adsabs/SciX_UAT_keywords huggingface dataset:
The GMRT High Resolution Southern Sky Survey for Pulsars and Transients. V. Localization of Two Millisecond Pulsars

The timing follow-up of newly discovered millisecond pulsars (MSPs) is hindered by the larger positional uncertainty (a few tens of arcminutes) associated with the discovery. In this paper, we present the localization of two MSPs, discovered by the GMRT High Resolution Southern Sky survey, up to arcsecond accuracy using a 33 MHz offline coherently dedispersed gated correlator. This gated correlator is an upgraded version of the earlier 16 MHz design. This new development with a factor of 2 enhancement in the observing bandwidth offers better sensitivity in the image domain, leading to more precise localization. Aided by the precise position, we followed up these two MSPs with sensitive phased-array (PA) beams of upgraded GMRT from 300 to 1460 MHz. More sensitive observations in the PA mode for these two MSPs yield precise (~sub-μs) time-of-arrivals, with dispersion measure uncertainties in the range of 10-4-10-5 pc cm-3. We also report the profile evolution of the two MSPs over 300-1460 MHz. Finally, we discuss the suitability of these MSPs for the pulsar timing array experiments aimed to detect low-frequency gravitational waves.

Keywords: pulsars; millisecond pulsars; astronomical techniques
Simultaneous Deep Measurements of CO Isotopologues and Dust Emission in Giant Molecular Clouds in the Andromeda Galaxy

We present simultaneous measurements of emission from dust continuum at 230 GHz and the J = 2-1 12CO, 13CO, and C18O isotopologues at ∼15 pc resolution from individual giant molecular clouds (GMCs) in the Andromeda galaxy (M31). These observations were obtained in an ongoing survey of this galaxy being conducted with the Submillimeter Array. Initial results describing the continuum and 12CO emission have been published earlier. Here, we primarily analyze the observations of 13CO and C18O emission and compare them to the measurements of dust continuum and 12CO emission. We also report additional dust continuum and CO measurements from newly added GMCs to the M31 sample. We detect spatially resolved 13CO emission with high signal-to-noise ratios in 31 objects. We find the extent of the 13CO emission to be nearly comparable to that of 12CO, typically covering 75% of the area of the 12CO emission. We derive 13CO and C18O abundances of 2.9 × 10-6 and 4.4 × 10-7 relative to H2, respectively, by comparison with hydrogen column densities of the same regions derived from the dust continuum observations assuming a Milky Way gas-to-dust ratio. We find the isotopic abundance ratio [13CO]/[C18O] = 6.7 ± 2.9 to be consistent with the Milky Way value (8.1). Finally, we derive the mass-to-light conversion factors for all three CO species to be α12 = 8.7 ± 3.9, α13 = 48.9 ± 20.4, and ${\alpha }_{18}={345}_{-31}^{+25}$ M⊙ (K km s-1 pc2)-1 for the J = 2-1 transitions of 12CO, 13CO, and C18O, respectively.

Keywords: andromeda galaxy; giant molecular clouds; dust continuum emission; co line emission
The Distance of the Narrow FeKalpha Emitting Region for a Sample of Compton-thin Type-II Active Galactic Nuclei

I have studied the variability of the FeKα emission line flux in response to changes in the 2-10 keV unabsorbed flux in a sample of Compton thin type-II active galactic nuclei. All of the 20 sources in the sample studied by Laha et al., exhibit the presence of a narrow FeKα emission line. Except for one source (NGC 2992), all other sources show no correlations between the FeKα emission line flux and 2-10 keV unabsorbed flux. This implies that although most of the sources have shown significant variations in their 2-10 keV flux, the FeKα emission line did not get enough time to respond to those changes. This helps us put lower limits on the distance of the FeKα emitters to >10 lt-yr from the central engine, equivalent to ∼3 pc which is consistent with the standard torus/narrow-line-region distance. I conclude that the FeKα emission lines of these sources arise from reflection of the hard X-ray photons off neutral materials located beyond pcscale.

