclude that surveys at z=3 offer a critical advantage in their\nability to access linear-regime clustering at scales smaller than any current\nsurvey and even the CMB. I discuss a possible implementation of such a survey\nand highlight some of the potential science return.", + "category": "astro-ph" + }, + { + "text": "The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra: We present a statistical analysis of the X-ray flux distribution of Sgr A*\nfrom the Chandra X-ray Observatory's 3 Ms Sgr A* X-ray Visionary Project (XVP)\nin 2012. Our analysis indicates that the observed X-ray flux distribution can\nbe decomposed into a steady quiescent component, represented by a Poisson\nprocess with rate $Q=(5.24\\pm0.08)\\times10^{-3}$ cts s$^{-1},$ and a variable\ncomponent, represented by a power law process ($dN/dF\\propto F^{-\\xi},$\n$\\xi=1.92_{-0.02}^{+0.03}$). This slope matches our recently-reported\ndistribution of flare luminosities. The variability may also be described by a\nlog-normal process with a median unabsorbed 2-8 keV flux of\n$1.8^{+0.9}_{-0.6}\\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$ and a shape parameter\n$\\sigma=2.4\\pm0.2,$ but the power law provides a superior description of the\ndata. In this decomposition of the flux distribution, all of the intrinsic\nX-ray variability of Sgr A* (spanning at least three orders of magnitude in\nflux) can be attributed to flaring activity, likely in the inner accretion\nflow. We confirm that at the faint end, the variable component contributes ~10%\nof the apparent quiescent flux, as previously indicated by our statistical\nanalysis of X-ray flares in these Chandra observations. Our flux distribution\nprovides a new and important observational constraint on theoretical models of\nSgr A*, and we use simple radiation models to explore the extent to which a\nstatistical comparison of the X-ray and infrared can provide insights into the\nphysics of the X-ray emission mechanism.", + "category": "astro-ph" + }, + { + "text": "Systematic bias in the estimate of cluster mass and the fluctuation\n amplitude from cluster abundance statistics: We revisit the estimate of the mass fluctuation amplitude, sigma_8, from the\nobservational X-ray cluster abundance. In particular, we examine the effect of\nthe systematic difference between the cluster virial mass estimated from the\nX-ray spectroscopy, M_{vir, spec}, and the true virial mass of the\ncorresponding halo, M_{vir}. Mazzotta et al. (2004) recently pointed out the\npossibility that alpha_M = M_{vir, spec}/M_{vir} is systematically lower than\nunity. We perform the statistical analysis combining the latest X-ray cluster\nsample and the improved theoretical models and find that sigma_8 \\sim 0.76 +/-\n0.01 + 0.50 (1-alpha_M) for 0.5 \\le alpha_M \\le 1, where the quoted errors are\nstatistical only. Thus if alpha_M \\sim 0.7, the value of sigma_8 from cluster\nabundance alone is now in better agreement with other cosmological data\nincluding the cosmic microwave background, the galaxy power spectrum and the\nweak lensing data. The current study also illustrates the importance of\npossible systematic effects in mapping real clusters to underlying dark halos\nwhich changes the interpretation of cluster abundance statistics.", + "category": "astro-ph" + }, + { + "text": "Tracing the Physical Conditions in Active Galactic Nuclei with\n Time-Dependent Chemistry: We present an extension of the code ProDiMo that allows for a modeling of\nprocesses pertinent to active galactic nuclei and to an ambient chemistry that\nis time dependent. We present a proof-of-concept and focus on a few\nastrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO\nand H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water\nis strongly suppressed and that this affects the bulk of the oxygen and carbon\nchemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly\ntime-dependent, with ratios that vary over orders of magnitude for times longer\nthan 10^4 years. Through ALMA observations this ratio can be used to probe how\nthe narrow-line region evolves under large fluctuations in the SMBH accretion\nrate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also\nfound in species such as H3O+, CO, and H2O. These reflect, respectively, time\ndependent effects in the ionization balance, the transient nature of the\nproduction of molecular gas, and the freeze-out/sublimation of water.", + "category": "astro-ph" + }, + { + "text": "Cosmological model: from initial conditions to structure formation: Observational cosmology is on the verge of new discoveries that will change\nthe essence of our world-view. The matter concerns origin of initial conditions\nand physics of dark matter.", + "category": "astro-ph" + }, + { + "text": "Multiple Populations and a CH Star Found in the 300S Globular Cluster\n Stellar Stream: Milky Way globular clusters (GCs) display chemical enrichment in a phenomenon\ncalled multiple stellar populations (MSPs). While the enrichment mechanism is\nnot fully understood, there is a correlation between a cluster's mass and the\nfraction of enriched stars found therein. However, present-day GC masses are\noften smaller than their masses at the time of formation due to dynamical mass\nloss. In this work, we explore the relationship between mass and MSPs using the\nstellar stream 300S. We present the chemical abundances of eight red giant\nbranch member stars in 300S with high-resolution spectroscopy from\nMagellan/MIKE. We identify one enriched star characteristic of MSPs and no\ndetectable metallicity dispersion, confirming that the progenitor of 300S was a\nglobular cluster. The fraction of enriched stars (12.5\\%) observed in our 300S\nstars is less than the 50\\% of stars found enriched in Milky Way GCs of\ncomparable present-day mass ($\\sim10^{4.5}$\\msun). We calculate the mass of\n300S's progenitor and compare it to the initial masses of intact GCs, finding\nthat 300S aligns well with the trend between the system mass at formation and\nenrichment. 300S's progenitor may straddle the critical mass threshold for the\nformation of MSPs and can therefore serve as a benchmark for the stellar\nenrichment process. Additionally, we identify a CH star, with high abundances\nof \\textit{s}-process elements, probably accreted from a binary companion. The\nrarity of such binaries in intact GCs may imply stellar streams permit the\nsurvival of binaries that would otherwise be disrupted.", + "category": "astro-ph" + }, + { + "text": "No self-shadowing instability in 2D radiation-hydrodynamical models of\n irradiated protoplanetary disks: Theoretical models of protoplanetary disks including stellar irradiation\noften show a spontaneous amplification of scale height perturbations, produced\nby the enhanced absorption of starlight in enlarged regions. In turn, such\nregions cast shadows on adjacent zones that consequently cool down and shrink,\neventually leading to an alternating pattern of overheated and shadowed\nregions. Previous investigations have proposed this to be a real self-sustained\nprocess, the so-called self-shadowing or thermal wave instability, which could\nnaturally form frequently observed disk structures such as rings and gaps, and\neven potentially enhance the formation of planetesimals. All of these, however,\nhave assumed in one way or another vertical hydrostatic equilibrium and\ninstantaneous radiative diffusion throughout the disk. In this work we present\nthe first study of the stability of accretion disks to self-shadowing that\nrelaxes these assumptions, relying instead on radiation-hydrodynamical\nsimulations. We first construct hydrostatic disk configurations by means of an\niterative procedure and show that the formation of a pattern of enlarged and\nshadowed regions is a direct consequence of assuming instantaneous radiative\ndiffusion. We then let these solutions evolve in time, which leads to a fast\ndamping of the initial shadowing features in layers close to the disk surface.\nThese thermally relaxed layers grow towards the midplane until all temperature\nextrema in the radial direction are erased in the entire disk. Our results\nsuggest that radiative cooling and gas advection at the disk surface prevent a\nself-shadowing instability from forming, by damping temperature perturbations\nbefore these reach lower, optically thick regions.", + "category": "astro-ph" + }, + { + "text": "The Structure of HE 1104-1805 from Infrared to X-Ray: The gravitationally lensed quasar HE 1104-1805 has been observed at a variety\nof wavelengths ranging from the mid-infrared to X-ray for nearly 20 years. We\ncombine flux ratios from the literature, including recent Chandra data, with\nnew observations from the SMARTS telescope and HST, and use them to investigate\nthe spatial structure of the central regions using a Bayesian Monte Carlo\nanalysis of the microlensing variability. The wide wavelength coverage allows\nus to constrain not only the accretion disk half-light radius r_1/2, but the\npower-law slope \\xi\\ of the size-wavelength relation r_1/2 ~ \\lambda^\\xi. With\na logarithmic prior on the source size, the (observed-frame) R-band half-light\nradius log(r_1/2/cm) is 16.0+0.3-0.4, and the slope \\xi\\ is 1.0+0.30-0.56. We\nput upper limits on the source size in soft (0.4-1.2 keV) and hard (1.2-8 keV)\nX-ray bands, finding 95% upper limits on log (r_1/2/cm) of 15.33 in both bands.\nA linear prior yields somewhat larger sizes, particularly in the X-ray bands.\nFor comparison, the gravitational radius, using a black hole mass estimated\nusing the H\\beta\\ line, is log(r_g/cm) = 13.94. We find that the accretion disk\nis probably close to face-on, with cos i = 1.0 being four times more likely\nthan cos i = 0.5. We also find probability distributions for the mean mass of\nthe stars in the foreground lensing galaxy, the direction of the transverse\npeculiar velocity of the lens, and the position angle of the projected\naccretion disk's major axis (if not face-on).", + "category": "astro-ph" + }, + { + "text": "The Quark-Hadron Phase Transition, QCD Lattice Calculations and\n Inhomogeneous Big-Bang Nucleosynthesis: We review recent lattice QCD results for the surface tension at the finite\ntemperature quark-hadron phase transition and discuss their implications on the\npossible scale of inhomogeneities. In the quenched approximation the average\ndistance between nucleating centers is smaller than the diffusion length of a\nprotron, so that inhomogeneities are washed out by the time nucleosynthesis\nsets in. Consequently the baryon density fluctuations formed by a QCD phase\ntransition in the early universe cannot significantly affect standard big-bang\nnucleosynthesis calculations and certainly cannot allow baryons to close the\nuniverse. At present lattice results are inconclusive when dynamical fermions\nare included.", + "category": "astro-ph" + }, + { + "text": "Modeling the flyby anomalies with dark matter scattering: update with\n additional data and further predictions: We continue our exploration of whether the flyby anomalies can be explained\nby scattering of spacecraft nucleons from dark matter gravitationally bound to\nthe earth, with the addition of data from five new flybys to that from the\noriginal six. We continue to use our model in which inelastic and elastic\nscatterers populate shells generated by the precession of circular orbits with\nnormals tilted with respect to the earth's axis. With 11 data points and 8\nparameters in the model, a statistically meaningful fit is obtained with a\nchi-squared of 2.7. We give plots of the anomalous acceleration along the\nspacecraft trajectory, and the cumulative velocity change, for the five flybys\nwhich exhibit a significant nonzero anomaly. We also discuss implications of\nthe fit for dark matter-nucleon cross sections, give the prediction of our fit\nfor the anomaly to be expected from the future Juno flyby, and give predictions\nof our fit for flyby orbit orientation changes. In addition we give formulas\nfor estimating the flyby temperature increase caused by dark matter inelastic\nscattering, and for the fraction of flyby nucleons undergoing such scatters.\nFinally, for circular satellite orbits, we give a table of predicted secular\nchanges in orbit radius. These are much too large to be reasonable -- comparing\nwith data for COBE and GP-B supplied to us by Edward Wright (after the first\nversion of this paper was posted), we find that our model predicts changes in\norbit radius that are too large by many orders of magnitude. So the model\nstudied here is ruled out. We conclude that further modeling of the flyby\nanomalies must simultaneously attempt to fit constraints coming from satellite\norbits.", + "category": "astro-ph" + }, + { + "text": "Ionizing photon production of Population III stars: effects of rotation,\n convection, and initial mass function: The first stars are thought to be one of the dominant sources of hydrogen\nreionization in the early Universe, with their high luminosities and surface\ntemperatures expected to drive high ionizing photon production rates. In this\nwork, we take our Geneva stellar evolution models of zero-metallicity stars and\npredict their production rates of photons capable to ionize H, He I and He II,\nbased on a blackbody approximation. We present analytical fits in the range\n1.7-500 solar masses. We then explore the impact of stellar initial mass,\nrotation, and convective overshooting for individual stars. We have found that\nionizing photon production rates increase with increasing initial mass. For the\nrotational velocities considered we see changes of up to 25% to ionizing\nphotons produced. This varies with initial mass and ionizing photon species and\nreflects changes to surface properties due to rotation. We have also found that\nhigher convective overshooting increases ionizing photon production by\napproximately 20% for the change in overshooting considered here. For stellar\npopulations, we explore how the production of ionizing photons varies as a\nfunction of the initial mass function (IMF) slope, and minimum and maximum\ninitial masses. For a fixed population mass we have found changes of the order\nof 20-30% through varying the nature of the IMF. This work presents ionizing\nphoton production predictions for the most up to date Geneva stellar evolution\nmodels of Population III stars, and provides insight into how key evolutionary\nparameters impact the contribution of the first stars to reionization.", + "category": "astro-ph" + }, + { + "text": "Reverberation measurement of the inner radius of the dust torus in NGC\n 4151 during 2008-2013: We investigate the correlation between infrared (JHKL) and optical (B) fluxes\nof the variable nucleus of the Seyfert galaxy NGC 4151 using partially\npublished data for the last 6 years (2008-2013.). Here we are using the same\ndata as in Oknyansky et al. (2014), but include also optical (B) data from Guo\net al. We find that the lag of flux in all the infrared bands is the same, 40\n+- 6 days, to within the measurement accuracy. Variability in the J and K bands\nis not quite simultaneous, perhaps due to the differing contributions of the\naccretion disk in these bands. The lag found for the K band compared with the B\nband is not significantly different from earlier values obtained for the period\n2000-2007. However, finding approximately the same lags in all IR bands for\n2008-2013 differs from previous results at earlier epochs when the lag\nincreased with increasing wavelength. Examples of almost the same lag in\ndifferent IR bands are known for some other active nuclei. In the case of NGC\n4151 it appears that the relative lags between the IR bands may be different in\ndifferent years. The available data, unfortunately, do not allow us to\ninvestigate a possible change in the lags during the test interval. We discuss\nour results in the framework of the standard model where the variable infrared\nradiation is mainly due to thermal re-emission from the part of the dusty torus\nclosest to the central source. There is also a contribution of some IR emission\nfrom the accretion disk, and this contribution increases with decreasing\nwavelength. Some cosmological applications of obtained results are discussed.", + "category": "astro-ph" + }, + { + "text": "Global 21-cm signal extraction from foreground and instrumental effects\n I: Pattern recognition framework for separation using training sets: The sky-averaged (global) highly redshifted 21-cm spectrum from neutral\nhydrogen is expected to appear in the VHF range of $\\sim20-200$ MHz and its\nspectral shape and strength are determined by the heating properties of the\nfirst stars and black holes, by the nature and duration of reionization, and by\nthe presence or absence of exotic physics. Measurements of the global signal\nwould therefore provide us with a wealth of astrophysical and cosmological\nknowledge. However, the signal has not yet been detected because it must be\nseen through strong foregrounds weighted by a large beam, instrumental\ncalibration errors, and ionospheric, ground and radio-frequency-interference\neffects, which we collectively refer to as \"systematics\". Here, we present a\nsignal extraction method for global signal experiments which uses Singular\nValue Decomposition (SVD) of \"training sets\" to produce systematics basis\nfunctions specifically suited to each observation. Instead of requiring precise\nabsolute knowledge of the systematics, our method effectively requires precise\nknowledge of how the systematics can vary. After calculating eigenmodes for the\nsignal and systematics, we perform a weighted least square fit of the\ncorresponding coefficients and select the number of modes to include by\nminimizing an information criterion. We compare the performance of the signal\nextraction when minimizing various information criteria and find that\nminimizing the Deviance Information Criterion (DIC) most consistently yields\nunbiased fits. The methods used here are built into our widely applicable,\npublicly available Python package, $\\texttt{pylinex}$, which analytically\ncalculates constraints on signals and systematics from given data, errors, and\ntraining sets.", + "category": "astro-ph" + }, + { + "text": "The iron and oxygen content of LMC Classical Cepheids and its\n implications for the Extragalactic Distance Scale and Hubble constant: Classical Cepheids are primary distance indicators and a crucial stepping\nstone to determining the present-day Hubble constant Ho to the precision and\naccuracy required to constrain apparent deviations from the LCDM Concordance\nCosmological Model. We have measured the iron and oxygen abundances of of 89\nCepheids in the LMC, one of the anchors of the local Distance Scale,\nquadrupling the prior sample and including 68 of the 70 Cepheids used to\nconstrain Ho by the SH0ES program. The goal is to constrain the extent to which\nthe Cepheid luminosity is influenced by their chemical composition, an\nimportant contributor to the uncertainty on the determination of the Ho itself\nand a critical factor in the internal consistency of the distance ladder. We\nhave derived stellar parameters and abundances from a self-consistent\nspectroscopic analysis based on Equivalent Width of absorption lines. The\n[Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of\n-0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex.\nThe latter is fully compatible with the measurement error and supports the low\ndispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The\nuniformity of the abundance has the important consequence that the LMC Cepheids\nalone cannot provide any meaningful constraint on the dependence of the Cepheid\nPeriod-Luminosity relation on chemical composition at any wavelength. This\nrevises a prior claim based on a small sample of 22 LMC Cepheids that there was\nlittle dependence (or uncertainty) between composition and NIR luminosity, a\nconclusion which would produce a conflict between anchors of the distance\nladder with different mean abundance. The chemical homogeneity of the LMC\nCepheid population makes it an ideal environment to calibrate the metallicity\ndependence between the more metal poor SMC and metal rich Milky Way and\nNGC4258.", + "category": "astro-ph" + }, + { + "text": "Dwarf pulses of 10 pulsars detected by FAST: How pulsars radiate is a long-standing problem. Detailed polarization\nmeasurements of individual pulses shed light on currently unknown emission\nprocesses. Recently, based on supersensitive observations, dwarf pulses have\nbeen recognized as weak narrow pulses often appearing during the nulling state.\nIn this study, we report the detection of dwarf pulses from ten pulsars, PSRs\nB0525+21, B1237+25, J1538+2345, J1824$-$0127, J1851$-$0053, B1901+10, J1939+10,\nB1944+17, B2000+40 and J2112+4058, based on observations conducted with the\nFive-hundred-meter Aperture Spherical radio Telescope. Dwarf pulses of five\npulsars are clearly discernible in the two-dimensional distribution of pulse\nintensity and pulse width. For the other five pulsars, PSRs J1538+2345,\nJ1824$-$0127, J1939+10, B2000+40, and J2112+4058, only a few dwarf pulses are\ndetected from pulse stacks. The dwarf pulses can emerge in both cone and core\nemission components for PSR B1237+25, and the polarization angles of these\ndwarf pulses are mostly in the orthogonal polarization mode of normal pulses\nfor PSR B1944+17. In general, pulsars with detected dwarf pulses tend to be\nlocated within the \"death valley\" region of the distribution of pulsar periods\nand period derivatives.", + "category": "astro-ph" + }, + { + "text": "Sunward propagating whistler waves collocated with localized magnetic\n field holes in the solar wind: Parker Solar Probe observations at 35.7 Sun\n radii: Observations by the Parker Solar Probe mission of the solar wind at about\n35.7 solar radii reveal the existence of whistler wave packets with frequencies\nbelow 0.1 f/fce (20-80 Hz in the spacecraft frame). These waves often coincide\nwith local minima of the magnetic field magnitude or with sudden deflections of\nthe magnetic field that are called switchbacks. Their sunward propagation leads\nto a significant Doppler frequency downshift from 200-300 Hz to 20-80 Hz (from\n0.2 f/fce to 0.5 f/fce). The polarization of these waves varies from\nquasi-parallel to significantly oblique with wave normal angles that are close\nto the resonance cone. Their peak amplitude can be as large as 2 to 4 nT. Such\nvalues represent approximately 10% of the background magnetic field, which is\nconsiderably more than what is observed at 1 a.u. Recent numerical studies show\nthat such waves may potentially play a key role in breaking the heat flux and\nscattering the Strahl population of suprathermal electrons into a halo\npopulation.", + "category": "astro-ph" + }, + { + "text": "Probing the Galactic Bulge with deep Adaptive Optics imaging: the age of\n NGC 6440: We present first results of a pilot project aimed at exploiting the\npotentiality of ground based adaptive optics imaging in the near infrared to\ndetermine the age of stellar clusters in the Galactic Bulge. We have used a\ncombination of high resolution adaptive optics (ESO-VLT NAOS-CONICA) and\nwide-field (ESO-NTT-SOFI) photometry of the metal rich globular cluster NGC\n6440 located towards the inner Bulge, to compute a deep color magnitude diagram\nfrom the tip of the Red Giant Branch down to J~22$, two magnitudes below the\nMain Sequence Turn Off (TO). The magnitude difference between the TO level and\nthe red Horizontal Branch has been used as an age indicator. It is the first\ntime that such a measurement for a bulge globular cluster has been obtained\nwith a ground based telescope. From a direct comparison with 47 Tuc and with a\nset of theoretical isochrones, we concluded that NGC 6440 is old and likely\ncoeval to 47 Tuc. This result adds a new evidence that the Galactic Bulge is ~2\nGyr younger at most than the pristine, metal poor population of the Galactic\nHalo.", + "category": "astro-ph" + }, + { + "text": "Dark Energy Probes in Light of the CMB: CMB observables have largely fixed the expansion history of the universe in\nthe deceleration regime and provided two self-calibrated absolute standards for\ndark energy studies: the sound horizon at recombination as a standard ruler and\nthe amplitude of initial density fluctuations. We review these inferences and\nexpose the testable assumptions about recombination and reionization that\nunderly them. Fixing the deceleration regime with CMB observables, deviations\nin the distance and growth observables appear most strongly at z=0 implying\nthat accurate calibration of local and CMB standards may be more important than\nredshift range or depth. The single most important complement to the CMB for\nmeasuring the dark energy equation of state at z~0.5 is a determination of the\nHubble constant to better than a few percent. Counterintuitively, with fixed\nfractional distance errors and relative standards such as SNe, the Hubble\nconstant measurement is best achieved in the high redshift deceleration regime.\nDegeneracies between the evolution and current value of the equation of state\nor between its value and spatial curvature can be broken if percent level\nmeasurement and calibration of distance standards can be made at intermediate\nredshifts or the growth function at any redshift in the acceleration regime. We\ncompare several dark energy probes available to a wide and deep optical survey:\nbaryon features in galaxy angular power spectra and the growth rate from\ngalaxy-galaxy lensing, shear tomography and the cluster abundance.", + "category": "astro-ph" + }, + { + "text": "X-ray and radio studies of SNR CTB 37B hosting the magnetar CXOU\n J171405.7-381031: We present a Chandra and XMM-Newton study of the SNR CTB 37B, along with\narchival radio observations. In radio wavelengths, CTB 37B is an incomplete\nshell showing bright emission from the eastern side while the X-ray morphology\nshows diffuse emission from regions surrounding the magnetar CXOU\nJ171405.7-381031. We used archival HI absorption measurements to constrain the\ndistance to the remnant as 9.8+/-1.5 kpc. The X-ray spectrum of the remnant is\ndescribed by a thermal model in the 1-5 keV energy range, with a temperature of\n1.3+/-0.1 keV. The abundances from the spectral fits are consistent with being\nsolar or sub-solar. A small region of diffuse emission is seen to the southern\nside of the remnant, best fitted by a nonthermal spectrum with an unusually\nhard photon index of 1.3+/-0.3. Assuming a distance of 9.8 kpc to the SNR, we\ninfer a shock velocity of 915+/-70 km/s and explosion energy of (1.8+/-0.6)e50\nergs. The overall imaging and spectral properties of CTB 37B favor the\ninterpretation of a young SNR (6200 yr) propagating in a low-density medium,\nunder the assumption of a Sedov evolutionary phase.", + "category": "astro-ph" + }, + { + "text": "Concentration, Ellipsoidal Collapse, and the Densest Dark Matter haloes: The smallest dark matter haloes are the first objects to form in the\nhierarchical structure formation of cold dark matter (CDM) cosmology and are\nexpected to be the densest and most fundamental building blocks of CDM\nstructures in our universe. Nevertheless, the physical characteristics of these\nhaloes have stayed illusive, as they remain well beyond the current resolution\nof N-body simulations (at redshift zero). However, they dominate the\npredictions (and uncertainty) in expected dark matter annihilation signal,\namongst other astrophysical observables. Using the conservation of total energy\nand the ellipsoidal collapse framework, we can analytically find the mean and\nscatter of concentration $c$ and 1-D velocity dispersion $\\sigma_{\\rm 1d}$ for\nhaloes of different virial mass $M_{200}$. Both $c$ and $\\sigma_{\\rm\n1d}/M_{200}^{1/3}$ are in good agreement with numerical results within the\nregime probed by simulations -- slowly decreasing functions of mass that\napproach constant values at large masses. In particular, the predictions for\nthe 1-D velocity dispersion of cluster mass haloes are surprisingly robust as\nthe inverse heat capacity of cosmological haloes crosses zero at $M_{200} \\sim\n10^{14} M_\\odot$. However, we find that current extrapolations from simulations\nto smallest CDM haloes dramatically depend on the assumed profile (e.g. NFW vs.\nEinasto) and fitting function, which is why theoretical considerations, such as\nthe one presented here, can significantly constrain the range of feasible\npredictions.", + "category": "astro-ph" + }, + { + "text": "Resurrecting Quartic and Quadratic inflaton potentials in two-field\n inflationary model: After the release of the PLANCK data, it is evident that inflationary\nparadigm has stood the test of time. Even though, it is difficult to realise\ninflationary paradigm in a particle physics model as the present observations\nhave ruled out the simplest quartic and quadratic inflationary potentials,\nwhich generically arise in particle physics. We would show that such simplest\ninflationary potentials can evade discrepancies with observations, if the\ninflaton field is assisted by another scalar during inflation. Moreover, unlike\nother multifield models, our model yields no isocurvature perturbations and\nnegligible non-Gaussianity, making it more compatible with the present data.\nAbove all, our model can also be realised in the framework of SUGRA.", + "category": "astro-ph" + }, + { + "text": "A \"metric\" semi-Lagrangian Vlasov-Poisson solver: We propose a new semi-Lagrangian Vlasov-Poisson solver. It employs elements\nof metric to follow locally the flow and its deformation, allowing one to find\nquickly and accurately the initial phase-space position $Q(P)$ of any test\nparticle $P$, by expanding at second order the geometry of the motion in the\nvicinity of the closest element. It is thus possible to reconstruct accurately\nthe phase-space distribution function at any time $t$ and position $P$ by\nproper interpolation of initial conditions, following Liouville theorem. When\ndistorsion of the elements of metric becomes too large, it is necessary to\ncreate new initial conditions along with isotropic elements and repeat the\nprocedure again until next resampling. To speed up the process, interpolation\nof the phase-space distribution is performed at second order during the\ntransport phase, while third order splines are used at the moments of\nremapping. We also show how to compute accurately the region of influence of\neach element of metric with the proper percolation scheme. The algorithm is\ntested here in the framework of one-dimensional gravitational dynamics but is\nimplemented in such a way that it can be extended easily to four or\nsix-dimensional phase-space. It can also be trivially generalised to plasmas.", + "category": "astro-ph" + }, + { + "text": "The sigma - L correlation in Nearby Early-Type Galaxies: Early-type galaxy velocity dispersions and luminosities are correlated. The\ncorrelation estimated in local samples (< 100 Mpc) differs from that measured\nmore recently in the SDSS. This is true even when systematics in the SDSS\nphotometric and spectroscopic parameters have been accounted-for. We show that\nthis is also true for the ENEAR sample if galaxy luminosities are estimated\nusing distances which have been corrected for peculiar motions. We then show\nthat, because the estimate of the `true' distance is derived from a correlation\nwith velocity dispersion, in this case the D_n-sigma relation, using it in the\nsigma-L relation leads to an artificially tight relation with a biased slope.\nMaking no correction for peculiar velocities results in a sigma-L relation\nwhich is very similar to that of the SDSS, although with larger scatter. We\nalso measure the sigma-L correlation in a mock ENEAR catalog, in which the\nunderlying galaxy sample has the same sigma-L correlation as seen in the SDSS.\nThe mock catalog produces the same D_n-sigma relation as the data, the same\nbiased slope when D_n-sigma distances are used to estimate luminosities, and\ngood agreement with the input sigma-L relation when redshift is used as the\ndistance indicator. This provides further evidence that the true sigma-L\nrelation of ENEAR galaxies is indeed very similar to that of SDSS early-types.\nOur results suggest that local sigma-L relations which are based on Fundamental\nPlane distances should also be re-evaluated. Our findings also have important\nimplications for black hole demographics; the best direct estimates of the\nmasses of supermassive black holes come from local galaxies, so estimates of\nthe black hole mass function are more safely made by working with the Mbh-sigma\ncorrelation than with Mbh-L.", + "category": "astro-ph" + }, + { + "text": "On the methanol masers in G9.62+0.20E and G188.95+0.89: A comparison between the observed light curves of periodic masers in\nG9.62+0.20E and G188.95+0.89 and the results of a simple colliding-wind binary\nmodel is made to establish whether the flaring and other time-dependent\nbehaviour of the masers in these two star forming regions can be ascribed to\nchanges in the environment of the masers or in the continuum emission from\nparts of the background \\ion{H}{2} region. It is found that the light curves of\nwidely different shape and amplitude in these two objects can be explained\nwithin the framework of a periodic pulse of ionizing radiation that raises the\nelectron density in a volume of partially ionized gas against which the masers\nare projected. It is also shown that the decay of the 11.405 $\\kmps$ maser in\nG188.95+0.89 can be explained very well in terms of the recombination of the\nionized gas against which the maser is projected while it would require very\nspecial conditions to explain it in terms of changes in environment of the\nmaser. We conclude that for G9.62+0.20E and G188.95+0.89 the observed changes\nin the masers are most likely due to changes in the background free-free\nemission which is amplified by the masers.", + "category": "astro-ph" + }, + { + "text": "On the phase-space structure of the Milky Way dark-matter halo: We analyse a high resolution simulation of the formation of a cluster's\ndark-matter halo in a $\\Lambda$CDM cosmology (Springel et al. 2001). The\nresolution achieved allows us to map the phase-space structure in detail, and\ncharacterize its evolution and degree of lumpiness. Scaling down the cluster\nhalo to a Milky-Way size halo, we probe the substructure expected in the solar\nneighbourhood. Here we specifically address the relevance of such substructure\nfor direct detection experiments aimed at determining the nature of\ndark-matter.", + "category": "astro-ph" + }, + { + "text": "Viscosity driven instability in rotating relativistic stars: We investigate the viscosity driven instability in rotating relativistic\nstars by means of an iterative approach. We focus on polytropic rotating\nequilibrium stars and impose an m=2 perturbationin the lapse. We vary both the\nstiffness of the equation of state and the compactness of the star to study\nthose effects on the value of the threshold. For a uniformly rotating star, the\ncriterion T/W, where T is the rotational kinetic energy and W is the\ngravitational binding energy, mainly depends on the compactness of the star and\ntakes values around 0.13 ~ 0.16, which differ slightly from that of Newtonian\nincompressible stars (~ 0.14). For differentially rotating stars, the critical\nvalue of T/W is found to span the range 0.17 - 0.25. This is significantly\nlarger than the uniformly rotating case with the same compactness of the star.\nFinally we discuss a possibility of detecting gravitational waves from\nviscosity driven instability with ground-based interferometers.", + "category": "astro-ph" + }, + { + "text": "A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies\n of the Binary X-ray Pulsar 4U0115+63 with RXTE: The present paper reports on the RXTE observations of the binary X-ray pulsar\n4U0115+63, covering an outburst in 1999 March-April with 44 pointings. The 3-30\nkeV PCA spectra and the 15-50 keV HEXTE spectra were analyzed jointly for the\ncyclotron resonance features. When the 3-50 keV luminosity at an assumed\ndistance of 7 kpc was in the range (5-13)x10^{37} erg s^{-1}, harmonic double\ncyclotron features were observed in absorption at ~11 and ~22 keV, as was\nmeasured previously during typical outbursts. As the luminosity decreased below\n\\~5x10^{37} erg s^{-1}, the second resonance disappeared, and the fundamental\nresonance energy gradually increased, up to $\\sim$16 keV at 0.16x10^{37} erg\ns^{-1}. These results reconfirm the report by Mihara et al. (2004) using Ginga,\nwho observed a single absorption at ~16 keV in a minor (~10^{37} erg s^{-1})\noutburst of this object. The luminosity-dependent cyclotron resonance energy\nmay be understood as a result of a decrease in the accretion column height, in\nresponse to a decrease in the mass accretion rate.", + "category": "astro-ph" + }, + { + "text": "Astrometric asteroid masses: a simultaneous determination: Using over 89 million astrometric observations of 349,737 numbered minor\nplanets, an attempt was made to determine the masses of 230 of them by\nsimultaneously solving for corrections to all orbital elements and the masses.\nFor 132 minor planets an acceptable result was obtained, 50 of which appear to\nbe new.", + "category": "astro-ph" + }, + { + "text": "Evidence Against a Redshift z>6 for the Galaxy STIS 123627+621755: The identification of galaxies at extreme distances provides our most direct\ninformation on the earliest phases of galaxy formation. The distance implied by\nredshifts z > 5 makes this a challenging endeavor for even the most luminous\nsources; interpretation of low signal-to-noise ratio observations of faint\ngalaxies is difficult and occasional misidentifications will occur. Here we\nreport on STIS 123627+621755, a galaxy with a suggested spectroscopic redshift\nof z = 6.68 and the most distant spectroscopically-identified object claimed.\nFor the suggested redshift and reported spectral energy distribution, the\ngalaxy should be essentially invisible shortward of 9300 Angstroms because the\nintervening intergalactic medium absorbs essentially all light energetic enough\nto ionize neutral hydrogen (lambda < (1 + z) x 912 Angstroms; the redshifted\nLyman limit). The galaxy should be relatively bright in the near-infrared with\nf(nu) ~ 1 microJy. Here we report a detection of the galaxy at 6700 Angstroms,\nbelow the Lyman limit for z = 6.68. We also report a non-detection at 1.2\nmicrons, implying the flux has dropped by a factor of three or more between\nrest 1216 Angstroms and rest 1560 Angstroms for z = 6.68. Our observations are\ninconsistent with the suggested extreme distance of STIS 123627+621755 and\nconservatively require z < 6.", + "category": "astro-ph" + }, + { + "text": "BeppoSAX observations of the nearby low-mass X-ray binary and fast\n transient SAX J1819.3-2525: SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large\nX-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and\nthe Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525\nat various stages of its activity before that, in the spring and fall of 1999.\nThe fluxes range between 0.012 and 0.3 Crab units (2-10 keV). The NFI\nobservation is unique because it is the longest semi-continuous observation of\nSAX J1819.3-2525 so far, and it offers a study of the spectrum at a relatively\nhigh resolution of 8% full width at half maximum at 6 keV. We discuss the\nobservations with emphasis on the X-ray spectrum. A strong Fe-K emission line\nwas detected in SAX J1819.3-2525 with an equivalent width between 0.3 and 1\nkeV. The line energy is up to 6.85 +/- 0.02 keV and suggests the presence of\nhighly ionized iron. We identify this as fluorescent emission from a\nphoto-ionized plasma. The continuum spectrum is typical for a low-mass X-ray\nbinary in which emission from an accretion disk corona plays an important role.\nThere is no sign of an eclipse or periodic signal due to the binary orbit in\nthis exposure, despite the fact that the twin jets seen at radio wavelengths\nsuggest a high inclination angle.", + "category": "astro-ph" + }, + { + "text": "Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus\n GJ3470b: A Hint for Cloud-free Atmosphere: We present optical (g', R_c, and I_c) to near-infrared (J) simultaneous\nphotometric observations for a primary transit of GJ3470b, a Uranus-mass\ntransiting planet around a nearby M dwarf, by using the 50-cm MITSuME telescope\nand the 188-cm telescope, both at Okayama Astrophysical Observatory. From these\ndata, we derive the planetary mass, radius, and density as 14.1 \\pm 1.3\nM_earth, 4.32^{+0.21}_{-0.10} R_earth, and 0.94 \\pm 0.12 g cm^{-3},\nrespectively, thus confirming the low density that was reported by Demory et\nal. based on the Spitzer/IRAC 4.5-micron photometry (0.72^{+0.13}_{-0.12} g\ncm^{-3}). Although the planetary radius is about 10% smaller than that reported\nby Demory et al., this difference does not alter their conclusion that the\nplanet possesses a hydrogen-rich envelope whose mass is approximately 10% of\nthe planetary total mass. On the other hand, we find that the planet-to-star\nradius ratio (R_p/R_s) in the J band (0.07577^{+0.00072}_{-0.00075}) is smaller\nthan that in the I_c (0.0802 \\pm 0.0013) and 4.5-micron\n(0.07806^{+0.00052}_{-0.00054}) bands by 5.9% \\pm 2.0% and 3.0% \\pm 1.2%,\nrespectively. A plausible explanation for the differences is that the planetary\natmospheric opacity varies with wavelength due to absorption and/or scattering\nby atmospheric molecules. Although the significance of the observed R_p/R_s\nvariations is low, if confirmed, this fact would suggest that GJ3470b does not\nhave a thick cloud layer in the atmosphere. This property would offer a wealth\nof opportunity for future transmission-spectroscopic observations of this\nplanet to search for certain molecular features, such as H2O, CH4, and CO,\nwithout being prevented by clouds.", + "category": "astro-ph" + }, + { + "text": "Exploring the Variable Sky with LINEAR. I. Photometric Recalibration\n with SDSS: We describe photometric recalibration of data obtained by the asteroid survey\nLINEAR. Although LINEAR was designed for astrometric discovery of moving\nobjects, the dataset described here contains over 5 billion photometric\nmeasurements for about 25 million objects, mostly stars. We use SDSS data from\nthe overlapping ~10,000 deg^2 of sky to recalibrate LINEAR photometry, and\nachieve errors of 0.03 mag for sources not limited by photon statistics, with\nerrors of 0.2 mag at r~18. With its 200 observations per object on average,\nLINEAR data provide time domain information for the brightest 4 magnitudes of\nSDSS survey. At the same time, LINEAR extends the deepest similar wide-area\nvariability survey, the Northern Sky Variability Survey, by 3 mag. We briefly\ndiscuss the properties of about 7,000 visually confirmed periodic variables,\ndominated by roughly equal fractions of RR Lyrae stars and eclipsing binary\nstars, and analyze their distribution in optical and infra-red color-color\ndiagrams. The LINEAR dataset is publicly available from the SkyDOT website\n(http://skydot.lanl.gov).", + "category": "astro-ph" + }, + { + "text": "Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase\n Measurements of the Event Horizon Telescope: General relativistic magnetohydrodynamic (GRMHD) simulations of accretion\ndisks and jets associated with supermassive black holes show variability on a\nwide range of timescales. On timescales comparable to or longer than the\ngravitational timescale $t_G=GM/c^3$, variation may be dominated by orbital\ndynamics of the inhomogeneous accretion flow. Turbulent evolution within the\naccretion disk is expected on timescales comparable to the orbital period,\ntypically an order of magnitude larger than $t_G$. For Sgr A*, $t_G$ is much\nshorter than the typical duration of a VLBI experiment, enabling us to study\nthis variability within a single observation. Closure phases, the sum of\ninterferometric visibility phases on a triangle of baselines, are particularly\nuseful for studying this variability. In addition to a changing source\nstructure, variations in observed closure phase can also be due to interstellar\nscattering, thermal noise, and the changing geometry of projected baselines\nover time due to Earth rotation. We present a metric that is able to\ndistinguish the latter two from intrinsic or scattering variability. This\nmetric is validated using synthetic observations of GRMHD simulations of Sgr\nA*. When applied to existing multi-epoch EHT data of Sgr A*, this metric shows\nthat the data are most consistent with source models containing intrinsic\nvariability from source dynamics, interstellar scattering, or a combination of\nthose. The effects of black hole inclination, orientation, spin, and morphology\n(disk or jet) on the expected closure phase variability are also discussed.", + "category": "astro-ph" + }, + { + "text": "Characterisation of pulsed Carbon fiber illuminators for FIR instrument\n calibration: We manufactured pulsed illuminators emitting in the far infrared for the\nPlanck-HFI bolometric instrument ground calibrations. Specific measurements\nhave been conducted on these light sources, based on Carbon fibers, to\nunderstand and predict their properties. We present a modelisation of the\ntemperature dependence of the thermal conductivity and the calorific\ncapacitance of the fibers. A comparison between simulations and bolometer data\nis given, that shows the coherence of our model. Their small time constants,\ntheir stability and their emission spectrum pointing in the submm range make\nthese illuminators a very usefull tool for calibrating FIR instruments.", + "category": "astro-ph" + }, + { + "text": "Inside-out or Outside-in: The topology of reionization in the\n photon-starved regime suggested by Lyman-alpha forest data: We use a set of semi-numerical simulations based on Zel'dovich approximation,\nfriends-of-friends algorithm and excursion set formalism to generate\nreionization maps of high dynamic range with a range of assumptions regarding\nthe distribution and luminosity of ionizing sources and the spatial\ndistribution of sinks for the ionizing radiation. We find that ignoring the\ninhomogeneous spatial distribution of regions of high gas density where\nrecombinations are important -- as is often done in studies of this kind -- can\nlead to misleading conclusions regarding the topology of reionization,\nespecially if reionization occurs in the photon-starved regime suggested by Lya\nforest data. The inhomogeneous spatial distribution of recombinations\nsignificantly reduces the mean free path of ionizing photons and the typical\nsize of coherently ionized regions. Reionization proceeds then much more as an\noutside-in process. Low-density regions far from ionizing sources become\nionized before regions of high gas density not hosting sources of ionizing\nradiation. The spatial distribution of sinks of ionization radiation also\nsignificantly affects shape and amplitude the power spectrum of fluctuations of\n21cm emission. The slope of the 21cm power spectrum as measured by upcoming\n21cm experiments should be able to distinguish to what extent the topology of\nreionization proceeds outside-in or inside-out while the evolution of the\namplitude of the power spectrum with increasing ionized mass fraction should be\nsensitive to the spatial distribution and the luminosity of ionizing sources.", + "category": "astro-ph" + }, + { + "text": "The ALMA Survey of 70 \u03bcm Dark High-mass Clumps in Early Stages\n (ASHES). X: Hot Gas Reveals Deeply Embedded Star Formation: Massive infrared dark clouds (IRDCs) are considered to host the earliest\nstages of high-mass star formation. In particular, 70 $\\mu$m dark IRDCs are the\ncolder and more quiescent clouds. At a scale of about 5000 au using\nformaldehyde (H2CO) emission, we investigate the kinetic temperature of dense\ncores in 12 IRDCs obtained from the pilot ALMA Survey of 70 $\\mu$m dark\nHigh-mass clumps in Early Stages (ASHES). Compared to 1.3 mm dust continuum and\nother molecular lines, such as C18O and deuterated species, we find that H2CO\nis mainly sensitive to low-velocity outflow components rather than to quiescent\ngas expected in the early phases of star formation. The kinetic temperatures of\nthese components range from 26 to 300 K. The Mach number reaches about 15 with\nan average value of about 4, suggesting that the velocity distribution of gas\ntraced by H2CO is significantly influenced by a supersonic non-thermal\ncomponent. In addition, we detect warm line emission from HC3N and OCS in 14\nprotostellar cores, which requires high excitation temperatures (Eu/k ~ 100 K).\nThese results show that some of the embedded cores in the ASHES fields are in\nan advanced evolutionary stage, previously unexpected for 70 $\\mu$m dark IRDCs.", + "category": "astro-ph" + }, + { + "text": "X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31: This study represents the most sensitive Chandra X-ray point source catalogue\nof M31. Using 133 publicly available Chandra ACIS-I/S observations totalling ~1\nMs, we detected 795 X-ray sources in the bulge, northeast, and southwest fields\nof M31, covering an area of approximately 0.6 deg$^{2}$, to a limiting\nunabsorbed 0.5-8.0 keV luminosity of $10^{34}$ erg/s. In the inner bulge, where\nexposure is approximately constant, X-ray fluxes represent average values\nbecause they were determined from many observations over a long period of time.\nSimilarly, our catalogue is more complete in the bulge fields since monitoring\nallowed more transient sources to be detected. The catalogue was\ncross-correlated with a previous XMM-Newton catalogue of M31's $D_{25}$\nisophote consisting of 1948 X-ray sources, with only 979 within the field of\nview of our survey. We found 387 (49%) of our Chandra sources (352 or 44%\nunique sources) matched to within 5 arcsec of 352 XMM-Newton sources. Combining\nthis result with matching done to previous Chandra X-ray sources we detected\n259 new sources in our catalogue. We created X-ray luminosity functions (XLFs)\nin the soft (0.5-2.0 keV) and hard (2.0-8.0 keV) bands that are the most\nsensitive for any large galaxy based on our detection limits.\nCompleteness-corrected XLFs show a break around $1.3\\times10^{37}$ erg/s,\nconsistent with previous work. As in past surveys, we find the bulge XLFs are\nflatter than the disk, indicating a lack of bright high-mass X-ray binaries in\nthe disk and an aging population of low-mass X-ray binaries in the bulge.", + "category": "astro-ph" + }, + { + "text": "Window function dependence of the novel mass function of primordial\n black holes: We investigate the ambiguity of the novel mass function of primordial black\nholes, which has succeeded in identifying the black hole mass in a given\nconfiguration of fluctuations, due to the choice of window function of smoothed\ndensity fluctuations. We find that while the window function dependence of the\nexponential factor in the novel mass function is the same as the one in the\nconventional mass function around the top-hat scale, the dependences are\ndifferent on other scales, which leads to the narrower mass function in the\nnovel formulation for some window functions.", + "category": "astro-ph" + }, + { + "text": "Toward a global model of the interactions in low-lying states of methyl\n cyanide: rotational and rovibrational spectroscopy of the $v_4 = 1$ state and\n tentative interstellar detection of the $v_4 = v_8 = 1$ state in Sgr B2(N): New and existing rotational spectra of methyl cyanide were analyzed to extend\nthe global model of low-lying vibrational states and their interactions to\n$v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the\n36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16,\nrespectively. Information on the $K$ level structure of CH$_3$CN is obtained\nfrom IR spectra. A spectrum of $2\\nu_8$ around 717 cm$^{-1}$, analyzed in our\nprevious study, covered also the $\\nu_4$ band. The assignments in this band\ncover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13,\nrespectively.\n The most important interaction of $v_4=1$ appears to be with $v_8=3$, $\\Delta\nK=0$, $\\Delta l=+3$, a previously characterized anharmonic resonance. We report\nnew analyses of interactions with $\\Delta K=-2$ and $\\Delta l=+1$, with $\\Delta\nK=-4$ and $\\Delta l=-1$, and with $\\Delta K=-6$ and $\\Delta l=-3$; these four\ntypes of interactions connect all $l$ substates of $v_8=3$ in energy to\n$v_4=1$. A known $\\Delta K=-2$, $\\Delta l=+1$ interaction with $v_7=1$ was also\nanalyzed, and investigations of the $\\Delta K=+1$, $\\Delta l=-2$ and $\\Delta\nK=+3$, $\\Delta l=0$ resonances with $v_8=2$ were improved, as were interactions\nbetween successive states with $v_8\\le 3$, mainly through new $v_8\\le 2$\nrotational data.\n A preliminary single state analysis of the $v_4=v_8=1$ state was carried out\nbased on rotational transition frequencies and on $\\nu_4+\\nu_8-\\nu_8$ hot band\ndata. A considerable fraction of the $K$ levels was reproduced within\nuncertainties in its entirety or in part, despite obvious widespread\nperturbations in $v_4=v_8=1$.\n We detect rotational transitions of methyl cyanide from within all\nvibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot\nmolecular core of Sagittarius B2(N) employing the Atacama Large Millimeter\nArray.", + "category": "astro-ph" + }, + { + "text": "Matching Radio Catalogs with Realistic Geometry: Application to SWIRE\n and ATLAS: Crossmatching catalogs at different wavelengths is a difficult problem in\nastronomy, especially when the objects are not point-like. At radio wavelengths\nan object can have several components corresponding, for example, to a core and\nlobes. {Considering not all radio detections correspond to visible or infrared\nsources, matching these catalogs can be challenging.} Traditionally this is\ndone by eye for better quality, which does not scale to the large data volumes\nexpected from the next-generation of radio telescopes. We present a novel\nautomated procedure, using Bayesian hypothesis testing, to achieve reliable\nassociations by explicit modelling of a particular class of radio-source\nmorphology. {The new algorithm not only assesses the likelihood of an\nassociation between data at two different wavelengths, but also tries to assess\nwhether different radio sources are physically associated, are double-lobed\nradio galaxies, or just distinct nearby objects.} Application to the SWIRE and\nATLAS CDF-S catalogs shows that this method performs well without human\nintervention.", + "category": "astro-ph" + }, + { + "text": "ALMA observations of cold molecular gas filaments trailing rising radio\n bubbles in PKS0745-191: We present ALMA observations of the CO(1-0) and CO(3-2) line emission tracing\nfilaments of cold molecular gas in the central galaxy of the cluster\nPKS0745-191. The total molecular gas mass of 4.6 +/- 0.3 x 10^9 solar masses,\nassuming a Galactic X_{CO} factor, is divided roughly equally between three\nfilaments each extending radially 3-5 kpc from the galaxy centre. The emission\npeak is located in the SE filament roughly 1 arcsec (2 kpc) from the nucleus.\nThe velocities of the molecular clouds in the filaments are low, lying within\n+/-100 km/s of the galaxy's systemic velocity. Their FWHMs are less than 150\nkm/s, which is significantly below the stellar velocity dispersion. Although\nthe molecular mass of each filament is comparable to a rich spiral galaxy, such\nlow velocities show that the filaments are transient and the clouds would\ndisperse on <10^7 yr timescales unless supported, likely by the indirect effect\nof magnetic fields. The velocity structure is inconsistent with a merger origin\nor gravitational free-fall of cooling gas in this massive central galaxy. If\nthe molecular clouds originated in gas cooling even a few kpc from their\ncurrent locations their velocities would exceed those observed. Instead, the\nprojection of the N and SE filaments underneath X-ray cavities suggests they\nformed in the updraft behind bubbles buoyantly rising through the cluster\natmosphere. Direct uplift of the dense gas by the radio bubbles appears to\nrequire an implausibly high coupling efficiency. The filaments are coincident\nwith low temperature X-ray gas, bright optical line emission and dust lanes\nindicating that the molecular gas could have formed from lifted warmer gas that\ncooled in situ.", + "category": "astro-ph" + }, + { + "text": "Statistical Analysis of Filament Features Based on the H\u03b1 Solar\n Images from 1988 to 2013 by Computer Automated Detection Method: We improve our filament automated detection method which was proposed in our\nprevious works. It is then applied to process the full disk H$\\alpha$ data\nmainly obtained by Big Bear Solar Observatory (BBSO) from 1988 to 2013,\nspanning nearly 3 solar cycles. The butterfly diagrams of the filaments,\nshowing the information of the filament area, spine length, tilt angle, and the\nbarb number, are obtained. The variations of these features with the calendar\nyear and the latitude band are analyzed. The drift velocities of the filaments\nin different latitude bands are calculated and studied. We also investigate the\nnorth-south (N-S) asymmetries of the filament numbers in total and in each\nsubclass classified according to the filament area, spine length, and tilt\nangle. The latitudinal distribution of the filament number is found to be\nbimodal. About 80% of all the filaments have tilt angles within [0{\\deg},\n60{\\deg}]. For the filaments within latitudes lower (higher) than 50{\\deg} the\nnortheast (northwest) direction is dominant in the northern hemisphere and the\nsoutheast (southwest) direction is dominant in the southern hemisphere. The\nlatitudinal migrations of the filaments experience three stages with declining\ndrift velocities in each of solar cycles 22 and 23, and it seems that the drift\nvelocity is faster in shorter solar cycles. Most filaments in latitudes lower\n(higher) than 50{\\deg} migrate toward the equator (polar region). The N-S\nasymmetry indices indicate that the southern hemisphere is the dominant\nhemisphere in solar cycle 22 and the northern hemisphere is the dominant one in\nsolar cycle 23.", + "category": "astro-ph" + }, + { + "text": "New Insights: the Accretion Process and Variable Wind from TW Hya: For the first time in a classical T Tauri star, we are able to trace an\naccretion event signaled by an hour-long enhancement of X-rays from the\naccretion shock and revealed through substantial sequential changes in optical\nemission line profiles. Downflowing turbulent material appears in H-alpha and\nH-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in\nflux. Two hours after the X-ray accretion event, the optical veiling increases\ndue to continuum emission from the hot splashdown region. The response of the\nstellar coronal emission to the heated photosphere follows about 2.4 hours\nlater, giving direct evidence that the stellar corona is heated in part by\naccretion. Then, the stellar wind becomes re-established. A model that\nincorporates the dynamics of this sequential series of events includes: an\naccretion shock, a cooling downflow in a supersonically turbulent region,\nfollowed by photospheric and later, coronal heating. This model naturally\nexplains the presence of broad optical and ultraviolet lines, and affects the\nmass accretion rates currently determined from emission line profiles. These\nresults, coupled with the large heated coronal region revealed from X-ray\ndiagnostics, suggest that current models are not adequate to explain the\naccretion process in young stars.", + "category": "astro-ph" + }, + { + "text": "Origin and Dynamical Evolution of Neptune Trojans - II: Long Term\n Evolution: We present results examining the fate of the Trojan clouds produced in our\nprevious work. We find that the stability of Neptunian Trojans seems to be\nstrongly correlated to their initial post-migration orbital elements, with\nthose objects that survive as Trojans for billions of years displaying\nnegligible orbital evolution. The great majority of these survivors began the\nintegrations with small eccentricities (e < 0.2) and small libration amplitudes\n(A < 30 - 40{\\deg}). The survival rate of \"pre-formed\" Neptunian Trojans (which\nin general survived on dynamically cold orbits (e < 0.1, i < 5 - 10{\\deg}))\nvaried between ~5 and 70%. By contrast, the survival rate of \"captured\" Trojans\n(on final orbits spread across a larger region of e-i element space) were\nmarkedly lower, ranging between 1 and 10% after 4 Gyr. Taken in concert with\nour earlier work, we note that planetary formation scenarios which involve the\nslow migration (a few tens of millions of years) of Neptune from an initial\nplanetary architecture that is both resonant and compact (aN < 18 AU) provide\nthe most promising fit of those we considered to the observed Trojan\npopulation. In such scenarios, we find that the current day Trojan population\nwould number ~1% of that which was present at the end of the planet's\nmigration, with the bulk being sourced from captured, rather than pre-formed\nobjects. We note, however, that even those scenarios still fail to reproduce\nthe currently observed portion of the Neptune Trojan population moving on\norbits with e < 0.1 but i > 20{\\deg}. Dynamical integrations of the currently\nobserved Trojans show that five out of the seven are dynamically stable on 4\nGyr timescales, while 2001 QR322, exhibits significant dynamical instability.\nThe seventh Trojan object, 2008 LC18, has such large orbital uncertainties that\nonly future studies will be able to determine its stability.", + "category": "astro-ph" + }, + { + "text": "Accurate mass estimates from the proper motions of dispersion-supported\n galaxies: Starting with the spherical Jeans equation, we show that there exists a\nradius where the mass enclosed depends only on the projected tangential\nvelocity dispersion, assuming that the anisotropy profile slowly varies. This\nis well-approximated at the radius where the log-slope of the stellar tracer\nprofile is $-2$: $r_{-2}$. The associated mass is $M(r_{-2}) = 2 G^{-1} \\langle\n\\sigma_{\\mathcal{T}}^{2}\\rangle^{*} r_{-2}$ and the circular velocity is\n$V^{2}({r_{-2}}) = 2\\langle \\sigma_{\\mathcal{T}}^{2}\\rangle^{*}$. For a Plummer\nprofile $r_{-2} \\simeq 4R_e/5$. Importantly, $r_{-2}$ is smaller than the\ncharacteristic radius for line-of-sight velocities derived by Wolf et al. 2010.\nTogether, the two estimators can constrain the mass profiles of\ndispersion-supported galaxies. We illustrate its applicability using published\nproper motion measurements of dwarf galaxies Draco and Sculptor, and find that\nthey are consistent with inhabiting cuspy NFW subhalos of the kind predicted in\nCDM but we cannot rule out a core. We test our combined mass estimators against\npreviously-published, non-spherical cosmological dwarf galaxy simulations done\nin both CDM and SIDM. For CDM, the estimates for the dynamic rotation curves\nare found to be accurate to $10\\%$ while SIDM are accurate to $15\\%$.\nUnfortunately, this level of accuracy is not good enough to measure slopes at\nthe level required to distinguish between cusps and cores of the type predicted\nin viable SIDM models without stronger priors. However, we find that this\nprovides good enough accuracy to distinguish between the normalization\ndifferences predicted at small radii ($r \\simeq r_{-2} < r_{\\rm core}$) for\ninteresting SIDM models. As the number of galaxies with internal proper motions\nincreases, mass estimators of this kind will enable valuable constraints on\nSIDM and CDM models.", + "category": "astro-ph" + }, + { + "text": "Inferring the magnetic field vector in the quiet Sun. III. Disk\n variation of the Stokes profiles and isotropism of the magnetic field: We have studied the angular distribution of the magnetic field vector in the\nsolar internetwork employing high-quality data (noise level $\\sigma \\approx\n3\\times 10^{-4}$ in units of the quiet-Sun intensity) at different latitudes\nrecorded with the Hinode/SP instrument. Instead of applying traditional\ninversion codes of the radiative transfer equation to retrieve the magnetic\nfield vector at each spatial point on the solar surface and studying the\nresulting distribution of the magnetic field vector, we surmised a theoretical\ndistribution function of the magnetic field vector and used it to obtain the\ntheoretical histograms of the Stokes profiles. These histograms were then\ncompared to the observed ones. Any mismatch between them was ascribed to the\ntheoretical distribution of the magnetic field vector, which was subsequently\nmodified to produce a better fit to the observed histograms. With this method\nwe find that Stokes profiles with signals above $2\\times 10^{-3}$ (in units of\nthe continuum intensity) cannot be explained by an isotropic distribution of\nthe magnetic field vector. We also find that the differences between the\nhistograms of the Stokes profiles observed at different latitudes cannot be\nexplained in terms of line-of-sight effects. However, they can be explained by\na distribution of the magnetic field vector that inherently varies with\nlatitude. We note that these results are based on a series of assumptions that,\nalthough briefly discussed in this paper, need to be considered in more detail\nin the future.", + "category": "astro-ph" + }, + { + "text": "On the description of the GCR intensity in the last three solar minima: We discuss the main characteristic features in the heliospheric parameters\nimportant for the GCR intensity modulation for the last three solar minima\n(1986--1987, 1996--1997 and 2008--2009). The model for the GCR intensity\nmodulation is considered and the set of the model parameters is chosen which\nallows the description of the observed GCR intensity distributions at the\nmoments of the maximum GCR intensity in two solar minima (1987 and 1997) normal\nfor the second half of the last century. Then we try to describe with the above\nmodel and set of parameters the unusually soft GCR energy spectra at the\nmoments of the maximum GCR intensity in the last solar minimum between cycles\n23 and 24 (2009). Our main conclusion is that the most simple way to do so is\nto reduce the size of the modulation region and, probably, change the rigidity\ndependence of the diffusion coefficient. The change of both parameters is\nsubstantiated by the observations of the solar wind and heliospheric magnetic\nfield.", + "category": "astro-ph" + }, + { + "text": "The supercluster-void network V. Alternative evidence for its regularity: The distribution of Abell clusters of galaxies is analysed to study the\nregularity of the supercluster-void network. A new geometric method sensitive\nto the regularity of the location of clusters is applied. We find that the\nsupercluster-void network resembles a cubical lattice over the whole space\ninvestigated. The distribution of rich superclusters is not isotropic: along\nthe main axis of the network it is periodic with a step of length about 130 Mpc\n(for Hubble constant h=1), whereas along the diagonal of the network the period\nis larger. This large-scale inhomogeneity is compatible with recent CMB data.", + "category": "astro-ph" + }, + { + "text": "Detection of heavy-metal lines in the spectrum of the circumstellar\n envelope of a post-AGB star: Splitting of the strongest absorption lines with a lower-level excitation\npotential $\\chi<$1eV has been detected for the first time in the optical\nspectra of the post-AGB star V354Lac obtained with a spectral resolution\nR=60000 at the 6-m telescope BTA. Analysis of the kinematics shows that the\nshort-wavelength component of the split line originates in the star's thick\ngas-dust envelope. Disregarding the splitting of strong lines when the chemical\ncomposition is calculated leads to overestimated excess of s-process elements\n(Ba, La, Ce, Nd) in the stellar atmosphere. The profiles of strong absorption\nlines have been found to be variable. The available radial-velocity data\nsuggest the absence of any trend in the velocity field in the atmosphere and\ncircumstellar envelope of V354Lac over 15 years of its observations.", + "category": "astro-ph" + }, + { + "text": "Study of muons from ultra-high energy cosmic ray air showers measured\n with the Telescope Array experiment: One of the uncertainties in interpretation of ultra-high energy cosmic ray\n(UHECR) data comes from the hadronic interaction models used for air shower\nMonte Carlo (MC) simulations. The number of muons observed at the ground from\nUHECR-induced air showers is expected to depend upon the hadronic interaction\nmodel. One may therefore test the hadronic interaction models by comparing the\nmeasured number of muons with the MC prediction. In this paper, we present the\nresults of studies of muon densities in UHE extensive air showers obtained by\nanalyzing the signal of surface detector stations which should have high\n$\\it{muon \\, purity}$. The muon purity of a station will depend on both the\ninclination of the shower and the relative position of the station. In 7 years'\ndata from the Telescope Array experiment, we find that the number of particles\nobserved for signals with an expected muon purity of $\\sim$65% at a lateral\ndistance of 2000 m from the shower core is $1.72 \\pm 0.10{\\rm (stat.)