Sazuna/UAT_keywords huggingface dataset:
Stochastic Fragmentation in Protoplanetary Disks under External Irradiation. It has been shown that disk fragmentation within several tens of au from the star is very difficult when the gravitational instability and cooling time criterion are considered. However, in the stochastic fragmentation scenario, things may be different. We investigate stochastic fragmentation in protoplanetary disks. In the stochastic fragmentation model, we consider the effects of the external irradiation on the fragmentation process. For the stochastic fragmentation, owing to the probability of generating bound fragments at longer cooling times relative to the critical value and the short collapsing times in the external irradiation region, the inner boundary of the fragmentation region extends inward to 19 au. We find that the required self-gravitating lifetime for fragmentation in the external irradiation region is far less than the self-gravitating lifetime of the disk. Therefore, once a radius is in the external irradiation region, the fragmentation probability increases quickly to 1 after gravitational instability sets in, and fragmentation occurs within a short period of time. We also find that the self-gravitating lifetime required for fragmentation decreases significantly as the radius increases in the external irradiation region.

Keywords: Accretion, Gravitational instability, Stellar accretion disks
Possible Evidence from the Flaring Activity of Sgr A* for a Star at a Distance of ∼3.3 Schwarzschild Radii from the Black Hole. The frequent flaring events in the X-ray and the near-IR (NIR) radiation of Sgr A* seem not to be periodic in time. However, statistical regularities, here termed "modulations by a pacemaker," are found in the recorded arrival times of both types of events. The characteristic time of the X-ray pacemaker is 149 minutes, and that of the NIR pacemaker is 40 minutes. Their reality as derived from observed data can be accepted at larger than 4.6σ and 3.8σ levels of statistical confidence, respectively. These results can be interpreted as evidence for a star that revolves around the black hole (BH) of Sgr A* in a slightly elliptical precessing orbit, at a distance of 3-3.5 Schwarzschild radii of the BH. The period of the X-ray pacemaker, which is not a periodicity of the flare occurrences themselves, is the epicyclic period of the star orbital motion. This is the time interval between two successive passages of the star through the pericenter of its orbit. The NIR pacemaker period is the mean sidereal binary period of the star revolution. The origin of the X-ray flares is in episodes of intense mass loss from the star that occur preferably near the pericenter phase of the binary revolution. The NIR flares originate or are triggered by processes that are internal to the star. The radiation emitted in the direction of Earth is slightly modulated by the changing aspect ratio of the two components of the BH/star binary to the line of sight from Earth at the sidereal binary frequency.

Keywords: Black hole physics, Galactic center, Infrared sources, X-ray sources, X-ray bursts
The SAMI Galaxy Survey: Stellar Population Gradients of Central Galaxies. We examine the stellar population radial gradients (age, metallicity, and [α/Fe]) of 96 passive central galaxies up to ∼2 Re in the SAMI Galaxy Survey. The targeted groups have a halo mass range of $11\lt \mathrm{log}({M}_{200}/{M}_{\odot })\lt 15$ . The main goal of this work is to determine whether central galaxies have different stellar population properties when compared to similarly massive satellite galaxies. For the whole sample, we find negative metallicity radial gradients, which show evidence of becoming shallower with increasing stellar mass. The age and [α/Fe] gradients are slightly positive and consistent with zero, respectively. The [α/Fe] gradients become more negative with increasing mass, while the age gradients do not show any significant trend with mass. We do not observe a significant difference between the stellar population gradients of central and satellite galaxies at fixed stellar mass. The mean metallicity gradients are $\overline{{\rm{\Delta }}[{\rm{Z}}/{\rm{H}}]/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=-0.25\pm 0.03$ for central galaxies and $\overline{{\rm{\Delta }}[{\rm{Z}}/{\rm{H}}]/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=-0.30\pm 0.01$ for satellites. The mean age and [α/Fe] gradients are consistent between central and satellite galaxies, within the uncertainties, with a mean value of $\overline{{\rm{\Delta }}{\rm{log(Age/Gyr)}}/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=0.13\pm 0.03$ for centrals and $\overline{{\rm{\Delta }}{\rm{log(Age/Gyr)}}/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=0.17\pm 0.01$ for satellites and $\overline{{\rm{\Delta }}[\alpha /\mathrm{Fe}]/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=0.01\pm 0.03$ for centrals and $\overline{{\rm{\Delta }}[\alpha /\mathrm{Fe}]/{\rm{\Delta }}\mathrm{log}(r/{R}_{e})}=0.08\pm 0.01$ for satellites. The stellar population gradients of central and satellite galaxies show no difference as a function of halo mass. This evidence suggests that the inner regions of central passive galaxies form in a similar fashion to those of satellite passive galaxies, in agreement with a two-phase formation scenario.