Keywords: active galactic nuclei
The ALMA-QUARKS Survey: Detection of Two Extremely Dense Substructures in a Massive Prestellar Core

Only a handful of massive starless core candidates have been discovered so far, but none of them have been fully confirmed. Within the MM1 clump in the filamentary infrared dark cloud G34.43+0.24 that was covered by the Atacama Large Millimeter/submillimeter Array (ALMA) ATOMS survey at Band 3 (∼2″, 6000 au) and the ALMA-QUARKS survey at Band 6 (∼0.″3, 900 au), two prestellar core candidates MM1-C and E1 with masses of 71 and 20 M ⊙ and radii of 2100–4400 au were discovered. The two cores show no obvious sign of star formation activities. In particular, MM1-C is a very promising massive prestellar core candidate with a total gas mass of 71 M ⊙. Within MM1-C, we detected two extremely dense substructures, C1 and C2, as characterized by their high densities of ${n}_{{{\rm{H}}}_{2}}\sim {10}^{8\mbox{--}9}\,{\mathrm{cm}}^{-3}$ . Moreover, evidence of further fragmentation in C2 was also revealed. We have detected the primordial fragmentation in the earliest stage of massive star formation, and we speculate that MM1-C would be the birthplace of a massive multiple system. However, we cannot fully rule out the possibility that the massive prestellar core MM1-C will just form a cluster of low-mass stars if it undergoes further fragmentation.

Keywords: star formation; star forming regions; dark interstellar clouds; interstellar medium
Absorption of Gamma-Ray Burst X-Ray Afterglows by the Missing Baryons: Confronting Observations with Cosmological Simulations

A large fraction of the baryons at low redshift are undetected and likely reside in the tenuous, hot intergalactic medium (IGM). One way to probe the missing baryons is through their absorption of bright sources. The anomalous absorption excess in the X-ray afterglows of gamma-ray bursts (GRBs) has been suggested to result from the missing baryons. In order to test this hypothesis, the present paper employs IllustrisTNG simulations to compute the X-ray absorption effect on cosmological distances. The simulation shows that ionization of H and He in the IGM leaves the metals responsible for >60% of the X-ray opacity of high-z sources. The high-z asymptotic optical depth at 0.5 keV in the simulation reaches 0.15 ± 0.07, while the GRB afterglow values tend to ≈0.4, implying that the missing baryons can account for a significant fraction of the observed opacity. The remaining discrepancy is ascribed mainly to the low average metallicity in the simulation, which drops from 0.06 solar at z = 0 to 0.01 at z = 3, and which is below previously measured values.

Keywords: intergalactic medium; x-ray transient sources; gamma-ray bursts
The Active Chromospheres of Lithium-rich Red Giant Stars

We have gathered near-infrared zyJ-band high-resolution spectra of nearly 300 field red giant stars with known lithium abundances in order to survey their He I λ10830 absorption strengths. This transition is an indicator of chromospheric activity and/or mass loss in red giants. The majority of stars in our sample reside in the red clump or red horizontal branch based on their V - J, M V color-magnitude diagram, and Gaia T eff and log(g) values. Most of our target stars are Li-poor in the sense of having normally low Li abundances, defined here as log ϵ(Li) < 1.25. Over 90% of these Li-poor stars have weak λ10830 features. However, more than half of the 83 Li-rich stars (log ϵ(Li) > 1.25) have strong λ10830 absorptions. These large λ10830 lines signal excess chromospheric activity in Li-rich stars; there is almost no indication of significant mass loss. The Li-rich giants may also have a higher binary fraction than Li-poor stars, based on their astrometric data. It appears likely that both residence on the horizontal branch and present or past binary interaction play roles in the significant Li-He connection established in this survey. * Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Keywords: stellar spectral lines; stellar chromospheres; stellar photospheres; stellar abundances; red giant stars
How to Turn Jets into Cylinders near Supermassive Black Holes in 3D General Relativistic Magnetohydrodynamic Simulations