} \\pm 0.37\n{\\rm (syst.)}$ times larger than the MC prediction value using the QGSJET II-03\nmodel for proton-induced showers. A similar effect is also seen in comparisons\nwith other hadronic models such as QGSJET II-04, which shows a $1.67 \\pm 0.10\n\\pm 0.36$ excess. We also studied the dependence of these excesses on lateral\ndistances and found a slower decrease of the lateral distribution of muons in\nthe data as compared to the MC, causing larger discrepancy at larger lateral\ndistances.", + "category": "astro-ph" + }, + { + "text": "When does an old nova become a dwarf nova? Kinematics and age of the\n nova shell of the dwarf nova AT Cnc: The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell,\ndemonstrating that mass transfer in cataclysmic binaries decreases\nsubstantially after a CN eruption. The hibernation scenario of cataclysmic\nbinaries predicts such a decrease, on a timescale of a few centuries. In order\nto measure the time since AT Cnc's last CN eruption, we have measured the\nradial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's\nrecently commissioned imaging Fourier transform spectrometer. These range from\n-455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara\n2012), the size of AT Cnc's shell, and a simple model of nova ejecta\ndeceleration, we determine that the last CN eruption of this system occurred\n$330_{-90}^{+135}$ years ago. This is the most rapid transition from a high\nmass transfer rate, novalike variable to a low mass transfer rate, dwarf nova\nyet measured, and in accord with the hibernation scenario of cataclysmic\nbinaries. We conclude by noting the similarity in deduced outburst date (within\na century of 1686 CE) of AT Cnc with a \"guest star\" reported in the\nconstellation Cancer by Korean observers in 1645 CE.", + "category": "astro-ph" + }, + { + "text": "An updated catalogue of giant radio sources: We present a catalogue of 349 giant radio sources (GRSs including both\ngalaxies and quasars). The database contains all giants known to date from the\nliterature. These GRSs cover the redshift range of 0.016$<$z$<$3.22 and include\nradio sources of projected linear sizes larger than 0.7~Mpc which extend up to\n4.7~Mpc. We provide the principal parameters (i.e. exact position of the host\nin the sky, redshift, angular and projected linear size, red optical magnitude,\nradio morphology type, total radio flux density and luminosity) for all the\nsources as well as characteristics of the sample. Based on the distribution of\nGRSs in the sky we identify regions where there is a paucity of giants, so that\nfuture surveys for this type of objects could concentrate primarily in these\nfields. From the analysis presented here, we estimate a lower limit for the\nexpected number of GRSs as about 2000, for the resolution and sensitivity\nlimits of FIRST, NRAO VLA Sky Survey and Sloan Digital Sky Survey surveys.\nCompared with earlier compilations, there is a significant increase in the\nnumber of large giants with sizes $>$ 2 Mpc as well as those at high redshifts\nwith z$>$1. We discuss aspects of their evolution and suggest that these are\nconsistent with evolutionary models.", + "category": "astro-ph" + }, + { + "text": "Features of the inflaton potential and the power spectrum of\n cosmological perturbations: We discuss features of the inflaton potential that can lead to a strong\nenhancement of the power spectrum of curvature perturbations. We show that a\nsteep decrease of the potential induces an enhancement of the spectrum by\nseveral orders of magnitude, which may lead to the production of primordial\nblack holes. The same feature can also create a distinctive oscillatory pattern\nin the spectrum of gravitational waves generated through the scalar\nperturbations at second order. We study the additive effect of several such\nfeatures. We analyse a simplified potential, but also discuss the possible\napplication to supergravity models.", + "category": "astro-ph" + }, + { + "text": "X Ray Precursors in SGRs: Precessing Gamma Jet Tails: Weak isolated X-ray precursor events before the main Gamma Ray Burst, GRB,\nand also rare Soft Gamma Repeaters, SGR, events are in complete disagreement\nwith any Fireball, or Magnetar, one-shoot explosive scenarios. Fireball model\nin last two years has been deeply modified into a fountain beamed Jet exploding\nand interacting on external shells to explain GRB fine time structure. On the\ncontrary earlier we proposed a unified scenario for both GRBs-SGRs where a\nprecessing Gamma Jet (of different intensity) and its geometrical beaming is\nthe source of both GRB and SGRs wide morphology. GRBs are peaked SNs Jet\nspinning and precessing observed along the thin Jet axis. Their mysterious weak\nX precursors bursts, corresponding to non-negligible energy powers, up to\nmillion Supernova ones for GRB, are gamma Jet tails beamed off-axis, observed\nat X-Ray tails. They are rare, about (3-6)% of all GRBs, but not unique at all.\nComparable brief X-ray precursor flashes occurred in rarest and most detailed\nSGRs events as the 27 and the 29 August 1998 event from SGR 1900+14. The same\nsource has been in very power-full activity on recent 18 April 2001 once again\npreceded by X-Ray precursors. These events are inconsistent with any Fireball\nor Magnetar-Mini-Fireball models. We interpret them naturally as earlier\nmarginal blazing of outlying X conical precessing Jet, an off-axis tails\nsurrounding a narrower gamma precessing Jet. Only when the light-house Jet is\nin on-axis blazing mode toward the Earth we observe the harder power-full SGR\nevent. We predict such a rich X-Ray precursor signals (more numerous then gamma\nones) during Soft Gamma Repeater peak activities; they should be abundant and\nwithin detection threshold by a permanent monitoring SGRs by Beppo-Sax WFC or\nChandra X ray satellites while at peak activity.", + "category": "astro-ph" + }, + { + "text": "A Critical Look at the Mass-Metallicity-SFR Relation in the Local\n Universe. I. An Improved Analysis Framework and Confounding Systematics: It has been proposed that the mass-metallicity relation of galaxies exhibits\na secondary dependence on star formation rate (SFR), and that the resulting\nM-Z-SFR relation may be redshift-invariant, i.e., \"fundamental.\" However,\nconflicting results on the character of the SFR dependence, and whether it\nexists, have been reported. To gain insight into the origins of the conflicting\nresults, we (a) devise a non-parametric, astrophysically motivated analysis\nframework based on the offset from the star-forming (\"main\") sequence at a\ngiven stellar mass (relative specific SFR), (b) apply this methodology and\nperform a comprehensive re-analysis of the local M-Z-SFR relation, based on\nSDSS, GALEX, and WISE data, and (c) study the impact of sample selection, and\nof using different metallicity and SFR indicators. We show that metallicity is\nanti-correlated with specific SFR regardless of the indicators used. We do not\nfind that the relation is spurious due to correlations arising from biased\nmetallicity measurements, or fiber aperture effects. We emphasize that the\ndependence is weak/absent for massive galaxies ($\\log M_*>10.5$), and that the\noverall scatter in the M-Z-SFR relation does not greatly decrease from the M-Z\nrelation. We find that the dependence is stronger for the highest SSFR galaxies\nabove the star-forming sequence. This two-mode behavior can be described with a\nbroken linear fit in 12+log(O/H) vs. log (SFR$/M_*$), at a given $M_*$.\nPrevious parameterizations used for comparative analysis with higher redshift\nsamples that do not account for the more detailed behavior of the local M-Z-SFR\nrelation may incorrectly lead to the conclusion that those samples follow a\ndifferent relationship.", + "category": "astro-ph" + }, + { + "text": "Massive Star Evolution and Nucleosynthesis -Lower End of Fe-Core\n Collapse Supernova Progenitors and Remnant Neutron Star Mass Distribution-: In order to explore various aspects of stellar evolution, supernovae, gamma\nray bursts and nucleosynthesis, we have developed a new efficient stellar\nevolution code. In this paper we describe this new code and compare the results\nwith the ones calculated by the previous code. Specifically we focus on the\nprogenitor evolution of lower end of the Fe-core collapse supernovae, and mass\ndistribution of remnant neutron stars. We describe how different assumptions\nwill lead different neutron star mass distribution. We also review recent works\nof our research group.", + "category": "astro-ph" + }, + { + "text": "Impact of Scale Dependent Bias and Nonlinear Structure Growth on the ISW\n Effect: Angular Power Spectra: We investigate the impact of nonlinear evolution of the gravitational\npotentials in the LCDM model on the Integrated Sachs-Wolfe (ISW) contribution\nto the CMB temperature power spectrum, and on the cross-power spectrum of the\nCMB and a set of biased tracers of the mass. We use an ensemble of N-body\nsimulations to directly follow the potentials and compare results to\nperturbation theory (PT). The predictions from PT match the results to high\nprecision for k<0.2 h/Mpc. We compute the nonlinear corrections to the angular\npower spectrum and find them to be <10% of linear theory for l<100. These\ncorrections are swamped by cosmic variance. On scales l>100 the departures are\nmore significant, however the CMB signal is more than a factor 10^3 larger at\nthis scale. Nonlinear ISW effects therefore play no role in shaping the CMB\npower spectrum for l<1500. We analyze the CMB--density tracer cross-spectrum\nusing simulations and renormalized bias PT, and find good agreement. The usual\nassumption is that nonlinear evolution enhances the growth of structure and\ncounteracts linear ISW on small scales, leading to a change in sign of the\nCMB-LSS cross-spectrum at small scales. However, PT analysis suggests that this\ntrend reverses at late times when the logarithmic growth rate\nf(a)=dlnD/dlna<0.5 or om_m(a)<0.3. Numerical results confirm these expectations\nand we find no sign change in ISW-LSS cross-power for low redshifts.\nCorrections due to nonlinearity and scale dependence of the bias are found to\nbe <10% for l<100, therefore below the S/N of the current and future\nmeasurements. Finally, we estimate the CMB--halo cross-correlation coefficient\nand show that it can be made to match that for CMB--dark matter to within 5%\nfor thin redshift shells, mitigating the need to model bias evolution.", + "category": "astro-ph" + }, + { + "text": "3D Smoothed Particle Hydrodynamics Models of Betelgeuse's Bow Shock: Betelgeuse, the bright red supergiant (RSG) in Orion, is a runaway star. Its\nsupersonic motion through the interstellar medium has resulted in the formation\nof a bow shock, a cometary structure pointing in the direction of motion. We\npresent the first 3D hydrodynamic simulations of the formation and evolution of\nBetelgeuse's bow shock. We show that the bow shock morphology depends\nsubstantially on the growth timescale for Rayleigh-Taylor versus\nKelvin-Helmholtz instabilities. We discuss our models in light of the recent\nHerschel, GALEX and VLA observations. If the mass in the bow shock shell is low\n(~few x 0.001 Msun), as seems to be implied by the AKARI and Herschel\nobservations, then Betelgeuse's bow shock is very young and is unlikely to have\nreached a steady state. The circular, smooth bow shock shell is consistent with\nthis conclusion. We further discuss the implications of our results, in\nparticular, the possibility that Betelgeuse may have only recently entered the\nRSG phase.", + "category": "astro-ph" + }, + { + "text": "Temperature-dependent oscillation modes in rotating superfluid neutron\n stars: We calculate the spectrum of inertial oscillation modes in a slowly rotating\nsuperfluid neutron star, including, for the first time, both the effects of\nfinite temperatures and entrainment between superfluid neutrons and protons. We\nwork in the Newtonian limit and assume minimal core composition (neutrons,\nprotons and electrons). We also developed an approximate method that allows one\nto calculate the superfluid r-mode analytically. Finally, we derive and analyze\ndispersion relations for inertial modes in the superfluid NS matter in the\nshort wavelength limit.", + "category": "astro-ph" + }, + { + "text": "Chromaticity in all-reflective telescopes for astrometry: Chromatic effects are usually associated with refractive optics, so\nreflective telescopes are assumed to be free from them. We show that\nall-reflective optics still bears significant levels of such perturbations,\nwhich is especially critical to modern micro-arcsecond astrometric experiments.\nWe analyze the image formation and measurement process to derive a precise\ndefinition of the chromatic variation of the image position, and we evaluate\nthe key aspects of optical design with respect to chromaticity. The fundamental\nrequirement related to chromaticity is the symmetry of the optical design and\nof the wavefront errors. Finally, we address some optical engineering issues,\nsuch as manufacturing and alignment, providing recommendations to minimize the\ndegradation that chromaticity introduces into astrometry.", + "category": "astro-ph" + }, + { + "text": "Confirmation of double peaked Lyman-alpha emission at z=6.593:\n Witnessing a galaxy directly contributing to the reionisation of the Universe: Distant luminous Lyman-alpha emitters (LAEs) are excellent targets for\nspectroscopic observations of galaxies in the epoch of reionisation (EoR). We\npresent deep high-resolution (R=5000) VLT/X-SHOOTER observations, along with an\nextensive collection of photometric data of `COLA1', a proposed double peaked\nLAE at z=6.6 (Hu et al. 2016). We rule out that COLA1's emission line is an\n[OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and\nflux ratio of the peaks (blue/red=$0.31\\pm0.03$) and ii) an unphysical [OII]/Ha\nratio ([OII]/Ha > 22). We show that COLA1's observed B-band flux is explained\nby a faint extended foreground LAE, for which we detect Lya and [OIII] at\nz=2.142. We thus conclude that COLA1 is a real double-peaked LAE at z=6.593,\nthe first discovered at z>6, confirming the result from Hu et al. (2016). COLA1\nis UV luminous (M$_{1500}=-21.6\\pm0.3$), has a high equivalent width\n(EW$_{0}$~120 \\AA) and very compact Lya emission (r$_{50} = 0.3$ kpc).\nRelatively weak inferred Hb+[OIII] line-emission from Spitzer/IRAC indicates an\nextremely low metallicity of Z<1/20 Z$_{\\odot}$ or reduced strength of nebular\nlines due to high escape of ionising photons. The small Lya peak separation of\n$220\\pm20$ km/s implies a low HI column density and an ionising photon escape\nfraction of ~15-30 %, providing the first direct evidence that such galaxies\ncontribute actively to the reionisation of the Universe at z>6. Based on simple\nestimates, we find that COLA1 could have provided just enough photons to\nreionise its own ~0.3 pMpc bubble, allowing the blue Lya line to be observed.\nHowever, we also discuss alternative scenarios explaining the detected double\npeaked nature of COLA1. Our results show that future high-resolution\nobservations of statistical samples of double peaked LAEs at z>5 are a\npromising probe of the occurrence of ionised regions around galaxies in the\nEoR.", + "category": "astro-ph" + }, + { + "text": "Instability of a stalled accretion shock: evidence for the\n advective-acoustic cycle: We analyze the linear stability of a stalled accretion shock in a perfect gas\nwith a parametrized cooling function L ~ rho^{beta-alpha} P^alpha. The\ninstability is dominated by the l=1 mode if the shock radius exceeds 2-3 times\nthe accretor radius, depending on the parameters of the cooling function. The\ngrowth rate and oscillation period are comparable to those observed in the\nnumerical simulations of Blondin & Mezzacappa (2006). The instability mechanism\nis analyzed by separately measuring the efficiencies of the purely acoustic\ncycle and the advective-acoustic cycle. These efficiencies are estimated\ndirectly from the eigenspectrum, and also through a WKB analysis in the high\nfrequency limit. Both methods prove that the advective-acoustic cycle is\nunstable, and that the purely acoustic cycle is stable. Extrapolating these\nresults to low frequency leads us to interpret the dominant mode as an\nadvective-acoustic instability, different from the purely acoustic\ninterpretation of Blondin & Mezzacappa (2006). A simplified characterization of\nthe instability is proposed, based on an advective-acoustic cycle between the\nshock and the radius r_nabla where the velocity gradients of the stationary\nflow are strongest. The importance of the coupling region in this mechanism\ncalls for a better understanding of the conditions for an efficient\nadvective-acoustic coupling in a decelerated, nonadiabatic flow, in order to\nextend these results to core-collapse supernovae.", + "category": "astro-ph" + }, + { + "text": "The orbital period of the recurrent X-ray transient in Terzan 6: Four or five new outbursts were detected of the bright X-ray transient GRS\n1747-312 in the globular cluster Terzan 6 between 1996 and 1999, through\nmonitoring campaigns with the Wide Field Cameras (WFCs) on BeppoSAX and the\nProportional Counter Array (PCA) on RossiXTE. This is the first time that the\nsource is seen to exhibit recurrent outbursts after the discovery in September\n1990 with ART-P on Granat. Three target-of-opportunity observations in 1998 and\n1999, with the narrow-field instruments on BeppoSAX and the PCA, revealed one\nsharp drop in the flux which we identify as an eclipse of the compact X-ray\nsource by the companion star. A detailed analysis of WFC data identifies\nfurther eclipses and we measure the orbital period at 12.360+/-0.009 hr. This\nis consistent with an identification as a low-mass X-ray binary, as suggested\nalready by the association with a globular cluster. The eclipse duration is\n0.72+/-0.06 hr. This implies that the inclination angle is larger than 74 deg.\nThe 0.1-200 keV unabsorbed peak luminosity is 7X10^36 erg/s. The nature of the\ncompact object is unclear.", + "category": "astro-ph" + }, + { + "text": "Diagnostics for specific PAHs in the far-IR: searching neutral\n naphthalene and anthracene in the Red Rectangle: Context. In the framework of the interstellar polycyclic aromatic\nhydrocarbons (PAHs) hypothesis, far-IR skeletal bands are expected to be a\nfingerprint of single species in this class. Aims. We address the question of\ndetectability of low energy PAH vibrational bands, with respect to spectral\ncontrast and intensity ratio with ``classical'' Aromatic Infrared Bands (AIBs).\nMethods. We extend our extablished Monte-Carlo model of the photophysics of\nspecific PAHs in astronomical environments, to include rotational and\nanharmonic band structure. The required molecular parameters were calculated in\nthe framework of the Density Functional Theory. Results. We calculate the\ndetailed spectral profiles of three low-energy vibrational bands of neutral\nnaphthalene, and four low-energy vibrational bands of neutral anthracene. They\nare used to establish detectability constraints based on intensity ratios with\n``classical'' AIBs. A general procedure is suggested to select promising\ndiagnostics, and tested on available Infrared Space Observatory data for the\nRed Rectangle nebula. Conclusions. The search for single, specific PAHs in the\nfar-IR is a challenging, but promising task, especially in view of the\nforthcoming launch of the Herschel Space Observatory.", + "category": "astro-ph" + }, + { + "text": "On mass distribution of coalescing black holes: Available data on the chirp mass distribution of the coalescing black hole\nbinaries in O1-O3 LIGO/Virgo runs are analyzed and compared statistically with\nthe distribution calculated under the assumption that these black holes are\nprimordial with a log-normal mass spectrum. The theoretically calculated chirp\nmass distribution with the inferred best acceptable mass spectrum parameters,\n$M_0=17 M_\\odot$ and $\\gamma=0.9$, perfectly describes the data. The value of\n$M_0$ very well agrees with the theoretically expected one. On the opposite,\nthe chirp mass distribution of black hole binaries originated from massive\nbinary star evolution requires additional model adjustments to reproduce the\nobserved chirp mass distribution", + "category": "astro-ph" + }, + { + "text": "A New Numerical Method for Solving Radiation Driven Winds from Hot Stars: We present a general method for solving the non--linear differential equation\nof monotonically increasing steady--state radiation driven winds. We\ngraphically identify all the singular points before transforming the momentum\nequation to a system of differential equations with all the gradients\nexplicitly give. This permits a topological classification of all singular\npoints and to calculate the maximum and minimum mass--loss of the wind. We use\nour method to analyse for the first time the topology of the non--rotating\nfrozen in ionisation m--CAK wind, with the inclusion of the finite disk\ncorrection factor and find up to 4 singular points, three of the x--type and\none attractor--type. The only singular point (and solution passing through)\nthat satisfies the boundary condition at the stellar surface is the standard\nm--CAK singular point.", + "category": "astro-ph" + }, + { + "text": "A Large Scale, Low Frequency Murchison Widefield Array Survey of\n Galactic HII regions between 260< l <\\340: We have compiled a catalogue of HII regions detected with the Murchison\nWidefield Array (MWA) between 72 and 231MHz. The multiple frequency bands\nprovided by the MWA allow us identify the characteristic spectrum generated by\nthe thermal Bremsstrahlung process in HII regions. We detect 302 HII regions\nbetween 260 < l < 340 and report on the positions, sizes, peak, integrated flux\ndensity, and spectral indices of these HII regions. By identifying the point at\nwhich HII regions transition from the optically thin to thick regime we derive\nthe physical properties including the electron density, ionised gas mass and\nionising photon flux, towards 61 HII regions. This catalogue of HII regions\nrepresents the most extensive and uniform low frequency survey of HII regions\nin the Galaxy to date.", + "category": "astro-ph" + }, + { + "text": "Mass-sheet degeneracy, power-law models and external convergence: Impact\n on the determination of the Hubble constant from gravitational lensing: The light travel time differences in strong gravitational lensing systems\nallows an independent determination of the Hubble constant. This method has\nbeen successfully applied to several lens systems. The formally most precise\nmeasurements are, however, in tension with the recent determination of $H_0$\nfrom the Planck satellite for a spatially flat six-parameters $\\Lambda CDM$\ncosmology. We reconsider the uncertainties of the method, concerning the mass\nprofile of the lens galaxies, and show that the formal precision relies on the\nassumption that the mass profile is a perfect power law. Simple analytical\narguments and numerical experiments reveal that mass-sheet like transformations\nyield significant freedom in choosing the mass profile, even when exquisite\nEinstein rings are observed. Furthermore, the characterization of the\nenvironment of the lens does not break that degeneracy which is not physically\nlinked to extrinsic convergence. We present an illustrative example where the\nmultiple imaging properties of a composite (baryons + dark matter) lens can be\nextremely well reproduced by a power-law model having the same velocity\ndispersion, but with predictions for the Hubble constant that deviate by $\\sim\n20%$. Hence we conclude that the impact of degeneracies between parametrized\nmodels have been underestimated in current $H_0$ measurements from lensing, and\nneed to be carefully reconsidered.", + "category": "astro-ph" + }, + { + "text": "Luminosity versus Rotation in a Supermassive Star: We determine the effect of rotation on the luminosity of supermassive stars.\nWe apply the Roche model to calculate analytically the emitted radiation from a\nuniformly rotating, radiation-dominated supermassive configuration. We find\nthat the luminosity at maximum rotation, when mass at the equator orbits at the\nKepler period, is reduced by ~36% below the usual Eddington luminosity from the\ncorresponding nonrotating star. A supermassive star is believed to evolve in a\nquasistationary manner along such a maximally rotating ``mass-shedding''\nsequence before reaching the point of dynamical instability; hence this reduced\nluminosity determines the evolutionary timescale. Our result therefore implies\nthat the lifetime of a supermassive star prior to dynamical collapse is ~56%\nlonger than the value typically estimated by employing the usual Eddington\nluminosity.", + "category": "astro-ph" + }, + { + "text": "The Li dip : a probe of angular momentum transport in low mass stars: We use the measures of Li and rotational velocities in F Hyades stars to\nassess the role of the wind-driven meridian circulation and of shear turbulence\nin the transport of angular momentum in stars of different masses. Our models\ninclude both element segregation and rotation-induced mixing, and we treat\nsimultaneously the transport of matter and angular momentum as described by\nZahn (1992) and Maeder (1995).\n We show that the hot side of the Li dip in the Hyades is well explained\nwithin this framework, which was also successfully used to reproduce the C and\nN anomalies in B type stars (Talon et al. 1997). On the cool side of the dip,\nanother mechanism must participate in the transport of angular momentum; its\nefficiency is linked to the depth of the surface convection zone. That\nmechanism should also be responsible for the Sun's flat rotation profile.", + "category": "astro-ph" + }, + { + "text": "Synchrotron Outbursts in Galactic and Extra-galactic Jets, Any\n Difference?: We discuss differences and similarities between jets powered by super-massive\nblack holes in quasars and by stellar-mass black holes in microquasars. The\ncomparison is based on multi-wavelength radio-to-infrared observations of the\ntwo active galactic nuclei 3C 273 and 3C 279, as well as the two galactic\nbinaries GRS 1915+105 and Cyg X-3. The physical properties of the jet are\nderived by fitting the parameters of a shock-in-jet model simultaneously to all\navailable observations. We show that the variable jet emission of galactic\nsources is, at least during some epochs, very similar to that of extra-galactic\njets. As for quasars, their observed variability pattern can be well reproduced\nby the emission of a series of self-similar shock waves propagating down the\njet and producing synchrotron outbursts. This suggests that the physical\nproperties of relativistic jets is independent of the mass of the black hole.", + "category": "astro-ph" + }, + { + "text": "Parallel Programming with MatlabMPI: MatlabMPI is a Matlab implementation of the Message Passing Interface (MPI)\nstandard and allows any Matlab program to exploit multiple processors.\nMatlabMPI currently implements the basic six functions that are the core of the\nMPI point-to-point communications standard. The key technical innovation of\nMatlabMPI is that it implements the widely used MPI ``look and feel'' on top of\nstandard Matlab file I/O, resulting in an extremely compact (~100 lines) and\n``pure'' implementation which runs anywhere Matlab runs. The performance has\nbeen tested on both shared and distributed memory parallel computers. MatlabMPI\ncan match the bandwidth of C based MPI at large message sizes. A test image\nfiltering application using MatlabMPI achieved a speedup of ~70 on a parallel\ncomputer.", + "category": "astro-ph" + }, + { + "text": "Hunting for anti-solar differentially rotating stars using the Rossby\n number -- An application to the Kepler field: Anti-solar differential rotation profiles have been found for decades in\nnumerical simulations of convective envelopes of solar-type stars. These\nprofiles are characterized by a slow equator and fast poles (i.e., reversed\nwith respect to the Sun) and have been found in simulations for high Rossby\nnumbers (slow rotators). Rotation profiles like this have been reported\nobservationally in evolved stars, but have never been unambiguously observed\nfor cool solar-type stars on the main sequence. In this context, detecting this\nregime in main-sequence solar-type stars would improve our understanding of\ntheir magnetorotational evolution. The goal of this study is to identify the\nmost promising cool main-sequence stellar candidates for anti-solar\ndifferential rotation in the \\textit{Kepler} sample. First, we introduce a new\ntheoretical formula to estimate fluid Rossby numbers, $Ro_{\\rm f}$, of\nmain-sequence solar-type stars, from observational quantities, and taking the\ninfluences of the internal structure and metallicity into account. We obtain a\nlist of the most promising stars that are likely to show anti-solar\ndifferential rotation. We identify two samples: one at solar metallicity,\nincluding 14 targets, and another for other metallicities, including 8 targets.\nWe find that the targets with the highest $Ro_{\\rm f}$ are likely to be early-G\nor late-F stars at about log$_{10}g=4.37$~dex. We conclude that cool\nmain-sequence stellar candidates for anti-solar differential rotation exist in\nthe \\textit{Kepler} sample. The most promising candidate is KIC~10907436, and\ntwo other particularly interesting candidates are the solar analog KIC~7189915\nand the seismic target KIC~12117868. Future characterization of these 22 stars\nis expected to help us understand how dynamics can impact magnetic and\nrotational evolution of old solar-type stars at high Rossby number.", + "category": "astro-ph" + }, + { + "text": "Probing the reach of the Intermediate Polar Cataclysmic Variable\n Population with Swift J183920.1-045350: We report on the Swift/XRT Deep Galactic Plane Survey discovery and\nmulti-wavelength follow-up observations of a new intermediate polar Cataclysmic\nVariable, Swift J183920.1-045350. A 449.7 s spin period is found in Xmm-Newton\nand NuSTAR data, accompanied by a 459.9 s optical period that is most likely\nthe synodic, or beat period, produced from a 5.6 h orbital period. The orbital\nperiod is seen with moderate significance in independent long-baseline optical\nphotometry observations with ZTF and SAAO. We find that the source X-ray pulsed\nfraction decreases with increasing energy. The X-ray spectra are consistent\nwith the presence of an Fe emission line complex with both local and\ninterstellar absorption. In the optical spectra, strong H$\\alpha{}$, H I, He I\nand He II emission lines are observed, all common features in magnetic CVs. The\nsource properties are thus typical of known intermediate polars, with the\nexception of its estimated distance of 2.26$^{+1.93}_{-0.83}$ kpc, which is\nlarger than typical, extending the reach of the CV population in our Galaxy.", + "category": "astro-ph" + }, + { + "text": "The dual origin of the nitrogen deficiency in comets: selective volatile\n trapping in the nebula and postaccretion radiogenic heating: We propose a scenario that explains the apparent nitrogen deficiency in\ncomets in a way consistent with the fact that the surfaces of Pluto and Triton\nare dominated by nitrogen-rich ice. We use a statistical thermodynamic model to\ninvestigate the composition of the successive multiple guest clathrates that\nmay have formed during the cooling of the primordial nebula from the most\nabundant volatiles present in the gas phase. These clathrates agglomerated with\nthe other ices (pure condensates or stoichiometric hydrates) and formed the\nbuilding blocks of comets. We report that molecular nitrogen is a poor\nclathrate former, when we consider a plausible gas phase composition of the\nprimordial nebula. This implies that its trapping into cometesimals requires a\nlow disk temperature ($\\sim$20 K) in order to allow the formation of its pure\ncondensate. We find that it is possible to explain the lack of molecular\nnitrogen in comets as a consequence of their postformation internal heating\nengendered by the decay of short-lived radiogenic nuclides. This scenario is\nfound consistent with the presence of nitrogen-rich ice covers on Pluto and\nTriton. Our model predicts that comets should present xenon-to-water and\nkrypton-to-water ratios close to solar xenon-to-oxygen and krypton-to-oxygen\nratios, respectively. In contrast, the argon-to-water ratio is predicted to be\ndepleted by a factor of $\\sim$300 in comets compared to solar argon-to-oxygen,\nas a consequence of poor trapping efficiency and radiogenic heating.", + "category": "astro-ph" + }, + { + "text": "Statistics of Photospheric Supergranular Cells Observed by SDO/HMI: Aims: The statistics of the photospheric granulation pattern are investigated\nusing continuum images observed by Solar Dynamic Observatory (SDO)/Helioseismic\nand Magnetic Imager (HMI) taken at 6713~\\AA.\n Methods: The supergranular boundaries can be extracted by tracking\nphotospheric velocity plasma flows. The local ball-tracking method is employed\nto apply on the HMI data gathered over the years 2011-2015 to estimate the\nboundaries of the cells. The edge sharpening techniques are exerted on the\noutput of ball-tracking to precisely identify the cells borders. To study the\nfractal dimensionality (FD) of supergranulation, the box counting method is\nused.\n Results: We found that both the size and eccentricity follow the log-normal\ndistributions with peak values about 330 Mm$^2$ and 0.85, respectively. The\nfive-year mean value of the cells number appeared in half-hour sequences is\nobtained to be about 60 $\\pm$ 6 within an area of\n$350^{\\prime\\prime}\\times350^{\\prime\\prime}$. The cells orientation\ndistribution presents the power-law behavior.\n Conclusions: The orientation of supergranular cells ($O$) and their size\n($S$) follows a power-law function as $|O| \\propto S^{9.5}$. We found that the\nnon-roundish cells with smaller and larger sizes than 600 Mm$^2$ are aligned\nand perpendicular with the solar rotational velocity on the photosphere,\nrespectively. The FD analysis shows that the supergranular cells form the\nself-similar patterns.", + "category": "astro-ph" + }, + { + "text": "A search for technosignatures from 14 planetary systems in the Kepler\n field with the Green Bank Telescope at 1.15-1.73 GHz: Analysis of Kepler mission data suggests that the Milky Way includes billions\nof Earth-like planets in the habitable zone of their host star. Current\ntechnology enables the detection of technosignatures emitted from a large\nfraction of the Galaxy. We describe a search for technosignatures that is\nsensitive to Arecibo-class transmitters located within ~420 ly of Earth and\ntransmitters that are 1000 times more effective than Arecibo within ~13 000 ly\nof Earth. Our observations focused on 14 planetary systems in the Kepler field\nand used the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank\nTelescope. Each source was observed for a total integration time of 5 minutes.\nWe obtained power spectra at a frequency resolution of 3 Hz and examined\nnarrowband signals with Doppler drift rates between +/-9 Hz/s. We flagged any\ndetection with a signal-to-noise ratio in excess of 10 as a candidate signal\nand identified approximately 850 000 candidates. Most (99%) of these candidate\nsignals were automatically classified as human-generated radio-frequency\ninterference (RFI). A large fraction (>99%) of the remaining candidate signals\nwere also flagged as anthropogenic RFI because they have frequencies that\noverlap those used by global navigation satellite systems, satellite downlinks,\nor other interferers detected in heavily polluted regions of the spectrum. All\n19 remaining candidate signals were scrutinized and none were attributable to\nan extraterrestrial source.", + "category": "astro-ph" + }, + { + "text": "Determination of electron density and filling factor for soft X-ray\n flare kernels: In a standard method of determining electron density for soft X-ray (SXR)\nflare kernels it is necessary to assume what is the extension of a kernel along\nthe line of sight. This is a source of significant uncertainty of the obtained\ndensities. In our previous paper (Bak-Steslicka and Jakimiec, 2005) we have\nworked out another method of deriving electron density, in which it is not\nnecessary to assume what is the extension of a kernel along the line of sight.\nThe point is that many flares, during their decay phase, evolve along the\nsequence of steady-state models [quasi-steady-state (QSS) evolution] and then\nthe scaling law, derived for steady-state models, can be used to determine the\nelectron density. The aim of the present paper is: (1) to improve the two\nmethods of density determination, (2) to compare the densities obtained with\nthe two methods. We have selected a number of flares which showed QSS evolution\nduring the decay phase. For these flares the electron density, N, has been\nderived by means of standard method and with our QSS method. Comparison of the\nN values obtained with the two different methods allowed us: (1) to test the\nobtained densities, (2) to evaluate the volume filling factor of the SXR\nemitting plasma. Generally, we have found good agreement (no large systematic\ndifference) between the values of electron density obtained with the two\nmethods, but for some cases the values can differ by a factor up to 2. For most\nflare kernels estimated filling factor turned out to be about 1, near the flare\nmaximum.", + "category": "astro-ph" + }, + { + "text": "Radio AGN in nearby dwarf galaxies: the important role of AGN in\n dwarf-galaxy evolution: We combine deep optical and radio data, from the Hyper Suprime-Cam and the\nLow-Frequency Array (LOFAR) respectively, to study 78 radio AGN in nearby\n(z<0.5) dwarf galaxies. Comparison to a control sample, matched in stellar mass\nand redshift, indicates that the AGN and controls reside in similar\nenvironments, show similar star-formation rates (which trace gas availability)\nand exhibit a comparable incidence of tidal features (which indicate recent\ninteractions). We explore the AGN properties by combining the predicted gas\nconditions in dwarfs from a cosmological hydrodynamical simulation with a\nMonte-Carlo suite of simulated radio sources, based on a semi-analytical model\nfor radio-galaxy evolution. In the subset of LOFAR-detectable simulated\nsources, which have a similar distribution of radio luminosities as our\nobserved AGN, the median jet powers, ages and accretion rates are $\\sim\n10^{35}$ W, $\\sim 5$ Myr and $\\sim 10^{-3.4}$ M$_{\\odot}$ yr$^{-1}$\nrespectively. The median mechanical energy output of these sources is $\\sim100$\ntimes larger than the median binding energy expected in dwarf gas reservoirs,\nmaking AGN feedback plausible. Since special circumstances (in terms of\nenvironment, gas availability and interactions) are not necessary for the\npresence of AGN, and the central gas masses are predicted to be an order of\nmagnitude larger than that required to fuel the AGN, AGN triggering in dwarfs\nis likely to be stochastic and a common phenomenon. Together with the\nplausibility of energetic feedback, this suggests that AGN could be important\ndrivers of dwarf-galaxy evolution, as is the case in massive galaxies.", + "category": "astro-ph" + }, + { + "text": "Statistical characterization of polychromatic absolute and differential\n squared visibilities obtained from AMBER/VLTI instrument: In optical interferometry, the visibility squared modulus are generally\nassumed to follow a Gaussian distribution and to be independent of each other.\nA quantitative analysis of the relevance of such assumptions is important to\nhelp improving the exploitation of existing and upcoming multi-wavelength\ninterferometric instruments. Analyze the statistical behaviour of both the\nabsolute and the colour-differential squared visibilities: distribution laws,\ncorrelations and cross-correlations between different baselines. We use\nobservations of stellar calibrators obtained with AMBER instrument on VLTI in\ndifferent instrumental and observing configurations, from which we extract the\nframe-by-frame transfer function. Statistical hypotheses tests and diagnostics\nare then systematically applied. For both absolute and differential squared\nvisibilities and under all instrumental and observing conditions, we find a\nbetter fit for the Student distribution than for the Gaussian, log-normal and\nCauchy distributions. We find and analyze clear correlation effects caused by\natmospheric perturbations. The differential squared visibilities allow to keep\na larger fraction of data with respect to selected absolute squared\nvisibilities and thus benefit from reduced temporal dispersion, while their\ndistribution is more clearly characterized. The frame selection based on the\ncriterion of a fixed SNR value might result in either a biased sample of frames\nor in a too severe selection.", + "category": "astro-ph" + }, + { + "text": "Gipsy 3D: Analysis, Visualization and Vo-Tools: The scientific goals of the AMIGA project are based on the analysis of a\nsignificant amount of spectroscopic 3D data. In order to perform this work we\npresent an initiative to develop a new VO compliant package, including present\ncore applications and tasks offered by the Groningen Image Processing System\n(GIPSY), and new ones based on use cases elaborated in collaboration with ad-\nvanced users. One of the main goals is to provide local interoperability\nbetween GIPSY (visualization and data analysis) and other VO software. The\nconnectivity with the Virtual Observatory environment will provide general\naccess to 3D data VO archives and services, maximizing the potential for\nscientific discovery.", + "category": "astro-ph" + }, + { + "text": "Multi-wavelength analysis of the dust emission in the Small Magellanic\n Cloud: We present an analysis of dust grain emission in the diffuse interstellar\nmedium of the Small Magellanic Cloud (SMC). This study is motivated by the\navailability of 170 microns ISOPHOT data covering a large part of the SMC, with\na resolution enabling to disentangle the diffuse medium from the star forming\nregions. After data reduction and subtraction of Galactic foreground emission,\nwe used the ISOPHOT data together with HiRes IRAS data and ATCA/Parkes combined\nHI column density maps to determine dust properties for the diffuse medium. We\nfound a far infrared emissivity per hydrogen atom 30 times lower than the Solar\nNeighborhood value. The modeling of the spectral energy distribution of the\ndust, taking into account the enhanced interstellar radiation field, gives a\nsimilar conclusion for the smallest grains (PAHs and very small grains)\nemitting at shorter wavelength. Assuming Galactic dust composition in the SMC,\nthis result implies a difference in the gas-to-dust ratio (GDR) 3 times larger\nthan the difference in metallicity. This low depletion of heavy elements in\ndust could be specific of the diffuse ISM and not apply for the whole SMC dust\nif it results from efficient destruction of dust by supernovae explosions.", + "category": "astro-ph" + }, + { + "text": "The 2-10 keV emission properties of PSR B1937+21: We present the results of a BeppoSAX observation of the fastest pulsar known:\nPSR B1937+21. The ~ 200 ks observation (78.5 (34) ks MECS (LECS) exposure\ntimes) allowed us to investigate with high statistical significance both the\nspectral properties and the pulse profile shape. The absorbed power law\nspectral model gave a photon index of ~ 1.7 and N_H ~ 2.3 x 10^22 cm^-2. These\nvalues explain both a) the ROSAT non-detection and b) the deviant estimate of a\nphoton index of ~ 0.8 obtained by ASCA. The pulse profile appears, for the\nfirst time, clearly double peaked with the main component much stronger than\nthe other. The statistical significance is 10 sigma (main peak) and 5 sigma\n(secondary peak). The 1.6-10 keV pulsed fraction is consistent with 100%; only\nin the 1.6-4 keV band there is a ~ 2 sigma indication for a DC component. The\nsecondary peak is detected significantly only for energies above 3 / 4 keV. The\nunabsorbed (2-10 keV) flux is F_2-10 = 3.7 x 10^-13 erg cm^-2 s^-1, implying a\nluminosity of L_X = 4.6 x 10^31 Theta (d/3.6 kpc)^2 erg s^-1 and an X-ray\nefficiency of eta = 4 x 10^-5 Theta, where Theta is the solid angle spanned by\nthe emission beam. These results are in agreement with those obtained by ASCA.", + "category": "astro-ph" + }, + { + "text": "WALLABY Pilot Survey: Public release of HI kinematic models for more\n than 100 galaxies from phase 1 of ASKAP pilot observations: We present the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY)\nPilot Phase I HI kinematic models. This first data release consists of HI\nobservations of three fields in the direction of the Hydra and Norma clusters,\nand the NGC 4636 galaxy group. In this paper, we describe how we generate and\npublicly release flat-disk tilted-ring kinematic models for 109/592 unique HI\ndetections in these fields. The modelling method adopted here - which we call\nthe WALLABY Kinematic Analysis Proto-Pipeline (WKAPP) and for which the\ncorresponding scripts are also publicly available - consists of combining\nresults from the homogeneous application of the FAT and 3DBAROLO algorithms to\nthe subset of 209 detections with sufficient resolution and S/N in order to\ngenerate optimized model parameters and uncertainties. The 109 models presented\nhere tend to be gas rich detections resolved by at least 3-4 synthesized beams\nacross their major axes, but there is no obvious environmental bias in the\nmodelling. The data release described here is the first step towards the\nderivation of similar products for thousands of spatially-resolved WALLABY\ndetections via a dedicated kinematic pipeline. Such a large publicly available\nand homogeneously analyzed dataset will be a powerful legacy product that that\nwill enable a wide range of scientific studies.", + "category": "astro-ph" + }, + { + "text": "BLR Modeling: A New Approach: We present a new scheme for modeling the broad line region in active galactic\nnuclei. It involves photoionization calculations applied to a number of\nvariable emission lines at {\\it all times}. We demonstrate how fitting all\nlines simultaneously provide strong constraints on several of the more\nimportant parameters, such as the density and column density, and the radial\ndistribution of the emission line clouds.\n When applying the model to the Seyfert 1 galaxy NGC 5548, we are able to\nreconstruct the light curves of four emission-lines, in time and in absolute\nflux. We argue that the Balmer line light curves, and possibly also the MgII\nlight curve, do not fit this scheme because of the limitations of present-day\nphotoionization codes. We rule out models where the particle density scales as\nr^{-2} and favor models where it scales as r^{-(1-1.5)}. We can place lower\nlimits on the column density at a distance of 10 ld, of N_{col}(r=10)>10^{22}\ncm^{-2}, and limit the particle density to be in the range of\n10^{11}>N(r=10)>10^{9.5} cm^{-3}.", + "category": "astro-ph" + }, + { + "text": "Grantecan spectroscopic observations and confirmations of Planetary\n Nebulae candidates in the Northern Galactic Plane: We present Grantecan 10 m telescope (GTC) spectroscopic confirmations of 55\nfaint Planetary Nebulae (PNe) candidates discovered largely in the INT\nPhotometric H$_\\alpha$ Survey of the Northern Galactic Plane (IPHAS) by our\npro-am collaboration. We confirm 46 of them as 'True' (T), 4 as 'Likely' (L)\nand 5 as 'Possible' (P) PNe and including 5 new PNe central star (CSPN)\ndiscoveries. This was from observations of 62 new candidates yielding a maximum\nPN discovery success rate of 89%. The sensitivity and longer wavelength\ncoverage of IPHAS allows PNe to be found in regions of greater extinction and\nat these lower Galactic latitudes, including PNe in a more advanced\nevolutionary state and at larger distances compared to previously known\nGalactic PNe. We use an holistic set of observed characteristics and optical\nemission-line diagnostics to confirm candidates. Plasma properties have been\ndetermined in a self-consistent way using PyNeb. This work is facilitated by\nthe functionality of our powerful, multi-wavelength database 'HASH' (Hong Kong,\nAustralian Astronomical Observatory, Strasbourg Observatory H-alpha Planetary\nNebula catalogue) that federates known imaging, spectroscopy and other\npertinent data for all Galactic T, L, P PNe and the significant numbers of\nmimics. Reddenings, corrected radial velocities and PNe electron density and\ntemperature estimates are provided for these new PNe where possible.", + "category": "astro-ph" + }, + { + "text": "The chemical composition of the stellar cluster Gaia1: no surprise\n behind Sirius: We observed 6 He-clump stars of the intermediate-age stellar cluster Gaia1\nwith the MIKE/MAGELLAN spectrograph. A possible extra-galactic origin of this\ncluster, recently discovered thanks to the first data release of the ESA Gaia\nmission, has been suggested, based on its orbital parameters. Abundances for\nFe, alpha, proton- and neutron-capture elements have been obtained. We find no\nevidence of intrinsic abundance spreads. The iron abundance is solar\n([FeI/H]=+0.00 +-0.01; sigma = 0.03 dex). All the other abundance ratios are,\nby and large, solar-scaled, similar to the Galactic thin disk and open clusters\nstars of similar metallicity. The chemical composition of Gaia1 does not\nsupport an extra-galactic origin for this stellar cluster, that can be\nconsidered as a standard Galactic open cluster.", + "category": "astro-ph" + }, + { + "text": "Space density of optically-selected type 2 quasars: Type 2 quasars are luminous active galactic nuclei (AGN) whose central\nregions are obscured by large amounts of gas and dust. In this paper, we\npresent a catalog of type 2 quasars from the Sloan Digital Sky Survey (SDSS),\nselected based on their optical emission lines. The catalog contains 887\nobjects with redshifts z < 0.83; this is six times larger than the previous\nversion and is by far the largest sample of type 2 quasars in the literature.\nWe derive the [OIII]5008 luminosity function for 10^8.3 Lsun < L[OIII] < 10^10\nLsun (corresponding to intrinsic luminosities up to M[2400A]-28 mag or\nbolometric luminosities up to 4x10^47 erg/sec). This luminosity function\nprovides strong lower limits to the actual space density of obscured quasars,\ndue to our selection criteria, the details of the spectroscopic target\nselection, as well as other effects. We derive the equivalent luminosity\nfunction for the complete sample of type 1 (unobscured) quasars; then, we\ndetermine the ratio of type 2/type 1 quasar number densities. Our best data\nconstrain this ratio to be at least 1.5:1 for 10^8.3 Lsun < L[OIII] < 10^9.5\nLsun at z < 0.3, and at least 1.2:1 for L[OIII]=10^10 Lsun at 0.3 < z < 0.83.\nType 2 quasars are at least as abundant as type 1 quasars in the relatively\nnearby Universe (z < 0.8) for the highest luminosities.", + "category": "astro-ph" + }, + { + "text": "An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar\n Medium: We present a survey of diffuse O VI emission in the interstellar medium\nobtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Spanning 5.5\nyears of FUSE observations, from launch through 2004 December, our data set\nconsists of 2925 exposures along 183 sight lines, including all of those with\npreviously-published O VI detections. The data were processed using an\nimplementation of CalFUSE v3.1 modified to optimize the signal-to-noise ratio\nand velocity scale of spectra from an aperture-filling source. Of our 183 sight\nlines, 73 show O VI 1032 emission, 29 at > 3-sigma significance. Six of the\n3-sigma features have velocities |v_LSR| > 120 km/s, while the others have\n|v_LSR| < 50 km/s. Measured intensities range from 1800 to 9100 LU, with a\nmedian of 3300 LU. Combining our results with published O VI absorption data,\nwe find that an O VI-bearing interface in the local ISM yields an electron\ndensity n_e = 0.2--0.3 cm^-3^ and a path length of 0.1 pc, while O VI-emitting\nregions associated with high-velocity clouds in the Galactic halo have\ndensities an order of magnitude lower and path lengths two orders of magnitude\nlonger. Though the O VI intensities along these sight lines are similar, the\nemission is produced by gas with very different properties.", + "category": "astro-ph" + }, + { + "text": "H$_2$O$_2$-induced Greenhouse Warming on Oxidized Early Mars: The existence of liquid water within an oxidized environment on early Mars\nhas been inferred by the Mn-rich rocks found during recent explorations on\nMars. The oxidized atmosphere implied by the Mn-rich rocks would basically be\ncomprised of CO$_2$ and H$_2$O without any reduced greenhouse gases such as\nH$_2$ and CH$_4$. So far, however, it has been thought that early Mars could\nnot have been warm enough to sustain water in liquid form without the presence\nof reduced greenhouse gases. Here, we propose that H$_2$O$_2$ could have been\nthe gas responsible for warming the surface of the oxidized early Mars. Our\none-dimensional atmospheric model shows that only 1 ppm of H$_2$O$_2$ is enough\nto warm the planetary surface because of its strong absorption at far-infrared\nwavelengths, in which the surface temperature could have reached over 273~K for\na CO$_2$ atmosphere with a pressure of 3~bar. A wet and oxidized atmosphere is\nexpected to maintain sufficient quantities of H$_2$O$_2$ gas in its upper\natmosphere due to its rapid photochemical production in slow condensation\nconditions. Our results demonstrate that a warm and wet environment could have\nbeen maintained on an oxidized early Mars, thereby suggesting that there may be\nconnections between its ancient atmospheric redox state and possible aqueous\nenvironment.", + "category": "astro-ph" + }, + { + "text": "Search for dormant black holes in the OGLE data: Light curves of ellipsoidal variables collected by the Optical Gravitational\nLensing Experiment (OGLE) were analyzed, in order to search for dormant black\nhole candidates. After the preselection based on the amplitude of ellipsoidal\nmodulation, each object was investigated by means of the spectral energy\ndistribution fit, which allowed us to select objects that are in close\nagreement with the spectrum of a single stellar object. After this final step\nof the preselection process, we were left with only fourteen objects that were\nthen investigated in detail. For each candidate, we estimated basic physical\nparameters such as temperature, mass, luminosity, and, in some cases, radial\nvelocity semi-amplitude. One of the objects turned out to be a spotted star\nwhile the rest are considered black-hole binary candidates. In the end, we\npresent an alternative explanation for the ellipsoidal modulation in the form\nof contact binaries, which are not only vast in number, contrary to black-hole\nbinaries, but are also in much better agreement with the radial velocity\nestimates for some of the systems analyzed. Even if the presented arguments\nsuggest a noncompact character of the companion objects, each of them should be\nobserved spectroscopically in order to verify the compact object hypothesis.", + "category": "astro-ph" + }, + { + "text": "Collisional Ionization Equilibrium for Optically Thin Plasmas. I.\n Updated Recombination Rate Coefficients for Bare though Sodium-like Ions: Reliably interpreting spectra from electron-ionized cosmic plasmas requires\naccurate ionization balance calculations for the plasma in question. However,\nmuch of the atomic data needed for these calculations have not been generated\nusing modern theoretical methods and are often highly suspect. This translates\ndirectly into the reliability of the collisional ionization equilibrium (CIE)\ncalculations. We make use of state-of-the-art calculations of dielectronic\nrecombination (DR) rate coefficients for the hydrogenic through Na-like ions of\nall elements from He up to and including Zn. We also make use of\nstate-of-the-art radiative recombination (RR) rate coefficient calculations for\nthe bare through Na-like ions of all elements from H through to Zn. Here we\npresent improved CIE calculations for temperatures from $10^4$ to $10^9$ K\nusing our data and the recommended electron impact ionization data of\n\\citet{Mazz98a} for elements up to and including Ni and Mazzotta (private\ncommunication) for Cu and Zn. DR and RR data for ionization stages that have\nnot been updated are also taken from these two additional sources. We compare\nour calculated fractional ionic abundances using these data with those\npresented by Mazzotta et al. for all elements from H to Ni. The differences in\npeak fractional abundance are up to 60%. We also compare with the fractional\nionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR\ncalculations of \\citet{Gu03a,Gu04a} for the H-like through Na-like ions, and\nthe RR calculations of \\citet{Gu03b} for the bare through F-like ions. These\nresults are in better agreement with our work, with differences in peak\nfractional abundance of less than 10%.", + "category": "astro-ph" + }, + { + "text": "Self-consistent Mean Field theory in weakly ionized media: We present a self-consistent mean field theory of the dynamo in 3D and\nturbulent diffusion in 2D in weakly ionized gas. We find that in 3D, the\nbackreaction does not alter the beta effect while it suppresses the alpha\neffect when the strength of a mean magnetic field exceeds a critical value.\nThese results suggest that a mean field dynamo operates much more efficiently\nin weakly ionized gas compared to the fully ionized gas. Furthermore, we show\nthat in 2D, the turbulent diffusion is suppressed by back reaction when a mean\nmagnetic field reaches the same critical strength, with the upper bound on\nturbulent diffusion given by its kinematic value. Astrophysical implications\nare discussed.", + "category": "astro-ph" + }, + { + "text": "Negative Energy Cosmology and the Cosmological Constant: It is well known that string theories naturally compactify on anti-de Sitter\nspaces, and yet cosmological observations show no evidence of a negative\ncosmological constant in the early Universe's evolution. In this letter we\npresent two simple nonlocal modifications of the standard Friedmann cosmology\nthat can lead to observationally viable cosmologies with an initial (negative)\ncosmological constant. The nonlocal operators we include are toy models for the\nquantum cosmological backreaction. In Model I an initial quasiperiodic\noscillatory epoch is followed by inflation and a late time matter era,\nrepresenting a dark matter candidate. The backreaction in Model II quickly\ncompensates the negative cosmological term such that the Ricci curvature scalar\nrapidly approaches zero, and the Universe ends up in a late time radiation era.", + "category": "astro-ph" + }, + { + "text": "The Most Massive White Dwarfs in the Solar Neighborhood: We present an analysis of the most massive white dwarf candidates in the\nMontreal White Dwarf Database 100 pc sample. We identify 25 objects that would\nbe more massive than $1.3~M_{\\odot}$ if they had pure H atmospheres and CO\ncores, including two outliers with unusually high photometric mass estimates\nnear the Chandrasekhar limit. We provide follow-up spectroscopy of these two\nwhite dwarfs and show that they are indeed significantly below this limit. We\nexpand our model calculations for CO core white dwarfs up to $M=1.334\\\nM_\\odot$, which corresponds to the high-density limit of our equation-of-state\ntables, $\\rho = 10^9$ g cm$^{-3}$. We find many objects close to this maximum\nmass of our CO core models. A significant fraction of ultramassive white dwarfs\nare predicted to form through binary mergers. Merger populations can reveal\nthemselves through their kinematics, magnetism, or rapid rotation rates. We\nidentify four outliers in transverse velocity, four likely magnetic white\ndwarfs (one of which is also an outlier in transverse velocity), and one with\nrapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs\nin our sample are likely merger products.", + "category": "astro-ph" + }, + { + "text": "Optical identification of the transient supersoft X-ray source RX\n J0527.8-6954, in the LMC: Context. Close binary supersoft X-ray sources (CBSS) are binary systems that\ncontain a white dwarf with stable nuclear burning on its surface. These\nsources, first discovered in the Magellanic Clouds, have high accretion rates\nand near-Eddington luminosities (10^37 - 10^38 erg/s) with high temperatures (T\n= 2 - 7 x 10^5 K). Aims. The total number of known objects in the MC is still\nsmall and, in our galaxy, even smaller. We observed the field of the\nunidentified transient supersoft X-ray source RX J0527.8-6954 in order to\nidentify its optical counterpart. Methods. The observation was made with the\nIFU-GMOS on the Gemini South telescope with the purpose of identifying stars\nwith possible He II or Balmer emission or else of observing nebular extended\njets or ionization cones, features that may be expected in CBSS. Results. The\nX-ray source is identified with a B5e V star that is associated with\nsubarcsecond extended Halpha emission, possibly bipolar. Conclusions. If the\nprimary star is a white dwarf, as suggested by the supersoft X-ray spectrum,\nthe expected orbital period exceeds 21 h; therefore, we believe that the 9.4 h\nperiod found so far is not associated to this system.", + "category": "astro-ph" + }, + { + "text": "Horizontally Polarized Kink Oscillations Supported by Solar Coronal\n Loops in an Asymmetric Environment: Kink oscillations are ubiquitously observed in solar coronal loops, their\nunderstanding being crucial in the contexts of coronal seismology and\natmospheric heating. We study kink modes supported by a straight coronal loop\nembeded in an asymmetric environment using three-dimensional\nmagnetohydrodynamic (MHD) simulations. We implement the asymmetric effect by\nsetting different exterior densities below and above the loop interior, and\ninitiate the simulation using a kink-like velocity perturbation perpendicular\nto the loop plane, mimicking the frequently measured horizontally polarized\nkink modes. We find that the external velocity fields show fan blade structures\npropagating in the azimuthal direction as a result of the successive excitation\nof higher azimuthal Fourier modes. Resonant absorption and phase mixing can\nstill occur despite an asymmetric environment, leading to the development of\nsmall scales at loop boundaries. These small scales nonetheless develop\nasymmetrically at the upper and lower boundaries due to the different gradients\nof the Alfven speed. These findings enrich our understanding of kink modes in\ncoronal loops embedded within an asymmetric environment, providing insights\nhelpful for future high-resolution observations.", + "category": "astro-ph" + }, + { + "text": "Preliminary Spectral Analysis of SN 1994I: We present optical spectra of the Type Ic supernova 1994I in M51 and\npreliminary non-LTE analysis of the spectra. Our models are not inconsistent\nwith the explosions of C+O cores of massive stars. While we find no direct\nevidence for helium in the optical spectra, our models cannot rule out small\namounts of helium. More than 0.1~\\msol\\ of helium seems unlikely.", + "category": "astro-ph" + }, + { + "text": "Mechanisms and sites of ultra high energy cosmic ray origin: We shortly discuss several astrophysical scenarios leading to cosmic ray\nacceleration up to extremely high energies reaching the scale of 10^{20} eV.