Keywords: Galaxy abundances, Galaxy evolution, Galaxy environments
On the Origin of the Gamma-Ray Emission toward SNR CTB 37A with Fermi-LAT. The middle-aged supernova remnant (SNR) CTB 37A is known to interact with several dense molecular clouds through the detection of shocked H2 and OH 1720 MHz maser emission. In the present work, we use eight years of Fermi-LAT Pass 8 data, with an improved point-spread function and an increased acceptance, to perform detailed morphological and spectral studies of the γ-ray emission toward CTB 37A from 200 MeV to 200 GeV. The best fit of the source extension is obtained for a very compact Gaussian model with a significance of 5.75σ and a 68% containment radius of 0°116 ± 0°014stat ± 0°017sys above 1 GeV, which is larger than the TeV emission size. The energy spectrum is modeled as a LogParabola, resulting in a spectral index α = 1.92 ± 0.19 at 1 GeV and a curvature β = 0.18 ± 0.05, which becomes softer than the TeV spectrum above 10 GeV. The SNR properties, including a dynamical age of 6000 yr, are derived assuming the Sedov phase. From the multiwavelength modeling of emission toward the remnant, we conclude that the nonthermal radio and GeV emission is mostly due to the reacceleration of preexisting cosmic rays (CRs) by radiative shocks in the adjacent clouds. Furthermore, the observational data allow us to constrain the total kinetic energy transferred to the trapped CRs in the clouds. Based on these facts, we infer a composite nature for CTB 37A to explain the broadband spectrum and to elucidate the nature of the observed γ-ray emission.

Keywords: Supernova remnants, Non-thermal radiation sources, Galactic cosmic rays
The PHLEK Survey: A New Determination of the Primordial Helium Abundance. We present Keck NIRSPEC and Keck NIRES spectroscopy of sixteen metal-poor galaxies that have pre-existing optical observations. The near-infrared (NIR) spectroscopy specifically targets the He I λ10830 Å emission line, due to its sensitivity to the physical conditions of the gas in H II regions. We use these NIR observations, combined with optical spectroscopy, to determine the helium abundance of sixteen galaxies across a metallicity range $12+{{\rm{log}}}_{10}({\rm{O}}/{\rm{H}})$ = 7.13-8.00. This data set is combined with two other samples where metallicity and helium abundance measurements can be secured: star-forming galaxies selected from the Sloan Digital Sky Survey spectroscopic database, and existing low-metallicity systems in the literature. We calculate a linear fit to these measurements, accounting for intrinsic scatter, and report a new determination of the primordial helium number abundance, ${y}_{{\rm{P}}}={0.0805}_{-0.0017}^{+0.0017}$, which corresponds to a primordial helium mass fraction ${Y}_{{\rm{P}}}={0.2436}_{-0.0040}^{+0.0039}$ . Using our determination of the primordial helium abundance in combination with the latest primordial deuterium measurement, ${({\rm{D}}/{\rm{H}})}_{{\rm{P}}}\times {10}^{5}=2.527\pm 0.030$, we place a bound on the baryon density ${{\rm{\Omega }}}_{{\rm{b}}}{h}^{2}={0.0215}_{-0.0005}^{+0.0005}$ and the effective number of neutrino species ${N}_{\mathrm{eff}}={2.85}_{-0.25}^{+0.28}$ . These values are in 1.3σ agreement with those deduced from the Planck satellite observations of the temperature fluctuations imprinted on the cosmic microwave background.