Accreting supermassive black holes (SMBHs) produce highly magnetized relativistic jets that tend to collimate gradually as they propagate outward. However, recent radio interferometric observations of the 3C 84 galaxy reveal a stunning, cylindrical jet already at several hundred SMBH gravitational radii, r ≳ 350r g. We explore how such extreme collimation emerges via a suite of 3D general relativistic magnetohydrodynamic simulations. We consider an SMBH surrounded by a magnetized torus immersed in a constant-density ambient medium that starts at the edge of the SMBH sphere of influence, chosen to be much larger than the SMBH gravitational radius, r B = 103 r g. We find that radiatively inefficient accretion flows (e.g., M87) produce winds that collimate the jets into parabolas near the black hole. After the disk winds stop collimating the jets at r ≲ r B, they turn conical. Once outside r B, the jets run into the ambient medium and form backflows that collimate the jets into cylinders some distance beyond r B. Interestingly, for radiatively efficient accretion, as in 3C 84, the radiative cooling saps the energy out of the disk winds; at early times, they cannot efficiently collimate the jets, which skip the initial parabolic collimation stage, start out conical near the SMBH, and turn into cylinders already at r ≃ 300r g, as observed in 3C 84. Over time, the jet power remains approximately constant, whereas the mass accretion rate increases; the winds grow in strength and start to collimate the jets, which become quasi-parabolic near the base, and the transition point to a nearly cylindrical jet profile moves outward while remaining inside r B.

Keywords: high energy astrophysics; active galactic nuclei; black holes; jets; magnetohydrodynamical simulations; general relativity
Planetesimal Accretion at Short Orbital Periods

Formation models in which terrestrial bodies grow via the pairwise accretion of planetesimals have been reasonably successful at reproducing the general properties of the Solar System, including small-body populations. However, planetesimal accretion has not yet been fully explored in the context of the wide variety of recently discovered extrasolar planetary systems, in particular those that host short-period terrestrial planets. In this work, we use direct N-body simulations to explore and understand the growth of planetary embryos from planetesimals in disks extending down to ≃1 day orbital periods. We show that planetesimal accretion becomes nearly 100% efficient at short orbital periods, leading to embryo masses that are much larger than the classical isolation mass. For rocky bodies, the physical size of the object begins to occupy a significant fraction of its Hill sphere toward the inner edge of the disk. In this regime, most close encounters result in collisions, rather than scattering, and the system does not develop a bimodal population of dynamically hot planetesimals and dynamically cold oligarchs, as is seen in previous studies. The highly efficient accretion seen at short orbital periods implies that systems of tightly packed inner planets should be almost completely devoid of any residual small bodies. We demonstrate the robustness of our results to assumptions about the initial disk model, and we also investigate the effects that our simplified collision model has on the emergence of this non-oligarchic growth mode in a planet-forming disk.

Keywords: n-body problem; planet formation; exoplanet formation; n-body simulations; astronomical simulations
All-sky Kinematics and Chemistry of Monoceros Stellar Overdensity

We explore the kinematic and chemical properties of the Monoceros stellar overdensity by combining data from the Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, APOGEE, and Gaia. Monoceros is a structure located toward the Galactic anticenter and close to the disk. We have identified that its stars have azimuthal velocity in the range of 200 < v ϕ (km s-1) < 250. Combining their kinematics and spatial distribution, we designed a new method to select stars from this overdensity. This method allows us to easily identify the structure in both hemispheres and estimate their distances. Our analysis was supported by comparison with simulated data from the entire sky generated by the Galaxia code. Furthermore, we characterized, for the first time, the Monoceros overdensity in several chemical abundance spaces. Our results confirm its similarity to stars found in the thin disk of the Galaxy and suggest an in situ formation. Furthermore, we demonstrate that the southern and northern regions of Monoceros exhibit indistinguishable chemical compositions.