\nThe processes suggested in the literature include acceleration at relativistic\njet terminal shocks and shear boundary layers, shocks in large scale accretion\nflows onto supergalactic cosmic structures, particle reflections from\nultra-relativistic shocks postulated to exist in sources of gamma ray bursts,\nthe processes involving the neutron star rotating magnetospheres and dormant\nquasars. Some of these objects can explain cosmic rays with highest energies if\none tunes the model parameters to limits enabling the highest acceleration\nefficiency. We also note that some of the considered processes allow for\nacceleration efficiency in the Hillas diagram, beta, to be much larger than\nunity. The present paper is based on a review talk presented during the\nEuropean Cosmic Ray Symposium in Lodz (2000).", + "category": "astro-ph" + }, + { + "text": "Tensor to scalar ratio and large scale power suppression from pre-slow\n roll initial conditions: We study corrections to the power spectra of curvature and tensor\nperturbations and the tensor-to-scalar ratio in single field slow roll\ninflation due to initial conditions imprinted by a fast-roll stage prior to\nslow roll. For a wide range of initial inflaton kinetic energy, this stage\nlasts only a few e-folds and merges smoothly with slow-roll leading to\nnon-Bunch-Davies initial conditions for modes that exit the Hubble radius\nduring slow roll. We describe a program that yields the dynamics in the\nfast-roll stage while matching to the slow roll stage independent of the\ninflationary potentials. Corrections to the power spectra are encoded in a\ntransfer function $\\mathcal{T}_\\alpha(k)$. We obtain $\\mathcal{T}_\\alpha(k)$ to\nleading order in a Born approximation valid for modes of observational\nrelevance today. A fit yields $\\mathcal{T}_\\alpha(k) =1+\nA_{\\alpha}k^{-p}\\cos[2\\pi \\omega k/H_{sr}+\\varphi_\\alpha]$, with $1.5 \\lesssim\np \\lesssim 2$, $\\omega \\simeq 1$ and $H_{sr}$ the Hubble scale during slow roll\ninflation, where curvature and tensor perturbations feature the same $p,\\omega$\nfor a wide range of initial conditions. These corrections lead to both a\nsuppression of the quadrupole and oscillatory features in both $P_R(k)$ and\n$r(k_0)$ with a period of the order of the Hubble scale during slow roll\ninflation. The results are independent of the specific inflationary potentials,\ndepending solely on the ratio of kinetic to potential energy $\\kappa$ and the\nslow roll parameters to leading order. For a wide range of $\\kappa$ and the\nvalues of $\\epsilon_V;\\eta_V$ corresponding to the upper bounds from Planck, we\nfind that the low quadrupole is consistent with the results from Planck, and\nthe oscillations in $r(k_0)$ could be observable if the modes corresponding to\nthe quadrupole and the pivot scale crossed the Hubble radius a few e-folds\nafter the onset of slow roll.", + "category": "astro-ph" + }, + { + "text": "SPITZER Observations of z~3 Lyman Break Galaxies: stellar masses and\n mid-infrared properties: We describe the spectral energy distributions (SEDs) of Lyman Break Galaxies\n(LBGs) at z~3 using deep mid-infrared and optical observations of the Extended\nGroth Strip, obtained with IRAC and MIPS on board Spitzer and from the ground,\nrespectively. We focus on LBGs with detections at all four IRAC bands, in\nparticular the 26 galaxies with IRAC 8 micron band (rest--frame K-band)\ndetections. We use stellar population synthesis models and probe the stellar\ncontent of these galaxies. Based on best--fit continuous star-formation models\nwe derive estimates of the stellar mass for these LBGs. As in previous studies,\nwe find that a fraction of LBGs have very red colors and large estimated\nstellar masses (M_stellar > 5 x 10 ^{10} M_solar): the present Spitzer data\nallow us, for the first time, to study these massive LBGs in detail. We discuss\nthe link between these LBGs and submm-luminous galaxies.We find that the number\ndensity of these massive LBGs at high redshift is higher than predicted by\ncurrent semi-analytic models of galaxy evolution.", + "category": "astro-ph" + }, + { + "text": "Halo Mass Function and the Free Streaming Scale: The nature of structure formation around the particle free streaming scale is\nstill far from understood. Many attempts to simulate hot, warm, and cold dark\nmatter cosmologies with a free streaming cutoff have been performed with\ncosmological particle-based simulations, but they all suffer from spurious\nstructure formation at scales below their respective free streaming scales --\ni.e. where the physics of halo formation is most affected by free streaming. We\nperform a series of high resolution numerical simulations of different WDM\nmodels, and develop an approximate method to subtract artificial structures in\nthe measured halo mass function. The corrected measurements are then used to\nconstruct and calibrate an extended Press-Schechter (EPS) model with sharp-$k$\nwindow function and adequate mass assignment. The EPS model gives accurate\npredictions for the low redshift halo mass function of CDM and WDM models, but\nit significantly under-predicts the halo abundance at high redshifts. By taking\ninto account the ellipticity of the initial patches and connecting the\ncharacteristic filter scale to the smallest ellipsoidal axis, we are able to\neliminate this inconsistency and obtain an accurate mass function over all\nredshifts and all dark matter particle masses covered by the simulations. As an\nadditional application we use our model to predict the microhalo abundance of\nthe standard neutralino-CDM scenario and we give the first quantitative\nprediction of the mass function over the full range of scales of CDM structure\nformation.", + "category": "astro-ph" + }, + { + "text": "Mining the gap: evolution of the magnitude gap in X-ray galaxy groups\n from the 3 square degree XMM coverage of CFHTLS: We present a catalog of 129 X-ray galaxy groups, covering a redshift range\n0.046$. Recent ALMA observations of the cool gas\nand dust in $z\\gtrsim$6 quasars have discovered [CII]- and far infrared-bright\ngalaxies adjacent to several quasars. In this work, we present sensitive\nimaging and spectroscopic follow-up observations, with HST/WFC3, Spitzer/IRAC,\nVLT/MUSE, Magellan/FIRE and LBT/LUCI-MODS, of ALMA-detected, dust-rich\ncompanion galaxies of four quasars at $z\\gtrsim 6$, specifically acquired to\nprobe their stellar content and unobscured star formation rate. Three companion\ngalaxies do not show significant emission in the observed optical/IR wavelength\nrange. The photometric limits suggest that these galaxies are highly\ndust-enshrouded, with unobscured star formation rates SFR$_{\\rm UV}<$few\nM$_{\\odot}$ yr$^{-1}$, and a stellar content of $M_{*}<$10$^{10}$ M$_{\\odot}$\nyr$^{-1}$. However, the companion to PJ167-13 shows bright rest-frame UV\nemission (F140W AB = 25.48). Its SED resembles that of a star-forming galaxy\nwith a total SFR$\\sim$50 M$_{\\odot}$ yr$^{-1}$ and $M_{*}\\sim 9 \\times 10^{9}$\nM$_{\\odot}$. All the companion sources are consistent with residing on the\ngalaxy main sequence at $z\\sim$6. Additional, deeper data from future\nfacilities, such as JWST, are needed in order to characterize these gas-rich\nsources in the first Gyr of cosmic history.", + "category": "astro-ph" + }, + { + "text": "The MOSDEF Survey: Neon as a Probe of ISM Physical Conditions at High\n Redshift: We present results on the properties of neon emission in $z\\sim2$\nstar-forming galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF)\nsurvey. Doubly-ionized neon ([NeIII]3869) is detected at $\\geq3\\sigma$ in 61\ngalaxies, representing $\\sim$25% of the MOSDEF sample with H$\\alpha$, H$\\beta$,\nand [OIII]$5007$ detections at similar redshifts. We consider the neon\nemission-line properties of both individual galaxies with [NeIII]3869\ndetections and composite $z\\sim2$ spectra binned by stellar mass. With no\nrequirement of [NeIII]3869 detection, the latter provide a more representative\npicture of neon emission-line properties in the MOSDEF sample. The\n[NeIII]3869/[OII]3727 ratio (Ne3O2) is anti-correlated with stellar mass in\n$z\\sim2$ galaxies, as expected based on the mass-metallicity relation. It is\nalso positively correlated with the [OIII]$5007$/[OII]$3727$ ratio (O32), but\n$z\\sim2$ line ratios are offset towards higher Ne3O2 at fixed O32, compared\nwith both local star-forming galaxies and individual H~II regions. Despite the\noffset towards higher Ne3O2 at fixed O32 at $z\\sim2$, biases in inferred\nNe3O2-based metallicity are small. Accordingly, Ne3O2 may serve as an important\nmetallicity indicator deep into the reionization epoch. Analyzing additional\nrest-optical line ratios including [NeIII]$3869$/[OIII]$5007$ (Ne3O3) and\n[OIII]$5007$/H$\\beta$ (O3H$\\beta$), we conclude that the nebular emission-line\nratios of $z\\sim2$ star-forming galaxies suggest a harder ionizing spectrum\n(lower stellar metallicity, i.e., Fe/H) at fixed gas-phase oxygen abundance,\ncompared to systems at $z\\sim0$. These new results based on neon lend support\nto the physical picture painted by oxygen, nitrogen, hydrogen, and sulfur\nemission, of an ionized ISM in high-redshift star-forming galaxies irradiated\nby chemically young, $\\alpha$-enhanced massive stars.", + "category": "astro-ph" + }, + { + "text": "X-ray diagnostics of Cassiopeia A's \"Green Monster\": evidence for dense\n shocked circumstellar plasma: The recent survey of the core-collapse supernova remnant Cassiopeia A (CasA)\nwith the MIRI instrument on board the James Webb Space Telescope (JWST)\nrevealed a large structure in the interior region, referred to as the \"Green\nMonster\". Although its location suggests that it is an ejecta structure, the\ninfrared properties of the \"Green Monster\" hint at a circumstellar medium (CSM)\norigin. In this companion paper to the JWST Cas A paper, we investigate the\nfilamentary X-ray structures associated with the \"Green Monster\" using Chandra\nX-ray Observatory data. We extracted spectra along the \"Green Monster\" as well\nas from shocked CSM regions. Both the extracted spectra and a principal\ncomponent analysis show that the \"Green Monster\" emission properties are\nsimilar to those of the shocked CSM. The spectra are well-fit by a model\nconsisting of a combination of a non-equilibrium-ionization model and a\npower-law component, modified by Galactic absorption. All the \"Green Monster\"\nspectra show a blueshift corresponding to a radial velocity of around -2300\nkm/s, suggesting that the structure is on the near side of Cas A. The\nionization age is around $n_{e}t = 1.5 \\times 10^{11}$ cm$^{-3}s. This\ntranslates into a pre-shock density of ~12 cm$^{-3}$, higher than previous\nestimates of the unshocked CSM. The relatively high net and relatively low\nradial velocity suggest that this structure has a relatively high density\ncompared to other shocked CSM plasma. This analysis provides yet another piece\nof evidence that the CSM around Cas A's progenitor was not that of a smooth\nsteady wind profile.", + "category": "astro-ph" + }, + { + "text": "Dust temperature and the submillimeter-radio flux density ratio as a\n redshift indicator: It is difficult to identify the distant galaxies selected in existing\nsubmillimeter (submm)-wave surveys, because their positional accuracy is only\nseveral arcseconds. Currently, centimeter-wave VLA observations are required in\norder to determine sub-arcsec positions, and so to make reliable optical\nidentifications. Carilli & Yun (1999) pointed out that the ratio of the radio\nand submm-wave flux densities provides a redshift indicator for dusty\nstar-forming galaxies, when compared with the tight correlation observed\nbetween the far-infrared and radio flux densities for low-redshift galaxies.\nThis method provides a useful, albeit imprecise, indication of the distance to\na submm-selected galaxy. However, because the degeneracy between the effects of\nincreasing the redshift of a galaxy and decreasing its dust temperature is not\nbroken, it does not provide an unequivocal redshift estimate.", + "category": "astro-ph" + }, + { + "text": "Mixing Bispectrum Multipoles Under Geometric Distortions: We derive general expressions for how the Alcock-Paczynski distortions affect\nthe power spectrum and the bispectrum of cosmological fields. We compute\nexplicit formulas for the mixing coefficients of bispectrum multipoles in the\nlinear approximation. The leading-order effect for the bispectrum is the\nuniform dilation of all three wavevectors. The mixing coefficients depend on\nthe shape of the bispectrum triplet. Our results for the bispectrum multipoles\nare framed in terms of the \"natural\" basis of the lengths of three wavevectors\nbut can be easily generalized for other bases and reduction schemes. Our\nvalidation tests confirm that the linear approximation is extremely accurate\nfor all power spectrum multipoles. The linear approximation is accurate for the\nbispectrum monopole but results in sub-percent level inaccuracies for the\nbispectrum quadrupole and fails for the bispectrum hexadecapole. Our results\ncan be used to simplify the analysis of the bispectrum from galaxy surveys,\nespecially the measurement of the Baryon Acoustic Oscillation peak position.\nThey can be used to replace numeric schemes with exact analytic formulae.", + "category": "astro-ph" + }, + { + "text": "Machine Learning of Interstellar Chemical Inventories: The characterization of interstellar chemical inventories provides valuable\ninsight into the chemical and physical processes in astrophysical sources. The\ndiscovery of new interstellar molecules becomes increasingly difficult as the\nnumber of viable species grows combinatorially, even when considering only the\nmost thermodynamically stable. In this work, we present a novel approach for\nunderstanding and modeling interstellar chemical inventories by combining\nmethodologies from cheminformatics and machine learning. Using multidimensional\nvector representations of molecules obtained through unsupervised machine\nlearning, we show that identification of candidates for astrochemical study can\nbe achieved through quantitative measures of chemical similarity in this vector\nspace, highlighting molecules that are most similar to those already known in\nthe interstellar medium. Furthermore, we show that simple, supervised learning\nregressors are capable of reproducing the abundances of entire chemical\ninventories, and predict the abundance of not yet seen molecules. As a\nproof-of-concept, we have developed and applied this discovery pipeline to the\nchemical inventory of a well-known dark molecular cloud, the Taurus Molecular\nCloud 1 (TMC-1); one of the most chemically rich regions of space known to\ndate. In this paper, we discuss the implications and new insights machine\nlearning explorations of chemical space can provide in astrochemistry.", + "category": "astro-ph" + }, + { + "text": "Formation Scenario of Magnetars: The Puzzle of Isolation: Magnetars (SGRs and AXPs) are one of the most evolutionary paths of a neutron\nstar. These objects have an ultra-strong magnetic field $B \\sim 10^{15}$ G at\ntheir surface and show persistent X-ray pulsations and transient bursts. Till\ndate there are 14 magnetars known: 5 SGRs (4 confirmed, 1 candidate) and 9 AXPs\n(7 confirmed, 2 candidates). It is an open puzzle that all these objects are\nisolated and none have been found in binaries. We discuss the formation\nscenario which can lead to such a situation.", + "category": "astro-ph" + }, + { + "text": "Titan's Dynamic Love Number Implies Stably-Stratified Ocean: The dynamic quadrupole Love number of Titan measured by \\Cassini is\n$k_\\mathrm{2,obs}=0.616\\pm 0.067$, strongly indicating a global subsurface\nocean. However, the theoretical Love number due to equilibrium tides is at most\n$k_\\mathrm{2,eq}^\\mathrm{max}\\approx 0.48$ in the absence of an ice shell on\ntop of the ocean. In reality, there is an outer ice shell of thickness $\n100\\,\\mathrm{km}$, reducing the equilibrium-tide Love number to\n$k_\\mathrm{2,eq}\\approx 0.42$. Therefore, other types of tidal response, like\ndynamic tides, may be also present in Titan. We propose that the ocean is\nstably stratified. As a result, there exist standing ocean waves (gravity\nmodes) with eigen-frequencies close to the tidal frequency. Such a gravity mode\n(g-mode) is resonantly excited. It bends the outer ice shell radially and thus\nenhances the dynamic Love number by $k_\\mathrm{2,g}$. In order for\n$k_\\mathrm{2,g}$ to account for the discrepancy between $k_\\mathrm{2,eq}$ and\n$k_\\mathrm{2,obs}$, the Brunt-Vaisala frequency in the ocean is required to be\n$3.3\\times 10^{-4}\\,\\mathrm{rad\\, s^{-1}}$. It is compatible with the\nvolatile-rich model for Titan that was proposed to explain the methane-rich\natmosphere. The three components of the tidal potential with azimuthal degrees,\n$m=-2,0,2$, correspond to the three components of the quadrupole Love number,\n$k_\\mathrm{2,-2}$, $k_\\mathrm{2,0}$ and $k_\\mathrm{2,2}$. They can excite\nretrograde, axisymmetric and prograde g-modes equally in the absence of\nrotation. However, Coriolis force induced by Titan's rotation breaks the\nsymmetry among these modes. Most likely, only one of the Love-number components\nis significantly enhanced by a g-mode, while the other two are still attributed\nto equilibrium tides. This prediction is testable by observation. If confirmed,\nthe smaller components of the Love number can be used to constrain the\nthickness of the outer ice shell.", + "category": "astro-ph" + }, + { + "text": "The Stability of Tidal Equilibrium for Hierarchical Star-Planet-Moon\n Systems: Motivated by the current search for exomoons, this paper considers the\nstability of tidal equilibrium for hierarchical three-body systems containing a\nstar, a planet, and a moon. In this treatment, the energy and angular momentum\nbudgets include contributions from the planetary orbit, lunar orbit, stellar\nspin, planetary spin, and lunar spin. The goal is to determine the optimized\nenergy state of the system subject to the constraint of constant angular\nmomentum. Due to the lack of a closed form solution for the full three-body\nproblem, however, we must use use an approximate description of the orbits. We\nfirst consider the Keplerian limit and find that the critical energy states are\nsaddle points, rather than minima, so that these hierarchical systems have no\nstable tidal equilibrium states. We then generalize the calculation so that the\nlunar orbit is described by a time-averaged version of the circular restricted\nthree-body problem. In this latter case, the critical energy state is a shallow\nminimum, so that a tidal equilibrium state exists. In both cases, however, the\nlunar orbit for the critical point lies outside the boundary (roughly half the\nHill radius) where (previous) numerical simulations indicate dynamical\ninstability. These results suggest that star-planet-moon systems have no viable\nlong-term stable states analogous to those found for two-body systems.", + "category": "astro-ph" + }, + { + "text": "Fermi LAT detection of two high Galactic latitude gamma-ray sources,\n Fermi J1049.7+0435 and J1103.2+1145: The Second Fermi LAT source catalog (Nolan et al. 2012) includes as many as\n1,873 sources, but initial attempts to identify counterparts at other\nwavelengths resulted in 575 sources remaining unidentified. The 2FGL catalog is\nbased on the first 24 months of LAT observation since its launch in 2008, but\nthe LAT has now accumulated more than 5 years of high-energy gamma-ray data\nalmost flawlessly, presenting the possibility of finding new sources which were\ntoo faint to be detected in the first two years of data or showed flaring\nactivity after the catalog was created. In this paper we report on two new\ngamma-ray sources serendipitously discovered in the constellation Leo and\ndiscuss possible counterparts based on radio observations.", + "category": "astro-ph" + }, + { + "text": "Too Many, Too Few, or Just Right? The Predicted Number and Distribution\n of Milky Way Dwarf Galaxies: We predict the spatial distribution and number of Milky Way dwarf galaxies to\nbe discovered in the DES and LSST surveys, by completeness correcting the\nobserved SDSS dwarf population. We apply most massive in the past, earliest\nforming, and earliest infall toy models to a set of dark matter-only simulated\nMilky Way/M31 halo pairs from Exploring the Local Volume In Simulations\n(ELVIS). The observed spatial distribution of Milky Way dwarfs in the LSST-era\nwill discriminate between the earliest infall and other simplified models for\nhow dwarf galaxies populate dark matter subhalos. Inclusive of all toy models\nand simulations, at 90% confidence we predict a total of 37-114 L $\\gtrsim\n10^3$L$_{\\odot}$ dwarfs and 131-782 L $\\lesssim 10^3$L$_{\\odot}$ dwarfs within\n300 kpc. These numbers of L $\\gtrsim 10^3$L$_{\\odot}$ dwarfs are dramatically\nlower than previous predictions, owing primarily to our use of updated\ndetection limits and the decreasing number of SDSS dwarfs discovered per sky\narea. For an effective $r_{\\rm limit}$ of 25.8 mag, we predict: 3-13 L $\\gtrsim\n10^3$L$_{\\odot}$ and 9-99 L $\\lesssim 10^3$L$_{\\odot}$ dwarfs for DES, and\n18-53 L $\\gtrsim 10^3$L$_{\\odot}$ and 53-307 L $\\lesssim 10^3$L$_{\\odot}$\ndwarfs for LSST. These enormous predicted ranges ensure a coming decade of\nnear-field excitement with these next generation surveys.", + "category": "astro-ph" + }, + { + "text": "The Anisotropy of the Microwave Background to l = 3500: Mosaic\n Observations with the Cosmic Background Imager: Using the Cosmic Background Imager, a 13-element interferometer array\noperating in the 26-36 GHz frequency band, we have observed 40 sq deg of sky in\nthree pairs of fields, each ~ 145 x 165 arcmin, using overlapping pointings\n(mosaicing). We present images and power spectra of the cosmic microwave\nbackground radiation in these mosaic fields. We remove ground radiation and\nother low-level contaminating signals by differencing matched observations of\nthe fields in each pair. The primary foreground contamination is due to point\nsources (radio galaxies and quasars). We have subtracted the strongest sources\nfrom the data using higher-resolution measurements, and we have projected out\nthe response to other sources of known position in the power-spectrum analysis.\nThe images show features on scales ~ 6 - 15 arcmin, corresponding to masses ~\n(5 - 80)*10^{14} Msun at the surface of last scattering, which are likely to be\nthe seeds of clusters of galaxies. The power spectrum estimates have a\nresolution Delta-l = 200 and are consistent with earlier results in the\nmultipole range l <~ 1000. The power spectrum is detected with high\nsignal-to-noise ratio in the range 300 <~ l <~ 1700. For 1700 <~ l <~ 3000 the\nobservations are consistent with the results from more sensitive CBI deep-field\nobservations. The results agree with the extrapolation of cosmological models\nfitted to observations at lower l, and show the predicted drop at high l (the\n\"damping tail\").", + "category": "astro-ph" + }, + { + "text": "Radio-quiet neutron star 1E 1207.4-5209: a possible strong\n Gravitational-wave source: There are four puzzles on 1E 1207.4-5209: (1) the characteristic age of the\npulsar is much higher than the estimated age of the supernova remnant; (2) the\nmagnetic field inferred from spin-down is significantly different from the\nvalue obtained from the cyclotron absorption lines; (3) the spinning down of\nthe pulsar is non-monotonic; (4) the magnitude of the frequency's first\nderivative varies significantly and its sign is also variable. The third puzzle\ncan be explained by a wide binary system, with orbital period from 0.2 to 6 yr.\nThis letter proposes that all four puzzles can be explained naturally by an\nultra-compact binary with orbital period of between 0.5 and 3.3 min. With the\nshortest orbital period and a close distance of 2 kpc, the characteristic\namplitude of gravitational waves is $h\\sim3\\times10^{-21}$. It would be an\nexcellent source of gravitational-wave detectors such as the Laser\nInterferometer Space Antenna.", + "category": "astro-ph" + }, + { + "text": "Giant eruptions of very massive stars: Giant eruptions or supernova-impostor events are far more mysterious than\ntrue supernovae. An extreme example can release as much radiative energy as a\nSN, ejecting several M_sun of material. These events involve continuous\nradiation-driven outflows rather than blast waves. They constitute one of the\nmain unsolved problems in stellar astrophysics, but have received surprisingly\nlittle theoretical effort. Here I note some aspects that are not yet familiar\nto most astronomers.", + "category": "astro-ph" + }, + { + "text": "The SKA and the Unknown Unknowns: As new scientists and engineers join the SKA project and as the pressures\ncome on to maintain costs within a chosen envelope it is worth restating and\nupdating the rationale for the 'Exploration of the Unknown' (EoU). Maintaining\nan EoU philosophy will prove a vital ingredient for realizing the SKA's\ndiscovery potential. Since people make the discoveries enabled by technology a\nfurther axis in capability parameter space, the'human bandwidth' is emphasised.\nUsing the morphological approach pioneered by Zwicky, a currently unexploited\nregion of observational parameter space can be identified viz: time variable\nspectral patterns on all spectral and angular scales, one interesting example\nwould be 'spectral transients'. We should be prepared to build up to 10 percent\nless collecting area for a given overall budget in order to enhance the ways in\nwhich SKA1 can be flexibly utilized.", + "category": "astro-ph" + }, + { + "text": "Magnetic field emergence in mesogranular-sized exploding granules\n observed with SUNRISE/IMaX data: We report on magnetic field emergences covering significant areas of\nexploding granules. The balloon-borne mission SUNRISE provided high spatial and\ntemporal resolution images of the solar photosphere. Continuum images,\nlongitudinal and transverse magnetic field maps and Dopplergrams obtained by\nIMaX onboard SUNRISE are analyzed by Local Correlation Traking (LCT),\ndivergence calculation and time slices, Stokes inversions and numerical\nsimulations are also employed. We characterize two mesogranular-scale exploding\ngranules where $\\sim$ 10$^{18}$ Mx of magnetic flux emerges. The emergence of\nweak unipolar longitudinal fields ($\\sim$100 G) start with a single visible\nmagnetic polarity, occupying their respective granules' top and following the\ngranular splitting. After a while, mixed polarities start appearing,\nconcentrated in downflow lanes. The events last around 20 min. LCT analyses\nconfirm mesogranular scale expansion, displaying a similar pattern for all the\nphysical properties, and divergence centers match between all of them. We found\na similar behaviour with the emergence events in a numerical MHD simulation.\nGranule expansion velocities are around 1 \\kms while magnetic patches expand at\n0.65 \\kms. One of the analyzed events evidences the emergence of a loop-like\nstructure. Advection of the emerging magnetic flux features is dominated by\nconvective motion resulting from the exploding granule due to the magnetic\nfield frozen in the granular plasma. Intensification of the magnetic field\noccurs in the intergranular lanes, probably because of being directed by the\ndownflowing plasma.", + "category": "astro-ph" + }, + { + "text": "A transiting warm giant planet around the young active star TOI-201: We present the confirmation of the eccentric warm giant planet TOI-201 b,\nfirst identified as a candidate in \\textit{TESS} photometry (Sectors 1-8,\n10-13, and 27-28) and confirmed using ground-based photometry from NGTS and\nradial velocities from FEROS, HARPS, CORALIE, and \\textsc{Minerva}-Australis.\nTOI-201 b orbits a young ($\\mathrm{0.87^{+0.46}_{-0.49} \\, Gyr}$) and\nbright(V=9.07 mag) F-type star with a $\\mathrm{52.9781 \\, d}$ period. The\nplanet has a mass of $\\mathrm{0.42^{+0.05}_{-0.03}\\, M_J}$, a radius of\n$\\mathrm{1.008^{+0.012}_{-0.015}\\, R_J}$, and an orbital eccentricity of\n$0.28^{+0.06}_{-0.09}$; it appears to still be undergoing fairly rapid cooling,\nas expected given the youth of the host star. The star also shows long-term\nvariability in both the radial velocities and several activity indicators,\nwhich we attribute to stellar activity. The discovery and characterization of\nwarm giant planets such as TOI-201 b is important for constraining formation\nand evolution theories for giant planets.", + "category": "astro-ph" + }, + { + "text": "Supernovae and their host galaxies - IV. The distribution of supernovae\n relative to spiral arms: Using a sample of 215 supernovae (SNe), we analyze their positions relative\nto the spiral arms of their host galaxies, distinguishing grand-design (GD)\nspirals from non-GD (NGD) galaxies. We find that: (1) in GD galaxies, an offset\nexists between the positions of Ia and core-collapse (CC) SNe relative to the\npeaks of arms, while in NGD galaxies the positions show no such shifts; (2) in\nGD galaxies, the positions of CC SNe relative to the peaks of arms are\ncorrelated with the radial distance from the galaxy nucleus. Inside (outside)\nthe corotation radius, CC SNe are found closer to the inner (outer) edge. No\nsuch correlation is observed for SNe in NGD galaxies nor for SNe Ia in either\ngalaxy class; (3) in GD galaxies, SNe Ibc occur closer to the leading edges of\nthe arms than do SNe II, while in NGD galaxies they are more concentrated\ntowards the peaks of arms. In both samples of hosts, the distributions of SNe\nIa relative to the arms have broader wings. These observations suggest that\nshocks in spiral arms of GD galaxies trigger star formation in the leading\nedges of arms affecting the distributions of CC SNe (known to have short-lived\nprogenitors). The closer locations of SNe Ibc vs. SNe II relative to the\nleading edges of the arms supports the belief that SNe Ibc have more massive\nprogenitors. SNe Ia having less massive and older progenitors, have more time\nto drift away from the leading edge of the spiral arms.", + "category": "astro-ph" + }, + { + "text": "Transverse Sizes of CIV Absorption Systems Measured from Multiple QSO\n Sightlines: We present tomography of the circum-galactic metal distribution at redshift\n1.7 to 4.5 derived from echellete spectroscopy of binary quasars. We find CIV\nsystems at similar redshifts in paired sightlines more often than expected for\nsightline-independent redshifts. As the separation of the sightlines increases\nfrom 36 kpc to 907 kpc, the amplitude of this clustering decreases. At the\nlargest separations, the CIV systems cluster similar to Lyman-break galaxies\n(Adelberger et al. 2005a). The CIV systems are significantly less correlated\nthan these galaxies, however, at separations less than R_1 ~ 0.42 +/- 0.15 h-1\ncomoving Mpc. Measured in real space, i.e., transverse to the sightlines, this\nlength scale is significantly smaller than the break scale estimated from the\nline-of-sight correlation function in redshift space (Scannapieco et al.\n2006a). Using a simple model, we interpret the new real-space measurement as an\nindication of the typical physical size of enriched regions. We adopt this size\nfor enriched regions and fit the redshift-space distortion in the line-of-sight\ncorrelation function. The fitted velocity kick is consistent with the peculiar\nvelocity of galaxies as determined by the underlying mass distribution and\nplaces an upper limit on the outflow (or inflow) speed of metals. The implied\ntime scale for dispersing metals is larger than the typical stellar ages of\nLyman-break galaxies (Shapley et al. 2001), and we argue that enrichment by\ngalaxies at z > 4.3 played a greater role in dispersing metals. To further\nconstrain the growth of enriched regions, we discuss empirical constraints on\nthe evolution of the CIV correlation function with cosmic time. This study\ndemonstrates the potential of tomography for measuring the metal enrichment\nhistory of the circum-galactic medium.", + "category": "astro-ph" + }, + { + "text": "Radial velocities and membership of stars in the old, distant open\n cluster Berkeley 29: Multi slit spectroscopy at the Telescopio Nazionale Galileo was employed to\nmeasure radial velocities for 20 stars in the direction of the old open cluster\nBerkeley 29, the farthest known in our Galaxy. Membership information was\nderived for stars along all the red giant branch, in particular near its tip,\nand on the red clump. The sample of bona-fide cluster members was used to\nrevise the cluster distance to about 15 kpc, on the basis of an empirical\ncomparison with the red clump in open clusters with known distances. A\nmetallicity [Fe/H] = -0.74 +/- 0.18 was also estimated using the colours of\nspectroscopically confirmed red giant stars.", + "category": "astro-ph" + }, + { + "text": "Radial Migration in Disk Galaxies I: Transient Spiral Structure and\n Dynamics: We seek to understand the origin of radial migration in spiral galaxies by\nanalyzing in detail the structure and evolution of an idealized, isolated\ngalactic disk. To understand the redistribution of stars, we characterize the\ntime-evolution of properties of spirals that spontaneously form in the disk.\nOur models unambiguously show that in such disks, single spirals are unlikely,\nbut that a number of transient patterns may coexist in the disk. However, we\nalso show that while spirals are transient in amplitude, at any given time the\ndisk favors patterns of certain pattern speeds. Using several runs with\ndifferent numerical parameters we show that the properties of spirals that\noccur spontaneously in the disk do not sensitively depend on resolution. The\nexistence of multiple transient patterns has large implications for the orbits\nof stars in the disk, and we therefore examine the resonant scattering\nmechanisms that profoundly alter angular momenta of individual stars. We\nconfirm that the corotation scattering mechanism described by Sellwood & Binney\n(2002) is responsible for the largest angular momentum changes in our\nsimulations.", + "category": "astro-ph" + }, + { + "text": "Some caveats about the evolution of the N/O abundance and the star\n formation history: We carefully analyze how the abundance of Nitrogen over Oxygen evolves when\ndependent on metallicity stellar yields with a primary component of N\nproceeding from AGBs stars are used. We show the results obtained with a\nchemical evolution models grid, calculated with variable star formation\nefficiencies, which produce different star formation histories. Finally we see\nhow the N/O abundance is related on the evolutionary history.", + "category": "astro-ph" + }, + { + "text": "The TESS-Keck Survey I: A Warm Sub-Saturn-mass Planet and a Caution\n about Stray Light in TESS Cameras: We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI\n1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD\n332231, an F8 dwarf star with a V-band magnitude of 8.56, was observed by TESS\nin Sectors 14 and 15. We detect a single-transit event in the Sector 15\npresearch data conditioning (PDC) light curve. We obtain spectroscopic\nfollow-up observations of HD 332231 with the Automated Planet Finder, Keck I,\nand SONG telescopes. The orbital period we infer from the radial velocity (RV)\nobservations leads to the discovery of another transit in Sector 14 that was\nmasked by PDC due to scattered light contamination. A joint analysis of the\ntransit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size\n($0.867^{+0.027}_{-0.025} \\; R_{\\rm J}$), sub-Saturn-mass ($0.244\\pm0.021 \\;\nM_{\\rm J}$) exoplanet on a 18.71 day circular orbit. The low surface gravity of\nHD 332231 b and the relatively low stellar flux it receives make it a\ncompelling target for transmission spectroscopy. Also, the stellar obliquity is\nlikely measurable via the Rossiter-McLaughlin effect, an exciting prospect\ngiven the 0.14 au orbital separation of HD 332231 b. The spectroscopic\nobservations do not provide substantial evidence for any additional planets in\nthe HD 332231 system, but continued RV monitoring is needed to further\ncharacterize this system. We also predict that the frequency and duration of\nmasked data in the PDC light curves for TESS Sectors 14-16 could hide transits\nof some exoplanets with orbital periods between 10.5 and 17.5 days.", + "category": "astro-ph" + }, + { + "text": "Magnetospheres and Disk Accretion in Herbig Ae/Be Stars: We present evidence of magnetically-mediated disk accretion in Herbig Ae/Be\nstars. Magnetospheric accretion models of Balmer and sodium profiles calculated\nwith appropriate stellar and rotational parameters are in qualitative agreement\nwith the observed profiles of the Herbig Ae star UX Ori, and yield a mass\naccretion rate of ~ 10^{-8} Msun/yr. If more recent indications of an extremely\nlarge rotation rate for this object are correct, the magnetic field geometry\nmust deviate from that of a standard dipole in order to produce line emission\nconsistent with observed flux levels. Models of the associated accretion shock\nqualitatively explain the observed distribution of excess fluxes in the Balmer\ndiscontinuity for a large ensemble of Herbig Ae/Be stars, and imply typically\nsmall mass accretion rates, < 10^{-7} Msun/yr. In order for accretion to\nproceed onto the star, significant amounts of gas must exist inside the dust\ndestruction radius, which is potentially problematic for recently advocated\nscenarios of \"puffed\" inner dust wall geometries. However, our models of the\ninner gas disk show that for the typical accretion rates we have derived, the\ngas should be generally optically thin, thus allowing direct stellar\nirradiation of the inner dust edge of the disk.", + "category": "astro-ph" + }, + { + "text": "HST F160W Imaging of Very Massive Galaxies at $1.5 11.2)$ selected\nfrom a combination of ground-based near-infrared galaxy surveys (UltraVISTA,\nNMBS-II, UKIDSS UDS) at $1.56 and I-K>5) found in\ndeep optical-NIR surveys are presented. Very little is known about these\nobjects, the critical issue being whether they are old ellipticals at z>1 or\ndistant star-forming galaxies strongly reddened by dust extinction. We expect\nto shed light onto the unknown nature of these galaxies by completing our\nthree-step project: (1) the construction of two very deep optical/NIR surveys\nto select ERGs, (2) subsequent VLT/NIR spectroscopy; (3) observations in the\nsub-mm region with SCUBA at the JCMT and with MPIfRbolo at the IRAM 30m\nantenna.", + "category": "astro-ph" + }, + { + "text": "GD 244: asteroseismology of a pulsator in the middle of the ZZ Ceti\n instability strip: We present our preliminary results on the asteroseismological investigations\nof the ZZ Ceti star GD 244. We used literature values of the effective\ntemperature and surface gravity and utilized the White Dwarf Evolution Code of\nBischoff-Kim, Montgomery and Winget (2008, ApJ, 675, 1512) to build our model\ngrid for the seismological analysis. Five observed pulsational modes published\nup to now were used to find acceptable model solutions. We found that the best\nmodel fits have masses between 0.61 and 0.74 M_solar and constitute two groups\nwith hydrogen layer masses of either ~10^{-5} or 10^{-6} M_solar. Based on a\nstatistical analysis of a larger sample of possible model solutions, we assume\nthat the mass of the star is below ~0.68 M_solar and the oxygen content in the\ncentre is less than 60 percent.", + "category": "astro-ph" + }, + { + "text": "X-ray and Infrared Observations of Two Externally-Polluted White Dwarfs: With XMM-Newton and the Spitzer Space Telescope, we obtain upper bounds to\nthe X-ray fluxes from G29-38 and GD 362, and the 70 micron flux from G29-38.\nThese data provide indirect evidence that G29-38 is accreting from a\ntidally-disrupted asteroid: it is neither accreting large amounts of hydrogen\nand helium nor is its surrounding dusty disk being replenished from a reservoir\nof cold grains experiencing Poynting-Robertson drag. The upper bound to the\nX-ray flux from GD 362 is consistent with the estimated rate of mass accretion\nrequired to explain its pollution by elements heavier than helium. GD 362 also\npossesses 0.01 of an Earth's mass of hydrogen, an anomalously large amount for\na white dwarf with a helium-dominated atmosphere. One possibility is that\nbefore the current disk was formed, this hydrogen was accreted from either\nabout 100 Ceres-like asteroids or one large object. An alternative scenario\nwhich simultaneously explains all of GD 362's distinctive properties is that we\nare witnessing the consequences of the tidal-destruction of a single parent\nbody that had internal water and was at least as massive as Callisto and\nprobably as massive as Mars.", + "category": "astro-ph" + }, + { + "text": "Linear stability of magnetized massive protoplanetary disks: Magneto-rotational instability (MRI) and gravitational instability (GI) are\nthe two principle routes to turbulent angular momentum transport in accretion\ndisks. Protoplanetary disks may develop both. This paper aims to reinvigorate\ninterest in the study of magnetized massive protoplanetary disks, starting from\nthe basic issue of stability. The local linear stability of a self-gravitating,\nuniformly magnetized, differentially rotating, three-dimensional stratified\ndisk subject to axisymmetric perturbations is calculated numerically. The\nformulation includes resistivity. It is found that the reduction in the disk\nthickness by self-gravity can decrease MRI growth rates; the MRI becomes global\nin the vertical direction, and MRI modes with small radial length scales are\nstabilized. The maximum vertical field strength that permits the MRI in a\nstrongly self-gravitating polytropic disk with polytropic index $\\Gamma=1$ is\nestimated to be $B_{z,\\mathrm{max}} \\simeq c_{s0}\\Omega\\sqrt{\\mu_0/16\\pi G} $,\nwhere $c_{s0}$ is the midplane sound speed and $\\Omega$ is the angular\nvelocity. In massive disks with layered resistivity, the MRI is not\nwell-localized to regions where the Elsasser number exceeds unity. For MRI\nmodes with radial length scales on the order of the disk thickness,\nself-gravity can enhance density perturbations, an effect that becomes\nsignificant in the presence of a strong toroidal field, and which depends on\nthe symmetry of the underlying MRI mode. In gravitationally unstable disks\nwhere GI and MRI growth rates are comparable, the character of unstable modes\ncan transition smoothly between MRI and GI. Implications for non-linear\nsimulations are discussed briefly.", + "category": "astro-ph" + }, + { + "text": "Density PDFs of diffuse gas in the Milky Way: The probability distribution functions (PDFs) of the average densities of the\ndiffuse ionized gas (DIG) and the diffuse atomic gas are close to lognormal,\nespecially when lines of sight at |b|<5 degree and |b|>5 degree are considered\nseparately. Our results provide strong support for the existence of a lognormal\ndensity PDF in the diffuse ISM, consistent with a turbulent origin of density\nstructure in the diffuse gas.", + "category": "astro-ph" + }, + { + "text": "Disentangling Morphology, Star Formation, Stellar Mass, and Environment\n in Galaxy Evolution: We present a study of the spectroscopic and photometric properties of\ngalaxies in six nearby clusters. We perform a partial correlation analysis on\nour dataset to investigate whether the correlation between star formation rates\nin galaxies and their environment is merely another aspect of correlations of\nmorphology, stellar mass, or mean stellar age with environment, or whether star\nformation rates vary independently of these other correlations. We find a\nresidual correlation of ongoing star formation with environment, indicating\nthat even galaxies with similar morphologies, stellar masses, and mean stellar\nages have lower star formation rates in denser environments. Thus, the current\nstar formation gradient in clusters is not just another aspect of the\nmorphology-density, stellar mass-density, or mean stellar age-density\nrelations. Furthermore, the star formation gradient cannot be solely the result\nof initial conditions, but must partly be due to subsequent evolution through a\nmechanism (or mechanisms) sensitive to environment. Our results constitute a\ntrue ``smoking gun'' pointing to the effect of environment on the later\nevolution of galaxies.", + "category": "astro-ph" + }, + { + "text": "The effects of self-interacting dark matter on the stripping of galaxies\n that fall into clusters: We use the Cluster-EAGLE (C-EAGLE) hydrodynamical simulations to investigate\nthe effects of self-interacting dark matter (SIDM) on galaxies as they fall\ninto clusters. We find that SIDM galaxies follow similar orbits to their Cold\nDark Matter (CDM) counterparts, but end up with ${\\sim}$25 per cent less mass\nby the present day. One in three SIDM galaxies are entirely disrupted, compared\nto one in five CDM galaxies. However, the excess stripping will be harder to\nobserve than suggested by previous DM-only simulations because the most\nstripped galaxies form cores and also lose stars: the most discriminating\nobjects become unobservable. The best test will be to measure the\nstellar-to-halo mass relation (SHMR) for galaxies with stellar mass\n$10^{10-11}\\,\\mathrm{M}_{\\odot}$. This is 8 times higher in a cluster than in\nthe field for a CDM universe, but 13 times higher for an SIDM universe. Given\nintrinsic scatter in the SHMR, these models could be distinguished with\nnoise-free galaxy-galaxy strong lensing of ${\\sim}32$ cluster galaxies.", + "category": "astro-ph" + }, + { + "text": "J-state interference signatures in the Second Solar Spectrum: Modeling\n the Cr I triplet at 5204-5208 A: The scattering polarization in the solar spectrum is traditionally modeled\nwith each spectral line treated separately, but this is generally inadequate\nfor multiplets where J-state interference plays a significant role. Through\nsimultaneous observations of all the 3 lines of a Cr I triplet, combined with\nrealistic radiative transfer modeling of the data, we show that it is necessary\nto include J-state interference consistently when modeling lines with partially\ninteracting fine structure components. Polarized line formation theory that\nincludes J-state interference effects together with partial frequency\nredistribution for a two-term atom is used to model the observations.\nCollisional frequency redistribution is also accounted for. We show that the\nresonance polarization in the Cr I triplet is strongly affected by the partial\nfrequency redistribution effects in the line core and near wing peaks. The Cr I\ntriplet is quite sensitive to the temperature structure of the photospheric\nlayers. Our complete frequency redistribution calculations in semi-empirical\nmodels of the solar atmosphere cannot reproduce the observed near wing\npolarization or the cross-over of the Stokes Q/I line polarization about the\ncontinuum polarization level that is due to the J-state interference. When\nhowever partial frequency redistribution is included, a good fit to these\nfeatures can be achieved. Further, to obtain a good fit to the far wings, a\nsmall temperature enhancement of the FALF model in the photospheric layers is\nnecessary.", + "category": "astro-ph" + }, + { + "text": "Spectral and Temporal Properties of MAXI J1836-194 during 2011 Outburst: We study black hole candidate (BHC) MAXI~J1836-194 during its 2011 outburst\nwith Two Component Advective Flow (TCAF) model using RXTE/PCU2 data in\n$2.5-25$~keV band. From spectral fit, accretion flow parameters such as\nKeplerian disk rate ($\\dot{m_d}$), sub-Keplerian halo rate ($\\dot{m_h}$), shock\nlocation ($X_{s}$) and compression ratio (R) are extracted directly. During the\nentire phase of the outburst, quasi-periodic oscillations (QPOs) are observed\nsporadically. From the nature of the variation of accretion rate ratio\n(ARR=$\\dot{m_h}$ / $\\dot{m_d}$) and QPOs, entire period of the outburst is\nclassified in two spectral states, such as, hard (HS), hard-intermediate\n(HIMS). Unlike other transient BHCs, no signature of soft (SS) and\nsoft-intermediate (SIMS) spectral states are observed during entire phase of\nthe outburst", + "category": "astro-ph" + }, + { + "text": "Optical Design and Active Optics Methods in Astronomy: Optical designs for astronomy involve implementation of active optics and\nadaptive optics from X-ray to the infrared. Developments and results of active\noptics methods for telescopes, spectrographs and coronagraph planet finders are\npresented. The high accuracy and remarkable smoothness of surfaces generated by\nactive optics methods also allow elaborating new optical design types with high\naspheric and/or non-axisymmetric surfaces. Depending on the goal and\nperformance requested for a deformable optical surface analytical\ninvestigations are carried out with one of the various facets of elasticity\ntheory: small deformation thin plate theory, large deformation thin plate\ntheory, shallow spherical shell theory, weakly conical shell theory. The\nresulting thickness distribution and associated bending force boundaries can be\nrefined further with finite element analysis. Keywords: active optics, optical\ndesign, elasticity theory, astronomical optics, diffractive optics, X-ray\noptics", + "category": "astro-ph" + }, + { + "text": "The impact of interactions, bars, bulges, and AGN on star formation\n efficiency in local massive galaxies: Using observations from the GASS and COLD GASS surveys and complementary data\nfrom SDSS and GALEX, we investigate the nature of variations in gas depletion\ntime observed across the local massive galaxy population. The large and\nunbiased COLD GASS sample allows us to assess the relative importance of galaxy\ninteractions, bar instabilities, morphologies and the presence of AGN in\nregulating star formation efficiency. Both the H2 mass fraction and depletion\ntime vary as a function of the distance of a galaxy from the main sequence in\nthe SFR-M* plane. The longest gas depletion times are found in below-main\nsequence bulge-dominated galaxies that are either gas-poor, or else on average\nless efficient than disk-dominated galaxy at converting into stars any cold gas\nthey may have. We find no link between AGN and these long depletion times. The\ngalaxies undergoing mergers or showing signs of morphological disruptions have\nthe shortest molecular gas depletion times, while those hosting strong stellar\nbars have only marginally higher global star formation efficiencies as compared\nto matched control samples. Our interpretation is that depletion time\nvariations are caused by changes in the ratio between the gas mass traced by\nthe CO(1-0) observations, and the gas mass in high density star-forming cores,\nwith interactions, mergers and bar instabilities able to locally increase\npressure and raise the ratio of efficiently star-forming gas to CO-detected\ngas. Building a sample representative of the local massive galaxy population,\nwe derive a global Kennicutt-Schmidt relation of slope 1.18+/-0.24, and observe\nstructure within the scatter around this relation, with galaxies having low\n(high) stellar mass surface densities lying systematically above (below) the\nmean relation, suggesting that gas surface density is not the only parameter\ndriving the global star formation ability of a galaxy.", + "category": "astro-ph" + }, + { + "text": "Disentangling jet and disc emission from the 2005 outburst of XTE\n J1118+480: The black hole X-ray transient, XTE J1118+480, has now twice been observed in\noutburst - 2000 and 2005 - and on both occasions remained in the low/hard X-ray\nspectral state. Here we present radio, infrared, optical, soft X-ray and hard\nX-ray observations of the more recent outburst. We find that the lightcurves\nhave very different morphologies compared with the 2000 event and the optical\ndecay is delayed relative to the X-ray/radio. We attribute this lesser degree\nof correlation to contributions of emission from multiple components, in\nparticular the jet and accretion disc. Whereas the jet seemed to dominate the\nbroadband spectrum in 2000, in 2005 the accretion disc seems to be more\nprominent and we use an analysis of the lightcurves and spectra to distinguish\nbetween the jet and disc emission. There also appears to be an optically thin\ncomponent to the radio emission in the 2005 data, possibly associated with\nmultiple ejection events and decaying as the outburst proceeds. These results\nadd to the discussion that the term \"low/hard state'\" covers a wider range of\nproperties than previously thought, if it is to account for XTE J1118+480\nduring these two outbursts.", + "category": "astro-ph" + }, + { + "text": "Foreground influence on primordial non-Gaussianity estimates: needlet\n analysis of WMAP 5-year data: We constrain the amplitude of primordial non-Gaussianity in the CMB data\ntaking into account the presence of foreground residuals in the maps. We\ngeneralise the needlet bispectrum estimator marginalizing over the amplitudes\nof thermal dust, free-free and synchrotron templates. We apply our procedure to\nWMAP 5 year data, finding fNL= 38\\pm 47 (1 \\sigma), while the analysis without\nmarginalization provides fNL= 35\\pm 42. Splitting the marginalization over each\nforeground separately, we found that the estimates of fNL are positively cross\ncorrelated of 17%, 12% with the dust and synchrotron respectively, while a\nnegative cross correlation of about -10% is found for the free-free component.", + "category": "astro-ph" + }, + { + "text": "One-loop graviton corrections to the curvature perturbation from\n inflation: We compute one-loop corrections to the power spectrum of the curvature\nperturbation in single-field slow-roll inflation arising from gravitons and\ninflaton interactions. The quantum corrections due to gravitons to the power\nspectrum of the inflaton field are computed around the time of horizon crossing\nand their effect on the curvature perturbation is obtained on superhorizon\nscales through the delta-N formalism. We point out that one-loop corrections\nfrom the tensor modes are of the same magnitude as those coming from scalar\nself-interactions, therefore they cannot be neglected in a self-consistent\ncalculation.", + "category": "astro-ph" + }, + { + "text": "Properties of Original Impactors Estimated from Three-Dimensional\n Analysis of Whole Stardust Tracks: The Stardust mission captured comet Wild 2 particles in aerogel at 6.1\nkm/sec. We performed high resolution three-dimensional imaging and X-ray\nfluorescence mapping of whole cometary tracks in aerogel. We present the\nresults of a survey of track structures using Laser Scanning Confocal\nMicroscopy, including measurements of track volumes, entry hole size and\ncross-sectional profiles. We compare various methods for measuring track\nparameters. We demonstrate a methodology for discerning hypervelocity particle\nablation rates using synchrotron-based X-ray fluorescence, combined with mass\nand volume estimates of original impactors derived from measured track\nproperties. Finally, we present a rough framework for reconstruction of\noriginal impactor size, and volume of volatilized material, using our measured\nparameters. The bulk of this work is in direct support of non-destructive\nanalysis and identification of cometary grains in whole tracks, and its\neventual application to the reconstruction of the size, shape, porosity and\nchemical composition of whole Stardust impactors.", + "category": "astro-ph" + }, + { + "text": "ISO observations of the reflection nebula Ced 201: evolution of\n carbonaceous dust: We present spectrophotometric imaging mid-IR observations of the reflection\nnebula Ced201. Ced201 is a part of a molecular cloud illuminated by a B9.5V\nstar moving through it at more than 12 km/s. The spectra of Ced201 give\nevidence for transformation of very small carbonaceous grains into the carriers\nof the Aromatic Infrared Bands (AIBs), due to the radiation field of the\nilluminating star and/or to shock waves created by its motion. These very small\ngrains emit mainly very broad bands and a continuum. We suggest that they are\npresent everywhere in the interstellar medium but can only be detected in the\nmid-IR under special circumstances such as those prevailing in this reflection\nnebula. The efficiency of energy conversion of stellar light into mid-infrared\nemission is 7.5% for both the very small grains and the AIB carriers, and the\nfraction of interstellar carbon locked in these emitters is approximately 15%.", + "category": "astro-ph" + }, + { + "text": "Hydrodynamic simulations of merging clusters of galaxies: We present the results of high-resolution AP3M+SPH simulations of merging\nclusters of galaxies. We find that the compression and shocking of the core gas\nduring a merger can lead to large increases in bolometric X-ray luminosities\nand emission-weighted temperatures of clusters. Cooling flows are completely\ndisrupted during equal-mass mergers, with the mass deposition rate dropping to\nzero as the cores of the clusters collide. The large increase in the cooling\ntime of the core gas strongly suggests that cooling flows will not recover from\nsuch a merger within a Hubble time. Mergers with subclumps having 1/8th of the\nmass of the main cluster are also found to disrupt a cooling flow if the merger\nis head-on. However, in this case the entropy injected into the core gas is\nrapidly radiated away and the cooling flow restarts within a few Gyr of the\nmerger. Mergers in which the subcluster has an impact parameter of 500kpc do\nnot disrupt the cooling flow, although the mass deposition rate is reduced by\n\\~30%. Finally, we find that equal mass, off-centre mergers can effectively mix\ngas in the cores of clusters, while head on mergers lead to very little mixing.\nGas stripped from the outer layers of subclumps results in parts of the outer\nlayers of the main cluster being well mixed, although they have little effect\non the gas in the core of the cluster. None of the mergers examined here\nresulted in the ICM being well mixed globally.", + "category": "astro-ph" + }, + { + "text": "Orbital and escape dynamics in barred galaxies -- IV. Heteroclinic\n connections: Continuing the series of papers on a new model for a barred galaxy, we\ninvestigate the heteroclinic connections between the two normally hyperbolic\ninvariant manifolds sitting over the two index-1 saddle points of the effective\npotential. The heteroclinic trajectories and the nearby periodic orbits of\nsimilar shape populate the bar region of the galaxy and a neighbourhood of its\nnucleus. Thereby we see a direct relation between the important structures of\nthe interior region of the galaxy and the projection of the heteroclinic tangle\ninto the position space. As a side result, we obtain a detailed picture of the\nprimary heteroclinic intersection surface in the phase space.", + "category": "astro-ph" + }, + { + "text": "Is there a circumbinary planet around NSVS 14256825?: The cyclic behaviour of (O-C) residuals of eclipse timings in the sdB+M\neclipsing binary NSVS 14256825 was previously attributed to one or two\nJovian-type circumbinary planets. We report 83 new eclipse timings that not\nonly fill in the gaps in those already published but also extend the time span\nof the (O-C) diagram by three years. Based on the archival and our new data\nspanning over more than 17 years we re-examined the up to date system (O-C).\nThe data revealed systematic, quasi-sinusoidal variation deviating from an\nolder linear ephemeris by about 100 s. It also exhibits a maximum in the (O-C)\nnear JD 2,456,400 that was previously unknown. We consider two most credible\nexplanations of the (O-C) variability: the light propagation time due to the\npresence of an invisible companion in a distant circumbinary orbit, and\nmagnetic cycles reshaping one of the binary components, known as the Applegate\nor Lanza-Rodono effect. We found that the latter mechanism is unlikely due to\nthe insufficient energy budget of the M-dwarf secondary. In the framework of\nthe third-body hypothesis, we obtained meaningful constraints on the Keplerian\nparameters of a putative companion and its mass. Our best-fitting model\nindicates that the observed quasi-periodic (O-C) variability can be explained\nby the presence of a brown dwarf with the minimal mass of 15 Jupiter masses\nrather than a planet, orbiting the binary in a moderately elliptical orbit (~\n0.175) with the period of ~ 10 years. Our analysis rules out two planets model\nproposed earlier.", + "category": "astro-ph" + }, + { + "text": "Axion-Like Particles, Cosmic Magnetic Fields and Gamma-Ray Astrophysics: Axion-Like Particles (ALPs) are predicted by many extensions of the Standard\nModel and give rise to characteristic dimming and polarization effects in a\nlight beam travelling in a magnetic field. In this Letter, we demonstrate that\nphoton-ALP mixing in cosmic magnetic fields produces an observable distortion\nin the energy spectra of distant gamma-ray sources (like AGN) for ranges of the\nALP parameters allowed by all available constraints. The resulting effect is\nexpected to show up in the energy band 100 MeV - 100 GeV, and so it can be\nserched with the upcoming GLAST mission.", + "category": "astro-ph" + }, + { + "text": "A Search for Intrinsic Polarization in O Stars with Variable Winds: New observations of 9 of the brightest northern O stars have been made with\nthe Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the\nAnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the\nJohnson-Cousins UBVRI broadband filter system. Comparison with earlier\nmeasurements shows no clearly defined long-term polarization variability. For\nall 9 stars the wavelength dependence of the degree of polarization in the\noptical range can be fit by a normal interstellar polarization law. The\npolarization position angles are practically constant with wavelength and are\nconsistent with those of neighboring stars. Thus the simplest conclusion is\nthat the polarization of all the program stars is primarily interstellar.\n The O stars chosen for this study are generally known from ultraviolet and\noptical spectroscopy to have substantial mass loss rates and variable winds, as\nwell as occasional circumstellar emission. Their lack of intrinsic polarization\nin comparison with the similar Be stars may be explained by the dominance of\nradiation as a wind driving force due to higher luminosity, which results in\nlower density and less rotational flattening in the electron scattering inner\nenvelopes where the polarization is produced. However, time series of\npolarization measurements taken simultaneously with H-alpha and UV spectroscopy\nduring several coordinated multiwavelength campaigns suggest two cases of\npossible small-amplitude, periodic short-term polarization variability, and\ntherefore intrinsic polarization, which may be correlated with the more widely\nrecognized spectroscopic variations.", + "category": "astro-ph" + }, + { + "text": "The explosion energy of early stellar populations: The Fe-peak element\n ratios in low metallicity damped Lyman-alpha systems: The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest\nmetallicities are intimately linked to the physics of core-collapse supernova\nexplosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we\ninvestigate the trends of the Fe-peak element ratios with metallicity. For nine\nof the 25 DLAs, a direct measurement (or useful upper limit) of one or more of\nthe Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected\nabsorption lines. For the remaining systems (without detections), we devised a\nnew form of spectral stacking to estimate the typical Fe-peak element ratios of\nthe DLA population in this metallicity regime. We compare these data to\nanalogous measurements in metal-poor stars of the Galactic halo and to detailed\ncalculations of explosive nucleosynthesis in metal-free stars. We conclude that\nmost of the DLAs in our sample were enriched by stars that released an energy\nof < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally,\nwe discuss the exciting prospect of measuring Fe-peak element ratios in damped\nLyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes\nbecome available. Only then will we be able to pin down the energy that was\nreleased by the supernovae of the first stars.", + "category": "astro-ph" + }, + { + "text": "3C 273 - half a century later: We have presented an optical monitoring of 3C 273, the first quasar\ndiscovered fifty years ago. It does not show variability both on intra-night\nand long-term time scales. To facilitate the further monitoring of 3C 273, we\ncompiled the available calibrations of the comparison stars in its field into a\nmean sequence.", + "category": "astro-ph" + }, + { + "text": "Low Mass Star Formation in the Gum Nebula: The CG~30/31/38 complex: We present photometric and spectroscopic results for the low mass pre-main\nsequence (PMS) stars with spectral types K - M in the cometary globule (CG)\n30/31/38 complex. We obtained multi-object high resolution spectra for the\ntargets selected as possible PMS stars from multi-wavelength photometry. We\nidentified 11 PMS stars brighter than V = 16.5 with ages < 5 Myr at a distance\nof approximately 200 pc. The spatial distribution of the PMS stars, CG clouds,\nand ionizing sources (O stars and supernova remnants) suggests a possible\ntriggered origin of the star formation in this region. We confirm the youth of\nthe photometrically selected PMS stars using the lithium abundances. The radial\nvelocities of the low mass PMS stars are consistent with those of the cometary\nglobules. Most of the PMS stars show weak Halpha emission with W(Halpha) < 10\nA. Only 1 out of the 11 PMS stars shows a moderate near-IR excess, which\nsuggests a short survival time (t < 5 Myr) of circumstellar disks in this star\nforming environment. In addition, we find five young late type stars and one Ae\nstar which have no obvious relation to the CG 30/31/38 complex. We also discuss\na possible scenario of star formation history in the CG 30/31/38 region.", + "category": "astro-ph" + }, + { + "text": "Luminous Matter Distribution, Bulk Flows and Baryon Contents in\n Cosmological Models with a Local Void: First, we consider galaxy formation from the viewpoint of hierarchical\nclustering theory and discuss the possibility that inhomogeneous models with a\nlocal void may be compatible with the observed homogeneity of galactic\ndistributions found by recent redshift surveys, because their inhomogeneity can\nbe weakened by the difference in the feedback system of galaxy formation\nbetween the inner and outer regions. Next, it is shown with the results of\nnumerical simulations that the observed inhomogeneity of two-point correlations\nof galaxies can be accounted for by these models. Also, the natural appearance\nof bulk flows for an off-central observer is shown. Finally the inhomogeneity\nof baryon contents is discussed from the viewpoint of our inhomogeneous models.", + "category": "astro-ph" + }, + { + "text": "Hubble Space Telescope Observations of Dusty Filaments in Hercules A:\n Evidence for Entrainment: We present U, V, and I-band images of the host galaxy of Hercules A (3C 348)\nobtained with HST/WFC3/UVIS. We find a network of dusty filaments which are\nmore complex and extended than seen in earlier HST observations. The filaments\nare associated with a faint blue continuum light (possibly from young stars)\nand faint H-alpha emission. It seems likely that the cold gas and dust has been\nstripped from a companion galaxy now seen as a secondary nucleus. There are\ndusty filaments aligned with the base of the jets on both eastern and western\nsides of the galaxy. The morphology of the filaments is different on the two\nsides - the western filaments are fairly straight, while the eastern filaments\nare mainly in two loop-like structures. We suggest that despite the difference\nin morphologies, both sets of filaments have been entrained in a slow moving\nboundary layer outside the relativistic flow. As suggested by Fabian et al.\n(2008), magnetic fields in the filaments may stabilize them against disruption.\nWe consider a speculative scenario to explain the relation between the radio\nsource and the shock and cavities in the hot ICM seen in the Chandra data\n(Nulsen et al. 2005). We suggest the radio source originally (~60 Myr ago)\npropagated along a position angle of ~35 degrees where it created the shock and\ncavities. The radio source axis changed to its current orientation (~100\ndegrees) possibly due to a supermassive black hole merger and began its current\nepoch of activity about 20 Myr ago.", + "category": "astro-ph" + }, + { + "text": "Testing LCDM with the Growth Function \u03b4(a): Current Constraints: We have compiled a dataset consisting of 22 datapoints at a redshift range\n(0.15,3.8) which can be used to constrain the linear perturbation growth rate\nf=\\frac{d\\ln\\delta}{d\\ln a}. Five of these data-points constrain directly the\ngrowth rate f through either redshift distortions or change of the power\nspectrum with redshift. The rest of the datapoints constrain f indirectly\nthrough the rms mass fluctuation \\sigma_8(z) inferred from Ly-\\alpha at various\nredshifts. Our analysis tests the consistency of the LCDM model and leads to a\nconstraint of the Wang-Steinhardt growth index \\gamma (defined from\nf=\\Omega_m^\\gamma) as \\gamma=0.67^{+0.20}_{-0.17}. This result is clearly\nconsistent at $1\\sigma$ with the value \\gamma={6/11}=0.55 predicted by LCDM. A\nfirst order expansion of the index \\gamma in redshift space leads to similar\nresults.We also apply our analysis on a new null test of LCDM which is similar\nto the one recently proposed by Chiba and Nakamura (arXiv:0708.3877) but does\nnot involve derivatives of the expansion rate $H(z)$. This also leads to the\nfact that LCDM provides an excellent fit to the current linear growth data.", + "category": "astro-ph" + }, + { + "text": "Radio Recombination Lines at Decametre Wavelengths: Prospects for the\n Future: This paper considers the suitability of a number of emerging and future\ninstruments for the study of radio recombination lines (RRLs) at frequencies\nbelow 200 MHz. These lines arise only in low-density regions of the ionized\ninterstellar medium, and they may represent a frequency-dependent foreground\nfor next-generation experiments trying to detect H I signals from the Epoch of\nReionization and Dark Ages (\"21-cm cosmology\"). We summarize existing\ndecametre-wavelength observations of RRLs, which have detected only carbon\nRRLs. We then show that, for an interferometric array, the primary instrumental\nfactor limiting detection and study of the RRLs is the areal filling factor of\nthe array. We consider the Long Wavelength Array (LWA-1), the LOw Frequency\nARray (LOFAR), the low-frequency component of the Square Kilometre Array\n(SKA-lo), and a future Lunar Radio Array (LRA), all of which will operate at\ndecametre wavelengths. These arrays offer digital signal processing, which\nshould produce more stable and better defined spectral bandpasses; larger\nfrequency tuning ranges; and better angular resolution than that of the\nprevious generation of instruments that have been used in the past for RRL\nobservations. Detecting Galactic carbon RRLs, with optical depths at the level\nof 10^-3, appears feasible for all of these arrays, with integration times of\nno more than 100 hr. The SKA-lo and LRA, and the LWA-1 and LOFAR at the lowest\nfrequencies, should have a high enough filling factor to detect lines with much\nlower optical depths, of order 10^-4 in a few hundred hours. The amount of\nRRL-hosting gas present in the Galaxy at the high Galactic latitudes likely to\nbe targeted in 21-cm cosmology studies is currently unknown. If present,\nhowever, the spectral fluctuations from RRLs could be comparable to or exceed\nthe anticipated H I signals.", + "category": "astro-ph" + }, + { + "text": "Chemical Conditions on Hycean Worlds: Traditionally, the search for life on exoplanets has been predominantly\nfocused on rocky exoplanets. Hycean worlds are a class of habitable\nsub-Neptunes with planet-wide oceans and H2-rich atmospheres. Their broad range\nof possible sizes and temperatures lead to a wide habitable zone and high\npotential for discovery and atmospheric characterization using transit\nspectroscopy. Over a dozen candidate Hycean planets are already known to be\ntransiting nearby M dwarfs, making them promising targets for atmospheric\ncharacterization with the James Webb Space Telescope (JWST). In this work, we\ninvestigate possible chemical conditions on a canonical Hycean world, focusing\non (a) the present and primordial molecular composition of the atmosphere, and\n(b) the inventory of bioessential elements for the origin and sustenance of\nlife in the ocean. Based on photochemical and kinetic modeling for a range of\nconditions, we discuss the possible chemical evolution and observable\npresent-day composition of its atmosphere. In particular, for reduced\nprimordial conditions the early atmospheric evolution passes through a phase\nthat is rich in organic molecules that could provide important feedstock for\nprebiotic chemistry. We investigate avenues for delivering bioessential metals\nto the ocean, considering the challenging lack of weathering from a rocky\nsurface and the ocean separated from the rocky core by a thick icy mantle.