Keywords: Galaxy chemical evolution, Dwarf galaxies, Big Bang nucleosynthesis, Galaxy abundances
Pulsar Glitch Detection with a Hidden Markov Model. Pulsar timing experiments typically generate a phase-connected timing solution from a sequence of times of arrival (TOAs) by absolute pulse numbering, I.e., by fitting an integer number of pulses between TOAs in order to minimize the residuals with respect to a parameterized phase model. In this observing mode, rotational glitches are discovered, when the residuals of the no-glitch phase model diverge after some epoch, and glitch parameters are refined by Bayesian follow-up. Here, we present an alternative, complementary approach which tracks the pulse frequency f and its time derivative $\dot{f}$ with a hidden Markov model (HMM), whose dynamics include stochastic spin wandering (timing noise) and impulsive jumps in f and $\dot{f}$ (glitches). The HMM tracks spin wandering explicitly, as a specific realization of a discrete-time Markov chain. It discovers glitches by comparing the Bayes factor for glitch and no-glitch models. It ingests standard TOAs for convenience, and being fully automated, allows performance bounds to be calculated quickly via Monte Carlo simulations. Practical, user-oriented plots of the false-alarm probability and detection threshold (e.g., minimum resolvable glitch size) versus observational scheduling parameters (e.g., TOA uncertainty, mean delay between TOAs) and glitch parameters (e.g., transient and permanent jump sizes, exponential recovery timescale) are presented. The HMM is also applied to ∼1 yr of real data bracketing the 2016 December 12 glitch in PSR J0835-4510 as a proof of principle. It detects the known glitch and confirms that no other glitch exists in the same data with size ≳10-7f.

Keywords: Neutron stars, Stellar rotation, Gravitational waves, Pulsars
HST Survey of the Orion Nebula Cluster in the H<SUB>2</SUB>O 1.4 μm Absorption Band. I. A Census of Substellar and Planetary-mass Objects. In order to obtain a complete census of the stellar and substellar population, down to a few ${M}_{\mathrm{Jup}}$ in the ∼1 Myr old Orion Nebula Cluster, we used the infrared channel of the Wide Field Camera 3 of the Hubble Space Telescope with the F139M and F130N filters. These bandpasses correspond to the 1.4 μm H2O absorption feature and an adjacent line-free continuum region. Out of 4504 detected sources, 3352 (about 75%) appear fainter than m130 = 14 (Vega mag) in the F130N filter, a brightness corresponding to the hydrogen-burning limit mass ( $M\simeq 0.072\,{M}_{\odot }$ ) at ∼1 Myr. Of these, however, only 742 sources have a negative F130M-F139N color index, indicative of the presence of H2O vapor in absorption, and can therefore be classified as bona fide M and L dwarfs, with effective temperatures T ≲ 2850 K at an assumed 1 Myr cluster age. On our color-magnitude diagram (CMD), this population of sources with H2O absorption appears clearly distinct from the larger background population of highly reddened stars and galaxies with positive F130M-F139N color index and can be traced down to the sensitivity limit of our survey, m130 ≃ 21.5, corresponding to a 1 Myr old ≃3 ${M}_{\mathrm{Jup}}$ planetary-mass object under about 2 mag of visual extinction. Theoretical models of the BT-Settl family predicting substellar isochrones of 1, 2, and 3 Myr down to ∼1 ${M}_{\mathrm{Jup}}$ fail to reproduce the observed H2O color index at M ≲ 20 ${M}_{\mathrm{Jup}}$ . We perform a Bayesian analysis to determine extinction, mass, and effective temperature of each substellar member of our sample, together with its membership probability.

Keywords: Pre-main sequence stars, Young star clusters, Brown dwarfs
HST Survey of the Orion Nebula Cluster in the H<SUB>2</SUB>O 1.4 μm Absorption Band. II. The Substellar IMF Down to Planetary Masses. We utilize the ability of the Hubble Space Telescope to probe near-infrared water absorption present in the atmosphere of low-mass stars and brown-dwarf and planetary-mass objects to create a pure sample of Orion Nebula Cluster (ONC) members, not affected by contamination from background stars and galaxies that lack water absorption. Thanks to these data, we infer the Initial Mass Function (IMF) of the ONC in the 0.005-1.4M⊙ regime (I.e., down to a few Jupiter masses). The young age of the ONC, ∼1 Myr, provides a snapshot of the outcome of star formation for the present-day conditions (metallicity, temperature, pressure) of typical Milky Way disk molecular clouds. We demonstrate that the IMF of the ONC is well described by either a log-normal function or a broken power law, with parameter values qualitatively in agreement with the canonical Chabrier or Kroupa forms for the Milky Way disk IMF. This continuity in the mass distribution provides clues to the fact that the same physical processes may be regulating the formation of stars, brown dwarfs, and planetary-mass objects. Both the canonical IMF forms underpredict the observed number of very-low-mass members (below 0.1 M⊙), a regime where our data allows more precise constraints. Nevertheless, we do not observe a rise or secondary peak in the brown dwarfs or planetary-mass regimes. Our study thus contradicts findings based on broadband near-infrared ground-based photometry, which predict an extremely high number of free-floating planets, but likely suffer from unaccounted background contamination. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-13826.