Keywords: galactic archaeology; milky way disk; milky way dynamics; chemical abundances
Recurring Homologous Solar Eruptions in NOAA AR 11429

We present the study of three homologous solar eruptions from NOAA active region (AR) 11429 over four days. This large and complex AR is divided into two relatively simple subregions: northeast (NE) and southwest (SW). Recurrent eruptions occurred from the SW subregion over different evolutionary phases, which provided a unique opportunity to isolate the physical processes responsible for solar eruptions. Persistent shearing and convergence of opposite magnetic polarities led to continuous flux cancellation along the SW polarity inversion line (PIL). A filament persistently lying along the SW PIL was observed to survive each eruption, which suggests a partial eruption of the magnetic system. Further, following the first and second eruptions, a sigmoidal magnetic structure of similar morphology was reformed along the SW PIL. The photospheric motion of magnetic flux continuously injected and stored the negative helicity in the partially erupted magnetic system and built up the magnetic free energy for the successive eruptions. These results suggest that the shearing motion and magnetic flux cancellation of opposite fluxes were: (1) the dominant factor, irrespective of the evolutionary phase, that contributed to the recurrent homologous eruption, and (2) the key processes of forming the erupting structure, likely a magnetic flux rope; its long-lasting continuation results in the reformation of an identical erupting structure. The study also finds that similar magnetic topology could result in the magnetic reconnection at the same location, and such flares during the precursor phase would help in the eruption by decreasing the constraint of the overlying magnetic field.

Keywords: the sun; solar coronal mass ejections; solar flares
Local Proton Heating at Magnetic Discontinuities in Alfvénic and Non-Alfvénic Solar Wind

We investigate the local proton energization at magnetic discontinuities/intermittent structures and the corresponding kinetic signatures in velocity phase space in Alfvénic (high cross helicity) and non-Alfvénic (low cross helicity) wind streams observed by Parker Solar Probe. By means of the partial variance of increments method, we find that the hottest proton populations are localized around compressible, coherent magnetic structures in both types of wind. Analysis of parallel and perpendicular temperature distributions suggest that the Alfvénic wind undergoes preferential enhancements of T ∥ at such structures, whereas the non-Alfvénic wind experiences preferential T ⊥ enhancements. Although proton beams are present in both types of wind, the proton velocity distribution function displays distinct features. Hot beams, i.e., beams with beam-to-core perpendicular temperature T ⊥,b /T ⊥,c up to three times larger than the total distribution anisotropy, are found in the non-Alfvénic wind, whereas colder beams are in the Alfvénic wind. Our data analysis is complemented by 2.5D hybrid simulations in different geometrical setups, which support the idea that proton beams in Alfvénic and non-Alfvénic wind have different kinetic properties and different origins. The development of a perpendicular nonlinear cascade, favored in balanced turbulence, allows a preferential relative enhancement of the perpendicular plasma temperature and the formation of hot beams. Cold field-aligned beams are instead favored by Alfvén wave steepening. Non-Maxwellian distribution functions are found near discontinuities and intermittent structures, pointing to the fact that the nonlinear formation of small-scale structures is intrinsically related to the development of highly nonthermal features in collisionless plasmas. Our results contribute to understanding the role of different coherent structures in proton energization and their implication in collisionless energy dissipation processes in space plasmas.

Keywords: solar wind; interplanetary turbulence; alfven waves; interplanetary discontinuities
The Athena++ Adaptive Mesh Refinement Framework: Multigrid Solvers for Self-gravity

We describe the implementation of multigrid solvers in the Athena++ adaptive mesh refinement (AMR) framework and their application to the solution of the Poisson equation for self-gravity. The new solvers are built on top of the AMR hierarchy and TaskList framework of Athena++ for efficient parallelization. We adopt a conservative formulation for the Laplacian operator that avoids artificial accelerations at level boundaries. Periodic, fixed, and zero-gradient boundary conditions are implemented, as well as open boundary conditions based on a multipole expansion. Hybrid parallelization using both Message Passing Interface and OpenMP is adopted, and we present results of tests demonstrating the accuracy and scaling of the methods. On a uniform grid, we show that multigrid significantly outperforms methods based on fast Fourier transforms, and requires only a small fraction of the computing time required by the (highly optimized) magnetohydrodynamic solver in Athena++. As a demonstration of the capabilities of the methods, we present the results of a test calculation of magnetized protostellar collapse on an adaptive mesh.