\nBased on ocean depths from internal structure modelling and elemental estimates\nfor the early Earth's oceans, we estimate the requirements for bioessential\nmetals in such a planet. We find that the requirements can be met for plausible\nassumptions about impact history and atmospheric sedimentation, and\nsupplemented by other steady state sources. We discuss the observational\nprospects for atmospheric characterisation of Hycean worlds.", + "category": "astro-ph" + }, + { + "text": "Cosmography with Galaxy Clusters: In the present work we focus on future experiments using cluster abundance\nobservations to constraint the Dark Energy equation of state parameter, w. To\nobtain tight constraints from this kind of experiment, a reliable sample of\ngalaxy clusters must be obtained from deep and wide-field images. We therefore\npresent the computational environment (2DPHOT) that allow us to build the\ngalaxy catalog from the images and the Voronoi Tessellation cluster finding\nalgorithm that we use to identify the galaxy clusters on those catalogs. To\ntest our pipeline with data similar in quality to what will be gathered by\nfuture wide field surveys, we process images from the Deep fields obtained as\npart of the LEGACY Survey (four fields of one square degree each, in five\nbands, with depth up to r'=25). We test our cluster finder by determining the\ncompleteness and purity of the finder when applied to mock galaxy catalogs made\nfor the Dark Energy Survey cluster finder comparison project by Risa Wechsler\nand Michael Busha. This procedure aims to understand the selection function of\nthe underlying dark matter halos.", + "category": "astro-ph" + }, + { + "text": "Constraining the distribution of dark matter in inner galaxy with\n indirect detection signal: The case of tentative 130 gev \u03b3-ray line: The dark matter distribution in the very inner region of our Galaxy is still\nin debate. In the N-body simulations a cuspy dark matter halo density profile\nis favored. Several dissipative baryonic processes however are found to be able\nto significantly flatten dark matter distribution and a cored dark matter halo\ndensity profile is possible. The baryons dominate the gravitational potential\nin the inner Galaxy, hence a direct constrain on the abundance of the dark\nmatter particles is rather challenging. Recently, a few groups have identified\na tentative 130 GeV line signal in the Galactic center, which could be\ninterpreted as the signal of the dark matter annihilation. With current 130 GeV\nline data and adopting the generalized Navarro-Frenk-White profile of the dark\nmatter halo, for local dark matter density \\rho_0=0.4 GeV cm^{-3} and r_s=20\nkpc we obtain a 95% confidence level lower (upper) limit on the inner slope of\ndark matter density distribution \\alpha = 1.06 (the cross section of dark\nmatter annihilation into gamma-rays <\\sigma v >_{\\chi\\chi -> \\gamma\\gamma}=\n1.3\\times 10^{-27} cm^3 s^{-1}). Such a slope is consistent with the results of\nsome N-body simulations, and if the signal is due to dark matter, suggests that\nbaryonic processes may be unimportant.", + "category": "astro-ph" + }, + { + "text": "Stellar clusters in the Gaia era: Stellar clusters are important for astrophysics in many ways, for instance as\noptimal tracers of the Galactic populations to which they belong or as one of\nthe best test bench for stellar evolutionary models. Gaia DR1, with TGAS, is\njust skimming the wealth of exquisite information we are expecting from the\nmore advanced catalogues, but already offers good opportunities and indicates\nthe vast potentialities. Gaia results can be efficiently complemented by\nground-based data, in particular by large spectroscopic and photometric\nsurveys. Examples of some scientific results of the Gaia-ESO survey are\npresented, as a teaser for what will be possible once advanced Gaia releases\nand ground-based data will be combined.", + "category": "astro-ph" + }, + { + "text": "Improved kinematics for brown dwarfs and very low-mass stars in ChaI and\n a discussion of brown dwarf formation: We present a precise kinematic study of very young brown dwarfs (BDs) in the\nChaI cloud based on radial velocities (RVs) measured with UVES / VLT. This is\ncompared to the kinematics of T Tauri stars (TTS) in the same field, based on\nboth own measurements and on RVs from the literature. More UVES spectra were\ntaken compared with a former paper (Joergens & Guenther 2001), and the\nreduction of the spectra was improved, while studying the literature for RVs of\nT Tauri stars in ChaI led to a cleaned and enlarged sample of T Tauri stars.\nThe result is an improved empirical RV distribution of BDs as well as of TTS in\nChaI. We found that nine BDs/VLMSs (M6-M8) in ChaI have a RV dispersion of 0.9\nkm/s measured in terms of a standard deviation. This is consistent with the\ndispersion measured earlier in terms of fwhm of 2.1 km/s. The studied sample of\n25 TTS (G2-M5) has a dispersion of 1.3 km/s (standard deviation). The RV\ndispersion of the BDs is consistent within the errors with that of TTS, which\nis in line with the finding of no mass dependence in some theoretical models of\nthe ejection-scenario for the formation of brown dwarfs. In contrast to current\nN-body simulations, we did not find a high-velocity tail for the BDs RVs. We\nfound hints suggesting different kinematics for binaries compared to\npredominantly single objects in ChaI. The global RV dispersion for ChaI members\n(1.24 km/s) is significantly lower than for Taurus members (2.0 km/s), despite\nhigher stellar density in ChaI showing that a fundamental increase in velocity\ndispersion with stellar density of the star-forming region is not established\nobservationally. The RVs of BDs observed in ChaI are less dispersed than\npredicted by existing models for the ejection-scenario.", + "category": "astro-ph" + }, + { + "text": "Search for High Energy Neutrino Emission from Gamma-Ray Bursts with the\n A ntarctic Muon and Neutrino Detector Array (AMANDA): The photo-meson production of pions by shock-accelerated protons could\ngenerate a burst of ~10^14 eV neutrinos from gamma-ray bursts (GRBs) observable\nin the Antarctic Muon and Neutrino Detector Array (AMANDA) or its larger\nsuccessors. Measurement of this flux can test the hypothesis that GRBs are the\nsources of the highest-energy cosmic rays, and GRB neutrinos could permit\nhigh-precision experiments in neutrino limiting speed, neutrino oscillations,\nand the weak equivalence principle. Neutrino emission can be expected primarily\nduring the prompt gamma-ray flash and satellite coincidence provides a\nwell-defined window in position and time that can be searched for an excess of\nupgoing muon events in AMANDA from bursts in the Northern Hemisphere. Using an\nevent quality analysis to further reduce background in a sample of 78 GRBs from\nthe 1997 AMANDA-B10 data set, I find a fluence limit of (E_nu)^2\n(dN_nu)/(dE_nu)<3.8*10^-4 min(1,E_nu/E_break) [TeV cm^-2] per average burst,\nwhich is orders of magnitude more stringent than in similar previous searches.", + "category": "astro-ph" + }, + { + "text": "Cosmological Origin for Cosmic Rays Above $10^{19}$ eV: The cosmic ray spectrum at $10^{19}{\\rm eV}-10^{20}{\\rm eV}$, reported by the\nFly's Eye and the AGASA experiments, is shown to be consistent with a\ncosmological distribution of sources of protons, with a power law generation\nspectrum ${\\rm d}\\ln N/{\\rm d}\\ln E=-2.3\\pm0.5$ and energy production rate of\n$4.5\\pm1.5\\times10^{44}{\\rm erg}\\ {\\rm Mpc}^{-3}\\ {\\rm yr}^{-1}$. The two\nevents measured above $10^{20}{\\rm eV}$ are not inconsistent with this model.\nVerifying the existence of a ``black-body cutoff'', currently observed with low\nsignificance, would require $\\sim30$ observation-years with existing\nexperiments, but only $\\sim1$ year with the proposed $\\sim5000\\ {\\rm km}^2$\ndetectors. For a cosmological source distribution, no anisotropy is expected in\nthe angular distribution of events with energies up to $\\sim5\\times10^{19}{\\rm\neV}$.", + "category": "astro-ph" + }, + { + "text": "Filling Factors and Ionized Masses in Planetary Nebulae: We calculate filling factors (${\\varepsilon}$) and ionized masses (M$_{\\rm\ni}$) for a total of 84 galactic and extragalactic planetary nebulae (PNe) at\nknown distances. To do these calculations, we have chosen forbidden line\nelectron densities, observed angular diameters, and H${\\beta}$ fluxes, from the\nmost recent measurements available in the literature. Statistical analysis on\nthe distributions of ${\\varepsilon}$ and ${\\rm M_i}$ show that (1) the ranges\nof values of these parameters is wider than what was previously found; (2) the\nmean value of the filling factor is between $0.3$ and $0.4$, for the different\nsets; (3) the mean value of the ionized mass is between $0.1$ and $0.25$\n$M_{\\odot}$; (4) a clear correlation between the filling factors and the\ndimensions of the PNe was not found when distance-independent sets of PNe were\nused; (5) for extragalactic PNe, where distance errors are not a factor, the\nfilling factors and the ionized masses anticorrelate tightly with the electron\ndensities. The results indicate that the modified Shklowsky distance method is\ncorrect.", + "category": "astro-ph" + }, + { + "text": "Spatial Correlations in the Helium-Ionizing Background: After quasars ionize intergalactic HeII at z~3, a large radiation field\nbuilds up above the HeII ionization edge. Unlike the background responsible for\nHI ionizations, this field should be highly variable, thanks to the scarcity of\nbright quasars and the relatively short attenuation lengths (~50 Mpc) of these\nhigh-energy photons. Recent observations of the HeII and HI Lyman-alpha forests\nshow that this background does indeed vary strongly, with substantial\nfluctuations on scales as small as ~2 Mpc. Here we show that such spatial\nfluctuation scales are naturally expected in any model in which the sources are\nas rare as bright quasars, so long as the attenuation length is relatively\nsmall. The correlation length itself is comparable to the attenuation length\n(~10 Mpc) for the most plausible physical scenarios, but we find\norder-of-magnitude fluctuations on all scales smaller than ~6 Mpc. Moreover,\naliasing along the one-dimensional skewers probed by the HeII and HI\nLyman-alpha forests exaggerates these variations, so that order-of-magnitude\nfluctuations should be observed on all scales smaller than ~20 Mpc. Complex\nradiative transfer is therefore not required to explain the observed\nfluctuations, at least at the level of current data.", + "category": "astro-ph" + }, + { + "text": "Periodic and Phase-locked Modulation in PSR B1929+10 Observed with FAST: We present a detailed single-pulse analysis for PSR B1929+10 based on\nobservations with the Five-hundred-meter Aperture Spherical radio Telescope\n(FAST). The main pulse and interpulse are found to be modulated with a\nperiodicity of $\\sim12$ times the pulsar's rotational period ($P$). The\n$\\sim12P$ modulation is confirmed as a periodic amplitude modulation instead of\nsystematic drifting. The periodic amplitude modulation in the IP is found to be\nanti-correlated with that in the weak preceding component of the MP (MP_I), but\ncorrelated with that in the first two components of the MP (MP_II), which\nimplies that the modulation patterns in the IP and the MP are phase-locked.\nWhat is more interesting is that the modulation in MP_II is delayed that in the\nIP by about 1P. Furthermore, high sensitivity observations by FAST reveal that\nweak emission exists between the MP and the IP. In addition, we confirm that\nthe separation between the IP and the MP is independent of radio frequency. The\nabove results are a conundrum for pulsar theories and cannot be satisfactorily\nexplained by the current pulsar models. Therefore, our results observed with\nFAST provide an opportunity to probe the structure of pulsar emission and the\nneutron star's magnetosphere.", + "category": "astro-ph" + }, + { + "text": "The Gould's Belt distance survey: Very Long Baseline Interferometry (VLBI) observations can provide the\nposition of compact radio sources with an accuracy of order 50\nmicro-arcseconds. This is sufficient to measure the trigonometric parallax and\nproper motions of any object within 500 pc of the Sun to better than a few\npercent. Because they are magnetically active, young stars are often associated\nwith compact radio emission detectable using VLBI techniques. Here we will show\nhow VLBI observations have already constrained the distance to the most often\nstudied nearby regions of star-formation (Taurus, Ophiuchus, Orion, etc.) and\nhave started to provide information on their internal structure and kinematics.\nWe will then briefly describe a large project (called The Gould's Belt Distance\nSurvey) designed to provide a detailed view of star-formation in the Solar\nneighborhood using VLBI observations.", + "category": "astro-ph" + }, + { + "text": "Annual and daily ideal periods for deliquescence at the landing site of\n InSight based on GCM model calculations: Liquid water is one of the key elements in the search for possible life\noutside of the Earth and has a wide range of consequences on various chemical\nand geological processes. The InSight probe landed on Mars with a special\nequipment dedicated to examine geophysical characteristics and internal heat\nflow of the planet and some meteorological instruments also included in the\npayload. We examine the annual and daily variations of near-surface relative\nhumidity and surface temperature calculated from the General Circulation Model\n(GCM) at Elysium Planitia, the landing site of InSight and search for possible\nideal times for deliquescence. We inspect three different hygroscopic salts,\nbut find that out of the three only calcium-perchlorate could liquify at the\nenvironment of InSight. We find that nighttime ideal periods could occur in a\nlimited window between approximately Ls 90 and 150 at the late evening hours\ncentered around 9 PM. In our daily studies we find no instances where the whole\nnight could be ideal for deliquescence. This is mostly due to the temperatures\ndropping below eutectic level leading to a 0.5 - 2 hour long presumed ideal\nperiod before midnight. On multiple occasions the temperature is just a few\ndegrees below the necessary limit while relative humidity is high enough,\ntherefore the precise temperature measurements of InSight could be critical in\ndetermining ideal periods for deliquescence.", + "category": "astro-ph" + }, + { + "text": "Is Spectral Width a Reliable Measure of GRB Emission Physics?: The spectral width and sharpness of unfolded, observed GRB spectra have been\npresented as a new tool to infer physical properties about GRB emission via\nspectral fitting of empirical models. Following the tradition of the\n'line-of-death', the spectral width has been used to rule out synchrotron\nemission in a majority of GRBs. This claim is investigated via reexamination of\npreviously reported width measures. Then, a sample of peak-flux GRB spectra are\nfit with an idealized, physical synchrotron model. It is found that many\nspectra can be adequately fit by this model even when the width measures would\nreject it. Thus, the results advocate for fitting a physical model to be the\nsole tool for testing that model. Finally, a smoothly-broken power law is fit\nto these spectra allowing for the spectral curvature to vary during the fitting\nprocess in order to understand why the previous width measures poorly predict\nthe spectra. It is found that the failing of previous width measures is due to\na combination of inferring physical parameters from unfolded spectra as well as\nthe presence of multiple widths in the data beyond what the Band function can\nmodel.", + "category": "astro-ph" + }, + { + "text": "Asteroseismology of 1523 misclassified red giants using\n $\\textit{Kepler}$ data: We analysed solar-like oscillations in 1523 $\\textit{Kepler}$ red giants\nwhich have previously been misclassified as subgiants, with predicted $\\nu_{\\rm\nmax}$ values (based on the Kepler Input Catalogue) between 280$\\mu$Hz to\n700$\\mu$Hz. We report the discovery of 626 new oscillating red giants in our\nsample, in addition to 897 oscillators that were previously characterized by\nHekker et al. (2011) from one quarter of $\\textit{Kepler}$ data. Our sample\nincreases the known number of oscillating low-luminosity red giants by $26\\%$\n(up to $\\sim$ 1900 stars). About three quarters of our sample are classified as\nascending red-giant-branch stars, while the remainder are red-clump stars. A\nnovel scheme was applied to determine $\\Delta \\nu$ for 108 stars with $\\nu_{\\rm\nmax}$ close to the Nyquist frequency (240$\\mu$Hz < $\\nu_{\\rm max}$ <\n320$\\mu$Hz). Additionally, we identified 47 stars oscillating in the\nsuper-Nyquist frequency regime, up to 387$\\mu$Hz, using long-cadence light\ncurves. We show that the misclassifications are most likely due to large\nuncertainties in KIC surface gravities, and do not result from the absence of\nbroadband colors or from different physical properties such as reddening,\nspatial distribution, mass or metallicity. The sample will be valuable to study\noscillations in low-luminosity red giants and to characterize planet candidates\naround those stars.", + "category": "astro-ph" + }, + { + "text": "3D spectroscopic surveys: Exploring galaxy evolution mechanisms: I review the major surveys of high redshift galaxies observed using integral\nfield spectroscopy techniques in the visible and in the infrared. The\ncomparison of various samples has to be done with care since they have\ndifferent properties linked to their parent samples, their selection criteria\nand the methods used to study them. I present the various kinematic types of\ngalaxies that are identified within these samples (rotators, mergers, etc.) and\nsummarize the discussions on the mass assembly processes at various redshifts\ndeduced from these classifications: at intermediate redshift (z~0.6) merger may\nbe the main mass assembly process whereas the role of cold gas accretion along\ncosmic web filaments may increase with redshift. The baryonic Tully-Fisher\nrelation is also discussed. This relation seems to be already in place 3 Gyr\nafter the Big-Bang and is then evolving until the present day. This evolution\nis interpreted as an increase of the stellar mass content of dark matter haloes\nof a given mass. The discovery of positive abundance gradients in MASSIV and\nLSD/AMAZE samples is highlighted. At z~3 this discovery might be linked to cold\ngas accretion along cosmic filaments toward the centre whereas at lower\nredshift (z~1.3), this may be mainly due to accretion of gas from outer\nreservoirs toward the centre via tidal tails due to interactions.", + "category": "astro-ph" + }, + { + "text": "Wave reflection and transmission at interface of convective and stably\n stratified regions in a rotating star or planet: We use a simplified model to study wave reflection and transmission at\ninterface of convective region and stably stratified region (e.g. radiative\nzone in star or stratification layer in gaseous planet). Inertial wave in\nconvective region and gravito-inertial wave in stably stratified region are\nconsidered. We begin with polar area and then extend to any latitude. Six cases\nare discussed (see Table 1), and in Case 2 both waves co-exist in both regions.\nFour configurations are further discussed for Case 2. The angles and energy\nratios of wave reflection and transmission are calculated. It is found that\nwave propagation and transmission depend on the ratio of buoyancy frequency to\nrotational frequency. In a rapidly rotating star or planet wave propagates\nacross interface and most of energy of incident wave is transmitted to the\nother region, but in a slowly rotating star or planet wave transmission is\ninhibited.", + "category": "astro-ph" + }, + { + "text": "A simple model for the evolution of super-massive black holes and the\n quasar population: An empirically motivated model is presented for accretion-dominated growth of\nthe super massive black holes (SMBH) in galaxies, and the implications are\nstudied for the evolution of the quasar population in the universe. We\ninvestigate the core aspects of the quasar population, including space density\nevolution, evolution of the characteristic luminosity, plausible minimum masses\nof quasars, the mass function of SMBH and their formation epoch distribution.\nOur model suggests that the characteristic luminosity in the quasar luminosity\nfunction arises primarily as a consequence of a characteristic mass scale above\nwhich there is a systematic separation between the black hole and the halo\nmerging rates. At lower mass scales, black hole merging closely tracks the\nmerging of dark halos. When combined with a declining efficiency of black hole\nformation with redshift, the model can reproduce the quasar luminosity function\nover a wide range of redshifts. The observed space density evolution of quasars\nis well described by formation rates of SMBH above $\\sim 10^8 M_\\odot$. The\ninferred mass density of SMBH agrees with that found independently from\nestimates of the SMBH mass function derived empirically from the quasar\nluminosity function.", + "category": "astro-ph" + }, + { + "text": "Constraints on the explosion mechanism and progenitors of type Ia\n supernovae: Observations of SN 2011fe at early times reveal an evolution analogous to a\nfireball model of constant color. In contrast, our unmixed delayed detonations\nof Chandrasekhar-mass white dwarfs (DDC series) exhibit a faster brightening\nconcomitant with a shift in color to the blue. In this paper, we study the\norigin of these discrepancies. We find that strong chemical mixing largely\nresolves the photometric mismatch at early times, but it leads to an enhanced\nline broadening that contrasts, for example, with the markedly narrow SiII6355A\nline of SN 2011fe. We also explore an alternative configuration with\npulsational-delayed detonations (PDDEL model series). Because of the pulsation,\nPDDEL models retain more unburnt carbon, have little mass at high velocity, and\nhave a much hotter outer ejecta after the explosion. The pulsation does not\ninfluence the inner ejecta, so PDDEL and DDC models exhibit similar radiative\nproperties beyond maximum. However, at early times, PDDEL models show bluer\noptical colors and a higher luminosity, even for weak mixing. Their early-time\nradiation is derived primarily from the initial shock-deposited energy in the\nouter ejecta rather than radioactive decay heating. Furthermore, PDDEL models\nshow short-lived CII lines, reminiscent of SN 2013dy. They typically exhibit\nlines that are weaker, narrower, and of near-constant width, reminiscent of SN\n2011fe. In addition to multi-dimensional effects, varying configurations for\nsuch ``pulsations\" offer a source of spectral diversity amongst SNe Ia. PDDEL\nand DDC models also provide one explanation for low- and high-velocity gradient\nSNe Ia.", + "category": "astro-ph" + }, + { + "text": "Large Tensor Non-Gaussianity from Axion-Gauge Fields Dynamics: We show that an inflation model in which a spectator axion field is coupled\nto an SU(2) gauge field produces a large three-point function (bispectrum) of\nprimordial gravitational waves, $B_{h}$, on the scales relevant to the cosmic\nmicrowave background experiments. The amplitude of the bispectrum at the\nequilateral configuration is characterized by\n$B_{h}/P_h^2=\\mathcal{O}(10)\\times \\Omega_A^{-1}$, where $\\Omega_A$ is a\nfraction of the energy density in the gauge field and $P_h$ is the power\nspectrum of gravitational waves produced by the gauge field.", + "category": "astro-ph" + }, + { + "text": "Detecting the Glint of Starlight on the Oceans of Distant Planets: We propose that astronomers will be eventually be able to discriminate\nbetween extrasolar Earth-like planets with surface oceans and those without\nusing the shape of phase light curves in the visible and near-IR spectrum. We\nmodel the visible light curves of planets having Earth-like surfaces, seasons,\nand optically-thin atmospheres with idealized diffuse-scattering clouds. We\nshow that planets partially covered by water will appear measurably brighter\nnear crescent phase (relative to Lambertian planets) because of the efficient\nspecular reflection (i.e., glint) of starlight incident on their surfaces at a\nhighly oblique angle. Planets on orbits within 30 degrees of edge-on\norientation (half of all planets) will show pronounced glint over a sizeable\nrange of orbital longitudes, from quadrature to crescent, all outside the glare\nof their parent stars. Also, water-covered planets will appear darker than a\nLambertian disk near full illumination. Finally, we show that planets with a\nmixed land/water surface will polarize the reflected signal by as much as 30-70\npercent. These results suggest several new ways of directly identifying water\non distant planets.", + "category": "astro-ph" + }, + { + "text": "VLBI Scrutiny of a New Neutrino-Blazar Multiwavelength-Flare Coincidence: In the past years, evidence has started piling up that some high-energy\ncosmic neutrinos can be associated with blazars in flaring states. On February\n26, 2022, a new blazar-neutrino coincidence has been reported: the track-like\nneutrino event IC220225A detected by IceCube is spatially coincident with the\nflat-spectrum radio quasar PKS 0215+015. Like previous associations, this\nsource was found to be in a high optical and ${\\gamma}$-ray state. Moreover,\nthe source showed a bright radio outburst, which substantially increases the\nprobability of a true physical association. We have performed six observations\nwith the VLBA shortly after the neutrino event with a monthly cadence and are\nmonitoring the source with the Effelsberg 100m-Telescope, and with the\nAustralia Compact Telescope Array. Here, we present first results on the\ncontemporary parsec-scale jet structure of PKS 0215+015 in total intensity and\npolarization to constrain possible physical processes leading to neutrino\nemission in blazars.", + "category": "astro-ph" + }, + { + "text": "The Galactic WN stars: Spectral analyses with line-blanketed model\n atmospheres versus stellar evolution models with and without rotation: CONTEXT: Very massive stars pass through the Wolf-Rayet (WR) stage before\nthey finally explode. Details of their evolution have not yet been safely\nestablished, and their physics are not well understood. Their spectral analysis\nrequires adequate model atmospheres, which have been developed step by step\nduring the past decades and account in their recent version for line blanketing\nby the millions of lines from iron and iron-group elements. However, only very\nfew WN stars have been re-analyzed by means of line-blanketed models yet.\n AIMS: The quantitative spectral analysis of a large sample of Galactic WN\nstars with the most advanced generation of model atmospheres should provide an\nempirical basis for various studies about the origin, evolution, and physics of\nthe Wolf-Rayet stars and their powerful winds.\n METHODS: We analyze a large sample of Galactic WN stars by means of the\nPotsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron line\nblanketing and clumping. The results are compared with a synthetic population,\ngenerated from the Geneva tracks for massive star evolution. RESULTS: We obtain\na homogeneous set of stellar and atmospheric parameters for the Galactic WN\nstars, partly revising earlier results.\n CONCLUSIONS: Comparing the results of our spectral analyses of the Galactic\nWN stars with the predictions of the Geneva evolutionary calculations, we\nconclude that there is rough qualitative agreement. However, the quantitative\ndiscrepancies are still severe, and there is no preference for the tracks that\naccount for the effects of rotation. It seems that the evolution of massive\nstars is still not satisfactorily understood.", + "category": "astro-ph" + }, + { + "text": "The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable\n Star in NGC 2403: We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type\nII-narrow (IIn), has photometric and spectroscopic properties unlike those of\nnormal SNe. Its behavior, instead, is more typical of highly massive stars\nwhich experience the short-lived luminous blue variable (LBV) phase toward the\nend of their lives. The star, in fact, most resembles the LBV S Doradus in\noutburst. The precursor of SN 2002kg is the irregular, bright blue variable\nstar 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality\nground-based, multi-band images we can constrain the initial mass of V37 to be\nM_ini >~ 40 M_sun. We find that, although the spectra indicate a nitrogen\nenhancement, possibly revealing the products of CNO processing by V37 in the\nejecta, the star lacks a substantial LBV nebula. The outburst from SN\n2002kg/V37 is not nearly as energetic as the giant eruptions of the eta\nCarinae-like variables, such as SN 1954J/V12, also in NGC 2403. SN 2002kg/V37,\nhowever, is among a growing number of ``SN impostors'' exhibiting a broad range\nof outburst energetics during a pre-SN phase of massive-star evolution.", + "category": "astro-ph" + }, + { + "text": "The Distribution of Thermal Pressures in the Interstellar Medium from a\n Survey of C I Fine-Structure Excitation: We used the smallest entrance aperture (0.03 arc-sec wide slit) and highest\nresolution echelle gratings (E140H and E230H) of STIS on HST to record the\ninterstellar absorption features for 10 different multiplets of neutral carbon\nat a wavelength resolving power of 200,000 in the UV spectra of 21 early-type\nstars. We measured the amount of C I in each of its three fine-structure\nlevels, so that we could determine nT of the absorbing gas and how much it\nvaries in different regions. To obtain internally consistent results for all\nmultiplets, we had to modify the transition f-values so that generally weak\ntransitions were stronger than their published values. The fine-structure\npopulations indicate that the median thermal pressure for our entire sample is\np/k=2240 cm^-3 K, or slightly higher for temperatures that differ appreciably\nfrom 40 K. About 15% of the gas moving at peculiar velocities shows p/k > 10^4\ncm^-3 K, and this fraction drops to 1.5% for quiescent gas. Often, there are\nsmall amounts of gas at p/k > 10^5 cm^-3 K. These ubiquitous wisps of high\npressure material probably arise from small-scale density enhancements created\nby converging flows in a turbulent medium. The C I excitations indicate a\nbarytropic index gamma_eff > 0.90 when the gas is compressed, which is larger\nthan the value 0.72 expected for material in thermal equilibrium. This\nindicates that the regions have a dimension r < 0.01 pc which allows them to\ncompress very quickly and nearly adiabatically. Appendices of this paper\npresent evidence that STIS can indeed achieve R = 200,000, and that telluric\noxygen absorption lines are broadened by macroscopic motions.", + "category": "astro-ph" + }, + { + "text": "Determining Star Formation Rates for Infrared Galaxies: We show that measures of star formation rates (SFRs) for infrared galaxies\nusing either single-band 24 um or extinction-corrected Paschen-alpha\nluminosities are consistent in the total infrared luminosity = L(TIR) ~ 10^10\nL_sun range. MIPS 24 micron photometry can yield star formation rates\naccurately from this luminosity upward: SFR(M_sun/yr) = 7.8 x 10^-10 L(24 um,\nL_sun) from L(TIR) = 5 x 10^9 L_sun to 10^11 L_sun, and SFR = 7.8 x 10^-10 L(24\num, L_sun) x (7.76 x 10^-11 L(24))^0.048 for higher L(TIR). For galaxies with\nL(TIR) >= 10^10 L_sun, these new expressions should provide SFRs to within 0.2\ndex. For L(TIR) >= 10^11 L_sun, we find that the SFR of infrared galaxies is\nsignificantly underestimated using extinction-corrected Pa-alpha (and\npresumably using any other optical or near infrared recombination lines). As a\npart of this work, we constructed spectral energy distribution (SED) templates\nfor eleven luminous and ultraluminous purely star forming infrared galaxies\n(LIRGs and ULIRGs) and over the spectral range 0.4 microns to 30 cm. We use\nthese templates and the SINGS data to construct average templates from 5\nmicrons to 30 cm for infrared galaxies with L(TIR) = 5 x 10^9 to 10^13 L_sun.\nAll of these templates are made available on line.", + "category": "astro-ph" + }, + { + "text": "Measuring M31 globular cluster ages and metallicities using both\n photometry and spectroscopy: The ages and metallicities of globular clusters play an important role not\njust in testing models for their formation and evolution but in understanding\nthe assembly history for their host galaxies. Here we use a combination of\nimaging and spectroscopy to measure the ages and metallicities of globular\nclusters in M31, the closest massive galaxy to our own. We use the strength of\nthe near-infrared calcium triplet spectral feature to provide a relatively age\ninsensitive prior on the metallicity when fitting stellar population models to\nthe observed photometry. While the age-extinction degeneracy is an issue for\nglobular clusters projected onto the disc of M31, we find generally old ages\nfor globular clusters in the halo of M31 and in its satellite galaxy NGC 205 in\nline with previous studies. We measure ages for a number of outer halo globular\nclusters for the first time, finding that globular clusters associated with\nhalo substructure extend to younger ages and higher metallicities than those\nassociated with the smooth halo. This is in line with the expectation that the\nsmooth halo was accreted earlier than the substructured halo.", + "category": "astro-ph" + }, + { + "text": "Light curve analysis of ordinary type IIP supernovae based on\n neutrino-driven explosion simulations in three dimensions: Type II-plateau supernovae (SNe IIP) are the most numerous subclass of\ncore-collapse SNe originating from massive stars. In the framework of the\nneutrino-driven explosion mechanism, we study the SN outburst properties for a\nred supergiant progenitor model and compare the corresponding light curves with\nobservations of the ordinary Type IIP SN 1999em. Three-dimensional (3D)\nsimulations of (parametrically triggered) neutrino-driven explosions are\nperformed with the (explicit, finite-volume, Eulerian, multifluid\nhydrodynamics) code PROMETHEUS, using a presupernova model of a 15 Msun star as\ninitial data. At approaching homologous expansion, the hydrodynamical and\ncomposition variables of the 3D models are mapped to a spherically symmetric\nconfiguration, and the simulations are continued with the (implicit, Lagrangian\nradiation-hydrodynamics) code CRAB to follow the blast-wave evolution during\nthe SN outburst. Our 3D neutrino-driven explosion model with an explosion\nenergy of about 0.5x10^51 erg produces Ni-56 in rough agreement with the amount\ndeduced from fitting the radioactively powered light-curve tail of SN 1999em.\nThe considered presupernova model, 3D explosion simulations, and light-curve\ncalculations can explain the basic observational features of SN 1999em, except\nfor those connected to the presupernova structure of the outer stellar layers.\nOur 3D simulations show that the distribution of Ni-rich matter in velocity\nspace is asymmetric with a strong dipole component that is consistent with the\nobservations of SN 1999em. The monotonic luminosity decline from the plateau to\nthe radioactive tail in ordinary SNe IIP is a manifestation of the intense\nturbulent mixing at the He/H composition interface.", + "category": "astro-ph" + }, + { + "text": "Advection-Dominated Accretion Model of Sagittarius A$^*$ and Other\n Accreting Black Holes: Viscous rotating accretion flows around black holes become\nadvection-dominated when the accretion rate $\\dot M$ is sufficiently low. Most\nof the accretion energy in such flows is stored within the gas and advected\nradially inward. The temperature is therefore very high, and much of the\nradiation comes out in hard X-rays and $\\gamma$-rays. We have constructed an\nadvection-dominated accretion flow model for the Galactic Center source\nSagittarius A$^*$. The model consists of a $7\\times10^5M_\\odot$ black hole\naccreting at $\\dot M=1.2\\times10^{-5}\\alpha\\, M_\\odot{\\rm yr^{-1}}$, where\n$\\alpha$ is the usual viscosity parameter. The model spectrum fits the\nobservations from radio to $\\gamma$-rays quite well and explains the unusually\nlow luminosity of the source. Since the model explicitly makes use of a horizon\nat the inner edge to swallow the advected energy, the success of the model\nstrongly suggests that the central object in Sgr A$^*$ is a black hole. We\nfurther show that, if $\\alpha$ is not much smaller than unity, then\nadvection-dominated models can be applied even to higher luminosity black\nholes. The existence of Low and High States in black hole X-ray binaries, and\nthe abrupt transition between the two states, find a natural explanation. The\nmodels also explain the close similarity in the hard X-ray/$\\gamma$-ray spectra\nof black hole X-ray binaries and active galactic nuclei.", + "category": "astro-ph" + }, + { + "text": "A solar-cycle study of coronal rotation: large variations, rapid\n changes, and implications for solar wind models: Information on the rotation rate of the corona, and its variation over\nlatitude and solar cycle, is valuable for making global connections between the\ncorona and the Sun, for global estimates of reconnection rates, and as a basic\nparameter for solar wind modelling. Here, we use a time series of tomographical\nmaps gained from coronagraph observations between 2007 - 2020 to directly\nmeasure the longitudinal drift of high-density streamers over time. The method\nreveals abrupt changes in rotation rates, revealing a complex relationship\nbetween the coronal rotation and the underlying photosphere. The majority of\nrates are between -1.0 to +0.5$^\\circ$/day relative to the standard Carrington\nrate of 14.18$^\\circ$/day, although rates are measured as low as\n-2.2$^\\circ$/day and as high as 1.6$^\\circ$/day. Equatorial rotation rates\nduring the 2008 solar minimum are slightly faster than the Carrington rate,\nwith an abrupt switch to slow rotation in 2009, then a return to faster rates\nin 2017. Abrupt changes and large variations in rates are seen at all\nlatitudes. Comparison with a magnetic model suggests that periods of equatorial\nfast rotation are associated with times when a large proportion of the magnetic\nfootpoints of equatorial streamers are near the equator, and we interpret the\nabrupt changes in terms of the latitudinal distribution of the streamer\nphotospheric footpoints. The coronal rotation rate is a key parameter for solar\nwind models, and variations of up to a degree per day or more can lead to large\nsystematic errors over forecasting periods of longer than a few days. The\napproach described in this paper gives corrected values that can form a part of\nfuture forecasting efforts.", + "category": "astro-ph" + }, + { + "text": "The drop of the coherence of the lower kHz QPOs is also observed in XTE\n J1701-462: We investigate the quality factor and RMS amplitude of the lower kHz QPOs\nfrom XTE J1701-462, a unique X-ray source which was observed in both the\nso-called Z and atoll states. Correcting for the frequency drift of the QPO, we\nshow that, as in all sources for which such a correction can be applied, the\nquality factor and RMS amplitude drops sharply above above a critical\nfrequency. For XTE J1701-462 this frequency is estimated to be ~800 Hz, where\nthe quality factor reaches a maximum of ~200 (e.g. a value consistent with the\none observed from more classical systems, such as 4U~1636-536). Such a drop has\nbeen interpreted as the signature of the innermost stable circular orbit, and\nthat interpretation is consistent with the observations we report here. The kHz\nQPOs in the Z state are much less coherent and lower amplitude than they are in\nthe atoll state. We argue that the change of the QPO properties between the two\nsource states is related to the change of the scale height of the accretion\ndisk; a prediction of the toy model proposed by barret et al. (2007). As a\nby-product of our analysis, we also increased the significance of the upper kHz\nQPO detected in the atoll phase up to 4.8 sigma (single trial significance),\nand show that the frequency separation (266.5+/-13.1 Hz) is comparable with the\none measured from simultaneous twin QPOs the Z phase.", + "category": "astro-ph" + }, + { + "text": "The G305 star-forming complex: radio continuum and molecular line\n observations: We present 109-115 GHz (3 mm) wide-field spectral line observations of 12^CO,\n13^CO and C^18O J=1-0 molecular emission and 5.5 and 8.8 GHz (6 and 3 cm) radio\ncontinuum emission towards the high-mass star forming complex known as G305.\nThe morphology of G305 is dominated by a large evacuated cavity at the centre\nof the complex driven by clusters of O stars surrounded by molecular gas. Our\ngoals are to determine the physical properties of the molecular environment and\nreveal the relationship between the molecular and ionised gas and star\nformation in G305. This is in an effort to characterise the star-forming\nenvironment and constrain the star formation history in an attempt to evaluate\nthe impact of high-mass stars on the evolution of the G305 complex.\n Analysis of CO emission in G305 reveals 156 molecular clumps with the\nfollowing physical characteristics. The 5.5 and 8.8GHz radio continuum emission\nreveals an extended low surface brightness ionised environment within which we\nidentify 15 large-scale features with a further eight smaller sources projected\nwithin these features. By comparing to mid infrared emission and archival data,\nwe identify nine HII regions, seven compact HII regions, one UC HII region,\nfour extended regions. The total integrated flux of the radio continuum\nemission at 5.5 GHz is ~180 Jy corresponding to a Lyman continuum output of\n2.4x10^50 photons s^-1. We compare the ionised and molecular environment with\noptically identified high-mass stars and ongoing star formation, identified\nfrom the literature. Analysis of this dataset reveals a star formation rate of\n0.008--0.016 and efficiency of 7--12%, allows us to probe the star formation\nhistory of the region and discuss the impact of high-mass stars on the\nevolution of G305.", + "category": "astro-ph" + }, + { + "text": "Every Flare, Everywhere: An All-Sky Untriggered Search for Astrophysical\n Neutrino Transients Using IceCube Data: Recent results from IceCube regarding TXS 0506+056 suggest the presence of\nneutrino flares that are not temporally coincident with a significant\ncorresponding gamma ray flare. Such flares are particularly difficult to\nidentify, as their presence must be inferred from the temporal distribution of\nneutrino data alone. Here we present the results of using a novel method to\nsearch for all such flares across the entire neutrino sky in 10 years of\nIceCube data, using both Gaussian and box-shaped flare hypotheses. Unlike for\npast searches, that looked for only the most significant neutrino flare in the\ndata at a given direction, here we implement an algorithm to combine\ninformation from multiple flares associated with a single source candidate.\nThis represents the most detailed description of the neutrino sky to date,\nproviding the location and intensity of all neutrino cluster candidates in both\nspace and time. These results can be used to further constrain potential\npopulations of transient neutrino sources, serving as a complement to existing\ntime-integrated and time-dependent methods.", + "category": "astro-ph" + }, + { + "text": "Internal Dynamics of Globular Clusters: Galactic globular clusters, which are ancient building blocks of our Galaxy,\nrepresent a very interesting family of stellar systems in which some\nfundamental dynamical processes have taken place on time scales shorter than\nthe age of the universe. In contrast with galaxies, these clusters represent\nunique laboratories for learning about two-body relaxation, mass segregation\nfrom equipartition of energy, stellar collisions, stellar mergers, and core\ncollapse. In the present review, we summarize the tremendous developments, as\nmuch theoretical as observational, that have taken place during the last two\ndecades, and which have led to a quantum jump in our understanding of these\nbeautiful dynamical systems.", + "category": "astro-ph" + }, + { + "text": "The Physics of Wind-Fed Accretion: We provide a brief review of the physical processes behind the radiative\ndriving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and\naccretion of a fraction of the stellar wind by a compact object, typically a\nneutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we\ndescribe a program to develop global models of the radiatively-driven\nphotoionized winds and accretion flows of HMXBs, with particular attention to\nthe prototypical system Vela X-1. The models combine XSTAR photoionization\ncalculations, HULLAC emission models appropriate to X-ray photoionized plasmas,\nimproved models of the radiative driving of photoionized winds, FLASH\ntime-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo\nradiation transport. We present two- and three-dimensional maps of the density,\ntemperature, velocity, ionization parameter, and emissivity distributions of\nrepresentative X-ray emission lines, as well as synthetic global Monte Carlo\nX-ray spectra. Such models help to better constrain the properties of the winds\nof HMXBs, which bear on such fundamental questions as the long-term evolution\nof these binaries and the chemical enrichment of the interstellar medium.", + "category": "astro-ph" + }, + { + "text": "Clustering of 2PIGG galaxy groups with 2dFGRS galaxies: Prompted by indications from QSO lensing that there may be more mass\nassociated with galaxy groups than expected, we have made new dynamical infall\nestimates of the masses associated with 2PIGG groups and clusters. We have\nanalysed the redshift distortions in the cluster-galaxy cross-correlation\nfunction as a function of cluster membership, cross-correlating z<0.12 2PIGG\nclusters and groups with the full 2dF galaxy catalogue. We have made estimates\nof the dynamical infall parameter beta and new estimates of the group velocity\ndispersions. We first find that the amplitude of the full 3-D redshift space\ncross-correlation function, xi_{cg}, rises monotonically with group membership.\nWe use a simple linear-theory infall model to fit xi(sigma, pi) in the range\n50.95$ in the redshift range, $0.1\\leq z\\leq 0.33$. We\nuse the galaxy shapes from the Subaru Hyper Suprime-Cam (HSC) survey for this\npurpose. We bin satellite galaxies by their distance from the cluster centre\nand compare it to the signal around a control sample of galaxies which do not\nreside in clusters but have similar colours and magnitudes. We explore the\neffect of environmental processes on the dark matter mass around satellites. We\nsee hints of a difference in the mass of the subhalo of the satellite compared\nto the halo masses of galaxies in our control sample, especially in the\ninnermost cluster-centric radial bin ($0.1 15 degrees. Most of the observations were taken with the Integral\nField Unit of the Gemini Multi-Object Spectrograph, at the Gemini South\ntelescope, but some are also being taken with the Southern Astrophysical\nResearch Telescope (SOAR) Integral Field Spectrograph. The DIVING$^{3D}$ survey\nwas designed for the study of nuclear emission-line properties, circumnuclear\n(within scales of hundreds of pc) emission-line properties, stellar and gas\nkinematics and stellar archaeology. The data have a combination of high spatial\nand spectral resolution not matched by previous surveys and will result in\nsignificant contributions for studies related to, for example, the statistics\nof low-luminosity active galactic nuclei, the ionization mechanisms in\nLow-Ionization Nuclear Emission-Line Regions, the nature of transition objects,\namong other topics.", + "category": "astro-ph" + }, + { + "text": "The Fluorescence Detector of the Pierre Auger Observatory - A\n Calorimeter for UHECR: The Pierre Auger Observatory is a hybrid detector for ultrahigh energy cosmic\nrays (UHECR) with energies above 10$^{18.5}$ eV. Currently the first part of\nthe Observatory nears completion in the southern hemisphere in Argentina. One\ndetection technique uses over 1600 water Cherenkov tanks at ground where\nsamples of secondary particles of extensive air showers (EAS) are detected. The\nsecond technique is a calorimetric measurement of the energy deposited by EAS\nin the atmosphere. Charged secondary particles of EAS lose part of their energy\nin the atmosphere via ionization. The deposited energy is converted into\nexcitation of molecules of the air and afterwards partly emitted as\nfluorescence light mainly from nitrogen in the wavelength region between 300\nand 400 nm. This light is observed with 24 fluorescence telescopes in 4\nstations placed at the boundary of the surface array. This setup provides a\ncombined measurement of the longitudinal shower development and the lateral\nparticle distribution at ground of the same event. Details on the fluorescence\ntechnique and the necessary atmospheric monitoring will be presented, as well\nas first physics results on UHECR.", + "category": "astro-ph" + }, + { + "text": "High Redshift Radio Galaxies: Laboratories for Massive Galaxy and\n Cluster Formation in the early Universe: High redshift radio galaxies are among the largest, most luminous, most\nmassive, and most beautiful objects in the Universe. They are generally\nidentified from their radio emission, thought to be powered by accretion of\nmatter onto supermassive black holes in the nuclei of their host galaxies.\nObservations show that they are energetic sources of radiation throughout most\nof the electromagnetic spectrum, including relativistic plasma, gas and dust,\nstars and the active galactic nuclei (AGN). 1 HzRGs are inferred to be\nextremely massive, including old stars (up to $\\sim$ 10$^{12}$ M$_{\\odot}$),\nhot gas (up to $\\sim$ 10$^{12}$ M$_{\\odot}$) and molecular gas (up to $\\sim$\n10$^{11}$ M$_{\\odot}$).Because they are highly luminous and (unlike quasars)\nspatially resolvable from the ground, most components of HzRGs provide\nimportant diagnostic information about the spatial distributions of processes\nwithin HzRGs and their environment. The fact that the different constituents\nare present in the same objects and that the {\\bf {\\it interrelationships and\ninteractions between them}} can be studied make distant radio galaxies unique\nlaboratories for probing massive galaxy and cluster formation in the early\nUniverse.", + "category": "astro-ph" + }, + { + "text": "Fractional amplitude of kilohertz quasi-periodic oscillation from 4U\n 1728-34: evidence of decline at higher energies: A kilohertz quasi-periodic oscillation (kHz QPO) is an observationally robust\nhigh-frequency timing feature detected from neutron star low-mass X-ray\nbinaries (LMXBs). This feature can be very useful to probe the superdense core\nmatter of neutron stars, and the strong gravity regime. However, although many\nmodels exist in the literature, the physical origin of kHz QPO is not known,\nand hence this feature cannot be used as a tool yet. The energy dependence of\nkHz QPO fractional rms amplitude is an important piece of the jigsaw puzzle to\nunderstand the physical origin of this timing feature. It is known that the\nfractional rms amplitude increases with energy at lower energies. At higher\nenergies, the amplitude is usually believed to saturate, although this is not\nestablished. We combine tens of lower kHz QPOs from a neutron star LMXB 4U\n1728-34 in order to improve the signal-to-noise-ratio. Consequently, we, for\nthe first time to the best of our knowledge, find a significant and systematic\ndecrease of the fractional rms amplitude with energy at higher photon energies.\nAssuming an energy spectrum model, blackbody+powerlaw, we explore if the\nsinusoidal variation of a single spectral parameter can reproduce the above\nmentioned fractional rms amplitude behavior. Our analysis suggests that the\noscillation of any single blackbody parameter is favored over the oscillation\nof any single powerlaw parameter, in order to explain the measured amplitude\nbehavior. We also find that the quality factor of a lower kHz QPO does not\nplausibly depend on photon energy.", + "category": "astro-ph" + }, + { + "text": "Variations in the slope of the resolved star-forming main sequence: a\n tool for constraining the mass of star-forming regions: The correlation between galaxies' integrated stellar masses and star\nformation rates (the `star formation main sequence'; SFMS) is a\nwell-established scaling relation. Recently, surveys have found a relationship\nbetween the star formation rate and stellar mass surface densities on kpc and\nsub-kpc scales (the `resolved SFMS'; rSFMS). In this work, we demonstrate that\nthe rSFMS emerges naturally in FIRE-2 zoom-in simulations of Milky Way-mass\ngalaxies. We make SFR and stellar mass maps of the simulated galaxies at a\nvariety of spatial resolutions and star formation averaging time-scales and fit\nthe rSFMS using multiple methods from the literature. While the absolute value\nof the SFMS slope depends on the fitting method, the slope is steeper for\nlonger star formation time-scales and lower spatial resolutions regardless of\nthe fitting method employed. We present a toy model that quantitatively\ncaptures the dependence of the simulated galaxies' rSFMS slope on spatial\nresolution and use it to illustrate how this dependence can be used to\nconstrain the characteristic mass of star-forming clumps.", + "category": "astro-ph" + }, + { + "text": "The Mopra Southern Galactic Plane CO Survey - Data Release 3: We present observations of fifty square degrees of the Mopra carbon monoxide\n(CO) survey of the Southern Galactic Plane, covering Galactic longitudes $l =\n300$-$350^\\circ$ and latitudes $|b| \\le 0.5^\\circ$. These data have been taken\nat 0.6 arcminute spatial resolution and 0.1 km/s spectral resolution, providing\nan unprecedented view of the molecular clouds and gas of the Southern Galactic\nPlane in the 109-115 GHz $J = 1$-0 transitions of $^{12}$CO, $^{13}$CO,\nC$^{18}$O and C$^{17}$O. We present a series of velocity-integrated maps,\nspectra and position-velocity plots that illustrate Galactic arm structures and\ntrace masses on the order of $\\sim$10$^{6}$ M$_{\\odot}$ per square degree; and\ninclude a preliminary catalogue of C$^{18}$O clumps located between\n$l=330$-$340^\\circ$. Together with information about the noise statistics of\nthe survey these data can be retrieved from the Mopra CO website, the PASA data\nstore and the Harvard Dataverse (doi:10.7910/DVN/LH3BDN ).", + "category": "astro-ph" + }, + { + "text": "Radio Properties of z>4 Optically-Selected Quasars: We report on two programs to address differential evolution between the\nradio-loud and radio-quiet quasar populations at high (z>4) redshift. Both\nprograms entail studying the radio properties of optically-selected quasars.\nFirst, we have observed 32 optically-selected, high-redshift (z>4) quasars with\nthe VLA at 6 cm (5 GHz). These sources comprise a statistically complete and\nwell-understood sample. We detect four quasars above our 3-sigma limit of ~0.15\nmJy, which is sufficiently sensitive to detect all radio-loud quasars at the\nprobed redshift range. Second, we have correlated 134 z>4 quasars, comprising\nall such sources that we are aware of as of mid-1999, with FIRST and NVSS.\nThese two recent 1.4 GHz VLA sky surveys reach 3-sigma limits of approximately\n0.6 mJy and 1.4 mJy respectively. We identify a total of 15 z>4 quasars, of\nwhich six were not previously known to be radio-loud. The depth of these\nsurveys does not reach the radio-loud/radio-quiet demarcation luminosity\ndensity (L(1.4 GHz) = 10^32.5 h(50)^(-2) ergs/s/Hz) at the redshift range\nconsidered; this correlation therefore only provides a lower limit to the\nradio-loud fraction of quasars at high-redshift. The two programs together\nidentify eight new radio-loud quasars at z>4, a significant increase over the\nseven currently in the published literature. We find no evidence for radio-loud\nfraction depending on optical luminosity for -25 > M_B > -28 at z~2, or for\n-26>M_B>-28 at z>4. Our results also show no evolution in the radio-loud\nfraction between z~2 and z>4 (-26>M_B>-28).", + "category": "astro-ph" + }, + { + "text": "Nuclear reactions in hot stellar matter and nuclear surface deformation: Cross-sections for capture reactions of charged particles in hot stellar\nmatter turn out be increased by the quadrupole surface oscillations, if the\ncorresponding phonon energies are of the order of the star temperature. The\nincrease is studied in a model that combines barrier distribution induced by\nsurface oscillations and tunneling. The capture of charged particles by nuclei\nwith well-deformed ground-state is enhanced in stellar matter. It is found that\nthe influence of quadrupole surface deformation on the nuclear reactions in\nstars grows, when mass and proton numbers in colliding nuclei increase.", + "category": "astro-ph" + }, + { + "text": "Recent developments in Laue lens manufacturing and their impact on\n imaging performance: We report on recent progress in the development of Laue lenses for\napplications in hard X/soft gamma-ray astronomy. Here we focus on the\nrealization of a sector of such a lens made of 11 bent Germanium crystals and\ndescribe the technological challenges involved in their positioning and\nalignment with adhesive-based bonding techniques. The accurate alignment and\nthe uniformity of the curvature of the crystals are critical for achieving\noptimal X-ray focusing capabilities. We have assessed how the errors of\nmisalignment with respect to the main orientation angles of the crystals affect\nthe point spread function (PSF) of the image diffracted by a single sector. We\nhave corroborated these results with simulations carried out with our physical\nmodel of the lens, based on a Monte Carlo ray-tracing technique, adopting the\ngeometrical configuration of the Laue sector, the observed assembly accuracy\nand the measured curvatures of the crystals. An extrapolation of the\nperformances achieved on a single sector to an entire Laue lens based on this\nmodel has shown that a PSF with half-power-diameter of 4.8 arcmin can be\nachieved with current technology. This has the potential to lead to a\nsignificant improvement in sensitivity of spectroscopic and polarimetric\nobservations in the 50-600 keV band", + "category": "astro-ph" + }, + { + "text": "Neutrino-heated winds from millisecond proto-magnetars as sources of the\n weak r-process: We explore heavy element nucleosynthesis in neutrino-driven winds from\nrapidly-rotating, strongly magnetized proto-neutron stars for which the\nmagnetic dipole is aligned with the rotation axis, and the field is assumed to\nbe a static force-free configuration. We process the proto-magnetar wind\ntrajectories calculated by Vlasov et al 2014 through the r-process nuclear\nreaction network SkyNet using contemporary models for the evolution of the wind\nelectron fraction during the proto-neutron star cooling phase. Although we do\nnot find a successful second or third peak r-process for any rotation period P,\nwe show that proto-magnetars with P around 1-5 ms produce heavy element\nabundance distributions that extend to higher nuclear mass number than from\notherwise equivalent spherical winds (with the mass fractions of some elements\nenhanced by factors of 100-1000). The heaviest elements are synthesized by\noutflows emerging along flux tubes which graze the closed zone and pass near\nthe equatorial plane outside the light cylinder. Due to dependence of the\nnucleosynthesis pattern on the magnetic field strength and rotation rate of the\nproto-neutron star, natural variations in these quantities between core\ncollapse events could contribute to the observed diversity of the abundances of\nweak r-process nuclei in metal-poor stars. Further diversity, including\npossibly even a successful third-peak r-process, could be achieved for\nmisaligned rotators with non-zero magnetic inclination with respect to the\nrotation axis. If proto-magnetars are central engines for GRBs, their\nrelativistic jets should contain a high mass fraction of heavy nuclei of\ncharacteristic average mass number A of order 100, providing a possible source\nfor ultra-high energy cosmic rays comprised of heavy nuclei with an energy\nspectrum that extends beyond the nominal GZK cut-off for protons or iron\nnuclei.", + "category": "astro-ph" + }, + { + "text": "IGR J17329-2731: The birth of a symbiotic X-ray binary: We report on the results of the multiwavelength campaign carried out after\nthe discovery of the INTEGRAL transient IGR J17329-2731. The optical data\ncollected with the SOAR telescope allowed us to identify the donor star in this\nsystem as a late M giant at a distance of 2.7$^{+3.4}_{-1.2}$ kpc. The data\ncollected quasi-simultaneously with XMM-Newton and NuSTAR showed the presence\nof a modulation with a period of 6680$\\pm$3 s in the X-ray light curves of the\nsource. This unveils that the compact object hosted in this system is a slowly\nrotating neutron star. The broadband X-ray spectrum showed the presence of a\nstrong absorption ($\\gg$10$^{23}$ cm$^{-2}$) and prominent emission lines at\n6.4 keV, and 7.1 keV. These features are usually found in wind-fed systems, in\nwhich the emission lines result from the fluorescence of the X-rays from the\naccreting compact object on the surrounding stellar wind. The presence of a\nstrong absorption line around $\\sim$21 keV in the NuSTAR spectrum suggests a\ncyclotron origin, thus allowing us to estimate the neutron star magnetic field\nas $\\sim$2.4$\\times$10$^{12}$ G. All evidence thus suggests IGR J17329-2731 is\na symbiotic X-ray binary. As no X-ray emission was ever observed from the\nlocation of IGR J17329-2731 by INTEGRAL (or other X-ray facilities) during the\npast 15 yr in orbit and considering that symbiotic X-ray binaries are known to\nbe variable but persistent X-ray sources, we concluded that INTEGRAL caught the\nfirst detectable X-ray emission from IGR J17329-2731 when the source shined as\na symbiotic X-ray binary. The Swift/XRT monitoring performed up to $\\sim$3\nmonths after the discovery of the source, showed that it maintained a\nrelatively stable X-ray flux and spectral properties.", + "category": "astro-ph" + }, + { + "text": "Digging for the Truth: Photon Archeology with GLAST: Stecker, Malkan and Scully, have shown how ongoing deep surveys of galaxy\nluminosity functions, spectral energy distributions and backwards evolution\nmodels of star formation rates can be used to calculate the past history of\nintergalactic photon densities for energies from 0.03 eV to the Lyman limit at\n13.6 eV and for redshifts out to 6 (called here the intergalactic background\nlight or IBL). From these calculations of the IBL at various redshifts, they\npredict the present and past optical depth of the universe to high energy\ngamma-rays owing to interactions with photons of the IBL and the 2.7 K CMB. We\ndiscuss here how this proceedure can be reversed by looking for sharp cutoffs\nin the spectra of extragalactic gamma-ray sources such as blazars at high\nredshifts in the multi-GeV energy range with GLAST. By determining the cutoff\nenergies of sources with known redshifts, we can refine our determination of\nthe IBL photon densities in the past, i.e., the \"archeo-IBL\", and therefore get\na better measure of the past history of the total star formation rate.\nConversely, observations of sharp high energy cutoffs in the gamma-ray spectra\nof sources at unknown redshifts can be used instead of spectral lines to give a\nmeasure of their redshifts.", + "category": "astro-ph" + }, + { + "text": "Seasonal thaws under mid-to-low pressure atmospheres on Early Mars: Despite decades of scientific research on the subject, the climate of the\nfirst 1.5 Gyr of Mars history has not been fully understood yet. Especially\nchallenging is the need to reconcile the presence of liquid water for extended\nperiods of time on the martian surface with the comparatively low insolation\nreceived by the planet, a problem which is known as the Faint Young Sun (FYS)\nParadox. In this paper we use ESTM, a latitudinal energy balance model with\nenhanced prescriptions for meridional heat diffusion, and the radiative\ntransfer code EOS to investigate how seasonal variations of temperature can\ngive rise to local conditions which are conductive to liquid water runoffs. We\ninclude the effects of the martian dichotomy, a northern ocean with either 150\nor 550 m of Global Equivalent Layer (GEL) and simplified CO$_2$ or H$_2$O\nclouds. We find that 1.3-to-2.0 bar CO$_2$-dominated atmospheres can produce\nseasonal thaws due to inefficient heat redistribution, provided that the\neccentricity and the obliquity of the planet are sufficiently different from\nzero. We also studied the impact of different values for the argument of\nperihelion. When local favorable conditions exist, they nearly always persist\nfor $>15\\%$ of the martian year. These results are obtained without the need\nfor additional greenhouse gases (e.g. H$_2$, CH$_4$) or transient\nheat-injecting phenomena (e.g. asteroid impacts, volcanic eruptions). Moderate\namounts (0.1 to 1\\%) of CH$_4$ significantly widens the parameter space region\nin which seasonal thaws are possible.", + "category": "astro-ph" + }, + { + "text": "The Masses of Nuclear Black Holes in Luminous Elliptical Galaxies and\n Implications for the Space Density of the Most Massive Black Holes: Black hole masses predicted from the Mbh-sigma relationship conflict with\nthose predicted from the Mbh-L relationship for the most luminous galaxies,\nsuch as brightest cluster galaxies (BCGs). This is because stellar velocity\ndispersion, sigma, increases only weakly with L for BCGs and other giant\nellipticals. The Mbh-L relationship predicts that the most luminous BCGs may\nhave Mbh approaching 10^{10}M_sol, while the M-sigma relationship always\npredicts Mbh<3X10^9M_sol. We argue that the Mbh-L relationship is a plausible\nor even preferred description for BCGs and other galaxies of similar\nluminosity. If cores in central stellar density are formed by binary BHs, then\nthe inner-core cusp radius, r_gamma, may be an independent witness of Mbh.