Keywords: Luminosity function, Brown dwarfs, Initial mass function, Bayesian statistics, Star forming regions, Young star clusters, Stellar colors, Star formation, Low mass stars
HST Survey of the Orion Nebula Cluster in the H<SUB>2</SUB>O 1.4 μm Absorption Band. III. The Population of Substellar Binary Companions. We present new results concerning the substellar binary population in the Orion Nebula Cluster (ONC). Using the Karhunen-Loève Image Projection algorithm, we have reprocessed images taken with the IR channel of the Wide Field Camera 3 mounted on the Hubble Space Telescope to unveil faint, close companions in the wings of the stellar point-spread functions. Starting with a sample of 1392 bona fide unsaturated cluster members, we detect 39 close-pair cluster candidates with separation 0"16-0"77. The primary masses span a range Mp ∼ 0.015-1.27 M⊙, whereas for the companions we derive Mc ∼ 0.004-0.54 M⊙. Of these 39 binary systems, 18 were already known, while the remaining 21 are new detections. Correcting for completeness and combining our catalog with previously detected ONC binaries, we obtain an overall binary fraction of 11.5% ± 0.9%. Compared to other star-forming regions, our multiplicity function is ∼2 times smaller than, for example, Taurus, while compared to the binaries in the field we obtain comparable values. We analyze the mass functions of the binaries, finding differences between the mass distributions of binaries and single stars and between primary and companion mass distributions. The mass ratio shows a bottom-heavy distribution with median value Mc/Mp ∼ 0.25. Overall, our results suggest that ONC binaries may represent a template for the typical population of field binaries, supporting the hypothesis that the ONC may be regarded as a most typical star-forming region in the Milky Way.

Keywords: M dwarf stars, Multiple stars, Brown dwarfs, Binary stars, Substellar companion stars, Star forming regions, Low mass stars, Companion stars
Effects of General Relativistic Spin Precessions on the Habitability of Rogue Planets Orbiting Supermassive Black Holes. Recently, the possibility that several starless telluric planets may form around supermassive black holes (SMBHs) and receive energy input from the hole's accretion disk, which, under certain plausible circumstances, may make them habitable in a terrestrial sense, has gained increasing attention. In particular, an observer on a planet orbiting at distance r = 100 Schwarzschild radii from a maximally rotating Kerr SMBH with mass M• = 1 × 108 M⊙ in a plane slightly outside the equator of the latter, would see the gravitationally lensed accretion disk the same size as the Sun as seen from Earth. Moreover, the accretion rate might be imagined to be set in such a way that the apparent disk's temperature would be identical to that of the solar surface. We demonstrate that the post-Newtonian (pN) de Sitter and Lense-Thirring precessions of the spin axis of such a world would rapidly change, among other things, its tilt, ɛ, to its orbital plane by tens to hundreds of degrees over a time span of, say, just Δt = 400 yr, strongly depending on the obliquity η• of the SMBH's spin to the orbital plane. Thus, such relativistic features would have per se a relevant impact on the long-term habitability of the considered planet. Other scenarios are examined as well.

Keywords: Black holes, Exoplanets, Gravitation, Celestial mechanics, Astrobiology, General relativity
Discovery of a Universal Correlation for Long and Short GRBs and Its Application for the Study of Luminosity Function and Formation Rate. Gamma-ray bursts (GRBs) are known to be the most violent explosions in the universe, and a variety of correlations between observable GRB properties have been proposed in the literature, but none of these correlations are valid for both long and short GRBs. In this paper we report the discovery of a universal correlation that is suitable for both long and short GRBs using three prompt emission properties of GRBs, I.e., the isotropic peak luminosity Liso, the peak energy of the time-integrated prompt emission spectrum Epeak, and the "high signal" timescale T0.45, ${L}_{\mathrm{iso}}\propto {E}_{\mathrm{peak}}^{1.94}{T}_{0.45}^{0.37}$ . This universal correlation involves properties of GRB prompt emission and does not require knowledge of the afterglow phase, which can be used as a relatively unbiased redshift estimator. Here we use this correlation to estimate the pseudoredshifts for short GRBs and then use the Lynden-Bell method to obtain a nonparametric estimate of their luminosity function and formation rate. The luminosity function is $\psi ({L}_{0})\propto {L}_{0}^{-0.63\pm 0.07}$ for dim SGRBs and $\psi ({L}_{0})\propto {L}_{0}^{-1.96\pm 0.28}$ for bright SGRBs, with the break point ${6.95}_{-0.76}^{+0.84}\times {10}^{50}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ . The local formation rate of SGRBs is about 15 events Gpc-3 yr-1 . This universal correlation may have important implications for GRB physics, implying that the long and short GRBs should share similar radiation processes.