Keywords: astronomical simulations; hydrodynamical simulations; magnetohydrodynamical simulations; gravitation; star formation
On the Formation of Lyman β and the O I 1027 and 1028 Å Spectral Lines

We study the potential of Lyman β and the O I 1027 and 1028 Å spectral lines to help in understanding the properties of the chromosphere and transition region (TR). The oxygen transitions are located in the wing of Lyman β, which is a candidate spectral line for the solar missions Solar Orbiter/Spectral Imaging of the Coronal Environment and Solar-C (EUVST). We examine the general spectroscopic properties of the three transitions in the quiet Sun by synthesizing them assuming nonlocal thermal equilibrium and taking into account partial redistribution effects. We estimate the heights where the spectral lines are sensitive to the physical parameters, computing the response functions to temperature and velocity using a 1D semiempirical atmospheric model. We also synthesize the intensity spectrum using the 3D enhanced network simulation computed with the BIFROST code. The results indicate that Lyman β is sensitive to the temperature from the middle chromosphere to the TR, while it is mainly sensitive to the line-of-sight (LOS) velocity at the lower atmospheric layers, around 2000 km above the optical surface. The O I lines form lower in the middle chromosphere, being sensitive to the LOS velocities at heights lower than those covered by Lyman β. The spatial distribution of the intensity signals computed with the BIFROST atmosphere, as well as the inferred velocities from the line core Doppler shift, confirms the previous results. Therefore, these results indicate that the spectral window at 1025 Å contains several spectral lines that complement each other to seamlessly trace the thermal structure and gas dynamics from the middle chromosphere to the lower TR.

Keywords: radiative transfer; solar atmosphere; solar chromosphere
Taxonomic Classification of Asteroids Using the KMTNet Multiband Photometry Data Set

We report the multiband photometry of asteroids observed over 14 nights from 2015 December to 2017 December using the Korea Microlensing Telescope Network telescopes with the taxonomic classification of those objects. The data set contains the photometry of 6793 asteroids in the Sloan Digital Sky Survey griz bands. Following the method of DeMeo & Carry, we define classification criteria on the 2D color plane to assign nine taxonomic types (A, B, C, K, L&D, O, S, V, and X) for the observed objects. We also determine asteroid taxonomy in the newly defined 3D color space as suggested by Roh et al. with seven distinct types based on their novel semisupervised machine-learning model. Both methods distinguish between the S type and others but have difficulty separating the X and C types due to their weak and indistinguishable features and broad distribution in the color spaces. The heliocentric distribution of the observed asteroids with their taxonomic assignments confirms similar trends in the previous works; the number of S types decreases, while the fraction of C types increases with the heliocentric distance in the main belt. On the other hand, the D type dominates in the Jupiter Trojans.

Keywords: multi-color photometry; asteroid surfaces; asteroids; classification
Extreme X-Ray Reflection in the Nucleus of the Seyfert Galaxy NGC 5033

NGC 5033 is an intriguing Seyfert galaxy because its subclassification may change with time, and because optical and submillimeter observations find that the massive black hole does not sit at the dynamical center of the galaxy, pointing to a past merger. We obtained a new optical spectrum of NGC 5033 using the 200″ Hale telescope at Palomar that clearly reveals a broad Hβ line (FWHM = 5400 ± 300 km s-1). This signals a clear view of the optical broad line region and requires Seyfert-1.5 designation. Some spectra obtained in the past suggest a Seyfert-1.9 classification, potentially signaling a variable or "changing-look" geometry. Our analysis of a 2019 Chandra spectrum of the massive black hole reveals very little obscuration, also suggesting a clean view of the central engine. However, the narrow Fe Kα emission line is measured to have an equivalent width of EW $\,=\,{460}_{-90}^{+100}$ eV. This value is extremely high compared to typical values in unobscured active galactic nuclei . Indeed, the line is persistently strong in NGC 5033: the line equivalent width in a 2002 XMM-Newton snapshot is EW $\,=\,{250}_{-40}^{+40}$ eV, similar to the EW $\,=\,{290}_{-100}^{+100}$ eV equivalent width measured using ASCA in 1999. These results can likely be explained through a combination of an unusually high covering factor for reflection, and fluxes that are seen out of phase owing to light travel times. We examine the possibility that NGC 5033 may strengthen evidence for the X-ray Baldwin effect.

Keywords: black hole physics; active galaxies; agn host galaxies