\nUsing structural parameters derived from a large sample of early-type galaxies\nobserved by HST, we argue that L is superior to sigma as an indicator of\nr_gamma in luminous galaxies. The observed r_gamma-Mbh relationship for 11 core\ngalaxies with measured Mbh appears to be consistent with the Mbh-L relationship\nfor BCGs. BCGs have large cores appropriate for their large luminosities that\nmay be difficult to generate with the modest BH masses inferred from the\nMbh-sigma relationship. Mbh~L may be expected to hold for BCGs, if they were\nformed in dissipationless mergers, which should preserve ratio of BH to stellar\nmass. This picture appears to be consistent with the slow increase in sigma\nwith L and the more rapid increase in effective radii with L seen in BCGs. If\nBCGs have large BHs commensurate with their luminosities, then the local BH\nmass function for Mbh>3X10^9M_sol may be nearly an order of magnitude richer\nthan that inferred from the Mbh-sigma relationship. The volume density of QSOs\nat earlier epochs may favor the predictions from the Mbh-L relationship.", + "category": "astro-ph" + }, + { + "text": "Correlated timing and spectral behavior of 4U 1705-44: We follow the timing properties of the neutron star low-mass X-ray binary\nsystem 4U 1705-44 in different spectral states, as monitored by the Rossi X-ray\nTiming Explorer over about a month. We fit the power density spectra using\nmultiple Lorentzians. We show that the characteristic frequencies of these\nLorentzians, when properly identified, fit within the correlations previously\nreported. The time evolution of these frequencies and their relation with the\nparameters of the energy spectra reported in Barret & Olive (2002) are used to\nconstrain the accretion geometry changes. The spectral data were fitted by the\nsum of a blackbody and a Comptonized component and were interpreted in the\nframework of a truncated accretion disk geometry, with a varying truncation\nradius. If one assumes that the characteristic frequencies of the Lorentzians\nare some measure of this truncation radius, as in most theoretical models, then\nthe timing data presented here strengthen the above interpretation. The soft to\nhard and hard to soft transitions are clearly associated with the disk receding\nfrom and approaching the neutron star respectively. During the transitions,\ncorrelations are found between the Lorentzian frequencies and the flux and\ntemperature of the blackbody, which is thus likely to be coming from the disk.\nOn the other hand, in the hard state, the characteristic Lorentzians\nfrequencies which are at the lowest, remained nearly constant despite\nsignificant evolution of the spectra parameters. The disk no longer contributes\nto the X-ray emission, and the blackbody is now likely to be emitted by the\nneutron star surface which is providing the seed photons for the\nComptonization.", + "category": "astro-ph" + }, + { + "text": "Prospects for annihilating dark matter from M31 and M33 observations\n with the Cherenkov Telescope Array: M31 and M33 are the closest spiral galaxies and the largest members (together\nwith the Milky Way) of the Local group, which makes them interesting targets\nfor indirect dark matter searches. In this paper, we present studies of the\nexpected sensitivity of the Cherenkov Telescope Array (CTA) to an annihilation\nsignal from weakly interacting massive particles from M31 and M33. We show that\na 100 h long observation campaign will allow CTA to probe annihilation\ncross-sections up to $\\langle\\sigma\\upsilon\\rangle\\approx 5\\cdot10^{-25}$\ncm$^{3}$s$^{-1}$ for the $\\tau^{+}\\tau^{-}$ annihilation channel (for M31, at a\nDM mass of 0.3 TeV), improving the current limits derived by HAWC by up to an\norder of magnitude. We present an estimate of the expected CTA sensitivity, by\nalso taking into account the contributions of the astrophysical background and\nother possible sources of systematic uncertainty. We also show that CTA might\nbe able to detect the extended emission from the bulge of M31, detected at\nlower energies by the Fermi/LAT.", + "category": "astro-ph" + }, + { + "text": "The Ratio of Helium- to Hydrogen-Atmosphere White Dwarfs: Direct\n Evidence for Convective Mixing: We determine the ratio of helium- to hydrogen-atmosphere white dwarf stars as\na function of effective temperature from a model atmosphere analysis of the\ninfrared photometric data from the Two Micron All Sky Survey combined with\navailable visual magnitudes. Our study surpasses any previous analysis of this\nkind both in terms of the accuracy of the Teff determinations as well as the\nsize of the sample. We observe that the ratio of helium- to hydrogen-atmosphere\nwhite dwarfs increases gradually from a constant value of ~0.25 between Teff =\n15,000 K and 10,000 K to a value twice as large in the range 10,000 > Teff >\n8000 K, suggesting that convective mixing, which occurs when the bottom of the\nhydrogen convection zone reaches the underlying convective helium envelope, is\nresponsible for this gradual transition. The comparison of our results with an\napproximate model used to describe the outcome of this convective mixing\nprocess implies hydrogen mass layers in the range log M_H/M_tot = -10 to -8 for\nabout 15% of the DA stars that survived the DA to DB transition near Teff ~\n30,000 K, the remainder having presumably more massive layers above log\nM_H/M_tot ~ -6.", + "category": "astro-ph" + }, + { + "text": "Revisiting the Long-Period Transiting Planets from Kepler: Currently, we have only limited means to probe the presence of planets at\nlarge orbital separations. Foreman-Mackey et al. searched for long-period\ntransiting planets in the Kepler light curves using an automated pipeline.\nHere, we apply their pipeline, with minor modifications, to a larger sample and\nuse updated stellar parameters from Gaia DR2. The latter boosts the stellar\nradii for most of the planet candidates found by FM16, invalidating a number of\nthem as false positives. We identify 15 candidates, including two new ones. All\nhave sizes from 0.3 to 1 $R_{\\rm J}$, and all but two have periods from 2 to 10\nyr. We report two main findings based on this sample. First, the planet\noccurrence rate for the above size and period ranges is $0.70^{+0.40}_{-0.20}$\nplanets per Sun-like star, with the frequency of cold Jupiters agreeing with\nthat from radial velocity surveys. Planet occurrence rises with decreasing\nplanet size, roughly describable as $dN/d\\log R \\propto R^{\\alpha}$ with\n$\\alpha = -1.6^{+1.0}_{-0.9}$, i.e., Neptune-sized planets are some four times\nmore common than Jupiter-sized ones. Second, five out of our 15 candidates\norbit stars with known transiting planets at shorter periods, including one\nwith five inner planets. We interpret this high incidence rate to mean: (1)\nalmost all our candidates should be genuine; (2) across a large orbital range\n(from $\\sim 0.05$ to a few astronomical units), mutual inclinations in these\nsystems are at most a few degrees; and (3) large outer planets exist almost\nexclusively in systems with small inner planets.", + "category": "astro-ph" + }, + { + "text": "VLT-SINFONI integral field spectroscopy of low-z luminous and\n ultraluminous infrared galaxies I. Atlas of the 2D gas structure: We present an atlas of a sample of local (U)LIRGs covering the luminosity\nrange log(L_IR/L_sun)=11.1-12.4. The atlas is based on near-infrared H and\nK-band VLT-SINFONI IFS, and presents the ionised, partially ionised, and warm\nmolecular gas 2D flux distributions and kinematics over a FoV of 3x3 kpc\n(LIRGs) and 12x12kpc (ULIRGs) and with average linear resolutions of 0.2kpc and\n0.9kpc, respectively. The different phases of the gas show a wide morphological\nvariety with the nucleus as the brightest Br_g source for 33% of the LIRGs and\n71% of the ULIRGs, whereas all the (U)LIRGs have their maximum H_2 emission in\ntheir nuclear regions. In LIRGs, the ionised gas distribution is dominated by\nthe emission from the star-forming rings or giant HII regions in the spiral\narms. The Br_g and [FeII] line at 1.644 micron trace the same structures,\nalthough the emission peaks at different locations in some of the objects, and\nthe [FeII] seems to be more extended and diffuse. The ULIRG subsample contains\nmainly pre-coalescence interacting systems. Although the peaks of the molecular\ngas emission and the continuum coincide in 71% of the ULIRGs, regions with\nintense Pa_a (Br_g) emission tracing luminous star-forming regions located at\ndistances of 2-4kpc away from the nucleus are also detected, usually associated\nwith secondary nuclei or tidal tails. The gas kinematics in LIRGs are primarily\ndue to rotational motions around the centre of the galaxy, although local\ndeviations associated with radial flows and/or regions of higher velocity\ndispersions are present. The ionised and molecular gas share the same\nkinematics to first order, showing slight differences in the velocity\namplitudes in some cases, whereas the average velocity dispersions are\ncompatible within uncertainties. As expected, the kinematics of the ULIRG\nsubsample is more complex, owing to the interacting nature of the objects of\nthe sample.", + "category": "astro-ph" + }, + { + "text": "Clusters of Galaxies as Standard Candles for Global Observational\n Cosmology: As the largest gravitationally collapsed objects, and as objects with a\nrelatively low space density, clusters of galaxies offer one of the best sets\nof standard candles for trying to measure basic cosmological parameters such as\nthe injectivity diameter 2r_{inj} (the shortest distance between two\ntopologically lensed images of any object, e.g. cluster) and the out-diameter\n2r_{+} (the maximum `size' of the Universe). Present constraints indicate that\neither of these may be smaller or larger than the horizon diameter.", + "category": "astro-ph" + }, + { + "text": "Large Observatory for x-ray Timing (LOFT-P): A Probe-classs Mission\n Concept Study: LOFT-P is a concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing\nmission, based on the LOFT concept originally proposed to ESAs M3 and M4 calls.\nLOFT-P requires very large collecting area (>6 m^2, >10x RXTE), high time\nresolution, good spectral resolution, broad-band spectral coverage (2-30 keV),\nhighly flexible scheduling, and an ability to detect and respond promptly to\ntime-critical targets of opportunity. It addresses science questions such as:\nWhat is the equation of state of ultra dense matter? What are the effects of\nstrong gravity on matter spiraling into black holes? It would be optimized for\nsub-millisecond timing to study phenomena at the natural timescales of neutron\nstar surfaces and black hole event horizons and to measure mass and spin of\nblack holes. These measurements are synergistic to imaging and high-resolution\nspectroscopy instruments, addressing much smaller distance scales than are\npossible without very long baseline X-ray interferometry, and using\ncomplementary techniques to address the geometry and dynamics of emission\nregions. A sky monitor (2-50 keV) acts as a trigger for pointed observations,\nproviding high duty cycle, high time resolution monitoring of the X-ray sky\nwith ~20 times the sensitivity of the RXTE All-Sky Monitor, enabling\nmulti-wavelength and multi-messenger studies. A probe-class mission concept\nwould employ lightweight collimator technology and large-area solid-state\ndetectors, technologies which have been recently greatly advanced during the\nESA M3 study. Given the large community interested in LOFT (>800 supporters,\nthe scientific productivity of this mission is expected to be very high,\nsimilar to or greater than RXTE (~2000 refereed publications). We describe the\nresults of a study, recently completed by the MSFC Advanced Concepts Office,\nthat demonstrates that LOFT-P is feasible within a NASA probe-class mission\nbudget.", + "category": "astro-ph" + }, + { + "text": "The relationship between Class I and Class II methanol masers at high\n angular resolution: We have used the Australia Telescope Compact Array (ATCA) to make the first\nhigh resolution observations of a large sample of class~I methanol masers in\nthe 95-GHz ($8_0$--$7_1$A$^+$) transition. The target sources consist of a\nstatistically complete sample of 6.7-GHz class~II methanol masers with an\nassociated 95-GHz class~I methanol maser, enabling a detailed study of the\nrelationship between the two methanol maser classes at arcsecond angular\nresolution. These sources have been previously observed at high resolution in\nthe 36- and 44-GHz transitions, allowing comparison between all three class~I\nmaser transitions. In total, 172 95-GHz maser components were detected across\nthe 32 target sources. We find that at high resolution, when considering\nmatched maser components, a 3:1 flux density ratio is observed between the 95-\nand 44-GHz components, consistent with a number of previous lower angular\nresolution studies. The 95-GHz maser components appear to be preferentially\nlocated closer to the driving sources and this may indicate that this\ntransition is more strongly inverted nearby to background continuum sources. We\ndo not observe an elevated association rate between 95-GHz maser emission and\nmore evolved sources, as indicated by the presence of 12.2-GHz class~II masers.\nWe find that in the majority of cases where both class~I and class~II methanol\nemission is observed, some component of the class~I emission is associated with\na likely outflow candidate.", + "category": "astro-ph" + }, + { + "text": "NICER observations of the Crab pulsar glitch of 2017 November: Context: The Crab pulsar underwent its largest timing glitch on 2017 Nov 8.\nThe event was discovered at radio wavelengths, and was followed at soft X-ray\nenergies by observatories, such as XPNAV and NICER. aims: This work aims to\ncompare the glitch behavior at the two wavelengths mentioned above. Preliminary\nwork in this regard has been done by the X-ray satellite XPNAV. NICER with its\nfar superior sensitivity is expected to reveal much more detailed behavior.\nmethods: NICER has accumulated more than $301$ kilo seconds of data on the Crab\npulsar, equivalent to more than $3.3$ billion soft X-ray photons. These data\nwere first processed using the standard NICER analysis pipeline. Then the\narrival times of the X-ray photons were referred to the solar system's\nbarycenter. Then specific analysis was done to study the specific behavior\noutlined in the following sections, while taking dead time into account.\nresults: The variation of the rotation frequency of the Crab pulsar and its\ntime derivative during the glitch is almost exactly similar at the radio and\nX-ray energies. The following properties of the Crab pulsar remain essentially\nconstant before and after the glitch: the total X-ray flux; the flux, widths,\nand peaks of the two components of its integrated profile; and the soft X-ray\nspectrum. There is no evidence for giant pulses at X-ray energies. However, the\ntiming noise of the Crab pulsar shows quasi sinusoidal variation before the\nglitch, with increasing amplitude, which is absent after the glitch.\nconclusions: Even the strongest glitch in the Crab pulsar appears not to affect\nall but one of the properties mentioned above, at either frequency. The fact\nthat the timing noise appears to change due to the glitch is an important clue\nto unravel as this is still an unexplained phenomenon.", + "category": "astro-ph" + }, + { + "text": "Dark matter in Draco and the Local Group: Implications for direct\n detection experiments: We use a cosmological simulation of the Local Group to make quantitative and\nspeculative predictions for direct detection experiments. Cold dark matter\n(CDM) halos form via a complex series of mergers, accretion events and violent\nrelaxation which precludes the formation of significant caustic features\npredicted by axially symmetric collapse. The halo density profiles are combined\nwith observational constraints on the galactic mass distribution to constrain\nthe local density of cold dark matter to lie in the range 0.18 <~\nrho_CDM(R_solar)/GeV cm^-3 <~ 0.30. In velocity space, coherent streams of dark\nmatter from tidally disrupted halos fill the halo and provide a tracer of the\nmerging hierarchy. The particle velocities within triaxial CDM halos cannot be\napproximated by a simple Maxwellian distribution and is radially biased at the\nsolar position. The detailed phase space structure within the solar system will\ndepend on the early merger history of the progenitor halos and the importance\nof major mergers over accretion dominated growth. We follow the formation of a\n``Draco'' sized dSph halo of mass 10^8M_solar with several million particles\nand high force accuracy. Its internal structure and substructure resembles that\nof galactic or cluster mass halos: the density profile has a singular central\ncusp and it contains thousands of sub-halos orbiting within its virial radius\ndemonstrating a self-similar nature to collisionless dark matter\nsub-clustering. The singular cores of substructure halos always survive\ncomplete tidal disruption although mass loss is continuous and rapid.\nExtrapolating wildly to earth mass halos with velocity dispersion of 1 m s^-1\n(roughly equal to the free streaming scale for neutralinos) we find that most\nof the dark matter may remain attached to bound subhalos. (Abridged)", + "category": "astro-ph" + }, + { + "text": "A Census from JWST of Extreme Emission Line Galaxies Spanning the Epoch\n of Reionization in CEERS: We present a sample of 1165 extreme emission-line galaxies (EELGs) at 45000 AA. JWST/NIRSpec spectroscopic\nobservations of a subset (34) of the photometrically selected EELGs validate\nour selection method: all spectroscopically observed EELGs confirm our\nphotometric identification of extreme emission, including some cases where the\nSED-derived photometric redshifts are incorrect. We find that the medium-band\nF410M filter in CEERS is particularly efficient at identifying EELGs, both in\nterms of including emission lines in the filter and in correctly identifying\nthe continuum between Hb + [OIII] and Ha in the neighboring broad-band filters.\nWe present examples of EELGs that could be incorrectly classified at ultra-high\nredshift (z>12) as a result of extreme Hb + [OIII] emission blended across the\nreddest photometric filters. We compare the EELGs to the broader (sub-extreme)\ngalaxy population in the same redshift range and find that they are consistent\nwith being the bluer, high equivalent width tail of a broader population of\nemission-line galaxies. The highest-EW EELGs tend to have more compact\nemission-line sizes than continuum sizes, suggesting that active galactic\nnuclei are responsible for at least some of the most extreme EELGs.\nPhotometrically inferred emission-line ratios are consistent with ISM\nconditions with high ionization and moderately low metallicity, consistent with\nprevious spectroscopic studies.", + "category": "astro-ph" + }, + { + "text": "Time-resolved spectroscopy of the peculiar Halpha variable Be star HD\n 76534: We present time-resolved spectroscopy of the Be star HD 76534, which was\nobserved to have an Halpha outburst in 1995, when the line went from\nphotospheric absorption to emission at a level of more than two times the\ncontinuum within 2.5 hours. To investigate the short-term behaviour of the\nspectrum of HD 76534 we have obtained 30 spectra within two hours real-time and\nsearched for variations in the spectrum. Within the levels of statistical\nsignificance, no variability was found. Rather than periodic on short time\nscales, the Halpha behaviour seems to be commonly episodic on longer (>1 year)\ntime scales, as an assessment of the existing data on the Halpha line and the\nHipparcos photometry suggests. HD 76534 underwent only 1 photometric outburst\nin the 3 year span that the star was monitored by the Hipparcos satellite.", + "category": "astro-ph" + }, + { + "text": "Intrinsic errors of the central galactic mass derived from rotation\n curves under the influence of a weak non-axisymmetric potential: Rotation curves are often used to estimate the mass distribution of spiral\ngalaxies, assuming circular rotation of disks. However, non-circular motions\ncaused by a non-axisymmetric gravitational potential, such as a stellar bar,\nmay disturb the velocity field, resulting in errors in mass estimation,\nespecially in the central regions of galaxies, because the line-of-sight\nvelocity depends on the viewing angles in a non-axisymmetric flow. Observing\nrotation curves of edge-on galaxies in time-dependent numerical simulations\nfrom different viewing angles, we obtain errors in the estimation of galactic\nmass from the rotation curves. In the most extreme case, the ellipticity of gas\norbits is as high as 0.8 in the central regions, even if the bar potential is\nweak. When rotation curves are defined as the highest velocity envelope of\nposition-velocity diagrams, the mass estimated from the rotation curves is\nlarger than the true mass by a factor of five for 15% of the viewing angles,\nand the ratio between the apparent mass and true mass is less than six for any\nviewing angle. The overestimation in mass occurs more frequently than the\nunderestimation.", + "category": "astro-ph" + }, + { + "text": "3D Relativistic Magnetohydrodynamic Simulations of Magnetized\n Spine-Sheath Relativistic Jets: Numerical simulations of weakly magnetized and strongly magnetized\nrelativistic jets embedded in a weakly magnetized and strongly magnetized\nstationary or weakly relativistic (v = c/2) sheath have been performed. A\nmagnetic field parallel to the flow is used in these simulations performed by\nthe new GRMHD numerical code RAISHIN used in its RMHD configuration. In the\nnumerical simulations the Lorentz factor $\\gamma = 2.5$ jet is precessed to\nbreak the initial equilibrium configuration. In the simulations sound speeds\nare $\\lesssim c/\\sqrt 3$ in the weakly magnetized simulations and $\\lesssim\n0.3c$ in the strongly magnetized simulations. The Alfven wave speed is\n$\\lesssim 0.07c$ in the weakly magnetized simulations and $\\lesssim 0.56c$ in\nthe strongly magnetized simulations. The results of the numerical simulations\nare compared to theoretical predictions from a normal mode analysis of the\nlinearized relativistic magnetohydrodynamic (RMHD) equations capable of\ndescribing a uniform axially magnetized cylindrical relativistic jet embedded\nin a uniform axially magnetized relativistically moving sheath. The theoretical\ndispersion relation allows investigation of effects associated with maximum\npossible sound speeds, Alfven wave speeds near light speed and relativistic\nsheath speeds. The prediction of increased stability of the weakly magnetized\nsystem resulting from c/2 sheath speeds and the stabilization of the strongly\nmagnetized system resulting from c/2 sheath speeds is verified by the numerical\nsimulation results.", + "category": "astro-ph" + }, + { + "text": "Extending the view of ArH+ chemistry in diffuse clouds: One of the surprises of the Herschel mission was the detection of ArH+\ntowards the Crab Nebula in emission and in absorption towards strong Galactic\nbackground sources. Although these detections were limited to the first\nquadrant of the Galaxy, the existing data suggest that ArH+ ubiquitously and\nexclusively probes the diffuse atomic regions of the ISM. In this study, we\nextend the coverage of ArH+ to other parts of the Galaxy with new observations\nof its J = 1-0 transition along seven Galactic sight lines towards bright\nsub-mm continuum sources. We aim to benchmark its efficiency as a tracer of\npurely atomic gas by evaluating its correlation (or lack there of) with other\nwell-known atomic and molecular gas tracers. The observations of ArH+ near\n617.5 GHz were made feasible with the new, sensitive SEPIA660 receiver on the\nAPEX 12 m telescope. The two sidebands of this receiver allowed us to observe\np-H2O+ transitions of at 607.227 GHz simultaneously with the ArH+ line. By\nanalysing the steady state chemistry of OH+ and o-H2O+, we derive on average a\ncosmic-ray ionisation rate (CRIR), of 2.3e-16 s^-1 towards the sight lines\nstudied in this work. Using the derived values of the CRIR and the observed\nArH+ abundances we constrain the molecular fraction of the gas traced by ArH+\nto lie below 2e-2 with a median value of 8.8e-4. Combined, our observations of\nArH+, OH+, H2O+, and CH probe different regimes of the ISM, from diffuse atomic\nto diffuse and translucent molecular clouds. Over Galactic scales, we see that\nthe distribution of N(ArH+) is associated with that of N(H), particularly in\nthe inner Galaxy with potentially even contributions from the warm neutral\nmedium phase of atomic gas at larger galactocentric distances. We derive an\naverage o/p-ratio for H2O+ of 2.1, which corresponds to a nuclear spin\ntemperature of 41 K, consistent with the typical gas temperatures of diffuse\nclouds.", + "category": "astro-ph" + }, + { + "text": "Rotation curves of galaxies in GR: It has been suggested that the observed flat rotation curves of disk galaxies\ncan be a peculiar effect of General Relativity (GR) rather than evidence for\nthe presence of dark matter (DM) halos in Newtonian gravity. In Ciotti (2022)\nthe problem has been quantitatively addressed by using the well known\nweak-field, low-velocity gravitomagnetic limit of GR, for realistic exponential\nbaryonic (stellar) disks. As expected, the resulting GR and Newtonian rotation\ncurves are indistinguishable, with GR corrections at all radii of the order of\n$v^2/c^2\\approx 10^{-6}$. Here we list some astrophysical problems that must be\nfaced if the existence of DM halos is attributed to a misinterpretation of weak\nfield effects of GR.", + "category": "astro-ph" + }, + { + "text": "Hybrid magnetized stars within the Field Correlator Method: We present preliminary results of the study of intense magnetic fields\neffects on hybrid stars. For the description of the hadronic phase, we use the\nrelativistic mean field approximation. For the quark matter phase, we employ\nthe Field Correlator Method formalism. Once the the equation of state is built,\nwe discuss the pressure anisotropy due the presence of the strong magnetic\nfield. Finally, we calculate the structure of the compact stars using\nmagnetized hybrid equations of state and their oscillation modes related with\nthe emission of gravitational waves.", + "category": "astro-ph" + }, + { + "text": "Comment on \"Nonideal Fields Solve the Injection Problem in Relativistic\n Reconnection\": Recently, Sironi (PRL, 128, 145102; S22) reported the correlation between\nparticles accelerated into high energy and their crossings of regions with\nelectric field larger than magnetic field (E>B regions) in kinetic simulations\nof relativistic magnetic reconnection. They claim that electric fields in E>B\nregions (for a vanishing guide field) dominate in accelerating particles to the\ninjection energy. S22 presented test-particle simulations showing that if\nparticle energies are reset to low energies in E>B regions, efficient injection\nis suppressed. This Comment re-examines these claims by analyzing a simulation\nresembling the reference case in S22. We show that during crossings E>B\nacceleration only contributes a small fraction to the injection energy as E>B\nregions only host particles for a short duration. The energization before any\nE>B crossings has a comparable contribution, indicating E>B regions are not\nunique in pre-accelerating particles. A new test-particle simulation shows that\nzero-outing electric fields in E>B regions does not strongly influence the\ninjection. We suggest that the procedure used in S22 to exclude E>B\nacceleration partly removes acceleration outside E>B regions, leading to a\nfalse conclusion.", + "category": "astro-ph" + }, + { + "text": "The young, tight and low mass binary TWA22AB: a new calibrator for\n evolutionary models ? Orbit, spectral types and temperatures determination: Tight binaries discovered in young, nearby associations, with known\ndistances, are ideal targets to provide dynamical mass measurements to test the\nphysics of evolutionary models at young ages and very low masses. We report for\nthe first time the binarity of TWA22, possible new dynamical calibrator for\nevolutionary models at young ages. Based on an accurate trigonometric distance\n(17.53 +- 0.21 pc) determination, we infer a total dynamical mass of 220 +- 21\nMJup for the system. From the resolved near-infrared integral-field\nspectroscopy, we find an effective temperature Teff=2900+200-200 K for TWA22 A\nand Teff=2900+200-100 K for TWA22 B and surface gravities between 4.0 and 5.5\ndex. From our photometry and a M6 +- 1 spectral type for both components, we\nfind luminosities of log(L/Lsun)=-2.11 +- 0.13 dex and log(L/Lsun)=-2.30 +-\n0.16 dex for TWA22 A and B respectively. By comparing these parameters with\nevolutionary models, we question the age and the multiplicity of this system.\nWe also discuss a possible underestimation of the mass predicted by\nevolutionary models for young stars close to the substellar boundary.", + "category": "astro-ph" + }, + { + "text": "The broad line region of narrow-line Seyfert 1 galaxies: We have analyzed new and archival IUE observations of narrow-line Seyfert 1\ngalaxies (NLS1) in order to revise the ultraviolet (UV) properties of this\nsub-group of Active Galactic Nuclei (AGN). We have found broad wings in the\nstrongest UV emission lines, ruling out the hypothesis that there is no broad\nline emission region in this type of objects. Since the similarities in\nspectral energy distributions from the far-infrared (FIR) to the soft X rays in\nboth narrow-line and broad-line Seyfert 1 galaxies do not suggest that the\nnuclei of NLS1 are hidden from a direct view, we discuss the possibility that\nthe line emitting material in NLS1 is optically thin.", + "category": "astro-ph" + }, + { + "text": "On the nature of bulges in general and of box/peanut bulges in\n particular. Input from $N$-body simulations: Objects designated as bulges in disc galaxies do not form a homogeneous\nclass. I distinguish three types. The classical bulges, whose properties are\nsimilar to those of ellipticals and which form by collapse or merging. Boxy and\npeanut bulges, which are seen in near edge-on galaxies and which are in fact\njust a part of the bar seen edge-on. Finally disc-like bulges, which result\nfrom the inflow of (mainly) gas to the center-most parts, and subsequent star\nformation. I make a detailed comparison of the properties of boxy and peanut\nbulges with those of $N$-body bars seen edge-on and answer previously voiced\nobjections about the links between the two. I also present and analyse\nsimulations where a boxy /peanut feature is present at the same time as a\nclassical spheroidal bulge and compare them with observations. Finally, I\npropose a nomenclature that can help distinguish between the three types of\nbulges and avoid considerable confusion.", + "category": "astro-ph" + }, + { + "text": "Detection of anisotropic galaxy assembly bias in BOSS DR12: We present evidence of anisotropic galaxy assembly bias in the Baryon\nOscillation Spectroscopic Survey Data Release 12 galaxy sample at a level\nexceeding $5\\sigma$. We use measurements of the line-of-sight velocity\ndispersion $\\sigma_\\star$ and stellar mass $M_\\star$ to perform a simple split\ninto subsamples of galaxies. We show that the amplitude of the monopole and\nquadrupole moments of the power spectrum depend differently on $\\sigma_\\star$\nand $M_\\star$, allowing us to split the galaxy sample into subsets with\nmatching monopoles but significantly different quadrupoles on all scales.\nCombining data from the LOWZ and CMASS NGC galaxy samples, we find $>5\\sigma$\nevidence for anisotropic bias on scales $k<0.15\\,h\\,\\rm{Mpc}^{-1}$. We also\nexamine splits using other observed properties. For galaxy samples split using\n$M_\\star$ and projected size $R_0$, we find no significant evidence of\nanisotropic bias. Galaxy samples selected using additional properties exhibit\nstrongly varying degrees of anisotropic assembly bias, depending on which\ncombination of properties is used to split into subsets. This may explain why\nprevious searches for this effect using the Fundamental Plane found\ninconsistent results. We conclude that any selection of a galaxy sample that\ndepends on $\\sigma_\\star$ can give biased and incorrect Redshift Space\nDistortion measurements.", + "category": "astro-ph" + }, + { + "text": "CorrSim: A Multiwavelength Timing Observation Simulator: Studying the rapid variability of many astronomical objects is key to\nunderstanding the underlying processes at play. However, a combination of\nlimited telescope availability, viewing constraints, and the unpredictable\nnature of many sources mean that obtaining data well-suited to this task can be\ntricky, especially when it comes to simultaneous multiwavelength observations.\nResearchers can often find themselves tuning observational parameters in\nreal-time, or may realise later that their observation did not achieve their\ngoals. Here, we present CorrSim, a program to aid planning of multiwavelength\ncoordinated observations. CorrSim takes a model of a system (i.e. Power\nSpectra, Coherence, and Lags), and returns a simulated multiwavelength\nobservation, including effects of noise, telescope parameters, and finite\nsampling. The goals of this are: (i) To simulate a potential observation (to\ninform decisions about its feasibility); (ii) To investigate how different\nFourier models affect a system's variability (e.g. how altering the\nfrequency-dependent lags between bands can affect data products like\ncross-correlation functions); and (iii) To simulate existing data and\ninvestigate its trustworthiness. We outline the methodology behind CorrSim,\nshow how a variety of parameters (e.g. noise sources, observation length, and\ntelescope choice) can affect data, and present examples of the software in\naction.", + "category": "astro-ph" + }, + { + "text": "Ground Calibration of Solar X-ray Monitor On-board Chandrayaan-2 Orbiter: Chandrayaan-2, the second Indian mission to the Moon, carries a spectrometer\ncalled the Solar X-ray Monitor (XSM) to perform soft X-ray spectral\nmeasurements of the Sun while a companion payload measures the fluorescence\nemission from the Moon. Together these two payloads will provide quantitative\nestimates of elemental abundances on the lunar surface. XSM is also expected to\nprovide significant contributions to the solar X-ray studies with its highest\ntime cadence and energy resolution spectral measurements. For this purpose, the\nXSM employs a Silicon Drift Detector and carries out energy measurements of\nincident photons in the 1 -- 15 keV range with a resolution of less than 180 eV\nat 5.9 keV, over a wide range of solar X-ray intensities. Extensive ground\ncalibration experiments have been carried out with the XSM using laboratory\nX-ray sources as well as X-ray beam-line facilities to determine the instrument\nresponse matrix parameters required for quantitative spectral analysis. This\nincludes measurements of gain, spectral redistribution function, and effective\narea, under various observing conditions. The capability of the XSM to maintain\nits spectral performance at high incident flux as well as the dead-time and\npile-up characteristics have also been investigated. The results of these\nground calibration experiments of the XSM payload are presented in this\narticle.", + "category": "astro-ph" + }, + { + "text": "An \"Ultrasonic Image\" of the Embryonic Universe: CMB Polarization Tests\n of the Inflationary Paradigm: This chapter describes how the Cosmic Gravitational Wave Background induces a\nspecific type of CMB polarization and describes the first experiment dedicated\nto testing this most-promising signature of inflation. This experiment, the\nBackground Imaging of Cosmic Extragalactic Polarization (BICEP) project, has\nrecently embarked on its third observing season. We show preliminary data from\nthe BICEP's first season obtained with a novel polarization modulation\nmechanism called the \"Faraday Rotation Modulator\". Our discussion ends with a\ndescription of exciting new technology with the potential to probe inflation\ndown to the GUT-scale.", + "category": "astro-ph" + }, + { + "text": "Thermal instabilities in cooling galactic coronae: fuelling star\n formation in galactic discs: We investigate the means by which cold gas can accrete onto Milky Way mass\ngalaxies from a hot corona of gas, using a new smoothed particle hydrodynamics\ncode, 'SPHS'. We find that the 'cold clumps' seen in many classic SPH\nsimulations in the literature are not present in our SPHS simulations. Instead,\ncold gas condenses from the halo along filaments that form at the intersection\nof supernovae-driven bubbles from previous phases of star formation. This\npositive feedback feeds cold gas to the galactic disc directly, fuelling\nfurther star formation. The resulting galaxies in the SPH and SPHS simulations\ndiffer greatly in their morphology, gas phase diagrams, and stellar content. We\nshow that the classic SPH cold clumps owe to a numerical thermal instability\ncaused by an inability for cold gas to mix in the hot halo. The improved\ntreatment of mixing in SPHS suppresses this instability leading to a\ndramatically different physical outcome. In our highest resolution SPHS\nsimulation, we find that the cold filaments break up into bound clumps that\nform stars. The filaments are overdense by a factor of 10-100 compared to the\nsurrounding gas, suggesting that the fragmentation results from a physical\nnon-linear instability driven by the overdensity. This 'fragmenting filament'\nmode of disc growth has important implications for galaxy formation, in\nparticular the role of star formation in bringing cold gas into disc galaxies.", + "category": "astro-ph" + }, + { + "text": "Soft X-ray in-flight calibration of the ROSAT PSPC: We present an in-flight calibration of the ROSAT PSPC using the incident\nspectra of the hot white dwarf HZ43 and the polar AM Her. We derive an absolute\nflux calibration of the PSPC using the accurately known soft X-ray spectrum of\nHZ43. Corrections to the PSPC response matrix are derived from a comparison of\npredicted and observed PSPC spectra of HZ43, supplemented by results for AM\nHer. The calibration of the PSPC for photon energies E < 0.28 keV is found to\nbe accurate to better than 5% refuting earlier reports of a major\nmiscalibration. Our corrections to the detector response matrices remove\nsystematic residuals in the pulse height spectra of soft sources.", + "category": "astro-ph" + }, + { + "text": "Detection of Potential Transit Signals in 17 Quarters of Kepler Data:\n Results of the Final Kepler Mission Transiting Planet Search (DR25): We present results of the final Kepler Data Processing Pipeline search for\ntransiting planet signals in the full 17-quarter primary mission data set. The\nsearch includes a total of 198,709 stellar targets, of which 112,046 were\nobserved in all 17 quarters and 86,663 in fewer than 17 quarters. We report on\n17,230 targets for which at least one transit signature is identified that\nmeets the specified detection criteria: periodicity, minimum of three observed\ntransit events, detection statistic (i.e., signal-to-noise ratio) in excess of\nthe search threshold, and passing grade on three statistical transit\nconsistency tests. Light curves for which a transit signal is identified are\niteratively searched for additional signatures after a limb-darkened transiting\nplanet model is fitted to the data and transit events are removed. The search\nfor additional planets adds 16,802 transit signals for a total of 34,032; this\nfar exceeds the number of transit signatures identified in prior pipeline runs.\nThere was a strategic emphasis on completeness over reliability for the final\nKepler transit search. A comparison of the transit signals against a set of\n3402 well-established, high-quality Kepler Objects of Interest yields a\nrecovery rate of 99.8%. The high recovery rate must be weighed against a large\nnumber of false-alarm detections. We examine characteristics of the planet\npopulation implied by the transiting planet model fits with an emphasis on\ndetections that would represent small planets orbiting in the habitable zone of\ntheir host stars.", + "category": "astro-ph" + }, + { + "text": "GRB 091127: The cooling break race on magnetic fuel: Using high-quality, broad-band afterglow data for GRB 091127, we investigate\nthe validity of the synchrotron fireball model for gamma-ray bursts, and infer\nphysical parameters of the ultra-relativistic outflow. We used multi-wavelength\nfollow-up observations obtained with GROND and the XRT onboard the Swift\nsatellite. The resulting afterglow light curve is of excellent accuracy, and\nthe spectral energy distribution is well-sampled over 5 decades in energy.\nThese data present one of the most comprehensive observing campaigns for a\nsingle GRB afterglow and allow us to test several proposed emission models and\noutflow characteristics in unprecedented detail. Both the multi-color light\ncurve and the broad-band SED of the afterglow of GRB 091127 show evidence of a\ncooling break moving from high to lower energies. The early light curve is well\ndescribed by a broken power-law, where the initial decay in the optical/NIR\nwavelength range is considerably flatter than at X-rays. Detailed fitting of\nthe time-resolved SED shows that the break is very smooth with a sharpness\nindex of 2.2 +- 0.2, and evolves towards lower frequencies as a power-law with\nindex -1.23 +- 0.06. These are the first accurate and contemporaneous\nmeasurements of both the sharpness of the spectral break and its time\nevolution. The measured evolution of the cooling break (nu_c propto t^-1.2) is\nnot consistent with the predictions of the standard model, wherein nu_c propto\nt^-0.5 is expected. A possible explanation for the observed behavior is a time\ndependence of the microphysical parameters, in particular the fraction of the\ntotal energy in the magnetic field epsilon_B. This conclusion provides further\nevidence that the standard fireball model is too simplistic, and time-dependent\nmicro-physical parameters may be required to model the growing number of\nwell-sampled afterglow light curves.", + "category": "astro-ph" + }, + { + "text": "VLT K-band spectroscopy of massive stars deeply embedded in IRAS sources\n with UCHII colours: We have obtained high resolution (R = 10,000) K-band spectra of candidate\nyoung massive stars deeply embedded in (ultra-) compact HII regions (UCHIIs).\nIn these clusters, three types of objects are identified. The first type (38\nobjects) consists of ``naked'' OB stars whose K-band spectra are dominated by\nphotospheric emission. We classify the K-band spectra of the OB-type cluster\nmembers using near-infrared classification criteria. The spectral\nclassification provides an important constraint on the distance to the embedded\ncluster. The ionising power of the population thus derived is compared to the\ninformation obtained from the infrared and radio flux of these sources. In most\ncases these two different determinations of the ionising flux are consistent,\nfrom which we conclude that we have identified the ionising star(s) in about\n50% of the embedded clusters. The second type (7 objects) are point sources\nassociated with UCHII radio emission, that exhibit nebular emission lines in\nthe near-infrared. Six of the objects in this group produce HeI emission\nindicative of an embedded O-type star. These objects are more embedded than the\nOB stars and probably do not dominate the infrared flux as measured by IRAS.\nThe third type (20 objects) is characterised by broad (100--200 km/s) Brgamma\nemission and no photospheric absorption profiles. Bik et al (2005) show that\nthese objects are massive YSO candidates surrounded by dense circumstellar\ndisks.", + "category": "astro-ph" + }, + { + "text": "The Host Galaxies of Fast-Ejecta Core-Collapse Supernovae: Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN\nobserved at the locations of long-duration gamma-ray bursts (LGRBs), exhibit\nwide features indicative of high ejecta velocities (~0.1c). We study the host\ngalaxies of a sample of 245 low-redshift (z<0.2) core-collapse SN, including 17\nSN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous\nand dust-obscured z<1.2 LGRBs. We show that, in comparison with SDSS galaxies\nhaving similar stellar masses, the hosts of low-redshift SN Ic-BL and z<1.2\nLGRBs have high stellar-mass and star-formation-rate densities. Core-collapse\nSN having typical ejecta velocities, in contrast, show no preference for such\ngalaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN\nIb/Ic and SN II, exhibit high gas velocity dispersions for their stellar\nmasses. The patterns likely reflect variations among star-forming environments,\nand suggest that LGRBs can be used as probes of conditions in high-redshift\ngalaxies. They may be caused by efficient formation of massive binary\nprogenitors systems in densely star-forming regions, or, less probably, a\nhigher fraction of stars created with the initial masses required for a SN\nIc-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for\ngalaxies with high stellar-mass and star-formation-rate densities cannot be\nattributed to a preference for low metal abundances but must reflect the\ninfluence of a separate environmental factor.", + "category": "astro-ph" + }, + { + "text": "A Radio Nebula Surrounding the Ultra-luminous X-ray Source in NGC 5408: New radio observations of the counterpart of the ultraluminous X-ray source\nin NGC 5408 show for the first time that the radio emission is resolved with an\nangular size of 1.5 to 2.0 arcseconds. This corresponds to a physical size of\n35-46 pc, and rules out interpretation of the radio emission as beamed emission\nfrom a relativistic jet. In addition, the radio spectral index of the\ncounterpart is well determined from three frequencies and found to be\nalpha=-0.8 pm 0.2. The radio emission is likely to be optically-thin\nsynchrotron emission from a nebula surrounding the X-ray source. The radio\nluminosity of the counterpart is 3.8 x 10^34 erg/s and the minimum energy\nrequired to power the nebula is ~1 x 10^49 erg. These values are two orders of\nmagnitude larger than in any Galactic nebula powered by an accreting compact\nobject.", + "category": "astro-ph" + }, + { + "text": "The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic\n Giant Branch Bump, and Horizontal Branch Red Clump: Color-magnitude diagrams of globular clusters often exhibit a prominent\nhorizontal branch (HB) and may also show features such as the red giant branch\n(RGB) bump and the asymptotic giant branch (AGB) bump. Stellar evolution theory\npredicts that the luminosities of these features will depend on the metallicity\nand age of the cluster. We calculate theoretical lines of 2 to 12 Gyr constant\nage RGB-bumps and AGB-bumps in the V(HB-Bump)--[Fe/H] diagram, which shows the\nbrightness difference between the bump and the HB as a function of metallicity.\nIn order to test the predictions, we identify giant branch bumps in new Hubble\nSpace Telescope color-magnitude diagrams for 8 SMC clusters. First, we conclude\nthat the SMC cluster bumps are RGB-bumps. The data for clusters younger than ~6\nGyr are in fair agreement the relative age dependent luminosities of the HB and\nRGB-bump. The V(HB-Bump)--[Fe/H] data for clusters older then ~6 Gyr\ndemonstrate a less satisfactory agreement with our calculations. We conclude\nthat ~6 Gyr is a lower bound to the age of clusters for which the Galactic\nglobular cluster, age independent V(HB-Bump)--[Fe/H] calibration is valid.\nApplication of the V(HB-bump)--[Fe/H] diagram to stellar population studies is\ndiscussed.", + "category": "astro-ph" + }, + { + "text": "Optical observations of NEA 162173 (1999 JU3) during the 2011-2012\n apparition: Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid\nsample return missions, not only because of its accessibility but also because\nof the first C-type asteroid for exploration missions. The lightcurve-related\nphysical properties of this object were investigated during the 2011-2012\napparition. We aim to confirm the physical parameters useful for JAXA's\nHayabusa 2 mission, such as rotational period, absolute magnitude, and phase\nfunction. Our data complement previous studies that did not cover low phase\nangles. With optical imagers and 1-2 m class telescopes, we acquired the\nphotometric data at different phase angles. We independently derived the\nrotational lightcurve and the phase curve of the asteroid. We have analyzed the\nlightcurve of 162173 (1999 JU3), and derived a synodic rotational period of\n7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =\n18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained\nbased on the observations made during the 2011-2012 apparition.", + "category": "astro-ph" + }, + { + "text": "On the mean field dynamo with Hall effect: We study in the present paper how Hall effect modifies the quenching process\nof the electromotive force (e.m.f.) in Mean Field Dynamo (MFD) theories. We\nwrite down the evolution equations for the e.m.f. and for the large and small\nscale magnetic helicity, treat Hall effect as a perturbation and integrate the\nresulting equations assuming boundary conditions such that the total\ndivergencies vanish. For force-free large scale magnetic fields, Hall effect\nacts by coupling the small scale velocity and magnetic fields. For the range of\nparameters considered, the overall effect is a stronger quenching of the e.m.f.\nthan in standard MHD and a damping of the inverse cascade of magnetic helicity.\nIn astrophysical environments characterized by the parameters considered here,\nHall effect would produce an earlier quenching of the e.m.f. and consequently a\nweaker large scale magnetic field.", + "category": "astro-ph" + }, + { + "text": "Ultraviolet HST Observations of the Jet in M87: We present new ultraviolet photometry of the jet in M87 obtained from HST\nWFPC2 imaging. We combine these ultraviolet data with previously published\nphotometry for the knots of the jet in radio, optical, and X-ray, and fit three\ntheoretical synchrotron models to the full data set. The synchrotron models\nconsistently overpredict the flux in the ultraviolet when fit over the entire\ndataset. We show that if the fit is restricted to the radio through ultraviolet\ndata, the synchrotron models can provide a good match to the data. The break\nfrequencies of these fits are much lower than previous estimates. The implied\nsynchrotron lifetimes for the bulk of the emitting population are longer than\nearlier work, but still much shorter than the estimated kinematic lifetimes of\nthe knots. The observed X-ray flux cannot be successfully explained by the\nsimple synchrotron models that fit the ultraviolet and optical fluxes. We\ndiscuss the possible implications of these results for the physical properties\nof the M87 jet. We also observe increased flux for the HST-1 knot that is\nconsistent with previous results for flaring. This observation fills in a\nsignificant gap in the time coverage early in the history of the flare, and\ntherefore sets constraints on the initial brightening of the flare.", + "category": "astro-ph" + }, + { + "text": "Parametrized modified gravity constraints after Planck: We constrain $f(R)$ and chameleon-type modified gravity in the framework of\nthe Berstchinger-Zukin parametrization using the recent released Planck data,\nincluding both CMB temperature power spectrum and lensing potential power\nspectrum. Some other external data sets are included, such as BAO measurements\nfrom the 6dFGS, SDSS DR7 and BOSS DR9 surveys, HST $H_0$ measurement and\nsupernovae from Union2.1 compilation. We also use WMAP9yr data for consistency\ncheck and comparison. For $f(R)$ gravity, WMAP9yr results can only give quite a\nloose constraint on the modified gravity parameter $B_0$, which is related to\nthe present value of the Compton wavelength of the extra scalar degree of\nfreedom, $B_0<3.37$ at $95\\% {\\rm C.L.}$ We demonstrate that this constraint\nmainly comes from the late ISW effect. With only Planck CMB temperature\npower-spectrum data, we can improve the WMAP9yr result by a factor $3.7$\n($B_0<0.91$ at $95\\% {\\rm C.L.}$). If the Planck lensing potential\npower-spectrum data are also taken into account, the constraint can be further\nstrenghtened by a factor $5.1$ ($B_0<0.18$ at $95\\% {\\rm C.L.}$). This major\nimprovement mainly comes from the small-scale lensing signal. Furthermore, BAO,\nHST and supernovae data could slightly improve the $B_0$ bound ($B_0<0.12$ at\n$95\\% {\\rm C.L.}$).For the chameleon-type model, we find that the data set\nwhich we used cannot constrain the Compton wavelength $B_0$ and the potential\nindex $s$ of chameleon field, but can give a tight constraint on the parameter\n$\\beta_1=1.043^{+0.163}_{-0.104}$ at $95\\% {\\rm C.L.}$ ($\\beta_1=1$ in general\nrelativity), which accounts for the non-minimal coupling between the chameleon\nfield and the matter component. In addition, we find that both modified gravity\nmodels we considered favor a relatively higher Hubble parameter than the\nconcordance LCDM model in general relativity.", + "category": "astro-ph" + }, + { + "text": "Hydrodynamics of Cloud Collisions in 2D: The Fate of Clouds in a\n Multi-phase Medium: We have studied head-on collisions between equal-mass, mildly supersonic\n(Mach number 1.5) HI clouds, in a standard Two-phase ISM (T_cl = 74 K, n_cl =\n22 cm^-3, \\chi = 100). We explore the role of various factors, including the\nradiative cooling parameter \\eta = t_rad/t_coll (t_coll=R_c/v_c), evolutionary\nmodifications on the cloud structure (by colliding clouds ``evolved'' through\nindependent motion within the intercloud medium (WIM)), and the symmetry of the\nproblem (by colliding initially identical clouds, evolved to different ages\nbefore impact). The presence of bow shocks and ram pressure from material in\nthe cloud wake, developed during such evolution through the WIM, significantly\nalters these interactions with respect to the standard case of non-evolved\nclouds.\n In general, in our adiabatic collisions the clouds are disrupted and convert\ntheir gas into a few low density contrast clumps. By contrast, for symmetric\nradiative cases we find that the two clouds coalesce, with almost all the\ninitial kinetic energy radiated away. On the other hand, for both adiabatic and\nradiative collisions, asymmetric collisions have a much greater tendency to\ndisrupt the two clouds. Fragmentation of the clouds may occur, and\ninstabilities are in general enhanced. In addition, radiative cooling is less\nefficient in our asymmetric interactions, so that those parts of the clouds\nthat initially seem to merge are more likely to re-expand and fade into the\nWIM. Since the majority of real cloud collisions should be asymmetric for one\nreason or another, we conclude that most gasdynamical diffuse cloud collisions\nwill be disruptive, at least in the absence of significant self-gravity or of a\nsignificant magnetic field.", + "category": "astro-ph" + }, + { + "text": "A multi-wavelength analysis of Spitzer selected Coma Cluster galaxies:\n star formation rates and masses: We present a thorough study of the specific star formation rates for MIPS\n24um selected galaxies in the Coma cluster. We build galaxy spectral energy\ndistributions using optical (u',g',r',i',z'), Near-infrared (J,H,Ks), and Mid\nto Far-infrared (IRAC and MIPS) photometry. New and archival spectra confirm\n210 cluster members. Subsequently, the total infrared luminosity, galaxy\nstellar mass, and specific star formation rate for the members are determined\nby measuring best fit templates. Using an array of complementary diagnostics,\nwe search for contaminating AGN, but find few. We compare obscured star\nformation rates to unobscured rates derived from extinction-corrected H-alpha\nemission line measurements. The agreement between these two values leads us to\nconclude that there is no evidence for an additionally obscured component. In\nour spectroscopic sample, complete to 80% for r' < 19.5, we find that all\nstarbursts are blue and are dwarfs, having masses < 10^9 solar masses.\nExamining the location of these starbursts within the cluster, we confirm that\nthere is a lower fraction in the cluster core.", + "category": "astro-ph" + }, + { + "text": "The extreme initial kinetic energy allowed by a collapsing turbulent\n core: We present high-resolution hydrodynamical simulations aimed at following the\ngravitational collapse of a gas core, in which a turbulent spectrum of velocity\nis implemented only initially. We determine the maximal value of the ratio of\nkinetic energy to gravitational energy, denoted here by $\\left(\\frac{E_{\\rm\nkin} }{E_{\\rm grav}}\\right)_{\\rm max}$, so that the core (i) will collapse\naround one free-fall time of time evolution or (ii) will expand unboundedly,\nbecause it has a value of $\\frac{E_{\\rm kin}}{E_{\\rm grav}}$ larger than\n$\\left( \\frac{E_{\\rm kin}}{E_{\\rm grav}}\\right)_{\\rm max}$. We consider core\nmodels with a uniform or centrally condensed density profile and with velocity\nspectra composed of a linear combination of one-half divergence-free turbulence\ntype and the other half of a curl-free turbulence type. We show that the\noutcome of the core collapse are protostars forming either (i) a multiple\nsystem obtained from the fragmentation of filaments and (ii) a single primary\nsystem within a long filament. In addition, some properties of these protostars\nare also determined and compared with those obtained elsewhere.", + "category": "astro-ph" + }, + { + "text": "A Gaia astrometric view of the open clusters Pleiades, Praesepe and\n Blanco 1: Context. Near open clusters as Pleiades, Praesepe and Blanco 1 have been\nextensively studied due to their proximity to the Sun. The Gaia data brings the\nopportunity to investigate these clusters, since it contains valuable\nastrometric and photometric information which can be used to update their\nkinematic and stellar properties. Aims. Our goal is to carry out a star\nmembership study in these nearby open clusters employing an astrometric model\nwith proper motions and an unsupervised clustering machine learning algorithm\nusing positions, proper motions and parallaxes. The star members are selected\nfrom the cross-matching between both methods. Methods. We use the Gaia DR3\ncatalogue to determine star members using two approaches: a classical Bayesian\nmodel and the unsupervised machine learning algorithm DBSCAN. For star members\nwe build the radial density profiles, the spatial distributions and compute the\nKing parameters. The ages and metallicities were estimated using the BASE-9\nBayesian software. Results. We identified 958, 744 and 488 star members for the\nPleiades, Praesepe and Blanco 1 respectively. We corrected the distances and\nbuilt the spatial distributions, finding that Praesepe and Blanco 1 have\nelongated shape structures. The distances, ages and metallicities obtained were\nconsistent with the reported in the literature. Conclusions. We obtained\ncatalogues of star members, updated kinematic and stellar parameters for these\nopen clusters. We found that the proper motions model can find a similar number\nof members as the unsupervised clustering algorithm does when the cluster\npopulation form an overdensity in the vector point diagram. It allows to select\nan adequate size of the proper motions region to run these methods. Our\nanalysis found stars that are being directed towards the outskirts of the\nPraesepe and Blanco 1, which exhibit elongated shapes.", + "category": "astro-ph" + }, + { + "text": "Coronagraphic observations of Si X 1430 nm acquired by DKIST/Cryo-NIRSP\n with methods for telluric absorption correction: We report commissioning observations of the Si X 1430 nm solar coronal line\nobserved coronagraphically with the Cryogenic Near-Infrared Spectropolarimeter\n(Cryo-NIRSP) at the National Science Foundation's Daniel K. Inouye Solar\nTelescope (DKIST). These are the first known spatially resolved observations of\nthis spectral line, which has strong potential as a coronal magnetic field\ndiagnostic. The observations target a complex active region located on the\nsolar northeast limb on 4 March 2022. We present a first analysis of this data,\nwhich extracts the spectral line properties through a careful treatment of the\nvariable atmospheric transmission that is known to impact this spectral window.\nRastered images are created and compared with EUV observations from the SDO/AIA\ninstrument. A method for estimating the electron density from the Si X\nobservations is then demonstrated that makes use of the forbidden line's\ndensity-sensitive emissivity and an emission-measure analysis of the SDO/AIA\nbandpass observations. In addition, we derive an effective temperature and\nnon-thermal line width across the region. This study informs the calibration\napproaches required for more routine observations of this promising diagnostic\nline.", + "category": "astro-ph" + }, + { + "text": "Foreground Mismodeling and the Point Source Explanation of the Fermi\n Galactic Center Excess: The Fermi Large Area Telescope has observed an excess of ~GeV energy gamma\nrays from the center of the Milky Way, which may arise from near-thermal dark\nmatter annihilation. Firmly establishing the dark matter origin for this excess\nis however complicated by challenges in modeling diffuse cosmic-ray foregrounds\nas well as unresolved astrophysical sources, such as millisecond pulsars.\nNon-Poissonian Template Fitting (NPTF) is one statistical technique that has\npreviously been used to show that at least some fraction of the GeV excess is\nlikely due to a population of dim point sources. These results were recently\ncalled into question by Leane and Slatyer (2019), who showed that a synthetic\ndark matter annihilation signal injected on top of the real Fermi data is not\nrecovered by the NPTF procedure. In this work, we perform a dedicated study of\nthe Fermi data and explicitly show that the central result of Leane and Slatyer\n(2019) is likely driven by the fact that their choice of model for the Galactic\nforeground emission does not provide a sufficiently good description of the\ndata. We repeat the NPTF analyses using a state-of-the-art model for diffuse\ngamma-ray emission in the Milky Way and introduce a novel statistical\nprocedure, based on spherical-harmonic marginalization, to provide an improved\ndescription of the Galactic diffuse emission in a data-driven fashion. With\nthese improvements, we find that the NPTF results continue to robustly favor\nthe interpretation that the Galactic Center excess is due, in part, to\nunresolved astrophysical point sources across the analysis variations that we\nhave explored.", + "category": "astro-ph" + }, + { + "text": "Discovery of low-metallicity stars in the central parsec of the Milky\n Way: We present a metallicity analysis of 83 late-type giants within the central 1\npc of the Milky Way. K-band spectroscopy of these stars were obtained with the\nmedium-spectral resolution integral-field spectrograph NIFS on Gemini North\nusing laser-guide star adaptive optics. Using spectral template fitting with\nthe MARCS synthetic spectral grid, we find that there is large variation in\nmetallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity.\nAbout 6\\% of the stars have [M/H] $<$ -0.5. This result is in contrast to\nprevious observations, with smaller samples, that show stars at the Galactic\ncenter have approximately solar metallicity with only small variations. Our\ncurrent measurement uncertainties are dominated by systematics in the model,\nespecially at [M/H] $>$ 0, where there are stellar lines not represented in the\nmodel. However, the conclusion that there are low metallicity stars, as well as\nlarge variations in metallicity is robust. The metallicity may be an indicator\nof the origin of these stars. The low-metallicity population is consistent with\nthat of globular clusters in the Milky Way, but their small fraction likely\nmeans that globular cluster infall is not the dominant mechanism for forming\nthe Milky Way nuclear star cluster. The majority of stars are at or above solar\nmetallicity, which suggests they were formed closer to the Galactic center or\nfrom the disk. In addition, our results indicate that it will be important for\nstar formation history analyses using red giants at the Galactic center to\nconsider the effect of varying metallicity.", + "category": "astro-ph" + }, + { + "text": "Radio and Gamma-Ray Constraints on the Emission Geometry and Birthplace\n of PSR J2043+2740: We report on the first year of Fermi gamma-ray observations of pulsed\nhigh-energy emission from the old PSR J2043+2740. The study of the gamma-ray\nefficiency of such old pulsars gives us an insight into the evolution of\npulsars' ability to emit in gammma rays as they age. The gamma-ray lightcurve\nof this pulsar above 0.1 GeV is clearly defined by two sharp peaks,\n0.353+/-0.035 periods apart. We have combined the gamma-ray profile\ncharacteristics of PSR J2043+2740 with the geometrical properties of the\npulsar's radio emission, derived from radio polarization data, and constrained\nthe pulsar-beam geometry in the framework of a Two Pole Caustic and an Outer\nGap model. The ranges of magnetic inclination and viewing angle were determined\nto be {alpha,zeta}~{52-57,61-68} for the Two Pole Caustic model, and\n{alpha,zeta}~{62-73,74-81} and {alpha,zeta}~{72-83,60-75} for the Outer Gap\nmodel. Based on this geometry, we assess possible birth locations for this\npulsar and derive a likely proper motion, sufficiently high to be measurable\nwith VLBI. At a characteristic age of 1.2 Myr, PSR J2043+2740 is the third\noldest of all discovered, non-recycled, gamma-ray pulsars: it is twice as old\nas the next oldest, PSR J0357+32, and younger only than the recently discovered\nPSR J1836+5925 and PSR J2055+25, both of which are at least 5 and 10 times less\nenergetic, respectively.", + "category": "astro-ph" + }, + { + "text": "Constraining Ultralight Axions with Galaxy Surveys: Ultralight axions and other bosons are dark matter candidates present in many\nhigh energy physics theories beyond the Standard Model. In particular, the\nstring axiverse postulates the existence of up to $\\mathcal{O}(100)$ light\nscalar bosons constituting the dark sector. Considering a mixture of axions and\ncold dark matter, we obtain upper bounds for the axion relic density $\\Omega_a\nh^2 < 0.004$ for axions of mass $10^{-31}\\;\\mathrm{eV}\\leq m_a \\leq\n10^{-26}\\;\\mathrm{eV}$ at 95% confidence. We also improve existing constraints\nby a factor of over 4.5 and 2.1 for axion masses of $10^{-25}$ eV and\n$10^{-32}$ eV, respectively. We use the Fourier-space galaxy clustering\nstatistics from the Baryon Oscillation Spectroscopic Survey (BOSS) and\ndemonstrate how galaxy surveys break important degeneracies in the axion\nparameter space compared to the cosmic microwave background (CMB). We test the\nvalidity of the effective field theory of large-scale structure approach to\nmixed ultralight axion dark matter by making our own mock galaxy catalogs and\nfind an anisotropic ultralight axion signature in the galaxy quadrupole. We\nalso observe an enhancement of the linear galaxy bias from 1.8 to 2.4 when\nallowing for 5% of the dark matter to be composed of a $10^{-28}$ eV axion in\nour simulations. Finally, we develop an augmented interpolation scheme allowing\na fast computation of the axion contribution to the linear matter power\nspectrum leading to a 70% reduction of the computational cost for the full\nMonte Carlo Markov chains analysis.", + "category": "astro-ph" + }, + { + "text": "NGC5719/13: interacting spirals forming a counter-rotating stellar disc: (Context) When a galaxy acquires material from the outside, it is likely that\nthe resulting angular momentum of the accreted material is decoupled from that\nof the pre-existing galaxy. The presence of stars counter-rotating with respect\nto other stars and/or gas represents an extreme case of decoupling. (Aims)\nNGC5719, an almost edge-on Sab galaxy with a prominent skewed dust lane, shows\na spectacular on-going interaction with its face-on Sbc companion NGC5713.\nObservations of such interacting systems provide insight into the processes at\nwork in assembling and reshaping galaxies. (Methods) Studies were made of the\ndistribution and kinematics of neutral hydrogen in the NGC5719/13 galaxy pair\nand the ionised gas and stellar kinematics along the major axis of NGC5719.