Keywords: Cosmology, Burst astrophysics, Gamma-ray bursts, Cosmological parameters
The Three Young Nuclear Super Star Clusters in NGC 5253. The blue compact dwarf galaxy NGC 5253 hosts a very young central starburst. The center contains intense radio thermal emission from a massive ultracompact H II region (or supernebula) and two massive and very young super star clusters (SSCs), which are seen at optical and infrared wavelengths. The spatial correspondence between these three objects over an area of $\lt 0\buildrel{\prime\prime}\over{.} 5$ is very uncertain, and it is usually assumed that one of the optically detected SSCs coincides with the supernebula. Using the Gaia Data Release 2 catalog, we improve the absolute astrometry of Hubble Space Telescope ultraviolet, optical, and infrared images by a factor of ∼10 and match them to the radio observations with an accuracy of 10-20 mas. We find that there are three SSCs at the center of NGC 5253. At optical wavelengths, the two SSCs lie on either side of the supernebula, which coincides with a highly obscured region. In the infrared, all three SSCs are seen with the supernebula dominating at the longest wavelengths. We examine the properties of the SSCs, which have ages of ∼1 Myr, are very compact ( $\lt 0.6$ pc), and are separated by projected distances of only 1.5 and 5.8 pc. It seems likely that they will merge and may form the building blocks for nuclear star clusters.

Keywords: Starburst galaxies, Blue compact dwarf galaxies, Young star clusters
Very Long Baseline Astrometry of PSR J1012+5307 and its Implications on Alternative Theories of Gravity. PSR J1012+5307, a millisecond pulsar in orbit with a helium white dwarf (WD), has been timed with high precision for about 25 yr. One of the main objectives of this long-term timing is to use the large asymmetry in gravitational binding energy between the neutron star and the WD to test gravitational theories. Such tests, however, will be eventually limited by the accuracy of the distance to the pulsar. Here, we present very long baseline interferometry (VLBI) astrometry results spanning approximately 2.5 yr for PSR J1012+5307, obtained with the Very Long Baseline Array as part of the $\mathrm{MSPSR}\pi $ project. These provide the first proper motion and absolute position for PSR J1012+5307 measured in a quasi-inertial reference frame. From the VLBI results, we measure a distance of ${0.83}_{-0.02}^{+0.06}$ kpc (all the estimates presented in the abstract are at 68% confidence) for PSR J1012+5307, which is the most precise obtained to date. Using the new distance, we improve the uncertainty of measurements of the unmodeled contributions to orbital period decay, which, combined with three other pulsars, places new constraints on the coupling constant for dipole gravitational radiation ${\kappa }_{D}=(-1.7\pm 1.7)\times {10}^{-4}$ and the fractional time derivative of Newton's gravitational constant $\dot{G}/G=-{1.8}_{-4.7}^{+5.6}\times {10}^{-13}\,{\mathrm{yr}}^{-1}$ in the local universe. As the uncertainties of the observed decays of orbital period for the four leading pulsar-WD systems become negligible in ≈10 yr, the uncertainties for $\dot{G}/G$ and κD will be improved to ≤1.5 × 10-13 yr-1 and ≤1.0 × 10-4, respectively, predominantly limited by the distance uncertainties.

Keywords: Neutron stars, Parallax, Pulsar timing method, Galactic radio sources, Gravitation, Astrometry, Binary pulsars
Stabilizing Effect of Magnetic Helicity on Magnetic Cavities in the Intergalactic Medium. We investigate the effect of magnetic helicity on the stability of buoyant magnetic cavities as found in the intergalactic medium. In these cavities we insert helical magnetic fields and test whether or not helicity can increase their stability to shredding through the Kelvin-Helmholtz instability and, with that, their lifetime. This is compared to the case of an external vertical magnetic field that is known to reduce the growth rate of the Kelvin-Helmholtz instability. By comparing a low-helicity configuration with a high-helicity one with the same magnetic energy, we find that an internal helical magnetic field stabilizes the cavity. This effect increases as we increase the helicity content. Stabilizing the cavity with an external magnetic field requires instead a significantly stronger field at higher magnetic energy. We conclude that the presence of helical magnetic fields is a viable mechanism to explain the stability of intergalactic cavities on timescales longer than 100 Myr.

Keywords: Warm-hot intergalactic medium, Magnetic fields