\n(Results) Two HI tidal bridges that loop around NGC5719 and connect to NGC5713,\nand two HI tidal tails departing westward from NGC5713 were detected. There is\na correspondence between the HI condensations and the location of clumps of\nyoung stars within and outside the disc of NGC5719. The low-mass satellite\nPGC135857 at the tip of the northern tail was detected in HI, and is likely a\nby-product of the interaction. The neutral and ionised hydrogen in the disc of\nNGC5719 are counter-rotating with respect to the main stellar disc. The\ncounter-rotating stellar disc contains about 20% of the stars in the system,\nand has the same radial extension as the main stellar disc. This is the first\ninteracting system in which a counter-rotating stellar disc has been detected.\n(Conclusions) The data support a scenario where HI from the large reservoir\navailable in the galaxy's surroundings was accreted by NGC5719 onto a\nretrograde orbit and subsequently fuelled the in-situ formation of the\ncounter-rotating stellar disc.", + "category": "astro-ph" + }, + { + "text": "Proposal: The Neural Network Telescope: A neural network mechanism that can compensate for poor optical quality was\nrecently discovered in a biological context. We propose that this mechanism can\nand should be adopted for astronomical purposes. This would shift emphasis away\nfrom the quality of the optical equipment to information processing, hence\nshould decrease the cost and make larger instruments feasible.", + "category": "astro-ph" + }, + { + "text": "A 2-hr binary period for the black hole transient MAXI J0637-430: We revisit various sets of published results from X-ray and optical studies\nof the Galactic black hole (BH) candidate MAXI J0637-430, which went into\noutburst in 2019. Combining the previously reported values of peak outburst\nluminosity, best-fitting radii of inner and outer accretion disk, viewing\nangle, exponential decay timescale and peak-to-peak separation of the He II\n4686 disk emission line, we improve the constraints on the system parameters.\nWe estimate a heliocentric distance d = (8.7 +/- 2.3) kpc, a projected\nGalactocentric distance R = (13.2 +/- 1.8) kpc and a height |z| = (3.1 +/- 0.8)\nkpc from the Galactic plane. It is the currently known Milky Way BH candidate\nlocated farthest from the Galactic Centre. We infer a BH mass M_1 = (5.1 +/-\n1.6) M_{sun}, a spin parameter a* <~ 0.25, a donor star mass M_2 = (0.25 +/-\n0.07) M_{sun}, a peak Eddington ratio lambda = 0.17 +/- 0.11 and a binary\nperiod P_{orb} = 2.2^{+0.8}_{-0.6} hr. This is the shortest period measured or\nestimated so far for any Galactic BH X-ray binary. If the donor star is a\nmain-sequence dwarf, such a period corresponds to the evolutionary stage where\norbital shrinking is driven by gravitational radiation and the star has\nregained contact with its Roche lobe (low end of the period gap). The three\nGalactic BHs with the shortest period (<~3 hr) are also those with the highest\nvertical distance from the Galactic plane (>~2 kpc). This is probably because\nbinaries with higher binding energies can survive faster natal kicks.", + "category": "astro-ph" + }, + { + "text": "Quadratic genetic modifications: a streamlined route to cosmological\n simulations with controlled merger history: Recent work has studied the interplay between a galaxy's history and its\nobservable properties using \"genetically modified\" cosmological zoom\nsimulations. The approach systematically generates alternative histories for a\nhalo, while keeping its cosmological environment fixed. Applications to date\naltered linear properties of the initial conditions such as the mean\noverdensity of specified regions; we extend the formulation to include\nquadratic features such as local variance, which determines the overall\nimportance of smooth accretion relative to mergers in a galaxy's history. We\nintroduce an efficient algorithm for this new class of modification and\ndemonstrate its ability to control the variance of a region in a\none-dimensional toy model. Outcomes of this work are two-fold: (i) a\nclarification of the formulation of genetic modifications and (ii) a proof of\nconcept for quadratic modifications leading the way to a forthcoming\nimplementation in cosmological simulations.", + "category": "astro-ph" + }, + { + "text": "GIARPS High-resolution Observations of T Tauri stars (GHOsT). IV.\n Accretion properties of the Taurus-Auriga young association: In the framework of the GIARPS@TNG High-resolution Observations of T Tauri\nstars (GHOsT) project, we study the accretion properties of 37 Classical T\nTauri Stars of the Taurus-Auriga star forming region (SFR) with the aim of\ncharacterizing their relation with the properties of the central star, of jets\nand disk winds, and of the global disk structure, in synergy with complementary\nALMA millimiter observations. We derive stellar parameters, optical veiling,\naccretion luminosity ($\\rm L_{acc}$) and mass accretion rate ($\\rm \\dot\nM_{acc}$) in a homogeneous and self-consistent way using high-resolution\nspectra acquired at the Telescopio Nazionale Galileo with the HARPS-N and GIANO\nspectrographs, and flux-calibrated based on contemporaneous low-resolution\nspectroscopic and photometric ancillary observations. The $\\rm L_{acc}$-$\\rm\nL_{\\star}$, $\\rm \\dot{M}_{acc}$-$\\rm M_{\\star}$ and $\\rm \\dot{M}_{acc}$-$\\rm\nM_{disk}$ relationships of the Taurus sample are provided and compared with\nthose of the coeval SFRs of Lupus and Chamaeleon I. Our results demonstrate the\npotential of contemporaneous optical and near-infrared high-resolution\nspectroscopy to simultaneously provide precise measurements of stellar and\naccretion/wind properties of young stars.", + "category": "astro-ph" + }, + { + "text": "Automated Lensing Learner: Automated Strong Lensing Identification with\n a Computer Vision Technique: Forthcoming surveys such as the Large Synoptic Survey Telescope (LSST) and\nEuclid necessitate automatic and efficient identification methods of strong\nlensing systems. We present a strong lensing identification approach that\nutilizes a feature extraction method from computer vision, the Histogram of\nOriented Gradients (HOG), to capture edge patterns of arcs. We train a\nsupervised classifier model on the HOG of mock strong galaxy-galaxy lens images\nsimilar to observations from the Hubble Space Telescope (HST) and LSST. We\nassess model performance with the area under the curve (AUC) of a Receiver\nOperating Characteristic (ROC) curve. Models trained on 10,000 lens and\nnon-lens containing images images exhibit an AUC of 0.975 for an HST-like\nsample, 0.625 for one exposure of LSST, and 0.809 for 10-year mock LSST\nobservations. Performance appears to continually improve with the training set\nsize. Models trained on fewer images perform better in absence of the lens\ngalaxy light. However, with larger training data sets, information from the\nlens galaxy actually improves model performance, indicating that HOG captures\nmuch of the morphological complexity of the arc finding problem. We test our\nclassifier on data from the Sloan Lens ACS Survey and find that small scale\nimage features reduces the efficiency of our trained model. However, these\npreliminary tests indicate that some parameterizations of HOG can compensate\nfor differences between observed mock data. One example best-case\nparameterization results in an AUC of 0.6 in the F814 filter image with other\nparameterization results equivalent to random performance.", + "category": "astro-ph" + }, + { + "text": "Of `Cocktail Parties' and Exoplanets: The characterisation of ever smaller and fainter extrasolar planets requires\nan intricate understanding of one's data and the analysis techniques used.\nCorrecting the raw data at the 10^-4 level of accuracy in flux is one of the\ncentral challenges. This can be difficult for instruments that do not feature a\ncalibration plan for such high precision measurements. Here, it is not always\nobvious how to de-correlate the data using auxiliary information of the\ninstrument and it becomes paramount to know how well one can disentangle\ninstrument systematics from one's data, given nothing but the data itself. We\npropose a non-parametric machine learning algorithm, based on the concept of\nindependent component analysis, to de-convolve the systematic noise and all\nnon-Gaussian signals from the desired astrophysical signal. Such a `blind'\nsignal de-mixing is commonly known as the `Cocktail Party problem' in\nsignal-processing. Given multiple simultaneous observations of the same\nexoplanetary eclipse, as in the case of spectrophotometry, we show that we can\noften disentangle systematic noise from the original light curve signal without\nthe use of any complementary information of the instrument. In this paper, we\nexplore these signal extraction techniques using simulated data and two data\nsets observed with the Hubble-NICMOS instrument. Another important application\nis the de-correlation of the exoplanetary signal from time-correlated stellar\nvariability. Using data obtained by the Kepler mission we show that the desired\nsignal can be de-convolved from the stellar noise using a single time series\nspanning several eclipse events. Such non-parametric techniques can provide\nimportant confirmations of the existent parametric corrections reported in the\nliterature, and their associated results. Additionally they can substantially\nimprove the precision exoplanetary light curve analysis in the future.", + "category": "astro-ph" + }, + { + "text": "Venus Observations at 40 and 90 GHz with CLASS: Using the Cosmology Large Angular Scale Surveyor, we measure the\ndisk-averaged absolute Venus brightness temperature to be 432.3 $\\pm$ 2.8 K and\n355.6 $\\pm$ 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz,\nrespectively. At both frequency bands, these are the most precise measurements\nto date. Furthermore, we observe no phase dependence of the measured\ntemperature in either band. Our measurements are consistent with a\nCO$_2$-dominant atmospheric model that includes trace amounts of additional\nabsorbers like SO$_2$ and H$_2$SO$_4$.", + "category": "astro-ph" + }, + { + "text": "A Kiloparsec-Scale Binary Active Galactic Nucleus Confirmed by the\n Expanded Very Large Array: We report the confirmation of a kpc-scale binary active galactic nucleus\n(AGN) with high-resolution radio images from the Expanded Very Large Array\n(EVLA). SDSS J150243.1+111557 is a double-peaked [O III] AGN at z = 0.39\nselected from the Sloan Digital Sky Survey. Our previous near-infrared adaptive\noptics imaging reveals two nuclei separated by 1.4\" (7.4 kpc), and our optical\nintegral-field spectroscopy suggests that they are a type-1--type-2 AGN pair.\nHowever, these data alone cannot rule out the single AGN scenario where the\nnarrow emission-line region associated with the secondary is photoionized by\nthe broad-line AGN in the primary. Our new EVLA images at 1.4, 5.0, and 8.5 GHz\nshow two steep-spectrum compact radio sources spatially coincident with the\noptical nuclei. The radio power of the type-2 AGN is an order-of-magnitude in\nexcess of star-forming galaxies with similar extinction-corrected [O II] 3727\nluminosities, indicating that the radio emission is powered by accretion.\nTherefore, SDSS J150243.1+111557 is one of the few confirmed kpc-scale binary\nAGN systems. Spectral-energy-distribution modeling shows that SDSS\nJ150243.1+111557 is a merger of two ~10^{11} M_sun galaxies. With both black\nhole masses around 10^8 Msun, the AGNs are accreting at ~10 times below the\nEddington limit.", + "category": "astro-ph" + }, + { + "text": "INTEGRAL and Swift observations of the Be X-ray binary 4U 1036-56 (RX\n J1037.5-5647) and its possible relation with gamma-ray transients: We present timing, spectral, and long-term temporal analysis of the high mass\nX-ray binary (HMXB) 4U 1036-56 using INTEGRAL and Swift observations. We show\nthat it is a weak hard X-ray source spending a major fraction of the time in\nquiescence, and only occasionally characterized by X-ray outbursts. The\noutburst activity we report here lasts several days, with a dynamic range\nspanned by the luminosity in quiescence and in outburst as high as ~30. We\nreport the detection of pulse period at 854.75+/-4.39 s during an outburst,\nwhich is consistent with previous measurements. Finally, we analyze the\npossibility of 4U 1036--56's association with the unidentified transient\ngamma-ray sources AGL J1037--5708 & GRO J1036--55, as prompted by its\npositional correlation.", + "category": "astro-ph" + }, + { + "text": "Are spectral and timing correlations similar in different spectral\n states in black hole X-ray binaries?: We study the outbursts of the black hole X-ray binaries MAXI J1659-152, SWIFT\nJ1753.5--0127 and GX 339-4 with the Swift X-ray Telescope. The bandpass of the\nX-ray Telescope has access to emission from both components of the accretion\nflow: the accretion disk and the corona/hot flow. This allows a correlated\nspectral and variability study, with variability from both components of the\naccretion flow. We present for the first time, a combined study of the\nevolution of spectral parameters (disk temperature and radius) and timing\nparameters (frequency and strength) of all power spectral components in\ndifferent spectral states. Comparison of the correlations in different spectral\nstates shows that the frequency and strength of the power spectral components\nexhibit dependencies on the disk temperature that are different in the\n(low-)hard and the hard-intermediate states; most of these correlations that\nare clearly observed in the hard-intermediate state (in MAXI J1659-152 and GX\n339-4) are not seen in the (low-)hard state (in GX 339-4 and SWIFT\nJ1753.5-0127). Also, the responses of the individual frequency components to\nchanges in the disk temperature are markedly different from one component to\nthe next. Hence, the spectral-timing evolution cannot be explained by a single\ncorrelation that spans both these spectral states. We discuss our findings in\nthe context of the existing models proposed to explain the origin of\nvariability.", + "category": "astro-ph" + }, + { + "text": "Progress on the SOXS transients chaser for the ESO-NTT: SOXS (Son Of X-Shooter) is a single object spectrograph offering a\nsimultaneous spectral coverage from U- to H-band, built by an international\nconsortium for the 3.58-m ESO New Technology Telescope at the La Silla\nObservatory. It is designed to observe all kind of transients and variable\nsources discovered by different surveys with a highly flexible schedule\nmaintained by the consortium, based on the Target of Opportunity concept. SOXS\nis going to be a fundamental spectroscopic partner for any kind of imaging\nsurvey, becoming one of the premier transient follow-up instruments in the\nSouthern hemisphere. This paper gives an updated status of the project, when\nthe instrument is in the advanced phase of integration and testing in Europe,\nprior to the activities in Chile.", + "category": "astro-ph" + }, + { + "text": "Modeling Strong Lenses from Wide-Field Ground-Based Observations in KiDS\n and GAMA: Despite the success of galaxy-scale strong gravitational lens studies with\nHubble-quality imaging, the number of well-studied strong lenses remains small.\nAs a result, robust comparisons of the lens models to theoretical predictions\nare difficult. This motivates our application of automated Bayesian lens\nmodeling methods to observations from public data releases of overlapping large\nground-based imaging and spectroscopic surveys: Kilo-Degree Survey (KiDS) and\nGalaxy and Mass Assembly (GAMA), respectively. We use the open-source lens\nmodeling software PyAutoLens to perform our analysis. We demonstrate the\nfeasibility of strong lens modeling with large-survey data at lower resolution\nas a complementary avenue to studies that utilize more time-consuming and\nexpensive observations of individual lenses at higher resolution. We discuss\nadvantages and challenges, with special consideration given to determining\nbackground source redshifts from single-aperture spectra and to disentangling\nforeground lens and background source light. High uncertainties in the best-fit\nparameters for the models due to the limits of optical resolution in\nground-based observatories and the small sample size can be improved with\nfuture study. We give broadly applicable recommendations for future efforts,\nand with proper application this approach could yield measurements in the\nquantities needed for robust statistical inference.", + "category": "astro-ph" + }, + { + "text": "Revisited Mass-Radius relations for exoplanets below 120 Earth masses: The masses and radii of exoplanets are fundamental quantities needed for\ntheir characterisation. Studying the different populations of exoplanets is\nimportant for understanding the demographics of the different planetary types,\nwhich can then be linked to planetary formation and evolution. We present an\nupdated exoplanet catalog based on reliable, robust and as much as possible\naccurate mass and radius measurements of transiting planets up to 120\n$M_{\\oplus}$. The resulting mass-radius (M-R) diagram shows two distinct\npopulations, corresponding to rocky and volatile-rich exoplanets which overlap\nin both mass and radius. The rocky exoplanet population shows a relatively\nsmall density variability and ends at mass of $\\sim25 M_{\\oplus}$, possibly\nindicating the maximum core mass that can be formed. We use the composition\nline of pure-water to separate the two populations, and infer two new empirical\nM-R relations based on this data: $ M = (0.9 \\pm 0.06) \\ R^{(3.45 \\pm 0.12)}$\nfor the rocky population, and $ M = (1.74 \\pm 0.38) \\ R^{(1.58 \\pm 0.10)}$ for\nthe volatile-rich population. While our results for the two regimes are in\nagreement with previous studies, the new M-R relations better match the\npopulation in the transition-region from rocky to volatile-rich exoplanets,\nwhich correspond to a mass range of 5-25 $M_{\\oplus}$ and a radius range of 2-3\n$R_{\\oplus}$.", + "category": "astro-ph" + }, + { + "text": "Validation of HD 183579b using archival radial velocities: a\n warm-neptune orbiting a bright solar analog: As exoplanetary science matures into its third decade, we are increasingly\noffered the possibility of pre existing, archival observations for newly\ndetected candidates. This is particularly poignant for the TESS mission, whose\nsurvey spans bright, nearby dwarf stars in both hemispheres, which are\nprecisely the types of sources targeted by previous radial velocity (RV)\nsurveys. On this basis, we investigated whether any of the TESS Objects of\nInterest (TOIs) coincided with such observations, from which we find 18 single\nplanet candidate systems. Of these, one exhibits an RV signature that has the\ncorrect period and phase matching the transiting planetary candidate with a\nfalse alarm probability of less than 1 percent. After further checks, we\nexploit this fact to validate HD 183579b (TOI-1055b). This planet is less than\n4 Earth Radii and has better than 33 percent planetary mass measurements, thus\nadvancing the TESS primary objective of finding 50 such worlds. We find that\nthis planet is amongst the most accessible small transiting planets for\natmospheric characterization. Our work highlights that the efforts to confirm\nand even precisely measure the masses of new transiting planet candidates need\nnot always depend on acquiring new observations - that in some instances these\ntasks can be completed with existing data.", + "category": "astro-ph" + }, + { + "text": "A new calculation of Earth-skimming very- and ultra-high energy tau\n neutrinos: Cosmic neutrinos above a PeV are produced either within astrophysical sources\nor when ultra-high energy cosmic rays interact in transit through the cosmic\nbackground radiation. Detection of these neutrinos will be essential for\nunderstanding cosmic ray acceleration, composition and source evolution. By\nusing the Earth as a tau neutrino converter for upward-going extensive air\nshowers from tau decays, balloon-borne and space-based instruments can take\nadvantage of a large volume and mass of the terrestrial neutrino target. The\ntheoretical inputs and uncertainties in determining the tau lepton exit\nprobabilities and their translation to detection acceptance will be discussed\nin the context of a new calculation we have performed. We quantify the\nexperimental detection capability based on our calculation, including using the\nProbe of Extreme Multi-Messenger Astrophysics (POEMMA) concept study response\nparameters for optical air Cherenkov detection. These case studies are used to\nillustrate the features and uncertainties in upward tau air shower detection.", + "category": "astro-ph" + }, + { + "text": "On the distribution of collisionless particles in local potential well: The distribution of collisionless particles with infinite motion in the\npresence of a local potential well is discussed. Such distribution is important\nfor interpretation of results of dark matter searches. The relationship\nn/v=const, where n and v are respectively number density and velocity of\nparticles, is derived for particles crossing a local potential well. The limits\nof application of this relationship are specified.", + "category": "astro-ph" + }, + { + "text": "Mauna Kea Sky Transparency from CFHT SkyProbe Data: Nighttime sky transparency statistics on Mauna Kea are reported based on data\nfrom the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the\nperiod beginning with the start of MegaCam wide-field optical imager operations\nin 2003, and continuing for almost three years. Skies were clear enough to\nobserve on 76% of those nights; attenuations were less than 0.2 magnitudes up\nto 60% of the time. An empirical model of cloud attenuation and duration is\npresented allowing us to further characterize the photometric conditions. This\nis a good fit tothe SkyProbe data, and indicates that Mauna Kea skies are truly\nphotometric (without cloud) an average of 56% of the time, with moderate\nseasonal variation. Continuous monitoring of transparency during the night is\nnecessary to overcome fluctuations in attenuation due to thin cloud.", + "category": "astro-ph" + }, + { + "text": "All-spherical telescope with extremely wide field of view: An all-spherical catadioptic telescope with the angular field of view of\nseveral tens of degrees in diameter and spherical focal surface is proposed for\nthe monitoring of large sky areas. We provide a few examples of such a system\nwith the apertures up to 800 mm and the field of view $30^\\circ$ and $40^\\circ$\nin diameter. The curvature of the focal surface is repaid by high performance\nof the telescope. In particular, the diameter of a circle, that includes 80% of\nenergy in the polychromatic image of a star, is in the range $1.4'' - 1.9''$\nacross the field of $30^\\circ$ size and $2.2'' - 2.9''$ for the field of\n$40^\\circ$ size. Some ways of working with curved focal surfaces are discussed.", + "category": "astro-ph" + }, + { + "text": "Roche tomography of cataclysmic variables - IV. Starspots and slingshot\n prominences on BV Cen: We present Roche tomograms of the G5-G8 IV/V secondary star in the\nlong-period cataclysmic variable BV Cen reconstructed from MIKE echelle data\ntaken on the Magellan Clay 6.5-m telescope. The tomograms show the presence of\na number of large, cool starspots on BV Cen for the first time. In particular,\nwe find a large high-latitude spot which is deflected from the rotational axis\nin the same direction as seen on the K3-K5 IV/V secondary star in the\ncataclysmic variable AE Aqr. BV Cen also shows a similar relative paucity of\nspots at latitudes between 40-50 degrees when compared with AE Aqr.\nFurthermore, we find evidence for an increased spot coverage around longitudes\nfacing the white dwarf which supports models invoking starspots at the L1 point\nto explain the low-states observed in some cataclysmic variables. In total, we\nestimate that some 25 per cent of the northern hemisphere of BV Cen is spotted.\n We also find evidence for a faint, narrow, transient emission line with\ncharacteristics reminiscent of the peculiar low-velocity emission features\nobserved in some outbursting dwarf novae. We interpret this feature as a\nslingshot prominence from the secondary star and derive a maximum source size\nof 75,000 km and a minimum altitude of 160,000 km above the orbital plane for\nthe prominence.\n The entropy landscape technique was applied to determine the system\nparameters of BV Cen. We find M_1 = 1.18 (+0.28 -0.16) Msolar, M_2 = 1.05\n(+0.23 -0.14) Msolar and an orbital inclination of i = 53 degrees +- 4 degrees\nat an optimal systemic velocity of \\gamma = -22.3 km s-1. Finally, we also\nreport on the previously unknown binarity of the G5IV star HD 220492.", + "category": "astro-ph" + }, + { + "text": "First Solar energetic particles measured on the Lunar far-side: On 2019 May 6, the Lunar Lander Neutron & Dosimetry (LND) Experiment on board\nthe Chang'E-4 on the far-side of the Moon detected its first small solar\nenergetic particle (SEP) event with proton energies up to 21MeV. Combined\nproton energy spectra are studied based on the LND, SOHO/EPHIN and ACE/EPAM\nmeasurements which show that LND could provide a complementary dataset from a\nspecial location on the Moon, contributing to our existing observations and\nunderstanding of space environment. Velocity dispersion analysis (VDA) has been\napplied to the impulsive electron event and weak proton enhancement and the\nresults demonstrate that electrons are released only 22 minutes after the flare\nonset and $\\sim$15 minutes after type II radio burst, while protons are\nreleased more than one hour after the electron release. The impulsive\nenhancement of the in-situ electrons and the derived early release time\nindicate a good magnetic connection between the source and Earth. However,\nstereoscopic remote-sensing observations from Earth and STA suggest that the\nSEPs are associated with an active region nearly 100$^\\circ$ away from the\nmagnetic footpoint of Earth. This suggests that the propagation of these SEPs\ncould not follow a nominal Parker spiral under the ballistic mapping model and\nthe release and propagation mechanism of electrons and protons are likely to\ndiffer significantly during this event.", + "category": "astro-ph" + }, + { + "text": "The Carnegie Supernova Project-I. Optical spectroscopy of\n stripped-envelope supernovae: We present 170 optical spectra of 35 low-redshift stripped-envelope\ncore-collapse supernovae observed by the Carnegie Supernova Project-I between\n2004 and 2009. The data extend from as early as -19 days (d) prior to the epoch\nof B-band maximum to +322 d, with the vast majority obtained during the\nso-called photospheric phase covering the weeks around peak luminosity. In\naddition to histogram plots characterizing the red-shift distribution, number\nof spectra per object, and the phase distribution of the sample, spectroscopic\nclassification is also provided following standard criteria. The CSP-I spectra\nare electronically available and a detailed analysis of the data set is\npresented in a companion paper being the fifth and final paper of the series", + "category": "astro-ph" + }, + { + "text": "Testing Hybrid Natural Inflation with BICEP2: We analyse Hybrid Natural Inflation in view of the recent results for the\ntensor index reported by BICEP2. We find that it predicts a large running of\nthe scalar spectrum which is potentially detectable by large scale structure\nand $21\\, \\mathrm{cm} $ observations. The running of the running is also\nrelatively large becoming close to $10^{-2}$. Along the way, we find general\nconsistency relations at which observables are subject if the slow-roll\napproximation is imposed. Failure to satisfy these equations by the values\nobtained for the observables in surveys would be a failure of the slow-roll\napproximation itself.", + "category": "astro-ph" + }, + { + "text": "On the Application of Wesenheit Function in Deriving Distance to\n Galactic Cepheids: In this work, we explore the possibility of using the Wesenheit function to\nderive individual distances to Galactic Cepheids, as the dispersion of the\nreddening free Wesenheit function is smaller than the optical period-luminosity\n(P-L) relation. When compared to the distances from various methods, the\naveraged differences between our results and published distances range from\n-0.061 to 0.009, suggesting that the Wesenheit function can be used to derive\nindividual Cepheid distances. We have also constructed Galactic P-L relations\nand selected Wesenheit functions based on the derived distances. A by-product\nfrom this work is the derivation of Large Magellanic Cloud distance modulus\nwhen calibrating the Wesenheit function. It is found to be 18.531 \\pm 0.043\nmag.", + "category": "astro-ph" + }, + { + "text": "A redshifted excess in the broad emission lines after the flare of the\n $\u03b3$-ray narrow-line Seyfert 1 PKS 2004-447: PKS 2004-447 is a narrow-line Seyfert 1 (NLS1) harbouring a relativistic jet\nwith gamma-ray emission. On 2019-10-25, the Fermi-Large Area Telescope captured\na $\\gamma$-ray flare from this source, offering a chance to study the\nbroad-line region (BLR) and jet during such violent events. This can provide\ninsights to the BLR structure and jet interactions, which are important for\nactive galactic nuclei and host galaxy coevolution. We report X-Shooter\nobservations of enhancements in the broad line components of Balmer, Paschen\nand He I lines seen only during the post-flare and vanishing 1.5 years after.\nThese features are biased redward up to $\\sim$250 km s$^{-1}$ and are narrower\nthan the pre-existing broad line profiles. This indicates a connection between\nthe relativistic jet and the BLR of a young AGN, and how $\\gamma$-ray\nproduction can lead to localised addition of broad emission lines.", + "category": "astro-ph" + }, + { + "text": "Directionality preservation of nuclear recoils in an emulsion detector\n for directional dark matter search: Nuclear emulsion is a well-known detector type proposed also for the\ndirectional detection of dark matter. In this paper, we study one of the most\nimportant properties of direction-sensitive detectors: the preservation by\nnuclear recoils of the direction of impinging dark matter particles. For\nnuclear emulsion detectors, it is the first detailed study where a realistic\nnuclear recoil energy distribution with all possible recoil atom types is\nexploited. Moreover, for the first time we study the granularity effect on the\nemulsion detector directional performance. As well as we compare nuclear\nemulsion with other directional detectors: in terms of direction preservation\nnuclear emulsion outperforms the other detectors for WIMP masses above 100\nGeV/c$^2$.", + "category": "astro-ph" + }, + { + "text": "Experimental study of an advanced concept of moderate-resolution\n holographic spectrographs: We present the results of an experimental study of an advanced\nmoderate-resolution spectrograph based on a cascade of narrow-band holographic\ngratings. The main goal of the project is to achieve a moderately high spectral\nresolutionwith R up to 5000 simultaneously in the 4300-6800 A visible spectral\nrange on a single standard CCD, together with an increased throughput. The\nexperimental study consisted of (1) resolution and image quality tests\nperformed using the solar spectrum; and (2) a total throughput test performed\nfor a number of wavelengths using a calibrated lab monochromator. The measured\nspectral resolving power reaches values over R>4000 while the experimental\nthroughput is as high as 55%, which is in good agreement with the modeling\nresults. Comparing the obtained characteristics of the spectrograph under\nconsideration with the best existing spectrographs, we conclude that the used\nconcept can be considered a very competitive and cheap alternative to the\nexisting spectrographs of the given class. We propose several astrophysical\napplications for the instrument and discuss the prospect of creating its\nfull-scale version.", + "category": "astro-ph" + }, + { + "text": "Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray\n variability and photoionization: The clumping of massive star winds is an established paradigm confirmed by\nmultiple lines of evidence and supported by stellar wind theory. The purpose of\nthis paper is to bridge the gap between detailed models of inhomogeneous\nstellar winds in single stars and the phenomenological description of donor\nwinds in supergiant high-mass X-ray binaries (HMXBs). We use results from\ntime-dependent hydrodynamical models of the instability in the line-driven wind\nof a massive supergiant star to derive the time-dependent accretion rate onto a\ncompact object in the Bondi-Hoyle-Lyttleton approximation. The strong density\nand velocity fluctuations in the wind result in strong variability of the\nsynthetic X-ray light curves. The model predicts a large scale X-ray\nvariability, up to eight orders of magnitude, on relatively short timescales.\nThe apparent lack of evidence for such strong variability in the observed HMXBs\nindicates that the details of accretion process act to reduce the variability\ndue to the stellar wind velocity and density jumps. We, also, study the\nabsorption of X-rays in the clumped stellar wind by means of a 2-D stochastic\nwind model and find that absorption of X-rays changes strongly at different\norbital phases. Furthermore, we address the photoionization in the clumped\nwind, and show that the degree of ionization is affected by the wind clumping.\nA correction factor for the photoionization parameter is derived. It is shown\nthat the photoionization parameter is reduced by a factor Xi compared to the\nsmooth wind models with the same mass-loss rate, where Xi is the wind\ninhomogeneity parameter. We conclude that wind clumping must also be taken into\naccount when comparing the observed and model spectra of the photoionized\nstellar wind.", + "category": "astro-ph" + }, + { + "text": "Hunting for wandering massive black holes: We investigate low-density accretion flows onto massive black holes (BHs)\nwith masses of $\\gtrsim 10^5~M_\\odot$ orbiting around in the outskirts of their\nhost galaxies, performing three-dimensional hydrodynamical simulations. Those\nwandering BHs are populated via ejection from the galactic nuclei through\nmulti-body BH interactions and gravitational wave recoils associated with\ngalaxy and BH coalescences. We find that when a wandering BH is fed with hot\nand diffuse plasma with density fluctuations, the mass accretion rate is\nlimited at $\\sim 10-20\\%$ of the canonical Bondi-Hoyle-Littleton rate owing to\na wide distribution of inflowing angular momentum. We further calculate\nradiation spectra from radiatively inefficient accretion flows onto the\nwandering BH using a semi-analytical two-temperature disk model and find that\nthe predicted spectra have a peak at the millimeter band, where the Atacama\nLarge Millimeter/submillimeter Array (ALMA) has the highest sensitivity and\nspatial resolution. Millimeter observations with ALMA and future facilities\nsuch as the next generation Very Large Array (ngVLA) will enable us to hunt for\na population of wandering BHs and push the detectable mass limit down to\n$M_\\bullet \\simeq 2\\times10^7~M_\\odot$ for massive nearby ellipticals, e.g.,\nM87, and $M_\\bullet \\simeq 10^5~M_\\odot$ for the Milky Way. This radiation\nspectral model, combined with numerical simulations, will be applied to give\nphysical interpretations of off-nuclear BHs detected in dwarf galaxies, which\nmay constrain BH seed formation scenarios.", + "category": "astro-ph" + }, + { + "text": "Carbon-enhanced stars with short orbital and spin periods: Many characteristics of dwarf carbon stars are broadly consistent with a\nbinary origin, including mass transfer from an evolved companion. While the\npopulation overall appears to have old-disc or halo kinematics, roughly\n2$\\,$per cent of these stars exhibit H$\\alpha$ emission, which in low-mass\nmain-sequence stars is generally associated with rotation and relative youth.\nIts presence in an older population therefore suggests either irradiation or\nspin-up. This study presents time-series analyses of photometric and\nradial-velocity data for seven dwarf carbon stars with H$\\alpha$ emission. All\nare shown to have photometric periods in the range 0.2--5.2$\\,$d, and orbital\nperiods of similar length, consistent with tidal synchronisation. It is\nhypothesised that dwarf carbon stars with emission lines are the result of\nclose-binary evolution, indicating that low-mass, metal-weak or metal-poor\nstars can accrete substantial material prior to entering a common-envelope\nphase.", + "category": "astro-ph" + }, + { + "text": "Constraints on dark matter particles from theory, galaxy observations\n and N-body simulations: Mass bounds on dark matter (DM) candidates are obtained for particles\ndecoupling in or out of equilibrium with {\\bf arbitrary} isotropic and\nhomogeneous distribution functions. A coarse grained Liouville invariant\nprimordial phase space density $ \\mathcal D $ is introduced. Combining its\nvalue with recent photometric and kinematic data on dwarf spheroidal satellite\ngalaxies in the Milky Way (dShps), the DM density today and $N$-body\nsimulations, yields upper and lower bounds on the mass, primordial phase space\ndensities and velocity dispersion of the DM candidates. The mass of the DM\nparticles is bound in the few keV range. If chemical freeze out occurs before\nthermal decoupling, light bosonic particles can Bose-condense. Such\nBose-Einstein {\\it condensate} is studied as a dark matter candidate. Depending\non the relation between the critical($T_c$)and decoupling($T_d$)temperatures, a\nBEC light relic could act as CDM but the decoupling scale must be {\\it higher}\nthan the electroweak scale. The condensate tightens the upper bound on the\nparticle's mass. Non-equilibrium scenarios that describe particle production\nand partial thermalization, sterile neutrinos produced out of equilibrium and\nother DM models are analyzed in detail obtaining bounds on their mass,\nprimordial phase space density and velocity dispersion. Light thermal relics\nwith $ m \\sim \\mathrm{few} \\mathrm{keV}$ and sterile neutrinos lead to a\nprimordial phase space density compatible with {\\bf cored} dShps and disfavor\ncusped satellites. Light Bose condensed DM candidates yield phase space\ndensities consistent with {\\bf cores} and if $ T_c\\gg T_d $ also with cusps.\nPhase space density bounds from N-body simulations suggest a potential tension\nfor WIMPS with $ m \\sim 100 \\mathrm{GeV},T_d \\sim 10 \\mathrm{MeV} $.", + "category": "astro-ph" + }, + { + "text": "Hidden high ionization lines in the low luminosity type II SN 2021gmj: We present comprehensive optical observations of SN~2021gmj, a type II\nsupernova (SN~II) discovered within a day of explosion by the Distance Less\nThan 40~Mpc (DLT40) survey. Follow up observations show that SN~2021gmj is a\nlow luminosity SN~II (LL~SN~II), with a peak magnitude $M_V = -15.45$ and Fe II\nvelocity of $\\sim 1800 \\ \\mathrm{km} \\ \\mathrm{s}^{-1}$ at 50 days past\nexplosion. Using the expanding photosphere method we derive a distance of\n$17.8^{+0.6}_{-0.4}$~Mpc. From the tail of the light-curve we obtain a\nradioactive nickel mass of $0.014 \\pm 0.001$ $\\mathrm{M}_{\\odot}$. The presence\nof circumstellar material (CSM) is suggested by the early light curve, early\nspectra and the presence of high velocity H$\\alpha$ in absorption. Analytical\nshock-cooling models of the early light curve cannot reproduce the fast rise,\nalso supporting the idea that the early emission is partially powered by the\ninteraction of the SN ejecta and CSM. The inferred low CSM mass of 0.025\n$\\mathrm{M}_{\\odot}$ in our hydrodynamic-modeling light curve analysis is also\nconsistent with our spectroscopic observations. We observe a broad feature near\n4600 A, which may be high ionization lines of C, N or/and He II. This feature\nis reproduced by radiation hydrodynamic simulations of red supergiants with\nextended atmospheres. Several LL~SNe~II show similar spectral features implying\nthat high density material around the progenitor may be common among them.", + "category": "astro-ph" + }, + { + "text": "An X-ray Mini-survey of Nearby Edge-on Starburst Galaxies II. The\n Question of Metal Abundance: (abbreviated) We have undertaken an X-ray survey of a far-infrared flux\nlimited sample of seven nearby edge-on starburst galaxies. Here, we examine the\ntwo X-ray-brightest sample members NGC 253 and M 82 in a self-consistent\nmanner, taking account of the spatial distribution of the X-ray emission in\nchoosing our spectral models. There is significant X-ray absorption in the disk\nof NGC 253. When this is accounted for we find that multi-temperature thermal\nplasma models with significant underlying soft X-ray absorption are more\nconsistent with the imaging data than single-temperature models with highly\nsubsolar abundances or models with minimal absorption and non-equilibrium\nthermal ionization conditions. Our models do not require absolute abundances\nthat are inconsistent with solar values or unusually supersolar ratios of the\nalpha-burning elements with respect to Fe (as claimed previously). We conclude\nthat with current data, the technique of measuring abundances in starburst\ngalaxies via X-ray spectral modeling is highly uncertain.\n Based on the point-like nature of much of the X-ray emission in the PSPC\nhard-band image of NGC 253, we suggest that a significant fraction of the\n``extended'' X-ray emission in the 3-10 keV band seen along the disk of the\ngalaxy with ASCA and BeppoSAX (Cappi et al.) is comprised of discrete sources\nin the disk, as opposed to purely diffuse, hot gas. This could explain the low\nFe abundances of ~1/4 solar derived for pure thermal models.", + "category": "astro-ph" + }, + { + "text": "A Search for Lensed Lyman-Alpha Emitters within the Early HETDEX Data\n Set: The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a large-volume\nspectroscopic survey without pre-selection of sources, searching ~ 540 deg^2\nfor Lyman-alpha emitting galaxies (LAEs) at 1.9 < z < 3.5. Taking advantage of\nsuch a wide-volume survey, we perform a pilot study using early HETDEX data to\nsearch for lensed Lyman-alpha emitters. After performing a proof-of-concept\nusing a previously known lensed LAE covered by HETDEX, we perform a search for\npreviously unknown lensed LAEs in the HETDEX spectroscopic sample. We present a\ncatalog of 26 potential LAEs lensed by foreground, red, non-star-forming\ngalaxies at z ~ 0.4 - 0.7. We estimate the magnification for each candidate\nsystem, finding 12 candidates to be within the strong lensing regime\n(magnification $\\mu$ > 2). Follow-up observations of these potential lensed\nLAEs have the potential to confirm their lensed nature and explore these\ndistant galaxies in more detail.", + "category": "astro-ph" + }, + { + "text": "Improved Acceleration of the GPU Fourier Domain Acceleration Search\n Algorithm: We present an improvement of our implementation of the Correlation Technique\nfor the Fourier Domain Acceleration Search (FDAS) algorithm on Graphics\nProcessor Units (GPUs) (Dimoudi & Armour 2015; Dimoudi et al. 2017). Our new\nimproved convolution code which uses our custom GPU FFT code is between 2.5 and\n3.9 times faster the than our cuFFT-based implementation (on an NVIDIA P100)\nand allows for a wider range of filter sizes then our previous version. By\nusing this new version of our convolution code in FDAS we have achieved 44%\nperformance increase over our previous best implementation. It is also\napproximately 8 times faster than the existing PRESTO GPU implementation of\nFDAS (Luo 2013). This work is part of the AstroAccelerate project (Armour et\nal. 2002), a many-core accelerated time-domain signal processing library for\nradio astronomy.", + "category": "astro-ph" + }, + { + "text": "Discovery of a disrupting open cluster far into the Milky Way halo: a\n recent star formation event in the leading arm of the Magellanic stream?: We report the discovery of a young (${\\rm age} \\sim 130~{\\rm Myr}$), low-mass\n($M \\sim 1200~{\\rm M}_\\odot$), metal-poor ($[{\\rm Fe}/{\\rm H}] \\sim -1.1$)\nstellar association at a heliocentric distance $D \\approx 29~{\\rm kpc}$,\nplacing it far into the Milky Way halo. At its present Galactocentric position\n$(R, z) \\sim (23, 15)~{\\rm kpc}$, the association is (on the sky) near the\nleading arm of the gas stream emanating from the Magellanic cloud system, but\nis located $\\approx 60^\\circ$ from the Large Magellanic Cloud (LMC) center on\nthe other side of the Milky Way disk. If we assume that the cluster is\nco-located with HI gas in the stream, we directly measure the distance to the\nleading arm of the Magellanic stream. The measured distance is inconsistent\nwith stream predictions from models of the LMC/SMC interaction and infall into\nthe Milky Way that do not account for ram pressure and gas interaction with\nMilky Way disk. The estimated age of the cluster is consistent with the time of\nlast passage of the leading arm gas through the Galactic midplane, and we\ntherefore speculate that this star-formation event was triggered by its the\nlast disk midplane passage. Most details of this idea remain a puzzle: the\nMagellanic stream has low column density, the Milky Way disk at this large\nradius has low gas density, and the relative velocity of the leading arm gas\nand Milky Way gas is large. However it formed, the discovery of a young stellar\ncluster in the Milky Way halo presents an interesting opportunity for study.\nThis cluster was discovered with Gaia astrometry and photometry alone, but\nfolow-up DECam photometry was crucial for measuring its properties.", + "category": "astro-ph" + }, + { + "text": "The Unpredictability of the Most Energetic Solar Events: Observations over the past two solar cycles show a highly irregular pattern\nof occurrence for major solar flares, gamma-ray events, and solar energetic\nparticle (SEP) fluences. Such phenomena do not appear to follow the direct\nindices of solar magnetic activity, such as the sunspot number. I show that\nthis results from the non-Poisson occurrence for the most energetic events.\nThis Letter also points out a particularly striking example of this\nirregularity in a comparison between the declining phases of the recent two\nsolar cycles (1993-1995 and 2004-2006, respectively) and traces it through the\nradiated energies of the flares, the associated SEP fluences, and the sunspot\nareas. These factors suggest that processes in the solar interior involved with\nthe supply of magnetic flux up to the surface of the Sun have strong\ncorrelations in space and time, leading to a complex occurrence pattern that is\npresently unpredictable on timescales longer than active region lifetimes\n(weeks) and not correlated well with the solar cycle itself.", + "category": "astro-ph" + }, + { + "text": "Strategies for spectroscopy on Extremely Large Telescopes. II - Diverse\n field spectroscopy: The fields of view of Extremely Large Telescopes will contain vast numbers of\nspatial sampling elements (spaxels) as their Adaptive Optics systems approach\nthe diffraction limit over wide fields. Since this will exceed the detection\ncapabilities of any realistic instrument, the field must be dilutely sampled to\nextract spectroscopic data from selected regions of interest. The scientific\nreturn will be maximised if the sampling pattern provides an adaptable\ncombination of separated independent spaxels and larger contiguous sub-fields,\nseamlessly combining integral-field and multiple-object spectroscopy. We\nillustrate the utility of this Diverse Field Spectroscopy (DFS) to cosmological\nstudies of galaxy assembly. We show how to implement DFS with an instrument\nconcept: the Celestial Selector. This integrates highly-multiplexed monolithic\nfibre systems (MFS) and switching networks of the type currently available in\nthe telecommunications industry. It avoids bulky moving parts, whose\nlimitations were noted in Paper I. In Paper III we will investigate the\noptimisation of such systems by varying the input-output mapping.", + "category": "astro-ph" + }, + { + "text": "The New Model of Chemical Evolution of r-process Elements Based on The\n Hierarchical Galaxy Formation I: Ba and Eu: We investigate the chemical enrichment of r-process elements in the early\nevolutionary stages of the Milky Way halo within the framework of hierarchical\ngalaxy formation using a semi-analytic merger tree. In this paper, we focus on\nheavy r-process elements, Ba and Eu, of extremely metal-poor (EMP) stars and\ngive constraints on their astronomical sites. Our models take into account\nchanges of the surface abundances of EMP stars by the accretion of interstellar\nmatter (ISM). We also consider metal-enrichment of intergalactic medium (IGM)\nby galactic winds and the resultant pre-enrichment of proto-galaxies. The trend\nand scatter of the observed r-process abundances are well reproduced by our\nhierarchical model with $\\sim 10\\%$ of core-collapse supernovae in low-mass end\n($\\sim 10M_{\\odot}$) as a dominant r-process source and the star formation\nefficiency of $\\sim 10^{-10} \\hbox{yr}^{-1}$. For neutron star mergers as an\nr-process source, their coalescence timescale has to be $ \\sim 10^7$yrs, and\nthe event rates $\\sim 100$ times larger than currently observed in the Galaxy.\nWe find that the accretion of ISM is a dominant source of r-process elements\nfor stars with [Ba/H] < -3.5. In this model, a majority of stars at [Fe/H] < -3\nare formed without r-process elements but their surfaces are polluted by the\nISM accretion. The pre-enrichment affects $\\sim 4\\%$ of proto-galaxies, and\nyet, is surpassed by the ISM accretion in the surface of EMP stars.", + "category": "astro-ph" + }, + { + "text": "NuSTAR Tests of Sterile-Neutrino Dark Matter: New Galactic Bulge\n Observations and Combined Impact: We analyze two dedicated NuSTAR observations with exposure ${\\sim}190$ ks\nlocated ${\\sim}10^\\circ$ from the Galactic plane, one above and the other\nbelow, to search for x-ray lines from the radiative decay of sterile-neutrino\ndark matter. These fields were chosen to minimize astrophysical x-ray\nbackgrounds while remaining near the densest region of the dark matter halo. We\nfind no evidence of anomalous x-ray lines in the energy range 5--20 keV,\ncorresponding to sterile neutrino masses 10--40 keV. Interpreted in the context\nof sterile neutrinos produced via neutrino mixing, these observations provide\nthe leading constraints in the mass range 10--12 keV, improving upon previous\nconstraints in this range by a factor ${\\sim}2$. We also compare our results to\nMonte Carlo simulations, showing that the fluctuations in our derived limit are\nnot dominated by systematic effects. An updated model of the instrumental\nbackground, which is currently under development, will improve NuSTAR's\nsensitivity to anomalous x-ray lines, particularly for energies 3--5 keV.", + "category": "astro-ph" + }, + { + "text": "H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS\n 1830-211: PKS 1830-211 is a known macrolensed quasar located at a redshift of z=2.5.\nIts high-energy gamma-ray emission has been detected with the Fermi-LAT\ninstrument and evidence for lensing was obtained by several authors from its\nhigh-energy data.\n Observations of PKS 1830-211 were taken with the H.E.S.S. array of Imaging\nAtmospheric Cherenkov Telescopes in August 2014, following a flare alert by the\nFermi- LAT collaboration. The H.E.S.S observations were aimed at detecting a\ngamma-ray flare delayed by 20-27 days from the alert flare, as expected from\nobservations at other wavelengths.\n More than twelve hours of good quality data were taken with an analysis\nthreshold of $\\sim67$ GeV. The significance of a potential signal is computed\nas a function of the date as well as the average significance over the whole\nperiod. Data are compared to simultaneous observations by Fermi-LAT.\n No photon excess or significant signal is detected. An upper limit on PKS\n1830-211 flux above 67 GeV is computed and compared to the extrapolation of the\nFermi-LAT flare spectrum.", + "category": "astro-ph" + }, + { + "text": "X-ray Fading and Expansion in the \"Miniature Supernova Remnant\" of GK\n Persei: We report on a second epoch of Chandra X-ray imaging spectroscopy of the\nspatially-resolved old nova remnant GK Persei. An ACIS-S3 observation of 97.4\nks was conducted in November 2013 after a lapse of 13.8 years from the last\nvisit in 2000. The X-ray emitting nebula appeared more faint and patchy\ncompared with the first epoch. The flux decline was particularly evident in\nfainter regions and the mean decline was 30-40 % in the 0.5-1.2 keV energy\nband. A typical expansion of the brightest part of the remnant was 1.9 arcsec,\nwhich corresponds to an expansion rate of 0.14 arcsec yr^{-1}. The soft X-ray\nspectra extracted from both the 2000 and 2013 data can be explained by a\nnon-equilibrium ionization collisional plasma model convolved with interstellar\nabsorption, though do not allow us to constrain the origin of the flux\nevolution. The plasma temperature has not significantly evolved since the 2000\nepoch and we conclude that the fading of the X-ray emission is due largely to\nexpansion. This implies that recent expansion has been into a lower density\nmedium, a scenario that is qualitatively consistent with the structure of the\ncircumstellar environment photographed soon after the initial explosion more\nthan a century ago. Fainter areas are fading more quickly than brighter areas,\nindicating that they are fainter because of a lower ambient medium density and\nconsequently more rapid expansion.", + "category": "astro-ph" + }, + { + "text": "Test magnetohydrostatic extrapolation with radiative MHD simulation of a\n solar flare: Context. On the sun, the magnetic field vector is measured routinely only in\nthe photosphere. By using these photospheric measurements as boundary\ncondition, we developed the magnetohydrostatic (MHS) extrapolation to model the\nsolar atmosphere. The model makes assumption about the relative importance of\nmagnetic and non-magnetic forces. While the solar corona is force-free, this is\nnot the case in photosphere and chromosphere.\n Aim. The model has been tested with an exact equilibria in \\cite{zw18}. Here\nwe present a more challenging and realistic test of our model with radiative\nMHD simulation of a solar flare.\n Methods. By using the optimization method, the MHS model computes\nself-consistently the magnetic field, plasma pressure and density. The\nnonlinear force-free field (NLFFF) and gravity stratified atmosphere along the\nfield line are assumed as the initial condition of the optimization.\n Results. Compared with NLFFF, the MHS model gives an improved magnetic field\nnot only in magnitude and direction, but also in the magnetic connectivity.\nBesides, the MHS model is able to recover the main structure of the plasma in\nthe photosphere and chromosphere.", + "category": "astro-ph" + }, + { + "text": "Dust-trapping Rossby vortices in protoplanetary disks: One of the most challenging steps in planet formation theory is the one\nleading to the formation of planetesimals of kilometre size. A promising\nscenario involves the existence of vortices able to concentrate a large amount\nof dust and grains in their centres. Up to now this scenario has been studied\nmostly in 2D razor thin disks. A 3D study including, simultaneously, the\nformation and resulting dust concentration of the vortices with vertical\nsettling, was still missing. The Rossby wave instability self-consistently\nforms 3D vortices, which have the unique quality of presenting a large scale\nvertical velocity in their centre. Here we aim to study how this newly\ndiscovered effect can alter the dynamic evolution of the dust. We perform\nglobal 3D simulations of the RWI in a radially and vertically stratified disk\nusing the code MPI-AMRVAC. After the growth phase of the instability, the gas\nand solid phases are modelled by a bi-fluid approach, where the dust is\nconsidered as a fluid without pressure. Both the drag force of the gas on the\ndust and the back-reaction of the dust on the gas are included. Multiple grain\nsizes from 1mm to 5cm are used with a constant density distribution. We obtain\nin a short timescale a high concentration of the largest grains in the\nvortices. Indeed, in 3 rotations the dust-to-gas density ratio grows from 10^-2\nto unity leading to a concentration of mass up to that of Mars in one vortex.\nThe presence of the radial drift is also at the origin of a dust pile-up at the\nradius of the vortices. Lastly, the vertical velocity of the gas in the vortex\ncauses the sedimentation process to be reversed, the mm size dust is lifted and\nhigher concentrations are obtained in the upper layer than in the mid-plane.", + "category": "astro-ph" + }, + { + "text": "Mirror dark matter discovered?: Recent astrophysical data indicates that dark matter shows a controversial\nbehaviour in galaxy cluster collisions. In case of the notorious Bullet\ncluster, dark matter component of the cluster behaves like a collisionless\nsystem. However, its behaviour in the Abell 520 cluster indicates a significant\nself-interaction cross-section. It is hard for the WIMP based dark matter\nmodels to reconcile such a diverse behaviour. Mirror dark matter models, on the\ncontrary, are more flexible and for them diverse behaviour of the dark matter\nis a natural expectation.", + "category": "astro-ph" + }, + { + "text": "Effects of Quasi-Static Aberrations in Faint Companion Searches: We present the first results obtained at CFHT with the TRIDENT infrared\ncamera, dedicated to the detection of faint companions close to bright nearby\nstars. The camera's main feature is the acquisition of three simultaneous\nimages in three wavelengths (simultaneous differential imaging) across the\nmethane absorption bandhead at 1.6 micron, that enables a precise subtraction\nof the primary star PSF while keeping the companion signal. The main limitation\nis non-common path aberrations between the three optical paths that slightly\ndecorrelate the PSFs. Two types of PSF calibrations are combined with the\ndifferential simultaneous imaging technique to further attenuate the PSF:\nreference star subtraction and instrument rotation to smooth aberrations. It is\nshown that a faint companion with a DeltaH of 10 magnitudes would be detected\nat 0.5 arcsec from the primary.", + "category": "astro-ph" + }, + { + "text": "Non-Parametric Analysis for the Dark Matter Density Evolution: In this paper, we investigate a potential departure in the standard dark\nmatter density evolution law, $\\rho_{dm} = \\rho_{dm,0}(1+z)^3$. The method\ninvolves considering a deformed evolution model, denoted as $\\rho_{dm} =\n\\rho_{dm,0}(1+z)^3f(z)$, and searching the presence of any deviation ($f(z)\\neq\n1$). As one may see, $f(z)$ is a general function that parametrizes a\ndigression from the standard law. We use data of baryon acoustic oscillations,\ntype I Supernovae luminosity distances, and galaxy cluster gas mass fraction\nobservations to reconstruct $f(z)$ by Gaussian process regression. Unlike\nprevious works, it enables us to investigate a possible deviation without using\na specific function to describe it. We have obtained $f(z)=1$, the standard\nmodel scenario, within $2\\sigma$ c.l. in all the considered cases.", + "category": "astro-ph" + }, + { + "text": "Time-evolution of Peak Energy and Luminosity Relation within Pulses for\n GRB 061007: Probing Fireball Dynamics: We perform a time-resolved spectral analysis of bright, long Gamma-ray burst\nGRB 061007 using Suzaku/WAM and Swift/BAT. Thanks to the large effective area\nof the WAM, we can investigate the time evolution of the spectral peak energy,\nEt_peak and the luminosity Lt_iso with 1-sec time resolution, and we find that\nluminosity Lt_iso with 1-sec time resolution, and we find that the\ntime-resolved pulses also satisfy the Epeak-Liso relation, which was found for\nthe time-averaged spectra of other bursts, suggesting the same physical\nconditions in each pulse. Furthermore, the initial rising phase of each pulse\ncould be an outlier of this relation with higher Et_peak value by about factor\n2. This difference could suggest that the fireball radius expands by a factor\nof 2-4 and/or bulk Lorentz factor of the fireball is decelerated by a factor of\n4 during the initial phase, providing a new probe of the fireball dynamics in\nreal time.", + "category": "astro-ph" + }, + { + "text": "Exoplanet population inference and the abundance of Earth analogs from\n noisy, incomplete catalogs: No true extrasolar Earth analog is known. Hundreds of planets have been found\naround Sun-like stars that are either Earth-sized but on shorter periods, or\nelse on year-long orbits but somewhat larger. Under strong assumptions,\nexoplanet catalogs have been used to make an extrapolated estimate of the rate\nat which Sun-like stars host Earth analogs. These studies are complicated by\nthe fact that every catalog is censored by non-trivial selection effects and\ndetection efficiencies, and every property (period, radius, etc.) is measured\nnoisily. Here we present a general hierarchical probabilistic framework for\nmaking justified inferences about the population of exoplanets, taking into\naccount survey completeness and, for the first time, observational\nuncertainties. We are able to make fewer assumptions about the distribution\nthan previous studies; we only require that the occurrence rate density be a\nsmooth function of period and radius (employing a Gaussian process). By\napplying our method to synthetic catalogs, we demonstrate that it produces more\naccurate estimates of the whole population than standard procedures based on\nweighting by inverse detection efficiency. We apply the method to an existing\ncatalog of small planet candidates around G dwarf stars (Petigura et al. 2013).\nWe confirm a previous result that the radius distribution changes slope near\nEarth's radius. We find that the rate density of Earth analogs is about 0.02\n(per star per natural logarithmic bin in period and radius) with large\nuncertainty. This number is much smaller than previous estimates made with the\nsame data but stronger assumptions.", + "category": "astro-ph" + }, + { + "text": "Computed Rotational Collision Rate Coefficients for Recently Detected\n Anionic Cyanopolyynes: We report new results from quantum calculations of energy-transfer processes\ntaking place in interstellar environments and involving two newly observed\nmolecular species: C$_5$N$^-$ and C$_7$N$^-$ in collision with He atoms and the\np-H$_2$ molecules. These species are part of the anionic molecular chains\nlabeled as cyanopolyynes which have been observed over the years in\nmolecule-rich Circumstellar Envelopes and in molecular clouds. In the present\nwork, we first carry out new $ab$ $initio$ calculations for the C$_7$N$^-$\ninteraction potential with He atom and then obtain state-to-state rotationally\ninelastic cross sections and rate coefficients involving the same transitions\nwhich have been observed experimentally by emission in the interstellar medium\n(ISM) from both of these linear species. For the C$_5$N$^-$/He system we extend\nthe calculations already published in our earlier work (see reference below) to\ncompare more directly the two molecular anions. We extend further the quantum\ncalculations by also computing in this work collision rate coefficients for the\nhydrogen molecule interacting with C5N$^-$, using our previously computed\ninteraction potential. Additionally, we obtain the same rate coefficients for\nthe C$_7$N$^-$/H$_2$ system by using a scaling procedure that makes use of the\nnew C$_7$N$^-$/He rate coefficients, as discussed in detail in the present\npaper. Their significance in affecting internal state populations in ISM\nenvironments where the title anions have been found is analyzed by using the\nconcept of critical density indicators. Finally, similarities and differences\nbetween such species and the comparative efficiency of their collision rate\ncoefficients are discussed. These new calculations suggest that, at least for\nthe case of these longer chains, the rotational populations could reach local\nthermal equilibrium conditions within their observational environments.", + "category": "astro-ph" + }, + { + "text": "Line-of-sight Effects on Observability of Kink and Sausage Modes in\n Coronal Structures with Imaging Telescopes: Kink modes of solar coronal structures, perturbing the loop in the direction\nalong the line-of-sight (LOS), can be observed as emission intensity\ndisturbances propagating along the loop provided the angle between the LOS and\nthe structure is not ninety degrees. The effect is based upon the change of the\ncolumn depth of the loop (along the LOS) by the wave. The observed amplitude of\nthe emission intensity variations can be larger than the actual amplitude of\nthe wave by a factor of two and there is an optimal angle maximizing the\nobserved amplitude. For other angles this effect can also attenuate the\nobserved wave amplitude. The observed amplitude depends upon the ratio of the\nwave length of kink perturbations to the width of the structure and on the\nangle between the LOS and the axis of the structure. Sausage modes are always\naffected negatively from the observational point of view, as the observed\namplitude is always less than the actual one. This effect should be taken into\naccount in the interpretation of wave phenomena observed in the corona with\nspace-borne and ground-based imaging telescopes.", + "category": "astro-ph" + }, + { + "text": "Differential Rotation in Magnetized and Non-magnetized Stars: Effects of magnetic field on stellar differential rotation are studied by\ncomparing magnetohydrodynamic (MHD) models and their hydrodynamic (HD)\ncounterparts in the broad range of rotation rate and in varying initial\nrotation profile. Fully-compressible MHD simulations of rotating penetrative\nconvection are performed in a full-spherical shell geometry. Critical\nconditions for the transition of the differential rotation between faster\nequator (solar-type) and slower equator (anti-solar type) are explored with\nfocusing on the \"Rossby number (${\\rm Ro}$)\" and the \"convective Rossby number\n(${\\rm Ro}_{\\rm conv}$)\". It is confirmed that the transition is more gradual\nand the critical value for it is higher in the MHD model than the HD model in\nthe view of the ${\\rm Ro}_{\\rm conv}$-dependence. The rotation profile shows,\nas observed in earlier studies, the bistability near the transition in the HD\nmodel, while it disappears when allowing the growth of magnetic fields except\nfor the model with taking anti-solar type solution as the initial condition. We\nfind that the transition occurs at ${\\rm Ro} \\simeq 1$ both in the MHD and HD\nmodels independently of the hysteresis. Not only the critical value, the\nsharpness of the transition is also similar between the two models in the view\nof the ${\\rm Ro}$-dependence. The influences of the dynamo-generated magnetic\nfield and/or the hysteresis on convective motion are reflected in the ${\\rm\nRo}$. This would be the reason why the transition is unified in the view of the\n${\\rm Ro}$-dependence. We finally discuss the ${\\rm Ro}$-dependence of magnetic\ndynamo activities with emphasis on its possible relation to the kinetic\nhelicity profile.", + "category": "astro-ph" + }, + { + "text": "Hubble Space Telescope Grism Spectroscopy of Extreme Starbursts Across\n Cosmic Time: The Role of Dwarf Galaxies in the Star Formation History of the\n Universe: Near infrared slitless spectroscopy with the Wide Field Camera 3, onboard the\nHubble Space Telescope, offers a unique opportunity to study low-mass galaxy\npopulations at high-redshift ($z\\sim$1-2). While most high$-z$ surveys are\nbiased towards massive galaxies, we are able to select sources via their\nemission lines that have very-faint continua. We investigate the star formation\nrate (SFR)-stellar mass ($M_{\\star}$) relation for about 1000 emission-line\ngalaxies identified over a wide redshift range of $0.3 \\lesssim z \\lesssim\n2.3$. We use the H$_{\\alpha}$ emission as an accurate SFR indicator and correct\nthe broadband photometry for the strong nebular contribution to derive accurate\nstellar masses down to $M_{\\star} \\sim 10^{7} M_{\\odot}$. We focus here on a\nsubsample of galaxies that show extremely strong emission lines (EELGs) with\nrest-frame equivalent widths ranging from 200 to 1500 \\AA. This population\nconsists of outliers to the normal SFR-$M_{\\star}$ sequence with much higher\nspecific SFRs ($> 10$ Gyr$^{-1}$). While on-sequence galaxies follow a\ncontinuous star formation process, EELGs are thought to be caught during an\nextreme burst of star formation that can double their stellar mass in less than\n$100$ Myr. The contribution of starbursts to the total star formation density\nappears to be larger than what has been reported for more massive galaxies in\nprevious studies. In the complete mass range $8.2 <$ log($M_{\\star}/M_{\\odot}$)\n$< 10$ and a SFR lower completeness limit of about 2 $M_{\\odot}$ yr$^{-1}$ (10\n$M_{\\odot}$ yr$^{-1}$) at $z\\sim1$ ($z \\sim 2$), we find that starbursts having\nEW$_{rest}$(H$_{\\alpha}$)$>$ 300, 200, and 100 A contribute up to $\\sim13$, 18,\nand 34 %, respectively, to the total SFR of emission-line selected sample at\n$z\\sim1-2$. The comparison with samples of massive galaxies shows an increase\nin the contribution of starbursts towards lower masses.", + "category": "astro-ph" + }, + { + "text": "Simulating young star clusters with primordial binaries: We simulate a cluster of 144179 stars including 13107 primordial hard\nbinaries (10% of the total number of single stars and binary centers of mass),\nusing direct integration of the equations of motion of all stars and binaries\nand incorporating the effects of stellar and binary evolution. The initial\nconditions are representative of young dense star clusters in the Local Group\nand other nearby galaxies like the Antennae and M82.\n We find that the early phase of core collapse, driven by mass segregation, is\nnot appreciably delayed by the presence of a large number of hard binaries. By\nthe end of the simulation, at an age of 115Myr, the cluster radius has expanded\nby about a factor of two. This may be explained as adiabatic expansion driven\nby the loss (via stellar evolution) of about 40% of the initial total mass.\nBinary dynamics apparently has little effect on the early cluster expansion.\n During the evolution, the total binary fraction drops at a roughly constant\nrate of about 0.01% per Myr. The fraction of very hard binaries, however\nincreases at about 0.025% per Myr. By the end of the simulation the cluster\ncontains 37 binaries containing at least one black hole; roughly half (17) of\nthese contain two black holes.", + "category": "astro-ph" + }, + { + "text": "A Gradual Decline of Star Formation since Cluster In-fall: New Kinematic\n Insights into Environmental Quenching at 0.3 $< z <$ 1.1: The environments where galaxies reside crucially shape their star formation\nhistories. We investigate a large sample of 1626 cluster galaxies located\nwithin 105 galaxy clusters spanning a large range in redshift ($0.26 < z <\n1.13)$. The galaxy clusters are massive (M$_{500} \\gtrsim\n2\\times10^{14}$M$_{\\odot}$), and are uniformly selected from the SPT and ACT\nSunyaev-Zel'dovich (SZ) surveys. With spectra in-hand for thousands of cluster\nmembers, we use galaxies' position in projected phase space as a proxy for\ntheir in-fall times, which provides a more robust measurement of environment\nthan quantities such as projected cluster-centric radius. We find clear\nevidence for a gradual age increase of the galaxy's mean stellar populations\n($\\sim$ 0.71 $\\pm$ 0.4 Gyr based on a 4000 $\\r{A}$ break, $\\rm D_{\\rm n}4000$)\nwith the time spent in the cluster environment. This environmental quenching\neffect is found regardless of galaxy luminosity (faint or bright) and redshift\n(low-$z$ or high-$z$), although the exact stellar age of galaxies depends on\nboth parameters at fixed environmental effects. Such a systematic increase of\n$\\rm D_{\\rm n}4000$ with in-fall proxy would suggest that galaxies that were\naccreted into hosts earlier were quenched earlier, due to longer exposure to\nenvironmental effects such as ram pressure stripping and starvation. Compared\nto the typical dynamical time scales of $1-3$ Gyr of cluster galaxies, the\nrelatively small age increase ($\\sim$ 0.71 $\\pm$ 0.4 Gyr) found in our sample\ngalaxies seems to suggest that a slow environmental process such as starvation\nis the dominant quenching pathway. Our results provide new insights into\nenvironmental quenching effects spanning a large range in cosmic time ($\\sim\n5.2$ Gyr, $z=0.26$--1.13) and demonstrate the power of using a\nkinematically-derived in-fall time proxy.", + "category": "astro-ph" + }, + { + "text": "Kreutz Sungrazers: Summary of Recent Modeling and Orbits of the SOHO\n Objects: I summarize and streamline the results of recent modeling of the orbital\nevolution and cascading fragmentation of the Kreutz sungrazers. The model\nstarts with Aristotle's comet -- the progenitor whose nucleus is assumed to be\na contact binary -- splitting near aphelion into the two lobes and concludes\nwith the SOHO dwarf objects as the end products of the fragmentation process.\nThe Great March Comet of 1843, a member of Population I, and the Great\nSeptember Comet of 1882, a member of Population II, are deemed the largest\nsurviving masses of the lobes. I establish that the Kreutz system consists\ncurrently of nine populations, one of which -- associated with comet Pereyra --\nis a side branch of Population I. The additions to the Kreutz system proposed\nas part of the new model are the daylight comets of AD 363, recorded by the\nRoman historian Ammianus Marcellinus, and the Chinese comets of September 1041\nand September 1138, both listed in Ho's catalogue. The comets of 363 are the\nfirst-generation fragments, the latter -- together with the Great Comet of 1106\n-- the second-generation fragments. Attention is directed toward the\npopulations' histograms of perihelion distance of the SOHO sungrazers and the\nplots of this distance as a function of the longitude of the ascending node.\nArrival of bright, naked-eye Kreutz sungrazers in the coming decades is\npredicted.", + "category": "astro-ph" + }, + { + "text": "The Host Galaxy and Rapidly Evolving Broad-line Region in the\n Changing-look Active Galactic Nucleus 1ES 1927+654: Changing-look active galactic nuclei (AGNs) present an important laboratory\nto understand the origin and physical properties of the broad-line region\n(BLR). We investigate follow-up optical spectroscopy spanning $\\sim 500$ days\nafter the outburst of the changing-look AGN 1ES\\,1927+654. The emission lines\ndisplayed dramatic, systematic variations in intensity, velocity width,\nvelocity shift, and symmetry. Analysis of optical spectra and multi-band images\nindicate that the host galaxy contains a pseudobulge and a total stellar mass\nof $3.56_{-0.35}^{+0.38} \\times 10^{9}\\, M_\\odot$. Enhanced continuum radiation\nfrom the outburst produced an accretion disk wind, which condensed into BLR\nclouds in the region above and below the temporary eccentric disk. Broad Balmer\nlines emerged $\\sim 100$ days after the outburst, together with an unexpected,\nadditional component of narrow-line emission. The newly formed BLR clouds then\ntraveled along a similar eccentric orbit ($e \\approx 0.6$). The Balmer\ndecrement of the BLR increased by a factor of $\\sim 4-5$ as a result of secular\nchanges in cloud density. The drop in density at late times allowed the\nproduction of \\hei\\ and \\heii\\ emission. The mass of the black hole cannot be\nderived from the broad emission lines because the BLR is not virialized.\nInstead, we use the stellar properties of the host galaxy to estimate\n$M_\\mathrm{BH} = 1.38_{-0.66}^{+1.25} \\times 10^{6}\\, M_\\odot$. The nucleus\nreached near or above its Eddington limit during the peak of the outburst. We\ndiscuss the nature of the changing-look AGN 1ES\\,1927+654 in the context of\nother tidal disruption events.", + "category": "astro-ph" + }, + { + "text": "Unidentified 3EG gamma-ray sources at low galactic latitude: We present a study on the possible association of unidentified $\\gamma$-ray\nsources in the Third EGRET (3EG) catalog with different types of galactic\nobjects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB\nassociations (considered as pulsar tracers). We have made use of numerical\nsimulations of galactic populations of $\\gamma$-ray point sources in order to\ndetermine the statistical significance of the positional coincidences. New\nconstraints on pure chance association are presented for SNRs and OB\nassociations, and it is shown that massive stars present marginally significant\ncorrelation with 3EG sources at a $3\\sigma$ level.", + "category": "astro-ph" + }, + { + "text": "Modeling the MgI from the NUV to MIR: I. The Solar Case: Semi-empirical models of the solar atmosphere are used to study the radiative\nenvironment of any planet in our solar system. There is a need for reliable\natomic data for neutral atoms and ions in the atmosphere to obtain improved\ncalculated spectra. Atomic parameters are crucial to computing the correct\npopulation of elements through the whole stellar atmosphere. Although there is\na very good agreement between the observed and calculated spectra for the Sun,\nthere is still a mismatch in several spectral ranges due to the lack of atomic\ndata and its inaccuracies, particularly for neutrals like Mg I.\n To correctly represent many spectral lines of Mg I from the near-UV to the\nmid-IR is necessary to add and update the atomic data involved in the atomic\nprocesses that drive their formation. The improvements to the Mg I atomic model\nare as follows: i) 127 strong lines, including their broadening data, were\nadded. ii) To obtain these lines, we increased from 26 to 85 the number of\nenergy levels. iii) Photoionization cross-section parameters were added and\nupdated. iv) Effective Collision Strengths (ECS) parameters were updated for\nthe first 25 levels using the existing data from the convergent close-coupling\n(CCC) calculations. One of the most significant changes in our model is given\nby the new ECS parameters for transitions involving levels between 26 and 54,\nwhich were computed with a multi-configuration Breit-Pauli distorted-wave (DW)\nmethod.\n More than one hundred transitions were added to our calculations, increasing\nour capability of reproducing important features observed in the solar spectra.\nWe found a remarkable improvement in matching the solar spectra for wavelengths\nhigher than 3 um when our new DW ECS data was used in the model.", + "category": "astro-ph" + }, + { + "text": "Magnitude Offset between Lensed Stars and Observed Stars - a New Probe\n of the Structure of the Galactic Bar: We propose a new method that can be used to constrain the properties of the\nGalactic bar (bulge). If the majority of the lensing objects are in the\nGalactic bar, then we predict a systematic offset in the apparent magnitude\nbetween lensed stars and all observed stars. Using OGLE color-magnitude diagram\ndata we model this effect in the region of the diagram dominated by bulge red\nclump stars and find that for some models of the Galactic bar the expected\noffset in the apparent magnitude may be as large as $0.2 mag$. About 100 lensed\nstars in the red clump region of the color-magnitude diagram is needed to\nunambiguously detect this effect, a number within the reach of current\nmicrolensing projects. We find a good correlation between the extent of the bar\nalong the line of sight and the expected magnitude offset. We also obtain a\nconstraint for the extent of the bar along the line of sight using the observed\nluminosity function for the red clump stars.", + "category": "astro-ph" + }, + { + "text": "Ultrahigh energy neutrinos scattering off relic light neutrinos to\n explain UHECR above GZK cut off and thin blazars: UHE neutrinos may transfer highest cosmic-rays energies overcoming\n$2.75K^\\circ$ BBR and radio-waves opacities (the GZK cut off) from most distant\nAGN sources at the age of the Universe. These UHE $\\nu$ might scatter onto\nthose (light and cosmological) relic neutrinos clustered around our galactic\nhalo or nearby neutrino hot dark halo clustered around the AGN blazar and its\njets. The branched chain reactions from a primordial nucleon (via photo\nproduction of pions and decay to UHE neutrinos) toward the consequent beam dump\nscattering on galactic relic neutrinos is at least three order of magnitude\nmore efficient than any known neutrino interactions with Earth atmosphere or\ndirect nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV\nevent) might be originated at far $(\\tilde{>} 100 Mpc)$ distances (as Seyfert\ngalaxy MCG 8-11-11); its corresponding UHE radiation power is in agreement with\nthe observed one in MeV gamma energies. The final chain products observed on\nEarth by the Fly's Eye and AGASA detectors might be mainly neutron and\nanti-neutrons and delayed, protons and anti-protons at symmetric off-axis\nangles. These hadronic products are most probably secondaries of $W^+ W^-$ or\n$ZZ$ pair productions and might be consistent with the last AGASA discoveries\nof doublets and one triplet event.", + "category": "astro-ph" + }, + { + "text": "Impact of stochastic gas motions on galaxy cluster abundance profiles: The impact of stochastic gas motions on the metal distribution in cluster\ncore is evaluated. Peaked abundance profiles are a characteristic feature of\nclusters with cool cores and abundance peaks are likely associated with the\nbrightest cluster galaxies (BCGs) which dwell in cluster cores. The width of\nthe abundance peaks is however significantly broader than the BCG light\ndistribution, suggesting that some gas motions are transporting metals\noriginating from within the BCG. Assuming that this process can be treated as\ndiffusive and using the brightest X-ray cluster A426 (Perseus) as an example,\nwe estimate that a diffusion coefficient of the order of $2 10^{29} {\\rm cm^2\ns^{-1}}$ is needed to explain the width of the observed abundance profiles.\nMuch lower (higher) diffusion coefficients would result in too peaked (too\nshallow) profiles. Such diffusion could be produced by stochastic gas motions\nand our analysis provides constraints on the product of their characteristic\nvelocity and their spatial coherence scale. We speculate that the activity of\nthe supermassive black hole of the BCG is driving the stochastic gas motions in\ncluster cores. When combined with the assumption that the dissipation of the\nsame motions is a key gas heating mechanism, one can estimate both the velocity\nand the spatial scale of such a diffusive processes.", + "category": "astro-ph" + }, + { + "text": "Molecular gas streamers feeding and obscuring the active nucleus of\n NGC1068: We report the first direct observations of neutral, molecular gas streaming\nin the nucleus of NGC1068 on scales of <30 pc using SINFONI near-infrared\nintegral field spectroscopy. At a resolution of 0.075\", the flux map of 2.12\n$\\mu$m 1-0 S(1) molecular hydrogen emission around the nucleus in the central\narcsec reveals two prominent linear structures leading to the AGN from the\nnorth and south. The kinematics of the gas in these features are dominated by\nnon-circular motions and indicate that material is streaming towards the\nnucleus on highly elliptical or parabolic trajectories whose orientations are\ncompatible with that of the disk plane of the galaxy. We interpret the data as\nevidence for fueling of gas to the central region. The radial transport rate\nfrom ~30 pc to a few parsec from the nucleus is ~15 M$_\\sun$ yr$^{-1}$. One of\nthe infalling clouds lies directly in front of the central engine. We interpret\nit as a tidally disrupted streamer that forms the optically thick outerpart of\nan amorphous clumpy molecular/dusty structure which contributes to the nuclear\nobscuration.", + "category": "astro-ph" + }, + { + "text": "The Hemispheric Asymmetry of Solar Activity During the Twentieth Century\n and the Solar Dynamo: We believe the Babcock--Leighton process of poloidal field generation to be\nthe main source of irregularity in the solar cycle. The random nature of this\nprocess may make the poloidal field in one hemisphere stronger than that in the\nother hemisphere at the end of a cycle. We expect this to induce an asymmetry\nin the next sunspot cycle. We look for evidence of this in the observational\ndata and then model it theoretically with our dynamo code. Since actual polar\nfield measurements exist only from 1970s, we use the polar faculae number data\nrecorded by Sheeley (1991) as a proxy of the polar field and estimate the\nhemispheric asymmetry of the polar field in different solar minima during the\nmajor part of the twentieth century. This asymmetry is found to have a\nreasonable correlation with the asymmetry of the next cycle. We then run our\ndynamo code by feeding information about this asymmetry at the successive\nminima and compare with observational data. We find that the theoretically\ncomputed asymmetries of different cycles compare favourably with the\nobservational data, the correlation coefficient being 0.73. Due to the coupling\nbetween the two hemispheres, any hemispheric asymmetry tends to get attenuated\nwith time. The hemispheric asymmetry of a cycle either from observational data\nor from theoretical calculation statistically tends to be less than the\nasymmetry in the polar field (as inferred from the faculae data) in the\npreceding minimum. This reduction factor turns out to be 0.38 and 0.60\nrespectively in observational data and theoretical simulation.", + "category": "astro-ph" + }, + { + "text": "Super-horizon second-order perturbations for cosmological random\n fluctuations and the Hubble-constant problem: The super-horizon second-order density perturbations corresponding to\ncosmological random fluctuations are considered, their non-vanishing spatial\naverage is shown to be useful in solving the serious problem on the\ncosmological tension between measured Hubble constants at present and those at\nthe early stage, and the difference from previous works on the backreaction is\ndiscussed.", + "category": "astro-ph" + }, + { + "text": "Why Low-Mass Black-Hole Binaries Are Transient: We consider transient behavior in low-mass X-ray binaries. In short-period\nneutron-star systems (orbital period less than ~ 1d) irradiation of the\naccretion disk by the central source suppresses this except at very low mass\ntransfer rates. Formation constraints however imply that a significant fraction\nof these neutron star systems have nuclear-evolved main-sequence secondaries\nand thus mass transfer rates low enough to be transient. But most short-period\nlow-mass black-hole systems will form with unevolved main-sequence companions\nand have much higher mass transfer rates. The fact that essentially all of them\nare nevertheless transient shows that irradiation is weaker, as a direct\nconsequence of the fundamental black-hole property - the lack of a hard stellar\nsurface.", + "category": "astro-ph" + }, + { + "text": "Revisiting dynamical friction: the role of global modes and local wakes: The orbital decay of a perturber within a larger system plays a key role in\nthe dynamics of many astrophysical systems -- from nuclear star clusters or\nglobular clusters in galaxies, to massive black holes in galactic nuclei, to\ndwarf galaxy satellites within the dark matter halos of more massive galaxies.\nFor many decades, there have been various attempts to determine the underlying\nphysics and time-scales of the drag mechanism, ranging from the local dynamical\nfriction approach to descriptions based on the back-reaction of global modes\ninduced in the background system. We present ultra-high-resolution $N$-body\nsimulations of massive satellites orbiting a Milky Way-like galaxy (with $>\n10^8$ particles), that appear to capture both the local \"wake\" and the global\n\"mode\" induced in the primary halo. We address directly the mechanism of\norbital decay from the combined action of local and global perturbations and\nspecifically analyze where the bulk of the torque originates.", + "category": "astro-ph" + }, + { + "text": "Resonant Signatures of Heavy Scalar Fields in the Cosmic Microwave\n Background: We investigate the possibility that a heavy scalar field, whose mass exceeds\nthe Hubble scale during inflation, could leave non-negligible signatures in the\nCosmic Microwave Background (CMB) temperature anisotropy power spectrum through\nthe parametric resonance between its background oscillations and the inflaton\nfluctuations. By assuming the heavy scalar field couples with the inflaton\nderivatively, we show that the resonance can be efficient without spoiling the\nslow-roll inflation. The primordial power spectrum modulated by the resonance\nhas a sharp peak at a specific scale and could be an origin of the anomalies\nobserved in the angular power spectrum of the CMB. In some values of\nparameters, the modulated spectrum can fit the observed data better than the\nsimple power-law power spectrum, though the resultant improvement of the fit is\nnot large enough and hence other observations such as non-Gaussianity are\nnecessary to confirm that the CMB anomalies are originated from the resonant\neffect of the heavy scalar field. The resonant signatures can provide an\nopportunity to observe heavy degrees of freedom during inflation and improve\nour understanding of physics behind inflation.", + "category": "astro-ph" + }, + { + "text": "Orbital X-ray modulation study of three Supergiant HMXBs: We present the orbital X-ray modulation study of three high mass X- ray\nbinary systems, IGR J18027-2016, IGR J18483-0311 and IGR J16318-4848 using data\nobtained with RXTE-ASM, Swift-BAT and INTEGRAL-ISGRI. Using the long term light\ncurves of the eclipsing HMXB IGR J18027-2016, obtained with Swift-BAT in the\nenergy range 15-50 keV and INTEGRAL-ISGRI in the energy range 22-40 keV, we\nhave determined three new mid eclipse times. The newly determined mid eclipse\ntimes together with the known values were used to derive an accurate value of\nthe orbital period of 4.5693(4) d at MJD 52168 and an upper limit of\n3.9(1.2)x10^-7 d d^-1 on the period derivative. We have also accurately\ndetermined an orbital period of 18.5482(88) d for the intermediate system IGR\nJ18483-0311, which displays an unusual behaviour and shares many properties\nwith the known SFXTs and persistent supergiant systems. This is a transient\nsource and the outbursts occur intermittently at intervals of 18.55 d.\nSimilarly, in the third supergiant system, IGR J16318-4848, we have found that\nthe outbursts are separated by intervals of 80 d or its multiples, suggesting a\npossible orbital period.", + "category": "astro-ph" + }, + { + "text": "Massive Galaxy Mergers Have Distinctive Global HI Profiles: The global 21 cm HI emission-line profile of a galaxy encodes valuable\ninformation on the spatial distribution and kinematics of the neutral atomic\ngas. Galaxy interactions significantly influence the HI disk and imprint\nobservable features on the integrated HI line profile. In this work, we study\nthe neutral atomic gas properties of galaxy mergers selected from the Great\nObservatories All-sky LIRG Survey. The HI spectra come from new observations\nwith the Five-hundred-meter Aperture Spherical Telescope and from a collection\nof archival data. We quantify the HI profile of the mergers with a newly\ndeveloped method that uses the curve-of-growth of the line profile. Using a\ncontrol sample of non-merger galaxies carefully selected to match the stellar\nmass of the merger sample, we show that mergers have a larger proportion of\nsingle-peaked HI profiles, as well as a greater tendency for the HI central\nvelocity to deviate from the systemic optical velocity of the galaxy. By\ncontrast, the HI profiles of mergers are not significantly more asymmetric than\nthose of non-mergers.", + "category": "astro-ph" + }, + { + "text": "Bayes-X: a Bayesian inference tool for the analysis of X-ray\n observations of galaxy clusters: We present the first public release of our Bayesian inference tool, Bayes-X,\nfor the analysis of X-ray observations of galaxy clusters. We illustrate the\nuse of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as\nthey would be observed by a Chandra-like X-ray observatory. In both the\nsimulations and the analysis pipeline we assume that the dark matter density\nfollows a spherically-symmetric Navarro, Frenk and White (NFW) profile and that\nthe gas pressure is described by a generalised NFW (GNFW) profile. We then\nperform four sets of analyses. By numerically exploring the joint probability\ndistribution of the cluster parameters given simulated Chandra-like data, we\nshow that the model and analysis technique can robustly return the simulated\ncluster input quantities, constrain the cluster physical parameters and reveal\nthe degeneracies among the model parameters and cluster physical parameters. We\nthen analyse Chandra data on the nearby cluster, A262, and derive the cluster\nphysical profiles. To illustrate the performance of the Bayesian model\nselection, we also carried out analyses assuming an Einasto profile for the\nmatter density and calculated the Bayes factor. The results of the model\nselection analyses for the simulated data favour the NFW model as expected.\nHowever, we find that the Einasto profile is preferred in the analysis of A262.\nThe Bayes-X software, which is implemented in Fortran 90, is available at\nhttp://www.mrao.cam.ac.uk/facilities/software/bayesx/.", + "category": "astro-ph" + }, + { + "text": "The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. I.\n Spectroscopy of QSO Pairs with Arcminute Separations and Similar Redshifts: The Lyman-alpha forest has opened a new redshift regime for cosmological\ninvestigation. At z > 2 it provides a unique probe of cosmic geometry and an\nindependent constraint on dark energy that is not subject to standard candle or\nruler assumptions. In Paper I of this series on using the Lyman-alpha forest\nobserved in pairs of QSOs for a new application of the Alcock-Paczynski test,\nwe present and discuss the results of a campaign to obtain moderate-resolution\nspectroscopy (FWHM ~ 2.5 Angstroms) of the Lyman-alpha forest in pairs of QSOs\nwith small redshift differences (Delta z < 0.25, z > 2.2) and arcminute\nseparations (< 5'). This data set, composed of seven individual QSOs, 35 pairs,\nand one triplet, is also well-suited for future investigations of the coherence\nof Lyman-alpha absorbers on ~ 1 Mpc transverse scales and the transverse\nproximity effect. We note seven revisions for previously published QSO\nidentifications and/or redshifts.", + "category": "astro-ph" + }, + { + "text": "Stellar disks of Collisional Ring Galaxies I. New multiband images,\n Radial intensity and color profiles, and confrontation with N-body\n simulations: We present new multi-band imaging data in the optical (BVRI and Halpha) and\nnear infrared bands (JHK) of 15 candidate ring galaxies from the sample of\nAppleton & Marston (1997). We use these data to obtain color composite images,\nglobal magnitudes and colors of both the ring galaxy and its companion(s), and\nradial profiles of intensity and colors. We find that only nine of the observed\ngalaxies have multi-band morphologies expected for the classical collisional\nscenario of ring formation, indicating the high degree of contamination of the\nring galaxy sample by galaxies without a clear ring morphology. The radial\nintensity profiles, obtained by masking the off-centered nucleus, peak at the\nposition of the ring, with the profiles in the continuum bands broader than\nthat in the Halpha line. The images as well as the radial intensity and color\nprofiles clearly demonstrate the existence of the pre-collisional stellar disk\noutside the star-forming ring, which is in general bluer than the disk internal\nto the ring. The stellar disk seems to have retained its size, with the disk\noutside the ring having a shorter exponential scale length as compared to the\nvalues expected in normal spiral galaxies of comparable masses. The rings in\nour sample of galaxies are found to be located preferentially at around\nhalf-way through the stellar disk. The most likely reason for this preference\nis bias against detecting rings when they are close to the center (they would\nbe confused with the resonant rings), and at the edge of the disk the gas\nsurface density may be below the critical density required for star formation.\nMost of the observed characteristics point to relatively recent collisions (<80\nMyr ago) according to the N-body simulations of Gerber et al. (1996).", + "category": "astro-ph" + }, + { + "text": "SELENA: Semi-analytical Integrator for Lunar Artificial Satellites: The present report summarizes the main theory and implementation steps\nassociated with SELENA (SEmi-anaLytical intEgrator for a luNar Artificial\nsatellite), i.e. the semi-analytical propagator for lunar satellite orbits\ndeveloped in the framework of the the R&T R-S20/BS-0005-062 CNES research\nactivity in collaboration between the University of Padova (UniPd), and the\nAristotle University of Thessaloniki (AUTH), both acting as contractors with\nCNES.\n A detailed account of the method, algorithms and symbolic manipulations\nemployed in the derivation of the final theory are described in detail in this\nreport: they invoke the use of canonical perturbation theory in the form of Lie\nseries computed in `closed form', i.e., without expansions in the satellite's\norbital eccentricity. These algorithms are provided in the form of a symbolic\npackage accompanying the present report. The package contains symbolic algebra\nprograms, as well as explicit data files containing the final Hamiltonian,\nequations of motion and transformations (i.e. the coefficients and exponents of\neach variable in each term) leading to the averaging of the short-periodic\nterms in the satellite's equations of motion.", + "category": "astro-ph" + }, + { + "text": "Comparison of numerical methods for computing the repeated Compton\n scattering of photons in isotropic media: Repeated Compton scattering of photons with thermal electrons is one of the\nfundamental processes at work in many astrophysical plasma. Solving the exact\nevolution equations is hard and one common simplification is based on\nFokker-Planck (FP) approximations of the Compton collision term. Here we carry\nout a detailed numerical comparison of several FP approaches with the exact\nscattering kernel solution for a range of test problems assuming isotropic\nmedia and thermal electrons at various temperatures. The Kompaneets equation,\nbeing one of the most widely used FP approximations, fails to account for\nKlein-Nishina corrections and enhanced Doppler boosts and recoil at high\nenergies. These can be accounted for with an alternative FP approach based on\nthe exact first and second moments of the scattering kernel. As demonstrated\nhere, the latter approach works very well in dilute media, but inherently fails\nto reproduce the correct equilibrium solution in the limit of many scattering.\nConditions for the applicability of the FP approximations are clarified,\noverall showing that the Kompaneets equation provides the most robust\napproximation to the full problem, even if inaccurate in many cases. We close\nour numerical analysis by briefly illustrating the solutions for the spectral\ndistortions of the cosmic microwave background (CMB) after photon injection at\nredshift $z\\lesssim 10^5$, when double Compton and Bremsstrahlung emission can\nbe omitted. We demonstrate that the exact treatment using the scattering kernel\ncomputed with {\\tt CSpack} is often needed. This work should provide an\nimportant step towards accurate computations of the CMB spectral distortions\nfrom high-energy particle cascades.", + "category": "astro-ph" + }, + { + "text": "Burst and Outburst Characteristics of Magnetar 4U 0142+61: We have compiled the most comprehensive burst sample from magnetar 4U\n0142+61, comprising 27 bursts from its three burst-active episodes in 2011,\n2012 and the latest one in 2015 observed with Swift/BAT and Fermi/GBM. Bursts\nfrom 4U 0142+61 morphologically resemble typical short bursts from other\nmagnetars. However, 4U 0142+61 bursts are less energetic compared to the bulk\nof magnetar bursts. We uncovered an extended tail emission following a burst on\n2015 February 28, with a thermal nature, cooling over a time-scale of several\nminutes. During this tail emission, we also uncovered pulse peak phase aligned\nX-ray bursts , which could originate from the same underlying mechanism as that\nof the extended burst tail, or an associated and spatially coincident but\ndifferent mechanism.", + "category": "astro-ph" + }, + { + "text": "Multiple BeppoSAX Observations of IC 4329A to Probe the Origin of the\n Compton Reflection Component in Seyfert 1 Galaxies: IC 4329A is the brightest known Seyfert galaxy in hard (~2-30 keV) X-rays and\nis likely to be representative of Seyfert 1 galaxies as a class. A recent 100\nks BeppoSAX observation (Perola et al. 1999) clearly confirmed the presence of\na warm absorber, a reflection component (R~0.6), and a high-energy cut-off in\nthe power law at Ec~270 keV. Its richness in spectral features, combined with\nits large flux (~1.6 x 10**-10 erg/cm2s between 2-10 keV), make this target\nideal for multiple observations (in particular with BeppoSAX) to search for\nspectral variations. Results obtained from 3 follow-up observations (40 ks\neach) are presented here. The first and most important goal of this study was\nto probe the origin of the Compton reflection component observed in Seyfert\ngalaxies by monitoring the variability of the reflection continuum and FeK line\nin response to primary continuum variations. The second goal was to search for\nvariability in the high energy cutoff. We obtain however no conclusive results\non any of these issues. In fact, all four observations unfortunately caught the\nsource at almost the same flux, showing only little, and marginal, spectral\nchanges between different observations.", + "category": "astro-ph" + }, + { + "text": "Toward a tomographic analysis of the cross-correlation between Planck\n CMB lensing and H-ATLAS galaxies: We present an improved and extended analysis of the cross-correlation between\nthe map of the Cosmic Microwave Background (CMB) lensing potential derived from\nthe \\emph{Planck} mission data and the high-redshift galaxies detected by the\n\\emph{Herschel} Astrophysical Terahertz Large Area Survey (H-ATLAS) in the\nphotometric redshift range $z_{\\rm ph} \\ge 1.5$. We compare the results based\non the 2013 and 2015 \\textit{Planck} datasets, and investigate the impact of\ndifferent selections of the H-ATLAS galaxy samples. Significant improvements\nover our previous analysis have been achieved thanks to the higher\nsignal-to-noise ratio of the new CMB lensing map recently released by the\n\\textit{Planck} collaboration. The effective galaxy bias parameter, $b$, for\nthe full galaxy sample, derived from a joint analysis of the cross-power\nspectrum and of the galaxy auto-power spectrum is found to be $b =\n3.54^{+0.15}_{-0.14}$. Furthermore, a first tomographic analysis of the\ncross-correlation signal is implemented, by splitting the galaxy sample into\ntwo redshift intervals: $1.5 \\le z_{\\rm ph} < 2.1$ and $z_{\\rm ph}\\ge 2.1$. A\nstatistically significant signal was found for both bins, indicating a\nsubstantial increase with redshift of the bias parameter: $b=2.89\\pm0.23$ for\nthe lower and $b=4.75^{+0.24}_{-0.25}$ for the higher redshift bin.\nConsistently with our previous analysis we find that the amplitude of the cross\ncorrelation signal is a factor of $1.45^{+0.14}_{-0.13}$ higher than expected\nfrom the standard $\\Lambda$CDM model for the assumed redshift distribution. The\nrobustness of our results against possible systematic effects has been\nextensively discussed although the tension is mitigated by passing from 4 to\n3$\\sigma$.", + "category": "astro-ph" + }, + { + "text": "Application of chaos indicators in the study of dynamics of S-type\n extrasolar planets in stellar binaries: The orbits of two individual planets in two known binary star systems, \\gamma\nCephei and HD 196885 are numerically integrated using various numerical\ntechniques to assess the chaotic or quasi-periodic nature of the dynamical\nsystem considered. The Hill stability (HS) function which measures the orbital\nperturbation of a planet around the primary star due to the secondary star is\ncalculated for each system. The maximum Lyapunov exponent (MLE) time series are\ngenerated to measure the divergence/convergence rate of stable manifolds, which\nare used to differentiate between chaotic and non-chaotic orbits. Then, we\ncalculate dynamical Mean Exponential Growth factor of Nearby Orbits (MEGNO)\nmaps from solving the variational equations along with the equations of motion.\nThese maps allow us to accurately differentiate between stable and unstable\ndynamical systems. The results obtained from the analysis of HS, MLE, and MEGNO\nmaps are analysed for their dynamical variations and resemblance. The HS test\nfor the planets shows stability and quasi-periodicity for at least ten million\nyears. The MLE and the MEGNO maps have also indicated the local\nquasi-periodicity and global stability in a relatively short integration\nperiod. The orbital stability of the systems is tested using each indicator for\nvarious values of planet inclinations (i_{pl} \\le 25^\\circ) and binary\neccentricities. The reliability of HS criterion is also discussed based on its\nstability results compared with the MLE and MEGNO maps.", + "category": "astro-ph" + }, + { + "text": "The U.S. Eclipse Megamovie in 2017: a white paper on a unique outreach\n event: Totality during the solar eclipse of 2017 traverses the entire breadth of the\ncontinental United States, from Oregon to South Carolina. It thus provides the\nopportunity to assemble a very large number of images, obtained by amateur\nobservers all along the path, into a continuous record of coronal evolution in\ntime; totality lasts for an hour and a half over the continental U.S. While we\ndescribe this event here as an opportunity for public education and outreach,\nsuch a movie -with very high time resolution and extending to the chromosphere\n- will also contain unprecedented information about the physics of the solar\ncorona.", + "category": "astro-ph" + }, + { + "text": "Simulations of coronagraphy with a dynamic hologram for the direct\n detection of exo-planets: In a previous paper, we discussed an original solution to improve the\nperformances of coronagraphs by adding, in the optical scheme, an adaptive\nhologram removing most of the residual speckle starlight.\n In our simulations, the detection limit in the flux ratio between a host star\nand a very near planet (5 lambda/D) improves over a factor 1000 (resp. 10000)\nwhen equipped with a hologram for cases of wavefront bumpiness imperfections of\nlambda/20 (resp. lambda/100).\n We derive, in this paper, the transmission accuracy required on the hologram\npixels to achieve such goals. We show that preliminary tests could be performed\non the basis of existing technologies.", + "category": "astro-ph" + }, + { + "text": "Reconciling the Metallicity Distributions of Gamma-ray Burst, Damped\n Lyman-alpha, and Lyman-break Galaxies at z=3: We test the hypothesis that the host galaxies of long-duration gamma-ray\nbursts (GRBs) as well as quasar-selected damped Lyman-alpha (DLA) systems are\ndrawn from the population of UV-selected star-forming, high-z galaxies\n(generally referred to as Lyman-break galaxies). Specifically, we compare the\nmetallicity distributions of the GRB and DLA populations to simple models where\nthese galaxies are drawn randomly from the distribution of star-forming\ngalaxies according to their star-formation rate and HI cross-section\nrespectively. We find that it is possible to match both observational\ndistributions assuming very simple and constrained relations between\nluminosity, metallicity and HI sizes. The simple model can be tested by\nobserving the luminosity distribution of GRB host galaxies and by measuring the\nluminosity and impact parameters of DLA selected galaxies as a function of\nmetallicity. Our results support the expectation that GRB and DLA samples, in\ncontrast to magnitude limited surveys, provide an almost complete census of z=3\nstar-forming galaxies that are not heavily dust-obscured.", + "category": "astro-ph" + }, + { + "text": "Supernova ejecta interacting with a circumstellar disk. I.\n two-dimensional radiation-hydrodynamic simulations: We perform a series of two-dimensional radiation-hydrodynamic simulations of\nthe collision between supernova ejecta and circumstellar media (CSM). The\nhydrodynamic interaction of a fast flow and the surrounding media efficiently\ndissipates the kinetic energy of the fast flow and considered as a dominant\nenergy source for a specific class of core-collapse supernovae. Despite some\nobservational evidence for aspherical ejecta and/or CSM structure,\nmulti-dimensional effects in the ejecta-CSM interaction are relatively\nunexplored. Our numerical simulations equipped with an adaptive mesh refinement\ntechnique successfully reproduce hydrodynamic instabilities developing around\nthe ejecta-CSM interface. We also investigate effects of disk-like CSM on the\ndynamical evolution of supernova ejecta and bolometric light curves. We find\nthat emission powered by ejecta-disk interaction exhibits significant viewing\nangle dependence. For a line of sight close to the symmetry axis, the observer\ndirectly sees the supernova ejecta, leading to a short brightening timescale.\nFor an observer seeing the emission through the CSM disk, thermal photons\ndiffuse throughout the CSM and thus the light curve is severely smeared out.", + "category": "astro-ph" + }, + { + "text": "Deep Fields: The Faint sub-mJy and microJy Radio Sky - A VLBI\n Perspective: Until recently, VLBI targets have been drawn almost exclusively from the\nbrightest and most compact radio sources in the sky, with typical flux\ndensities well in excess of a few tens of mJy. These sources are predominantly\nidentified with Active Galactic Nuclei (AGN), located at cosmological\ndistances. In this lecture I will attempt to summarise what is currently known\nabout the general properties of the faint sub-mJy and microJy radio source\npopulation, as determined from deep multi-wavelength studies of the HDF-N. In\nparticular, I will try to provide a VLBI perspective, describing the first\ndeep, wide-field, VLBI pilot observations of the HDF, together with a summary\nof the main results. The role VLBI can play in future high resolution studies\nof faint radio sources is also addressed.", + "category": "astro-ph" + }, + { + "text": "On the stellar populations of massive galaxies: In this Letter, we analyse the predicted physical properties of massive\ngalaxies, in the framework of recent semi-analytic models of galaxy formation.\nAll models considered account for winds driven by supernovae explosions and\nsuppression of gas condensation at the centre of relatively massive haloes by\nactive galactic nuclei (AGN). We show that, while these models successfully\nreproduce the old stellar populations observed for massive galaxies, they fail\nin reproducing their observed chemical abundances. This problem is alleviate\nbut still present if AGN feedback is completely switched off. Moreover, in this\ncase, model predictions fail in accounting for the old stellar ages of massive\ngalaxies. We argue that the difficulty of semi-analytical models in\nsimultaneously reproducing the observed ages and metallicities of massive\ngalaxies, signals a fundamental problem with the schemes that are currently\nadopted to model star formation, feedback, and related recycling of gas and\nmetals.", + "category": "astro-ph" + }, + { + "text": "A Ubiquitous Unifying Degeneracy in Two-Body Microlensing Systems: While gravitational microlensing by planetary systems provides unique vistas\non the properties of exoplanets, observations of a given 2-body microlensing\nevent can often be interpreted with multiple distinct physical configurations.\nSuch ambiguities are typically attributed to the close-wide and inner-outer\ntypes of degeneracies that arise from transformation invariances and symmetries\nof microlensing caustics. However, there remain unexplained inconsistencies\nbetween aforementioned theories and observations. Here, leveraging a fast\nmachine learning inference framework, we present the discovery of the offset\ndegeneracy, which concerns a magnification-matching behaviour on the lens-axis\nand is formulated independent of caustics. This offset degeneracy unifies the\nclose-wide and inner-outer degeneracies, generalises to resonant topologies,\nand upon reanalysis, not only appears ubiquitous in previously published\nplanetary events with 2-fold degenerate solutions, but also resolves prior\ninconsistencies. Our analysis demonstrates that degenerate caustics do not\nstrictly result in degenerate magnifications and that the commonly invoked\nclose-wide degeneracy essentially never arises in actual events. Moreover, it\nis shown that parameters in offset degenerate configurations are related by a\nsimple expression. This suggests the existence of a deeper symmetry in the\nequations governing 2-body lenses than previously recognised.", + "category": "astro-ph" + }, + { + "text": "On the DM interpretation of the origin of non-thermal phenomena in\n galaxy clusters: (Abridged) We study the predictions of various annihilating Dark Matter (DM)\nmodels in order to interpret the origin of non-thermal phenomena in galaxy\nclusters. We consider three neutralino DM models with light (9 GeV),\nintermediate (60 GeV) and high (500 GeV) mass. The secondary particles created\nby neutralino annihilation produce a multi-frequency Spectral Energy\nDistribution (SED), as well as heating of the intracluster gas, that are tested\nagainst the observations available for the Coma cluster. The DM produced SEDs\nare normalized to the Coma radio halo spectrum. We find that it is not possible\nto interpret all non-thermal phenomena observed in Coma in terms of DM\nannihilation. The DM model with 9 GeV mass produces too small power at all\nfrequencies, while the DM model with 500 GeV produces a large excess power at\nall frequencies. The DM model with 60 GeV and $\\tau^{\\pm}$ composition is\nconsistent with the HXR and gamma-ray data but fails to reproduce the EUV and\nsoft X-ray data. The DM model with 60 GeV and $b{\\bar b}$ composition is always\nbelow the observed fluxes. The radio halo spectrum of Coma is well fitted only\nin the $b{\\bar b}$ or light and intermediate mass DM models. The heating\nproduced by DM annihilation in the center of Coma is always larger than the\nintracluster gas cooling rate for an NFW DM density profile and it is\nsubstantially smaller than the cooling rate only for a cored DM density profile\nin DM model with 9 GeV. We conclude that the possibility of interpreting the\norigin of non-thermal phenomena in galaxy clusters with DM annihilation models\nrequires a low neutralino mass and a cored DM density profile. If we then\nconsider the multimessenger constraints to the neutralino annihilation\ncross-section, it turns out that such scenario would also be excluded unless we\nintroduce a substantial boost factor due to the presence of DM substructures.", + "category": "astro-ph" + }, + { + "text": "Searching for Molecular Jets from High-Mass Protostars: We report Very Large Array (VLA) observations in the Q-band toward 10 ionized\njet candidates to search for SiO emission, a well-known shocked gas tracer. We\ndetected 7 mm continuum counterparts toward 90% of the jet candidates. In most\ncases, the jet candidate is located toward the center of the 7 mm core, and the\nhigh masses ($\\approx 100\\,M_\\odot$) and densities ($\\approx 10^7\\,\n\\text{cm}^{-3}$) of the cores suggest that the central objects are very young\nhigh-mass protostars. We detected SiO $J=1-0$ emission associated with 6 target\nsources. In all cases, the morphology and spectrum of the emission is\nconsistent with what is expected for molecular jets along an outflow axis, thus\nconfirming the jet nature of 60% of our sample. Our data suggest a positive\ncorrelation between the SiO luminosity $L_{SiO}$, and both the bolometric\nluminosity $L_{Bol}$ and the radio luminosity $S_\\nu d^2$ of the driving\nsources.", + "category": "astro-ph" + }, + { + "text": "CO Cameron band and CO2+ UV doublet emissions in the dayglow of Venus:\n Role of CO in the Cameron band production: Present study deals with the model calculations of CO Cameron band and CO2+\nultraviolet doublet emissions in the dayglow of Venus. The overhead and limb\nintensities of CO Cameron band and CO2+ UV doublet emissions are calculated for\nlow, moderate, and high solar activity conditions. Using updated cross\nsections, the impact of dierent e-CO cross section for Cameron band production\nis estimated. The electron impact on CO is the major source mechanism of\nCameron band, followed by electron and photon impact dissociation of CO2. The\noverhead intensities of CO Cameron band and CO2+ UV doublet emissions are about\na factor of 2 higher in solar maximum than those in solar minimum condition.\nThe effect of solar EUV flux models on the emission intensity is ~30-40% in\nsolar minimum condition and ~2-10% in solar maximum condition. At the altitude\nof emission peak (135 km), the model predicted limb intensity of CO Cameron\nband and CO2+ UV doublet emissions in moderate (F10.7 = 130) solar activity\ncondition is about 2400 and 300 kR, respectively, which is in agreement with\nthe very recently published SPICAV/Venus Express observation. The model limb\nintensity profiles of CO Cameron band and CO2+ UV doublet are compared with\nSPICAV observation. We also calculated intensities of N2 Vegard-Kaplan UV bands\nand OI 2972 {\\AA} emissions during moderate and high solar activity conditions.", + "category": "astro-ph" + }, + { + "text": "Early assembly of the most massive galaxies: The current consensus is that galaxies begin as small density fluctuations in\nthe early Universe and grow by in situ star formation and hierarchical merging.\nStars begin to form relatively quickly in sub-galactic sized building blocks\ncalled haloes which are subsequently assembled into galaxies. However, exactly\nwhen this assembly takes place is a matter of some debate. Here we report that\nthe stellar masses of brightest cluster galaxies, which are the most luminous\nobjects emitting stellar light, some 9 billion years ago are not significantly\ndifferent from their stellar masses today. Brightest cluster galaxies are\nalmost fully assembled 4-5 Gyrs after the Big Bang, having grown to more than\n90% of their final stellar mass by this time. Our data conflict with the most\nrecent galaxy formation models based on the largest simulations of dark matter\nhalo development. These models predict protracted formation of brightest\ncluster galaxies over a Hubble time, with only 22% of the stellar mass\nassembled at the epoch probed by our sample. Our findings suggest a new picture\nin which brightest cluster galaxies experience an early period of rapid growth\nrather than prolonged hierarchical assembly.", + "category": "astro-ph" + }, + { + "text": "The chemical composition of Ultracompact Dwarf Galaxies in the Virgo and\n Fornax Clusters: We present spectroscopic observations of ultra compact dwarf (UCD) galaxies\nin the Fornax and Virgo Clusters made to measure and compare their stellar\npopulations. The spectra were obtained on the Gemini-North (Virgo) and\nGemini-South (Fornax) Telescopes using the respective Gemini Multi-Object\nSpectrographs.\n We estimated the ages, metallicities and abundances of the objects from mea-\nsurements of Lick line-strength indices in the spectra; we also estimated the\nages and metallicities independently using a direct spectral fitting technique.\nBoth methods re- vealed that the UCDs are old (mean age 10.8 \\pm 0.7 Gyr) and\n(generally) metal-rich (mean [Fe/H] = -0.8 \\pm 0.1). The alpha-element\nabundances of the objects measured from the Lick indices are super-Solar.\n We used these measurements to test the hypothesis that UCDs are formed by the\ntidal disruption of present-day nucleated dwarf elliptical galaxies. The data\nare not consistent with this hypothesis because both the ages and abundances\nare significantly higher than those of observed dwarf galaxy nuclei (this does\nnot exclude disruption of an earlier generation of dwarf galaxies). They are\nmore consistent with the properties of globular star clusters, although at\nhigher mean metallicity. The UCDs display a very wide range of metallicity\n(-1.7 <[Fe/H]< 0.0), spanning the full range of both globular clusters and\ndwarf galaxy nuclei.\n We confirm previous reports that most UCDs have high metalliticities for\ntheir luminosities, lying significantly above the canonical\nmetallicitiy-luminosity relation followed by early-type galaxies. In contrast\nto previous work we find that there is no significant difference in either the\nmean ages or the mean metallicities of the Virgo and Fornax UCD populations.", + "category": "astro-ph" + }, + { + "text": "Polarization in microlensing towards the Galactic bulge: Gravitational microlensing, when finite size source effects are relevant,\nprovides an unique tool for the study of source star stellar atmospheres\nthrough an enhancement of a characteristic polarization signal. This is due to\nthe differential magnification induced during the crossing of the source star.\nIn this paper we consider a specific set of reported highly magnified, both\nsingle and binary exoplanetary systems, microlensing events towards the\nGalactic bulge and evaluate the expected polarization signal. To this purpose,\nwe consider several polarization models which apply to different types of\nsource stars: hot, late type main sequence and cool giants. As a result we\ncompute the polarization signal P,which goes up to P=0.04% for late type stars\nand up to a few percent for cool giants, depending on the underlying physical\npolarization processes and atmosphere model parameters. Given a I band\nmagnitude at maximum magnification of about 12, and a typical duration of the\npolarization signal up to 1 day, we conclude that the currently available\ntechnology, in particular the polarimeter in FORS2 on the VLT, potentially may\nallow the detection of such signals. This observational programme may take\nadvantage of the currently available surveys plus follow up strategy already\nroutinely used for microlensing monitoring towards the Galactic bulge (aimed at\nthe detection of exoplanets). In particular, this allows one to predict in\nadvance for which events and at which exact time the observing resources may be\nfocused to make intensive polarization measurements.", + "category": "astro-ph" + }, + { + "text": "Probing the Curious Case of a Galaxy Cluster Merger in Abell 115 with\n High Fidelity Chandra X-ray Temperature and Radio Maps: We present results from an X-ray and radio study of the merging galaxy\ncluster Abell 115. We use the full set of 5 Chandra observations taken of A115\nto date (360 ks total integration) to construct high-fidelity temperature and\nsurface brightness maps. We also examine radio data from the Very Large Array\nat 1.5 GHz and the Giant Metrewave Radio Telescope at 0.6 GHz. We propose that\nthe high X-ray spectral temperature between the subclusters results from the\ninteraction of the bow shocks driven into the intracluster medium by the motion\nof the subclusters relative to one another. We have identified morphologically\nsimilar scenarios in Enzo numerical N-body/hydrodynamic simulations of galaxy\nclusters in a cosmological context. In addition, the giant radio relic feature\nin A115, with an arc-like structure and a relatively flat spectral index, is\nlikely consistent with other shock-associated giant radio relics seen in other\nmassive galaxy clusters. We suggest a dynamical scenario that is consistent\nwith the structure of the X-ray gas, the hot region between the clusters, and\nthe radio relic feature.", + "category": "astro-ph" + }, + { + "text": "A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics: We present a new sample of M subdwarfs compiled from the 7th data release of\nthe Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample\nsignificantly increases the number of spectroscopically confirmed low-mass\nsubdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We\npresent the entire catalog including observed and derived quantities, and\ntemplate spectra created from co-added subdwarf spectra. We show color-color\nand reduced proper motion diagrams of the three metallicity classes, which are\nshown to separate from the disk dwarf population. The extreme and ultra\nsubdwarfs are seen at larger values of reduced proper motion as expected for\nmore dynamically heated populations. We determine 3D kinematics for all of the\nstars with proper motions. The color-magnitude diagrams show a clear separation\nof the three metallicity classes with the ultra and extreme subdwarfs being\nsignificantly closer to the main sequence than the ordinary subdwarfs. All\nsubdwarfs lie below (fainter) and to the left (bluer) of the main sequence.\nBased on the average $(U,V,W)$ velocities and their dispersions, the extreme\nand ultra subdwarfs likely belong to the Galactic halo, while the ordinary\nsubdwarfs are likely part of the old Galactic (or thick) disk. An extensive\nactivity analysis of subdwarfs is performed using H$\\alpha$ emission and 208\nactive subdwarfs are found. We show that while the activity fraction of\nsubdwarfs rises with spectral class and levels off at the latest spectral\nclasses, consistent with the behavior of M dwarfs, the extreme and ultra\nsubdwarfs are basically flat.", + "category": "astro-ph" + }, + { + "text": "Probing the Astrophysics of Cluster Outskirts: In galaxy clusters the entropy distribution of the IntraCluster Plasma\nmodulates the latter's equilibrium within the Dark Matter gravitational wells,\nas rendered by our Supermodel. We argue the entropy production at the boundary\nshocks to be reduced or terminated as the accretion rates of DM and\nintergalactic gas peter out; this behavior is enforced by the slowdown in the\noutskirt development at late times, when the Dark Energy dominates the\ncosmology while the outer wings of the initial perturbation drive the growth.\nIn such conditions, we predict the ICP temperature profiles to steepen into the\ncluster outskirts. The detailed expectations from our simple formalism agree\nwith the X-ray data concerning five clusters whose temperature profiles have\nbeen recently measured out to the virial radius. We predict steep temperature\ndeclines to prevail in clusters at low redshift, tempered only by rich environs\nincluding adjacent filamentary structures.", + "category": "astro-ph" + }, + { + "text": "Zel'dovich approximation and General Relativity: We show how the Zel'dovich approximation and the second order displacement\nfield of Lagrangian perturbation theory can be obtained from a general\nrelativistic gradient expansion in \\Lambda{}CDM cosmology. The displacement\nfield arises as a result of a second order non-local coordinate transformation\nwhich brings the synchronous/comoving metric into a Newtonian form. We find\nthat, with a small modification, the Zel'dovich approximation holds even on\nscales comparable to the horizon. The corresponding density perturbation is not\nrelated to the Newtonian potential via the usual Poisson equation but via a\nmodified Helmholtz equation. This is a consequence of causality not present in\nthe Newtonian theory. The second order displacement field receives relativistic\ncorrections that are subdominant on short scales but are comparable to the\nsecond order Newtonian result on scales approaching the horizon. The\ncorrections are easy to include when setting up initial conditions in large\nN-body simulations.", + "category": "astro-ph" + }, + { + "text": "APSYNSIM: An Interactive Tool To Learn Interferometry: The APerture SYNthesis SIMulator is a simple interactive tool to help the\nstudents visualize and understand the basics of the Aperture Synthesis\ntechnique, applied to astronomical interferometers. The users can load many\ndifferent interferometers and source models (and also create their own), change\nthe observing parameters (e.g., source coordinates, observing wavelength,\nantenna location, integration time, etc.), and even deconvolve the\ninterferometric images and corrupt the data with gain errors (amplitude and\nphase). The program is fully interactive and all the figures are updated in\nreal time. APSYNSIM has already been used in several interferometry schools and\nhas got very positive feedback from the students.", + "category": "astro-ph" + }, + { + "text": "Effects of Radiation Pressure on the Evaporative Wind of HD 209458b: The role of radiation pressure in shaping exoplanet photoevaporation remains\na topic of contention. Radiation pressure from the exoplanet's host star has\nbeen proposed as a mechanism to drive the escaping atmosphere into a \"cometary\"\ntail and explain the high velocities observed in systems where mass loss is\noccurring. In this paper we present results from high-resolution 3-D\nhydrodynamic simulations of a planet similar to HD 209458b. We\nself-consistently launch a wind flowing outward from the planet by calculating\nthe ionization and heating resulting from incident high-energy radiation, and\naccount for radiation pressure. We first present a simplified calculation,\nsetting a limit on the Lyman-$\\alpha$ flux required to drive the\nphoto-evaporated planetary material to larger radii and line-of-sight\nvelocities. We then present the results of our simulations, which confirm the\nlimits determined by our analytic calculation. We thus demonstrate that, within\nthe limits of our hydrodynamic simulation and for the Lyman-$\\alpha$ fluxes\nexpected for HD 209458, radiation pressure is unlikely to significantly affect\nphotoevaporative winds or to explain the high velocities at which wind material\nis observed, though further possibilities remain to be investigated.", + "category": "astro-ph" + }, + { + "text": "The GRB/SN Connection: An Improved Spectral Flux Distribution for the\n Supernova Candidate Associated with GRB 970228: We better determine the spectral flux distribution of the supernova candidate\nassociated with GRB 970228 by modeling the spectral flux distribution of the\nhost galaxy of this burst, fitting this model to measurements of the host\ngalaxy, and using the fitted model to better subtract out the contribution of\nthe host galaxy to measurements of the afterglow of this burst.", + "category": "astro-ph" + }, + { + "text": "Distinguishing Propagation vs. Launch Physics of Astrophysical Jets and\n the Role of Experiments: The absence of other viable momentum sources for collimated flows leads to\nthe likelihood that magnetic fields play a fundamental role in jet launch\nand/or collimation in astrophysical jets. To best understand the physics of\njets, it is useful to distinguish between the launch region where the jet is\naccelerated and the larger scales where the jet propagates as a collimated\nstructure. Observations presently resolve jet propagation, but not the launch\nregion. Simulations typically probe the launch and propagation regions\nseparately, but not both together. Here, I identify some of the physics of jet\nlaunch vs. propagation and what laboratory jet experiments to date have probed.\nReproducing an astrophysical jet in the lab is unrealistic, so maximizing the\nbenefit of the experiments requires clarifying the astrophysical connection.", + "category": "astro-ph" + }, + { + "text": "Evidence for a Non-Expanding Universe: Surface Brightness Data From HUDF: Surface brightness data can distinguish between a Friedman-Robertson-Walker\nexpanding universe and a non-expanding universe. For surface brightness\nmeasured in AB magnitudes per angular area, all FRW models, regardless of\ncosmological parameters, predict that surface brightness declines with redshift\nas (z+1)^-3, while any non-expanding model predicts that surface brightness is\nconstant with distance and thus with z. High-z UV surface brightness data for\ngalaxies from the Hubble Ultra Deep Field and low-z data from GALEX are used to\ntest the predictions of these two models up to z=6. A preliminary analysis\npresented here of samples observed at the same at-galaxy wavelengths in the UV\nshows that surface brightness is constant, mu=kz^0.026+-0.15, consistent with\nthe non-expanding model. This relationship holds if distance is linearly\nproportional to z at all redshifts, but seems insensitive to the particular\nchoice of d-z relationship. Attempts to reconcile the data with FRW predictions\nby assuming that high-z galaxies have intrinsically higher surface brightness\nthan low-z galaxies appear to face insurmountable problems. The intrinsic FUV\nsurface brightness required by the FRW models for high-z galaxies exceeds the\nmaximum FUV surface brightness of any low-z galaxy by as much as a factor of\n40. Dust absorption appears to make such extremely high intrinsic FUV surface\nbrightness physically impossible. If confirmed by further analysis, the\nimpossibility of such high-surface-brightness galaxies would rule out all FRW\nexpanding universe (big bang) models.", + "category": "astro-ph" + }, + { + "text": "Simulations at the Dwarf Scale: From Violent Dwarfs at Cosmic Dawn and\n Cosmic Noon to Quiet Discs today: Dwarf galaxies with stellar masses around 10^9 Msun can be explored at high\nand low redshifts and they give a glimpse of the different conditions of galaxy\nformation at different epochs. Using a large sample of about 300 zoom-in\ncosmological hydrodynamical simulations of galaxy formation I will briefly\ndescribe the formation of dwarfs at this mass scale at 3 different epochs:\ncosmic dawn (Ceverino, Klessen, Glover 2018), cosmic noon (Ceverino, Primack,\nDekel 2015), and today (Ceverino et al. 2017). I will describe the FirstLight\nsimulations of first galaxies at redshifts 5-15. These first dwarfs have\nextremely high star formation efficiencies due to high gas fractions and high\ngas accretion rates. These simulations will make predictions that will be\ntested for the first time with the James Webb Space Telescope (JWST). At cosmic\nnoon, z = 2, galaxy formation is still a very violent and dynamic process. The\nVELA simulations have generated a set of dispersion-dominated dwarfs that show\nan elongated morphology due to their prolate dark-matter halos. Between z = 1\nand 0, the AGORA simulation shows the formation of a low-mass disc due to slow\ngas accretion. The disc agrees with many local scaling relations, such as the\nstellar-mass-halo-mass and the baryonic Tully-Fisher relation.", + "category": "astro-ph" + }, + { + "text": "SN 2005ip: A Luminous Type IIn Supernova Emerging from a Dense\n Circumstellar Medium as Revealed by X-Ray Observations: We report on X-ray spectral evolution of the nearby Type IIn supernova (SN)\n2005ip, based on Chandra and Swift observations covering from ~1 to 6 years\nafter the explosion. X-ray spectra in all epochs are well fitted by a thermal\nemission model with kT > 7 keV. The somewhat high temperature suggests that the\nX-ray emission mainly arises from the circumstellar medium heated by the\nforward shock. We find that the spectra taken 2-3 years since the explosion are\nheavily absorbed N_H ~ 5e22 cm^{-2}, but the absorption gradually decreases to\nthe level of the Galactic absorption N_H ~ 4e20 cm^{-2} at the final epoch.\nThis indicates that the SN went off in a dense circumstellar medium and that\nthe forward shock has overtaken it. The intrinsic X-ray luminosity stays\nconstant until the final epoch when it drops by a factor of ~2. The intrinsic\n0.2-10 keV luminosity during the plateau phase is measured to be ~1.5e41 erg/s,\nranking SN 2005ip as one of the brightest X-ray SNe. Based on the column\ndensity, we derive a lower-limit of a mass-loss rate to be M_dot ~ 0.015\n(V_w/100 km/s) M_sun/yr, which roughly agrees with that inferred from the X-ray\nluminosity, M_dot ~ 0.02 (V_w/100 km/s) M_sun/yr, where V_w is the\ncircumstellar wind speed. Such a high mass-loss rate suggests that the\nprogenitor star had eruptive mass ejections like a luminous blue variable star.\nThe total mass ejected in the eruptive period is estimated to be ~15 M_sun,\nindicating that the progenitor mass is greater than ~25 M_sun.", + "category": "astro-ph" + }, + { + "text": "Kinematical evolution of multiple stellar populations in star clusters: We present the results of a suite of \\Nbody simulations aimed at\nunderstanding the fundamental aspects of the long-term evolution of the\ninternal kinematics of multiple stellar populations in globular clusters. Our\nmodels enable us to study the cooperative effects of internal,\nrelaxation-driven processes and external, tidally-induced perturbations on the\nstructural and kinematic properties of multiple-population globular clusters.\nTo analyse the dynamical behaviour of the multiple stellar populations in a\nvariety of spin-orbit coupling conditions, we have considered three reference\ncases in which the tidally perturbed star cluster rotates along an axis\noriented in different directions with respect to the orbital angular momentum\nvector. We focus specifically on the characterisation of the evolution of the\ndegree of differential rotation and anisotropy in the velocity space, and we\nquantify the process of spatial and kinematic mixing of the two populations. In\nlight of recent and forthcoming explorations of the internal kinematics of this\nclass of stellar systems by means of line-of sight and astrometric\nmeasurements, we also investigate the implications of projection effects and\nspatial distribution of the stars adopted as tracers. The kinematic and\nstructural richness emerging from our models further emphasises the need and\nthe importance of observational studies aimed at building a complete\nkinematical picture of the multiple population phenomenon.", + "category": "astro-ph" + }, + { + "text": "The X-ray activity-rotation relation of T Tauri stars in Taurus-Auriga: The Taurus-Auriga star-forming complex hosts the only population of T Tauri\nstars in which an anticorrelation of X-ray activity and rotation period has\nbeen observed. We have used XMM-Newton's European Photon Imaging Cameras to\nperform the most sensitive survey to date of X-ray emission (0.3-10 keV) from\nyoung stars in Taurus-Auriga and investigate the dependences of X-ray activity\nmeasures -- X-ray luminosity, Lx, its ratio with the stellar luminosity,\nLx/Lstar, and the surface-averaged X-ray flux, Fxs -- on rotation period. We\ntested for differences in the distributions of Lx/Lstar of fast and slow\nrotators, accretors and non-accretors, and compared the dependence of Lx/Lstar\non the ratio of the rotation period and the convective turnover timescale, the\nRossby number, with that of late-type main-sequence stars. We found significant\nanticorrelations of Lx and Fxs with rotation period, but these could be\nexplained by the typically higher stellar luminosity and effective temperature\nof fast-rotators in Taurus-Auriga and a near-linear dependence of Lx on Lstar.\nWe found no evidence for a dependence of Lx/Lstar on rotation period, but for\naccretors to have lower Lx/Lstar than non-accretors at all rotation periods.\nThe Rossby numbers of accretors and non-accretors were found to be the same as\nthose of late-type main-sequence stars showing saturated X-ray emission. We\nconclude that non-accreting T Tauri stars show X-ray activity entirely\nconsistent with the saturated activity of late-type main-sequence stars.\nAccreting T Tauri stars show lower X-ray activity, which cannot be attributed\nto their slower rotation.", + "category": "astro-ph" + }, + { + "text": "Galaxy and Mass Assembly (GAMA): Probing galaxy-group correlations in\n redshift space with the halo streaming model: We have studied the galaxy-group cross-correlations in redshift space for the\nGalaxy And Mass Assembly (GAMA) Survey. We use a set of mock GAMA galaxy and\ngroup catalogues to develop and test a novel 'halo streaming' model for\nredshift-space distortions. This treats 2-halo correlations via the streaming\nmodel, plus an empirical 1-halo term derived from the mocks, allowing accurate\nmodelling into the nonlinear regime. In order to probe the robustness of the\ngrowth rate inferred from redshift-space distortions, we divide galaxies by\ncolour, and divide groups according to their total stellar mass, calibrated to\ntotal mass via gravitational lensing. We fit our model to correlation data, to\nobtain estimates of the perturbation growth rate, $f\\sigma_8$, validating\nparameter errors via the dispersion between different mock realizations. In\nboth mocks and real data, we demonstrate that the results are closely\nconsistent between different subsets of the group and galaxy populations,\nconsidering the use of correlation data down to some minimum projected radius,\n$r_{\\rm min}$. For the mock data, we can use the halo streaming model to below\n$r_{\\rm min} = 5h^{-1}$ Mpc, finding that all subsets yield growth rates within\nabout 3% of each other, and consistent with the true value. For the actual GAMA\ndata, the results are limited by cosmic variance: $f\\sigma_8=0.29\\pm 0.10$ at\nan effective redshift of 0.20; but there is every reason to expect that this\nmethod will yield precise constraints from larger datasets of the same type,\nsuch as the DESI bright galaxy survey.", + "category": "astro-ph" + }, + { + "text": "A Novel Survey for Young Substellar Objects with the W band Filter.V. IC\n 348 and Barnard 5 in the Perseus Cloud: We report the discovery of substellar objects in the young star cluster IC\n348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the\nPerseus star-forming complex. The substellar candidates are selected using\nnarrowband imaging, i.e., on and off photometric technique with a filter\ncentered around the water absorption feature at 1.45 microns, a technique\nproven to be efficient in detecting water-bearing substellar objects. Our\nspectroscopic observations confirm three brown dwarfs in IC 348. In addition,\nthe source WBIS 03492858+3258064, reported in this work, is the first confirmed\nbrown dwarf discovered toward Barnard 5. Together with the young stellar\npopulation selected via near- and mid-infrared colors using the Two Micron All\nSky Survey and the Wide-field Infrared Survey Explorer, we diagnose the\nrelation between stellar versus substellar objects with the associated\nmolecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud\nmembers across the Perseus region, we propose the star formation scenario of\nthe complex under influence of the nearby OB association.", + "category": "astro-ph" + }, + { + "text": "Rotational quenching of rotationally-excited H$_2$O in collisions with\n He: Theoretical rotational quenching cross sections and rate coefficients of\northo- and para-H$_2$O due to collisions with He atoms are presented. The\ncomplete angular momentum close-coupling approach as well as the coupled-states\napproximation for angular momentum decoupling were applied to solve the\nscattering problem for a large range of rotationally-excited states of water.\nResults are obtained for quenching from initial levels 1$_{1,0}$, 2$_{1,2}$,\n2$_{2,1}$, 3$_{0,3}$, 3$_{1,2}$, 3$_{2,1}$, 4$_{1,4}$, 3$_{3,0}$, and 4$_{2,3}$\nof ortho-H$_2$O and from initial levels 1$_{1,1}$, 2$_{0,2}$, 2$_{1,1}$,\n2$_{2,0}$, 3$_{1,3}$, 3$_{2,2}$, 4$_{0,4}$, 4$_{1,3}$, and 3$_{3,1}$ of\npara-H$_2$O for kinetic energies from 10$^{-5}$ to 10$^4$ cm$^{-1}$.\nState-to-state and total deexcitation cross sections and rate coefficients for\ntemperatures between 0.1 and 3000 K are reported. The present state-to-state\nrate coefficients are found to be in good agreement with previous results\nobtained by Green and coworkers at high temperatures, but significant\ndiscrepancies are obtained at lower temperatures likely due to differences in\nthe adopted potential energy surfaces. Astrophysical applications of the\ncurrent rate coefficients are briefly discussed.", + "category": "astro-ph" + }, + { + "text": "Analytical Blowup Solutions to the Isothermal Euler-Poisson Equations of\n Gaseous Stars in R^N: This article is the continued version of the analytical blowup solutions for\n2-dimensional Euler-Poisson equations in \"M.W. Yuen, Analytical Blowup\nSolutions to the 2-dimensional Isothermal Euler-Poisson Equations of Gaseous\nStars, J. Math. Anal. Appl. 341 (1)(2008), 445-456.\" and \"M.W. Yuen, Analytical\nBlowup Solutions to the 2-dimensional Isothermal Euler-Poisson Equations of\nGaseous Stars II. arXiv:0906.0176v1\". With the extension of the blowup\nsolutions with radial symmetry for the isothermal Euler-Poisson equations in\nR^2, other special blowup solutions in R^N with non-radial symmetry are\nconstructed by the separation method. Key words: Analytical Solutions,\nEuler-Poisson Equations, Isothermal, Blowup, Special Solutions, Non-radial\nSymmetry", + "category": "astro-ph" + }, + { + "text": "UGC 7069: The largest ring galaxy: We find that UGC 7069 is the largest ring galaxy known to date. In this\nLetter, we present a multiwavelength study of this galaxy (combining radio,\n2MASS, optical and ultraviolet data). The ring of UGC 7069, whose diameter\nmeasures ~115 kpc, is also warped at its edges. The nucleus appears\ndouble-peaked and hosts a possible LINER. The ultraviolet data indicate a\nstrong blue colour and suggest that UGC 7069 is a starburst galaxy. We also\npresent N-body simulation results, which indicate that galaxy collisions can\nproduce such huge rings. Large inclination angles between the target and the\nintruder galaxy may account for the formation of warped rings. Multiwavelength\nobservations are highly essential to constrain our simulation results, which\nwill address the formation and evolution of such a rare galaxy.", + "category": "astro-ph" + }, + { + "text": "Counts and Colours of Faint Stars in 5 Fields Near the North Galactic\n Pole: Faint star number counts in the photographic \\jmag band and \\bvcol colour\ndistributions are presented for a 1.08 deg$^2$ field near the North Galactic\nPole. Due to the excellent star/galaxy discrimination we count stars as faint\nas \\jmag = 23. We compare the number counts and colour distributions in 5\nadjacent fields near SA57. The number counts and colour distributions are in\nvery good agreement with previous data. However, we find that the large\nfield-to-field scatter in the colour distributions, which we argue is real,\nmight prevent us setting strong limits on Galactic structure. A simple two\ncomponent standard model, Bahcall and Soneira (1984), fits the number counts\nreasonably well at the bright \\jmag $< 21$, but fails notably at the faint end,\neven if a third component is added, as in Reid and Majewski (1993). The\nstandard models are in good agreement with both the number counts and colour\ndistribution at $20 < $\\vmag$< 21$. Although the standard models bimodal shape\nof the colour distribution compares well with the data at $21 < $\\vmag$< 21.5$,\nthe number counts of stars are underestimated.", + "category": "astro-ph" + }, + { + "text": "A Vlbi Survey of Weak Extragalactic Radio Sources for the Alignment of\n the Icrf and the Future Gaia Frame: The space astrometry mission GAIA will construct a dense optical QSO-based\ncelestial reference frame. For consistency between the optical and radio\npositions, it will be important to align the GAIA frame and the International\nCelestial Reference Frame (ICRF) with the highest accuracy. Currently, it is\nfound that only 10% of the ICRF sources are suitable to establish this link,\neither because they are not bright enough at optical wavelengths or because\nthey have significant extended radio emission which precludes reaching the\nhighest astrometric accuracy. In order to improve the situation, we have\ninitiated a VLBI survey dedicated to finding additional high-quality radio\nsources for aligning the two frames. The sample consists of about 450 sources,\ntypically 20 times weaker than the current ICRF sources, which have been\nselected by cross-correlating optical and radio catalogues. The paper presents\nthe observing strategy and includes preliminary results of observation of 224\nof these sources with the European VLBI Network in June 2007.", + "category": "astro-ph" + }, + { + "text": "An internally consistent distance framework in the Local Group: Accurate and precise astronomical distance determinations are crucial for\nderivations of, among others, the masses and luminosities of a large variety of\ndistant objects. Astronomical distance determination has traditionally relied\non the concept of a `distance ladder.' Here we review our recent attempts to\nestablish a highly robust set of internally consistent distance determinations\nto Local Group galaxies, which we recommend as the statistical basis of an\nimproved extragalactic distance ladder.", + "category": "astro-ph" + }, + { + "text": "Voids and Halos in Voids statistics as a probe of the Expansion History\n of the Universe: Structures in the Universe are arranged into the cosmic web. Distributions,\nstatistics, and evolutions of the structures can be used as probes for\ncosmological models. We investigate the number density of voids and dark matter\nhalos-in-voids in the Excursion Set Theory (EST). We study the Markov and\nnon-Markov frameworks of EST in both spherical and ellipsoidal collapse models.\nAfterward, we compare the number density of voids and halos-in-voids in the\nstandard $\\Lambda$CDM and the reconstructed model. The reconstructed model is a\nmodel-independent reconstruction based on background observations. This work\nexplores the effects of the collapse model barrier in the different EST\nframeworks on the statistics of voids and the statistics of halos-in-voids.\nFinally, we find the hint that cosmological models can be distinguished by the\nnumber density of halos-in-voids in the $1.0-2.5$ redshift range. The maximum\ndifference is observed in $z\\sim1.9$.", + "category": "astro-ph" + }, + { + "text": "Radio light curves during the passage of cloud G2 near Sgr A*: We calculate radio light curves produced by the bow shock that is likely to\nform in front of the G2 cloud when it penetrates the accretion disk of Sgr A*.\nThe shock acceleration of the radio-emitting electrons is captured\nself-consistently by means of first-principles particle-in-cell simulations. We\nshow that the radio luminosity is expected to reach maximum in early 2013,\nroughly a month after the bow shock crosses the orbit pericenter. We estimate\nthe peak radio flux at 1.4 GHz to be 1.4 - 22 Jy depending on the assumed orbit\norientation and parameters. We show that the most promising frequencies for\nradio observations are in the 0.1~ 10^14-15 g/s) and moderately strong white dwarf magnetic\nmoments (>~ 10^30 G cm^3) stabilize CV disks in GCs and thus prevent most of\nthem from experiencing frequent outbursts. If it is so, rare cataclysms in GCs\nwould signal important evolutionary differences between field and cluster CVs.", + "category": "astro-ph" + }, + { + "text": "Universal protoplanetary disk size under complete non-ideal\n magnetohydrodynamics: The interplay between ion-neutral friction, Hall\n effect, and the Ohmic dissipation: The role of non-ideal magnetohydrodynamics has been proven critical during\nthe formation of the protoplanetary disk, particularly in regulating its size.\nWe provide a simple model to predict the disk size under the interplay among\nthe ambipolar diffusion, the Hall effect, and the Ohmic dissipation. The model\npredicts a small disk size of around 20 AU, that depends only sub-linearly on\ndisk parameters, for a wide range of initial conditions of sub-Solar mass and\nmoderate magnetization. It is able to explain phenomena manifested in existing\nnumerical simulations, including the bimodal disk behavior under parallel and\nanti-parallel alignment between the rotation and magnetic field. In the\nparallel configuration, the disk size decreases and eventually disappears. In\nthe anti-parallel configuration, and the disk has an outer partition (or\npseudo-disk) that is flat, shrinking , and short-lived, as well as a inner\npartition that grows slowly with mass and is long-lived. Even with significant\ninitial magnetization, the vertical field in the disk can only dominate at the\nearly stage when the mass is low, and the toroidal field eventually dominates\nin all disks.", + "category": "astro-ph" + }, + { + "text": "A Novel Estimator for the Equation of State of the IGM by Ly$\u03b1$\n Forest Tomography: We present a novel procedure to estimate the Equation of State of the\nintergalactic medium in the quasi-linear regime of structure formation based on\nLy$\\alpha$ forest tomography and apply it to 21 high quality quasar spectra\nfrom the UVES\\_SQUAD survey at redshift $z=2.5$. Our estimation is based on a\nfull tomographic inversion of the line of sight. We invert the data with two\ndifferent inversion algorithms, the iterative Gauss-Newton method and the\nregularized probability conservation approach, which depend on different priors\nand compare the inversion results in flux space and in density space. In this\nway our method combines fitting of absorption profiles in flux space with an\nanalysis of the recovered density distributions featuring prior knowledge of\nthe matter distribution. Our estimates are more precise than existing\nestimates, in particular on small redshift bins. In particular, we model the\ntemperature-density relation with a power law and observe for the temperature\nat mean density $T_0 = 13400^{+1700}_{-1300}\\,\\mathrm{K}$ and for the slope of\nthe power-law (polytropic index) $\\gamma = 1.42 \\pm 0.11$ for the power-law\nparameters describing the temperature-density relation. Moreover, we measure an\nphotoionization rate $\\Gamma_{-12} = 1.1^{+0.16}_{-0.17}$. An implementation of\nthe inversion techniques used will be made publicly available.", + "category": "astro-ph" + }, + { + "text": "C$^+$ detection of warm dark gas in diffuse clouds: We present the first results of the Herschel open time key program, Galactic\nObservations of Terahertz C$^+$ (GOT C+) survey of the [CII] fine-structure\nline at 1.9 THz (158 microns) using the HIFI instrument on Herschel. We\ndetected 146 interstellar clouds along sixteen lines-of-sight towards the inner\nGalaxy. We also acquired HI and CO isotopologue data along each line-of-sight\nfor analysis of the physical conditions in these clouds. Here we analyze 29\ndiffuse clouds (A$_{V}$ < 1.3 mag.) in this sample characterized by having\n[CII] and HI emission, but no detectable CO. We find that [CII] emission is\ngenerally stronger than expected for diffuse atomic clouds, and in a number of\nsources is much stronger than anticipated based on their HI column density. We\nshow that excess [CII] emission in these clouds is best explained by the\npresence of a significant diffuse warm H$_2$, dark gas, component. This first\n[CII] 158 micron detection of warm dark gas demonstrates the value of this\ntracer for mapping this gas throughout the Milky Way and in galaxies.", + "category": "astro-ph" + }, + { + "text": "Dynamical neutrino masses in the generalized Chaplygin gas scenario with\n mass varying CDM: Neutrinos coupled to an underlying scalar field in the scenario for\nunification of mass varying dark matter and cosmon-{\\em like} dark energy is\nexamined. In the presence of a tiny component of mass varying neutrinos, the\nconditions for the present cosmic acceleration and for the stability issue are\nreproduced. It is assumed that {\\em sterile} neutrinos behave like mass varying\ndark matter coupled to mass varying {\\em active} neutrinos through the {\\em\nseesaw} mechanism, in a kind of {\\em mixed} dark matter sector. The crucial\npoint is that the dark matter mass may also exhibit a dynamical behavior driven\nby the scalar field. The scalar field mediates the nontrivial coupling between\nthe mixed dark matter and the dark energy responsible for the accelerated\nexpansion of the universe. The equation of state of perturbations reproduce the\ngeneralized Chaplygin gas (GCG) cosmology so that all the effective results\nfrom the GCG paradigm are maintained, being perturbatively modified by\nneutrinos.", + "category": "astro-ph" + }, + { + "text": "VERITAS follow-up observation of the blazar TXS 0506+056: The gamma-ray blazar TXS 0506+056 was found with an enhanced gamma-ray\nemission state in spatial and temporal coincidence with the IceCube high energy\nneutrino event IC170922A. This is the most significant association by far\nbetween a high-energy neutrino event and a blazar in a flaring state. Studying\nthe time evolution and spectral behavior of the blazar emission may help in\nidentifying the sources of the diffuse neutrino flux observed by IceCube and\nthe origin of energetic cosmic rays. TXS 0506+056 was detected by the VERITAS\ngamma-ray observatory with a significance of 5.8 standard deviations above 110\nGeV in a 35 hour data set collected between September 23, 2017 and February 6,\n2018. Here we will present results from recent VERITAS observations and an\nassociated multiwavelength campaign, collected between October 10, 2018 to\nMarch 1, 2021. A relatively quiet very high energy gamma-ray emission state was\nobserved during this time period, and flux upper limits are used to constrain\nthe potential variability of this blazar.", + "category": "astro-ph" + }, + { + "text": "The molecular cloud S242: physical environment and star formation\n activities: We present a multi-wavelength study to probe the star formation (SF)\nprocesses on a larger scale (~1.05 deg x 0.56 deg) around the S242 site. The\nS242 molecular cloud is depicted in a velocity range from -3.25 to 4.55 km/s\nand has spatially elongated appearance. Based on the virial analysis, the cloud\nis prone to gravitational collapse. The cloud harbors an elongated filamentary\nstructure (EFS; length ~25 pc) evident in the Herschel column density map and\nthe EFS has an observed mass per unit length of ~200 M_sun/pc exceeding the\ncritical value of ~16 M_sun/pc (at T = 10 K). The EFS contains a chain of\nHerschel clumps (M_clump ~150 to 1020 M_sun), revealing the evidence of\nfragmentation along its length. The most massive clumps are observed at both\nthe EFS ends, while the S242 HII region is located at one EFS end. Based on the\nradio continuum maps at 1.28 and 1.4 GHz, the S242 HII region is ionized by a\nB0.5V - B0V type star and has a dynamical age of ~0.5 Myr. The photometric 1 -\n5 microns data analysis of point-like sources traces young stellar objects\n(YSOs) toward the EFS and the clusters of YSOs are exclusively found at both\nthe EFS ends, revealing the SF activities. Considering the spatial presence of\nmassive clumps and YSO clusters at both the EFS ends, the observed results are\nconsistent with the prediction of a SF scenario of the end-dominated collapse\ndriven by the higher accelerations of gas.", + "category": "astro-ph" + }, + { + "text": "Cosmology with the shear-peak statistics: Weak-lensing searches for galaxy clusters are plagued by low completeness and\npurity, severely limiting their usefulness for constraining cosmological\nparameters with the cluster mass function. A significant fraction of `false\npositives' are due to projection of large-scale structure and as such carry\ninformation about the matter distribution. We demonstrate that by constructing\na \"peak function\", in analogy to the cluster mass function, cosmological\nparameters can be constrained. To this end we carried out a large number of\ncosmological N-body simulations in the \\Omega_m-\\sigma_8 plane to study the\nvariation of this peak function. We demonstrate that the peak statistics is\nable to provide constraints competitive with those obtained from cosmic-shear\ntomography from the same data set. By taking the full cross-covariance between\nthe peak statistics and cosmic shear into account, we show that the combination\nof both methods leads to tighter constraints than either method alone can\nprovide.", + "category": "astro-ph" + }, + { + "text": "Optimising Spectroscopic and Photometric Galaxy Surveys: Efficient\n Target Selection and Survey Strategy: The next generation of spectroscopic surveys will have a wealth of\nphotometric data available for use in target selection. Selecting the best\ntargets is likely to be one of the most important hurdles in making these\nspectroscopic campaigns as successful as possible. Our ability to measure dark\nenergy depends strongly on the types of targets that we are able to select with\na given photometric data set. We show in this paper that we will be able to\nsuccessfully select the targets needed for the next generation of spectroscopic\nsurveys. We also investigate the details of this selection, including\noptimisation of instrument design and survey strategy in order to measure dark\nenergy. We use color-color selection as well as neural networks to select the\nbest possible emission line galaxies and luminous red galaxies for a\ncosmological survey. Using the Fisher matrix formalism we forecast the\nefficiency of each target selection scenario. We show how the dark energy\nfigures of merit change in each target selection regime as a function of target\ntype, survey time, survey density and other survey parameters. We outline the\noptimal target selection scenarios and survey strategy choices which will be\navailable to the next generation of spectroscopic surveys.", + "category": "astro-ph" + }, + { + "text": "A Frequency Comb calibrated Solar Atlas: The solar spectrum is a primary reference for the study of physical processes\nin stars and their variation during activity cycles. In Nov 2010 an experiment\nwith a prototype of a Laser Frequency Comb (LFC) calibration system was\nperformed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla\nduring which high signal-to-noise spectra of the Moon were obtained. We exploit\nthose Echelle spectra to study the optical integrated solar spectrum . The\nDAOSPEC program is used to measure solar line positions through gaussian\nfitting in an automatic way. We first apply the LFC solar spectrum to\ncharacterize the CCDs of the HARPS spectrograph. The comparison of the LFC and\nTh-Ar calibrated spectra reveals S-type distortions on each order along the\nwhole spectral range with an amplitude of +/-40 m/s. This confirms the pattern\nfound by Wilken et al. (2010) on a single order and extends the detection of\nthe distortions to the whole analyzed region revealing that the precise shape\nvaries with wavelength. A new data reduction is implemented to deal with CCD\npixel inequalities to obtain a wavelength corrected solar spectrum. By using\nthis spectrum we provide a new LFC calibrated solar atlas with 400 line\npositions in the range of 476-530, and 175 lines in the 534-585 nm range. The\nnew LFC atlas improves the accuracy of individual lines by a significant factor\nreaching a mean value of about 10 m/s. The LFC--based solar line wavelengths\nare essentially free of major instrumental effects and provide a reference for\nabsolute solar line positions. We suggest that future LFC observations could be\nused to trace small radial velocity changes of the whole solar photospheric\nspectrum in connection with the solar cycle and for direct comparison with the\npredicted line positions of 3D radiative hydrodynamical models of the solar\nphotosphere.", + "category": "astro-ph" + }, + { + "text": "Numerical Analysis of Relativistic Boltzmann-kinetic Equations to Solve\n Relativistic Shock Layer Problems: The relativistic shock layer problem was numerically analyzed by using two\nrelativistic Boltzmann-kinetic equations. One is Marle model, and the other is\nAnderson-Witting model. As with Marle model, the temperature of the gain term\nwas determined from its relation with the dynamic pressure in the framework of\n14-moments theory. From numerical results of the relativistic shock layer\nproblem, behaviors of projected moments in the nonequilibrium region were\nclarified. Profiles of the heat flux given by Marle model and Anderson-Witting\nmodel were quite adverse to the profile of the heat flux approximated by\nNavier-Stokes-Fourier law. On the other hand, profiles of the heat flux given\nby Marle model and Anderson-Witting model were similar to the profile\napproximated by Navier-Stokes-Fourier law. Additionally we discuss the\ndifferences between Anderson-Witting model and Marle model by focusing on the\nfact that the relaxational rate of the distribution function depends on both\nflow velocity and molecular velocity for Anderson-Witting model, while it\ndepends only on the molecular velocity for Marle model.", + "category": "astro-ph" + }, + { + "text": "A comparison between Fast Multipole Algorithm and Tree-Code to evaluate\n gravitational forces in 3-D: We present tests of comparison between our versions of the Fast Multipole\nAlgorithm (FMA) and ``classic'' tree-code to evaluate gravitational forces in\nparticle systems. We have optimized the Greengard's original version of FMA\nallowing for a more efficient criterion of well-separation between boxes, to\nimprove the adaptivity of the method (which is very important in highly\ninhomogeneous situations) and to permit the smoothing of gravitational\ninteractions. The results of our tests indicate that the tree-code is almost\nthree times faster than FMA for both a homogeneous and a clumped distribution,\nat least in the interval of N (N< 10^5) here investigated and at the same level\nof accuracy (error ~ 10^{-3)). This order of accuracy is generally considered\nas the best compromise between CPU-time consumption and precision for\nastrophysical simulation. Moreover, the claimed linear dependence on N of the\nCPU-time of FMA is not confirmed and we give a ``theoretical'' explanation for\nthat.", + "category": "astro-ph" + }, + { + "text": "A new insight into neutrino energy loss by electron capture of iron\n group nuclei in magnetars surface: Based on the relativistic mean-field effective interactions theory, and Lai\ndong model \\citep{b37, b38, b39}, we discuss the influences of superstrong\nmagnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and\nsingle-particle level structure in magnetars surface. By using the method of\nShell-Model Monte Carlo (SMMC), and the Random Phase Approximation (RPA)\ntheory, we detailed analyze the neutrino energy loss rates(NELRs) by electron\ncapture (EC) for iron group nuclei in SMFs.", + "category": "astro-ph" + }, + { + "text": "Ultraviolet Imaging Telescope (UVIT) observation of the Galactic\n Globular Cluster NGC 7492: We present detailed photometric observations of the Galactic globular cluster\nNGC 7492 using the data obtained with two far-ultraviolet (FUV: 1300 - 1800\n\\AA) and three near-ultraviolet (NUV: 2000 - 3000 \\AA) filters of Ultraviolet\nImaging Telescope (UVIT) on-board the \\textit{AstroSat} satellite. We confirmed\nthe cluster membership of the extracted sources using GAIA data release 2 (Gaia\nDR2) proper motion data. We have used color-magnitude diagrams (CMDs) using\nUVIT and GAIA filters to separate out different evolutionary stages of the\nstars present in the cluster. We have identified a new extreme horizontal\nbranch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The\nestimated distance-modulus of the cluster is $16.95\\pm0.05$ obtained by fitting\nBaSTI isochrones with cluster parameters, $[Fe/H] = -1.8$ dex and age $= 12.0$\nGyr on the V $-$ I vs V CMD. Interestingly, only the EHB star and blue\nhorizontal branch stars (BHBs) among the UV-bright hot sources are detected in\nFUV filters of UVIT. We have derived the effective temperature of BHBs using\ncolor-temperature relation and spectral energy distributions (SEDs) of\nmulti-band filters, which are in the range from 8,000 K to 10,500 K. We find a\nvariation of He abundance of BHBs by fitting the BaSTI ZAHB. The range in the\nHe abundance of the BHBs corresponding to the best fit isochrones is 0.247 to\n0.350. We have estimated various physical parameters of the newly identified\nEHB star in the cluster using SED fit and post-HB evolutionary tracks. We have\nstudied the radial distribution of all the sources of the cluster detected in\nUVIT. The sources detected in FUV filters extend beyond the half light radius\n(1.15$'$) of the cluster, whereas the sources detected in NUV filters extend\nbeyond the tidal radius (9.2$'$) of the cluster.", + "category": "astro-ph" + }, + { + "text": "High resolution CMB power spectrum from the complete ACBAR data set: In this paper, we present results from the complete set of cosmic microwave\nbackground (CMB) radiation temperature anisotropy observations made with the\nArcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We\ninclude new data from the final 2005 observing season, expanding the number of\ndetector-hours by 210% and the sky coverage by 490% over that used for the\nprevious ACBAR release. As a result, the band-power uncertainties have been\nreduced by more than a factor of two on angular scales encompassing the third\nto fifth acoustic peaks as well as the damping tail of the CMB power spectrum.\nThe calibration uncertainty has been reduced from 6% to 2.1% in temperature\nthrough a direct comparison of the CMB anisotropy measured by ACBAR with that\nof the dipole-calibrated WMAP5 experiment. The measured power spectrum is\nconsistent with a spatially flat, LambdaCDM cosmological model. We include the\neffects of weak lensing in the power spectrum model computations and find that\nthis significantly improves the fits of the models to the combined ACBAR+WMAP5\npower spectrum. The preferred strength of the lensing is consistent with\ntheoretical expectations. On fine angular scales, there is weak evidence (1.1\nsigma) for excess power above the level expected from primary anisotropies. We\nexpect any excess power to be dominated by the combination of emission from\ndusty protogalaxies and the Sunyaev-Zel'dovich effect (SZE). However, the\nexcess observed by ACBAR is significantly smaller than the excess power at ell\n> 2000 reported by the CBI experiment operating at 30 GHz. Therefore, while it\nis unlikely that the CBI excess has a primordial origin; the combined ACBAR and\nCBI results are consistent with the source of the CBI excess being either the\nSZE or radio source contamination.", + "category": "astro-ph" + }, + { + "text": "Optical Observations of the Type Ic Supernova 2007gr in NGC 1058 and\n Implications for the Properties of its Progenitor: We present extensive optical observations of the normal Type Ic supernova\n(SN) 2007gr, spanning from about one week before maximum light to more than one\nyear thereafter. The optical light and color curves of SN 2007gr are very\nsimilar to those of the broad-lined Type Ic SN 2002ap, but the spectra show\nremarkable differences. The optical spectra of SN 2007gr are characterized by\nunusually narrow lines, prominent carbon lines, and slow evolution of the line\nvelocity after maximum light. The earliest spectrum (taken at t=-8 days) shows\na possible signature of helium (He~I 5876 at a velocity of ~19,000 km s{-1}).\nMoreover, the larger intensity ratio of the [O I] 6300 and 6364 lines inferred\nfrom the early nebular spectra implies a lower opacity of the ejecta shortly\nafter the explosion. These results indicate that SN 2007gr perhaps underwent a\nless energetic explosion of a smaller-mass Wolf-Rayet star (~ 8--9 Msun) in a\nbinary system, as favored by an analysis of the progenitor environment through\npre-explosion and post-explosion Hubble Space Telescope images. In the nebular\nspectra, asymmetric double-peaked profiles can be seen in the [O~I] 6300 and\nMg~I] 4571 lines. We suggest that the two peaks are contributed by the\nblueshifted and rest-frame components. The similarity in velocity structure and\nthe different evolution of the strength of the two components favor an\naspherical explosion with the ejecta distributed in a torus or disk-like\ngeometry, but inside the ejecta the O and Mg have different distributions.", + "category": "astro-ph" + }, + { + "text": "New X-ray Clusters in the EMSS I: Modifications to the XLF: The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray\nimages has been re-processed and re-analyzed using a multi-aperture source\ndetection algorithm. A catalog of 772 new source candidates detected within the\ncentral regions of the 1435 IPC fields comprising the Extended Medium\nSensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources\nfall within the same area of sky. A randomly-selected subsample of 133 fields\nwas first examined. We found that most of these sources are either the\nsummation of two or more lower count rate point sources that fall within the\nlarger detection apertures or are single point sources, while \\leq 2.3% of the\nfull catalog of sources are extrapolated to be actual distant (z > 0.14)\nclusters whose extended X-ray structure kept them from being detected in the\nEMSS despite having sufficient total flux.\n We then constructed other subsamples specifically selected to contain those\nX-ray sources most likely to be clusters. Both a database search and an optical\nimaging campaign have found several new distant clusters, setting a firm lower\nlimit on the number of new clusters in the entire catalog. We estimate that the\noriginal EMSS cluster sample is 72-83% complete. We update the Henry et al.\n1992 EMSS distant cluster sample with more recent information, and use the\nredshifts and X-ray luminosities for these new EMSS clusters to compute a\nrevised X-ray Luminosity Function (XLF). The addition of these new high-z,\nhigh-L_X clusters to the EMSS is sufficient to remove the requirement for\n``negative'' evolution at high-L_X out to z~0.5. We conclude that the EMSS has\nsystematically missed clusters of low surface brightness.", + "category": "astro-ph" + }, + { + "text": "Near-IR observations of UCHII regions: We present adaptive-optics (AO) assisted J, H and K/K' images of 8 UCHII\nregions taken with the ALFA and ADONIS AO systems at Calar Alto and La Silla\nobservatories. The images show details of the stellar population and the\nnear-IR morphology of UCHIIs with unprecedented resolution. We have searched\nfor the ionizing sources of the regions using near-IR photometry. The spectral\ntype of the ionizing and most luminous stars inferred from our photometry has\nbeen compared with spectral type estimates from IRAS and published\nradio-continuum measurements. We find that the photometric near-IR spectral\ntypes are earlier than estimates from radio and IRAS data. This difference is\nalleviated when stellar spherical models including line blanketing and stellar\nwinds instead of non-LTE plane-parallel models are used to derive the radio-\nand IRAS-based spectral types. We also made an attempt to correlate the\nproperties of the near-IR ionizing population with MSX data and published CS\nmeasurements. No correlation was found. We note that in two of the regions\n(G309.92+0.48 and G61.48+0.09B1), the best candidate to ionize the region is\npossibly a super-giant.", + "category": "astro-ph" + }, + { + "text": "CMB anisotropy power spectrum statistics: Much attention has been given to the problem of estimating cosmological\nparameters from the $C_l$ measured by future experiments. Many of the\napproaches which are being used either invoke poorly controlled approximations\nor are computationally expensive. We derive exact results as well as fast and\nhighly accurate approximations for mapping a theoretical model onto the\nobserved power spectrum coefficients and computing their statistical\nproperties. These results obtain from an analytic framework which applies for\nany azimuthally symmetric sky coverage regardless of the fraction of the sky\nobserved by the experiment.", + "category": "astro-ph" + }, + { + "text": "WALLABY Pilot Survey: HI in the host galaxy of a Fast Radio Burst: We report on the commensal ASKAP detection of a fast radio burst (FRB),\nFRB20211127I, and the detection of neutral hydrogen (HI) emission in the FRB\nhost galaxy, WALLABYJ131913-185018 (hereafter W13-18). This collaboration\nbetween the CRAFT and WALLABY survey teams marks the fifth, and most distant,\nFRB host galaxy detected in HI, not including the Milky Way. We find that\nW13-18 has a HI mass of $M_{\\rm HI}$ = 6.5 $\\times$ 10$^{9}$ M$_{\\odot}$, a\nHI-to-stellar mass ratio of 2.17, and coincides with a continuum radio source\nof flux density at 1.4 GHz of 1.3 mJy. The HI global spectrum of W13-18 appears\nto be asymmetric, albeit the HI observation has a low S/N, and the galaxy\nitself appears modestly undisturbed. These properties are compared to the early\nliterature of HI emission detected in other FRB hosts to date, where either the\nHI global spectra were strongly asymmetric, or there were clearly disrupted HI\nintensity map distributions. W13-18 lacks sufficient S/N to determine whether\nit is significantly less asymmetric in its HI distribution than previous\nexamples of FRB host galaxies. However, there are no strong signs of a major\ninteraction in the HI or optical image of the host galaxy that would stimulate\na burst of star formation and hence the production of putative FRB progenitors\nrelated to massive stars and their compact remnants.", + "category": "astro-ph" + }, + { + "text": "A comprehensive comparison of cosmological models from latest\n observational data: We investigate in detail some popular cosmological models in light of the\nlatest observational data, including the Union2.1 supernovae compilation, the\nbaryon acoustic oscillation measurements from the WiggleZ Dark Energy Survey,\nthe cosmic microwave background information from the WMAP 7-year observations\nalong with the observational Hubble parameter data. Based on the model\nselection statistics such as the Akaike and the Bayesian information criterias,\nwe compare different models to assess the worth of them. We do not assume a\nflat universe in the fitting. Our results show that the concordance\n$\\Lambda$CDM model remains the best one to explain the data, while the DGP\nmodel is clearly disfavored by the data. Among these models, those whose\nparameters can reduce themselves to the $\\Lambda$CDM model provide good fits to\nthe data. These results indicate that for the current data, there is no obvious\nevidence supporting any more complex models over the simplest $\\Lambda$CDM\nmodel.", + "category": "astro-ph" + }, + { + "text": "Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2\n Data: We present the results of a search in LIGO O2 public data for continuous\ngravitational waves from the neutron star in the low-mass X-ray binary Scorpius\nX-1. We search for signals with $\\approx$ constant frequency in the range\n40-180 Hz. Thanks to the efficiency of our search pipeline we can use a long\ncoherence time and achieve unprecedented sensitivity, significantly improving\non existing results. This is the first search that has been able to probe\ngravitational wave amplitudes that could balance the accretion torque at the\nneutron star radius. Our search excludes emission at this level between 67.5 Hz\nand 131.5 Hz, for an inclination angle $44^\\circ \\pm 6^\\circ$ derived from\nradio observations (Fomalont et al. 2001), and assuming that the spin axis is\nperpendicular to the orbital plane. If the torque arm is $\\approx $ 26 km -- a\nconservative estimate of the \\alfven\\ radius -- our results are more\nconstraining than the indirect limit across the band. This allows us to exclude\ncertain mass-radius combinations and to place upper limits on the strength of\nthe star's magnetic field. We also correct a mistake that appears in the\nliterature in the equation that gives the gravitational wave amplitude at the\ntorque balance (Abbott et al. 2017b, 2019a) and we re-interpret the associated\nlatest LIGO/Virgo results in light of this.", + "category": "astro-ph" + }, + { + "text": "Magneto-Rotational Transport in the Early Sun: Angular momentum transport must have occurred in the Sun's radiative zone to\nexplain its current solid body rotation. We survey the stability of the early\nSun's radiative zone with respect to diffusive rotational instabilities, for a\nvariety of plausible past configurations. We find that the (faster rotating)\nearly Sun was prone to rotational instabilities even if only weak levels of\nradial differential rotation were present, while the current Sun is not.\nStability domains are determined by approximate balance between dynamical and\ndiffusive timescales, allowing generalizations to other stellar contexts.\nDepending on the strength and geometry of the weak magnetic field present, the\nfastest growing unstable mode can be hydrodynamic or magneto-hydrodynamic (MHD)\nin nature. Our results suggest that diffusive MHD modes may be more efficient\nat transporting angular momentum than their hydrodynamic\n(``Goldreich-Schubert-Fricke'') counterparts because the minimum spatial scale\nrequired for magnetic tension to be destabilizing limits the otherwise very\nsmall scales favored by double-diffusive instabilities. Diffusive\nmagneto-rotational instabilities are thus attractive candidates for angular\nmomentum transport in the early Sun's radiative zone.", + "category": "astro-ph" + }, + { + "text": "The Very Small Array: The Very Small Array (VSA) is a fourteen-element interferometer designed to\nstudy the cosmic microwave background on angular scales of 2.4 to 0.2 degrees\n(angular multipoles l = 150 to 1800). It operates at frequencies between 26 and\n36 GHz, with a bandwidth of 1.5 GHz, and is situated at the Teide Observatory,\nTenerife. The instrument also incorporates a single-baseline interferometer,\nwith larger collecting area, operating simultaneously with and at the same\nfrequency as the VSA main array. This provides accurate flux measurements of\ncontaminating radio sources in the VSA observations. Since September 2000, the\nVSA has been making observations of primordial CMB fluctuations. We describe\nthe instrument, observing strategy and current status of the first year of\nobservations.", + "category": "astro-ph" + }, + { + "text": "Optical and near-infrared photometric monitoring of the transient X-ray\n binary A0538-66 with REM: The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical\nvariability. Despite numerous studies, the intrinsic properties underlying its\nanomalous behaviour remain poorly understood. Since 2014 September we are\nconducting the first quasi-simultaneous optical and near-infrared photometric\nmonitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM)\ntelescope, aiming to understand the properties of this binary system. We found\nthat the REM lightcurves show fast flares lasting one or two days that repeat\nalmost regularly every ~16.6 days, the orbital period of the neutron star. If\nthe optical flares are powered by X-ray outbursts through photon reprocessing,\nthe REM lightcurves indicate that A0538-66 is still active in X-rays: bright\nX-ray flares (L_x > 1E37 erg/s) could be observable during the periastron\npassages. The REM lightcurves show a long-term variability that is especially\npronounced in the g band and decreases with increasing wavelength, until it no\nlonger appears in the near-infrared lightcurves. In addition, A0538-66 is\nfainter with respect to previous optical observations most likely due to the\nhigher absorption of the stellar radiation of a denser circumstellar disc. On\nthe basis of the current models, we interpret these observational results with\na circumstellar disc around the Be star observed nearly edge-on during a\npartial depletion phase. The REM lightcurves also show short-term variability\non timescales of ~1 day possibly indicative of perturbations in the density\ndistribution of the circumstellar disc caused by the tidal interaction with the\nneutron star.", + "category": "astro-ph" + }, + { + "text": "A Radio Observatory on the Lunar Surface for Solar studies (ROLSS): By volume, more than 99% of the solar system has not been imaged at radio\nfrequencies. Almost all of this space (the solar wind) can be traversed by fast\nelectrons producing radio emissions at frequencies lower than the terrestrial\nionospheric cutoff, which prevents observation from the ground. To date, radio\nastronomy-capable space missions consist of one or a few satellites, typically\nfar from each other, which measure total power from the radio sources, but\ncannot produce images with useful angular resolution. To produce such images,\nwe require arrays of antennas distributed over many wavelengths (hundreds of\nmeters to kilometers) to permit aperture synthesis imaging. Such arrays could\nbe free-flying arrays of microsatellites or antennas laid out on the lunar\nsurface. In this white paper, we present the lunar option. If such an array\nwere in place by 2020, it would provide context for observations during Solar\nProbe Plus perihelion passes. Studies of the lunar ionosphere's density and\ntime variability are also important goals. This white paper applies to the\nSolar and Heliospheric Physics study panel.", + "category": "astro-ph" + }, + { + "text": "CAOS spectroscopy of Am stars Kepler targets: The {\\it Kepler} space mission and its {\\it K2} extension provide photometric\ntime series data with unprecedented accuracy. These data challenge our current\nunderstanding of the metallic-lined A stars (Am stars) for what concerns the\nonset of pulsations in their atmospheres. It turns out that the predictions of\ncurrent diffusion models do not agree with observations. To understand this\ndiscrepancy, it is of crucial importance to obtain ground-based spectroscopic\nobservations of Am stars in the {\\it Kepler} and {\\it K2} fields in order to\ndetermine the best estimates of the stellar parameters.\n In this paper, we present a detailed analysis of high-resolution\nspectroscopic data for seven stars previously classified as Am stars. We\ndetermine the effective temperatures, surface gravities, projected rotational\nvelocities, microturbulent velocities and chemical abundances of these stars\nusing spectral synthesis. These spectra were obtained with {\\it CAOS}, a new\ninstrument recently installed at the observing station of the Catania\nAstrophysical Observatory on Mt. Etna. Three stars have already been observed\nduring quarters Q0-Q17, namely: HD\\,180347, HD\\,181206, and HD\\,185658, while\nHD\\,43509 was already observed during {\\it K2} C0 campaign.\n We confirm that HD\\,43509 and HD\\,180347 are Am stars, while HD 52403,\nHD\\,50766, HD\\,58246, HD\\,181206 and HD\\,185658 are marginal Am stars. By means\nof non-LTE analysis, we derived oxygen abundances from O{\\sc\nI}$\\lambda$7771--5{\\AA} triplet and we also discussed the results obtained with\nboth non-LTE and LTE approaches.", + "category": "astro-ph" + }, + { + "text": "Multi-wavelength spectral modelling of the candidate neutrino blazar PKS\n 0735+178: The BL Lac object PKS 0735+178 was in its historic $\\gamma$-ray brightness\nstate during December 2021. This period also coincides with the detection of a\nneutrino event IC211208A, which was localized close to the vicinity of PKS\n0735+178. We carried out detailed $\\gamma$-ray timing and spectral analysis of\nthe source in three epochs (a) quiescent state ($E_{1}$), (b) moderate activity\nstate ($E_{2}$) and (c) high activity state ($E_{3}$) coincident with the epoch\nof neutrino detection. During the epoch of neutrino detection ($E_{3}$), we\nfound the largest variability amplitude of 95%. The $\\gamma$-ray spectra\ncorresponding to these three epochs are well fit by the power law model and the\nsource is found to show spectral variations with a softer when brighter trend.\nIn the epoch $E_{3}$, we found the shortest flux doubling/halving time of 5.75\nhrs. Even though the spectral energy distribution in the moderate activity\nstate and in the high activity state could be modeled by the one-zone leptonic\nemission model, the spectral energy distribution in the quiescent state\nrequired an additional component of radiation over and above the leptonic\ncomponent. Here we show that a photo-meson process was needed to explain the\nexcess $\\gamma$-ray emission in the hundreds of GeV which could not be\naccounted for by the synchrotron self-Compton process.", + "category": "astro-ph" + }, + { + "text": "What can BeppoSAX tell us about short GRBs: An update from the Subsecond\n GRB Project: We present some statistical considerations on the BeppoSAX hunt for subsecond\nGRBs at the Scientific Operation Center. Archive analysis of a BATSE/SAX\nsub-sample of bursts indicates that the GRB Monitor is sensitive to short (< 2\nsec) events, that are in fact about 22% of the total. The non-detection of\ncorresponding prompt X-ray counterparts to short bursts in the Wide Field\nCameras, in about 3 years of operations, is discussed: with present data no\nimplications on the X-to-gamma-ray spectra of short vs long GRBs may be\ninferred. Finally, the status of searching procedures at SOC is reviewed.", + "category": "astro-ph" + }, + { + "text": "The aromatic infrared bands as seen by ISO-SWS: probing the PAH model: We discuss the Aromatic Infrared Band (AIB) profiles observed by ISO-SWS\ntowards a number of bright interstellar regions where dense molecular gas is\nilluminated by stellar radiation. Our sample spans a broad range of excitation\nconditions (exciting radiation fields with effective temperature, Teff, ranging\nfrom 23,000 to 45,000 K). The SWS spectra are decomposed coherently in our\nsample into Lorentz profiles and a broadband continuum. We find that the\nindividual profiles of the main AIBs at 3.3, 6.2, 8.6 and 11.3 microns are well\nrepresented with at most two lorentzians. Furthermore, we show that the\npositions and widths of these AIBs are remarkably stable (within a few cm-1).\nWe then extract the profiles of individual AIBs from the data and compare them\nto a model of Polycyclic Aromatic Hydrocarbon (PAH) cation emission which\nincludes the temperature dependence of the AIB profiles. The present similarity\nof the AIB profiles requires that the PAH temperature distribution remains\nroughly the same whatever the radiation field hardness. Deriving the\ntemperature distribution of interstellar PAHs, we show that its hot tail, which\ncontrols the AIB spectrum, sensitively depends on Nmin (the number of C-atoms\nin the smallest PAH) and Teff. Comparing the observed profiles of the\nindividual AIBs to our model results, we can match most of the AIB profiles if\nNmin is increased with Teff. We then discuss our results in the broader context\nof ISO observations of fainter interstellar regions where PAHs are expected to\nbe in neutral form.", + "category": "astro-ph" + }, + { + "text": "Application of Deep Learning Methods for Distinguishing Gamma-Ray Bursts\n from Fermi/GBM TTE Data: To investigate GRBs in depth, it is crucial to develop an effective method\nfor identifying GRBs accurately. Current criteria, e.g., onboard blind search,\nground blind search, and target search, are limited by manually set thresholds\nand perhaps miss GRBs, especially for sub-threshold events. We propose a novel\napproach that utilizes convolutional neural networks (CNNs) to distinguish GRBs\nand non-GRBs directly. We structured three CNN models, plain-CNN, ResNet, and\nResNet-CBAM, and endeavored to exercise fusing strategy models. Count maps of\nNaI detectors onboard Fermi/GBM were employed as the input samples of datasets\nand models were implemented to evaluate their performance on different time\nscale data. The ResNet-CBAM model trained on 64 ms dataset achieves high\naccuracy overall, which includes residual and attention mechanism modules. The\nvisualization methods of Grad-CAM and t-SNE explicitly displayed that the\noptimal model focuses on the key features of GRBs precisely. The model was\napplied to analyze one-year data, accurately identifying approximately 98% of\nGRBs listed in the Fermi burst catalog, 8 out of 9 sub-threshold GRBs, and 5\nGRBs triggered by other satellites, which demonstrated the deep learning\nmethods could effectively distinguish GRBs from observational data. Besides,\nthousands of unknown candidates were retrieved and compared with the bursts of\nSGR J1935+2154 for instance, which exemplified the potential scientific value\nof these candidates indeed. Detailed studies on integrating our model into\nreal-time analysis pipelines thus may improve their accuracy of inspection, and\nprovide valuable guidance for rapid follow-up observations of multi-band\ntelescopes.", + "category": "astro-ph" + }, + { + "text": "Development of a cosmic ray oriented trigger for the fluorescence\n telescope on EUSO-SPB2: The Extreme Universe Space Observatory on a Super Pressure Balloon 2\n(EUSO-SPB2), in preparation, aims to make the first observations of Ultra-High\nEnergy Cosmic Rays (UHECRs) from near space using optical techniques. EUSO-SPB2\nwill prototype instrumentation for future satellite-based missions, including\nthe Probe of Extreme Multi-Messenger Astrophysics (POEMMA) and K-EUSO. The\npayload will consist of two telescopes. The first is a Cherenkov telescope (CT)\nbeing developed to quantify the background for future below-the-limb very high\nenergy (E>10 PeV) astrophysical neutrino observations, and the second is a\nfluorescence telescope (FT) being developed for detection of UHECRs. The FT\nwill consist of a Schmidt telescope, and a 6192 pixel ultraviolet camera with\nan integration time of 1.05 microseconds. The first step in the data\nacquisition process for the FT is a hardware level trigger in order to decide\nwhich data to record. In order to maximize the number of UHECR induced\nextensive air showers (EASs) which can be detected, a novel trigger algorithm\nhas been developed based on the intricacies and limitations of the detector.\nThe expected performance of the trigger has been characterized by simulations\nand, pending hardware verification, shows that EUSO-SPB2 is well positioned to\nattempt the first near-space observation of UHECRs via optical techniques.", + "category": "astro-ph" + }, + { + "text": "Shock Waves and Cosmic Ray Acceleration in the Outskirts of Galaxy\n Clusters: The outskirts of galaxy clusters are continuously disturbed by mergers and\ngas infall along filaments, which in turn induce turbulent flow motions and\nshock waves. We examine the properties of shocks that form within $r_{200}$ in\nsample galaxy clusters from structure formation simulations. While most of\nthese shocks are weak and inefficient accelerators of cosmic rays (CRs), there\nare a number of strong, energetic shocks which can produce large amounts of CR\nprotons via diffusive shock acceleration. We show that the energetic shocks\nreside mostly in the outskirts and a substantial fraction of them are induced\nby infall of the warm-hot intergalactic medium from filaments. As a result, the\nradial profile of the CR pressure in the intracluster medium is expected to be\nbroad, dropping off more slowly than that of the gas pressure, and might be\neven temporarily inverted, peaking in the outskirts. The volume-integrated\nmomentum spectrum of CR protons inside $r_{200}$ has the power-law slope of\n$4.25 - 4.5$, indicating that the average Mach number of the shocks of main CR\nproduction is in the range of $\\left< M_s \\right>_{\\rm CR} \\approx 3 - 4$. We\nsuggest that some radio relics with relatively flat radio spectrum could be\nexplained by primary electrons accelerated by energetic infall shocks with $M_s\n>~ 3$ induced in the cluster outskirts.", + "category": "astro-ph" + }, + { + "text": "The Role of a Massive Central Singularity in Galactic Mergers on the\n Survival of the Core Fundamental Plane: In order for the core Fundamental Plane (cFP) to endure, small ellipticals\nmust not survive mergers with giant ellipticals, despite the fact the small\nsecondary galaxy can be as much as a million times more dense than the primary.\nHowever, our previous set of experiments has shown that, for purely stellar\ngalaxies, the secondary does in fact survive mergers with primaries up to 100\ntimes more massive. In this paper, we demonstrate the effect that a massive\ncentral black hole has on mergers of cFP galaxies. Our results indicate that\nthe addition of a massive central singularity inside the primary galaxy\nprovides strong enough tidal forces to destroy dense cFP companions when the\nsecondary's orbital decay is sufficiently elongated. The destruction of the\nsecondary acts to preserve the original low central density profile of the\nprimary in the giant merger remnant, which allows the remnant to remain on the\ncFP. On more circular orbits, though, the secondary is only disrupted near the\nend of the merger, and the degree to which the secondary particles disperse\ndepends on the amount of orbital energy left in the merger. Hence, there are\nsome mergers for which the cFP is not preserved in our experiments. We find\nthat if the secondary is not dispersed, it forms a spinning stellar disk with a\ncentral density that forces the merger remnant off the cFP.", + "category": "astro-ph" + }, + { + "text": "Hot One-Temperature Accretion Flows Around Black Holes: We describe hot, optically-thin solutions for one-temperature accretion disks\naround black holes. We include cooling by synchrotron, bremsstrahlung, and\nComptonization. Our solutions are thermally and viscously stable, with gas\ntemperatures on the order of $T \\sim 10^9-10^{10.7}$K. The thermal stability is\na direct result of the inclusion of synchrotron cooling.\n The new solution branch is related to the advection-dominated solution for a\ntwo-temperature gas described by Narayan \\& Yi (1995b). It is present only for\nmass accretion rates less than some critical $\\dot{M}_{crit}$ which depends on\nthe radius $R$ and viscosity parameter $\\alpha$. The solutions are\nadvection-dominated for extremely low values of $\\dot{M}$. However, for a range\nof intermediate accretion rates, the new solutions are both hot ($T \\sim\n10^{10}$K) and cooling-dominated. Because of this new feature, one-temperature\nsolutions are significantly more luminous than the corresponding two\ntemperature solutions.\n The radial profile of the new solutions is unusual. The inner parts of the\nflow are cooling-dominated and have a disk-like geometry, while the outer parts\nare fully advection-dominated and nearly quasi-spherical.", + "category": "astro-ph" + }, + { + "text": "Multi-messenger astronomy with Centaurus A: We calculated for the nearest active galactic nucleus (AGN), Centaurus A (Cen\nA), the flux of high energy cosmic rays and of accompanying secondary photons\nand neutrinos expected from hadronic interactions in the source. We used as two\nbasic models for the generation of ultrahigh energy cosmic rays (UHECR) shock\nacceleration in the radio jet and acceleration in the regular electromagnetic\nfield close to the core of the AGN, normalizing the UHECR flux to the\nobservations of the Auger experiment. Here we compare the previously obtained\nphoton fluxes with the recent data reported by the Fermi LAT and H.E.S.S.\ncollaborations. In the case of the core model, we find good agreement both for\nthe predicted spectral shape and the overall normalization between our earlier\nresults and the H.E.S.S. observations for a primary proton energy $dN/dE\\propto\nE^{-\\alpha}$ with $\\alpha\\sim 2$ or smaller. A broken-power law with\nhigh-energy part $\\alpha=-2.7$ leads to photon fluxes in excess of the Fermi\nmeasurements. The energy spectrum of the photon fluxes obtained by us for the\njet scenario is in all cases at variance with the H.E.S.S. and Fermi\nobservations.", + "category": "astro-ph" + }, + { + "text": "Binning is Sinning: Redemption for Hubble Diagram using Photometrically\n Classified Type Ia Supernovae: Bayesian Estimation Applied to Multiple Species (BEAMS) is implemented in the\nBEAMS with Bias Corrections (BBC) framework to produce a redshift-binned Hubble\ndiagram (HD) for Type Ia supernovae (SNe Ia). BBC corrects for selection\neffects and non-SNIa contamination, and systematic uncertainties are described\nby a covariance matrix with dimension matching the number of BBC redshift bins.\nFor spectroscopically confirmed SN Ia samples, a recent \"Binning is Sinning\"\narticle (BHS21, arxiv:2012.05900) showed that an unbinned HD and covariance\nmatrix reduces the systematic uncertainty by a factor of ~1.5 compared to the\nbinned approach. Here we extend their analysis to obtain an unbinned HD for a\nphotometrically identified sample processed with BBC. To test this new method,\nwe simulate and analyze 50 samples corresponding to the Dark Energy Survey\n(DES) witha low-redshift anchor; the simulation includes SNe Ia, and\ncontaminants from core-collapse SNe and peculiar SNe Ia. The analysis includes\nsystematic uncertainties for calibration, and measures the dark energy equation\nof state parameter (w). Compared to a redshift-binned HD, the unbinned HD with\nnearly 2000 events results in a smaller systematic uncertainty, in qualitative\nagreement with BHS21, and averaging results among the 50 samples we find no\nevidence for a w-bias. To reduce computation time for fitting an unbinned HD\nwith large samples, we propose an HD-rebinning method that defines the HD in\nbins of redshift, color, and stretch; the rebinned HD results in similar\nuncertainty as the unbinned case, and shows no evidence for a w-bias.", + "category": "astro-ph" + }, + { + "text": "Gaia view of primitive inner-belt asteroid families: Searching for the\n origins of asteroids Bennu and Ryugu: Near-Earth asteroids Ryugu and Bennu, were visited, characterised, and\nsampled by the Hayabusa2 and OSIRIS-REx missions: remote sensing data and\nsample return analysis showed that both asteroids have primitive, hydrated and\norganic-rich compositions. The dark families of the inner main belt (IMB) that\nbelong to the spectroscopic C-complex have been claimed to be the sources of\nboth Ryugu and Bennu. Hence, there has been large effort to characterise them.\nHere we used the Gaia Data Release 3 (DR3) asteroid reflectance spectra to\ninvestigate the 11 known IMB C-complex families (Chaldaea, Chimaera, Clarissa,\nErigone, Eulalia, Klio, Polana, Primordial, Sulamitis, Svea, Tamara). For each\nfamily, we extracted the family members that have known geometric visible\nalbedo values and Gaia DR3 data and we created an average reflectance spectrum\nper family between 370 and 950 nm. The average DR3 reflectance spectra of each\nfamily were compared with the previous literature data and to Bennu's and\nRyugu's spectra. We found that DR3 reflectance spectra of the IMB C-complex\nfamilies are in general consistent with previous findings with the only\nexception of the Svea family. We also showed that the Polana and the Eulalia\nfamilies can be distinguished in the wavelength region 370 - 500 nm. Among all\nthe IMB C-complex families, we determined that the average reflectance spectra\nof the Eulalia and Polana families are the most similar to those of Bennu and\nRyugu, respectively. In particular, Eulalia family's average spectrum is a good\nmatch to Bennu's in the wavelength range 450 - 800 nm, while beyond 800 nm the\nspectrum of Bennu is bluer than that of Eulalia. Moreover, the spectrum of the\nPolana family has the smallest discrepancy against the spectrum of Ryugu,\nalthough this match is formally unsatisfactory (reduced chi^2 ~ 1.9).", + "category": "astro-ph" + }, + { + "text": "A Comparison of Weak Lensing Measurements From Ground- and Space-Based\n Facilities: We assess the relative merits of weak lensing surveys, using overlapping\nimaging data from the ground-based Subaru telescope and the Hubble Space\nTelescope (HST). Our tests complement similar studies undertaken with simulated\ndata. From observations of 230,000 matched objects in the 2 square degree\nCOSMOS field, we identify the limit at which faint galaxy shapes can be\nreliably measured from the ground. Our ground-based shear catalog achieves\nsub-percent calibration bias compared to high resolution space-based data, for\ngalaxies brighter than i'~24.5 and with half-light radii larger than 1.8\". This\nselection corresponds to a surface density of ~15 galaxies per sq arcmin\ncompared to ~71 per sq arcmin from space. On the other hand the survey speed of\ncurrent ground-based facilities is much faster than that of HST, although this\ngain is mitigated by the increased depth of space-based imaging desirable for\ntomographic (3D) analyses. As an independent experiment, we also reconstruct\nthe projected mass distribution in the COSMOS field using both data sets, and\ncompare the derived cluster catalogs with those from X-ray observations. The\nground-based catalog achieves a reasonable degree of completeness, with minimal\ncontamination and no detected bias, for massive clusters at redshifts\n0.2