Sazuna/UAT_keywords huggingface dataset:
Accurate Metallicities for Very Metal-poor Stars from the Ca II Infrared Triplet. The Ca II H and K lines are among the few features available to infer the metallicity of extremely metal-poor stars from medium-resolution spectroscopy. Unfortunately, these lines can overlap with absorption produced in the intervening interstellar medium, introducing systematic errors in the derived metallicities. The strength of the Ca II infrared triplet lines can also be measured at extremely low metallicities, and it is not affected by interstellar absorption, but it suffers significant departures from local thermodynamic equilibrium (LTE). We investigate the feasibility of adopting the Ca II infrared triplet as a metallicity indicator in extremely metal-poor stars using state-of-the art non-LTE models including the most recent atomic data. We find that the triplet lines exhibit non-LTE abundance corrections that can exceed 0.5 dex. When interstellar absorption affecting the Ca II resonance lines is accounted for using high-resolution observations, the agreement between non-LTE abundances for the triplet and those for the resonance lines, with only minor departures from LTE, is excellent. Non-LTE effects strengthen the Ca II IR triplet lines, facilitating measurements at very low metallicities, compared with LTE estimates, down to [Fe/H] = -6.0. This result has important implications for the discovery of primitive stars in our Galaxy and others, since instruments are most sensitive at red/near-infrared wavelengths, and tens of millions of spectra covering the Ca II IR triplet will soon become available from the Gaia, DESI, WEAVE, and PFS missions.

Keywords: Interstellar line absorption, Stellar surfaces, Metallicity, Chemical abundances
Cosmic Reionization on Computers: Evolution of the Flux Power Spectrum. We explore the evolution of the flux power spectrum in the Cosmic Reionization On Computers simulations. We find that, contrary to some previous studies, the shape of the flux power spectrum is rather insensitive to the timing of reionization. However, the amplitude of the flux power spectrum does strongly evolve with time, and that evolution is almost perfectly correlated with the timing of reionization. We show how such correlation can be used in a (futuristic) measurement to determine the redshift of overlap of ionized bubbles.

Keywords: Reionization, Lyman alpha forest
Chemical Variations Across the TMC-1 Boundary: Molecular Tracers from the Translucent Phase to the Dense Phase. We investigated the chemical evolutions of gas-phase and grain-surface species across the Taurus molecular cloud-1 (TMC-1) filament from the translucent phase to the dense phase. By comparing observations with modeling results from an up-to-date chemical network, we examined the conversion processes for the carbon-, oxygen-, nitrogen-, and sulfur-bearing species, i.e., from their initial atomic form to their main molecular reservoir form both in the gas phase and on the grain surface. The conversion processes were found to depend on the species and A  V . The effect of initial carbon-to-oxygen elemental abundances ratio (C/O) by varying O on the chemistry was explored, and an initial carbon elemental abundance of 2.5 × 10-4 and a C/O ratio of 0.5 could best reproduce the abundances of most observed molecules at TMC-1 CP, where more than 90 molecules have been identified. Based on the TMC-1 condition, we predicted a varied grain ice composition during the evolutions of molecular clouds, with H2O ice as the dominant ice composition at A  V  &gt; 4 mag, CO2 ice as the dominant ice composition at A  V  &lt;4 mag, while CO ice severely decreased at A  V  around 4-5 mag.

Keywords: Interstellar molecules, Chemical abundances, Interstellar medium, Astrochemistry
On the Conservation of Turbulence Energy in Turbulence Transport Models. Zank et al. developed models describing the transport of low-frequency incompressible and nearly incompressible turbulence in inhomogeneous flows. The formalism was based on expressing the fluctuating variables in terms of the Elsässar variables and then taking "moments" subject to various closure hypotheses. The turbulence transport models are different according to whether the plasma beta regime is large, of order unity, or small. Here, we show explicitly that the three sets of turbulence transport models admit a conservation representation that resembles the well-known WKB transport equation for Alfvén wave energy density after introducing appropriate definitions of the "pressure" associated with the turbulent fluctuations. This includes introducing a distinct turbulent pressure tensor for 3D incompressible turbulence (the large plasma beta limit) and pressure tensors for quasi-2D and slab turbulence (the plasma beta order-unity or small regimes) that generalize the form of the WKB pressure tensor. Various limits of the different turbulent pressure tensors are discussed. However, the analogy between the conservation form of the turbulence transport models and the WKB model is not close for multiple reasons, including that the turbulence models express fully nonlinear physical processes unlike the strictly linear WKB description. The analysis presented here both serves as a check on the validity and correctness of the turbulence transport models and also provides greater transparency of the energy dissipation term and the "turbulent pressure" in our models, which is important for many practical applications.

Keywords: Interplanetary turbulence, Magnetohydrodynamics
Kinematic Decomposition of the H I Gaseous Component in the Large Magellanic Cloud. We perform a profile analysis of the combined H I data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. For the profile analysis, we use a newly developed algorithm that decomposes individual line profiles into an optimal number of Gaussian components based on a Bayesian nested sampling. The decomposed Gaussian components are then classified into kinematically cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ~12.2%, ~58.3%, and ~29.5% of the total H I mass of the LMC, respectively. Our analysis reveals the highly complex H I structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H I gas bulk motions and derive new H I gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H I rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ~60 km s-1 at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.

Keywords: Large Magellanic Cloud
The MASSIVE Survey. XVII. A Triaxial Orbit-based Determination of the Black Hole Mass and Intrinsic Shape of Elliptical Galaxy NGC 2693. We present a stellar dynamical mass measurement of a newly detected supermassive black hole (SMBH) at the center of the fast-rotating, massive elliptical galaxy NGC 2693 as part of the MASSIVE survey. We combine high signal-to-noise ratio integral field spectroscopy (IFS) from the Gemini Multi-Object Spectrograph with wide-field data from the Mitchell Spectrograph at McDonald Observatory to extract and model stellar kinematics of NGC 2693 from the central ~150 pc out to ~2.5 effective radii. Observations from Hubble Space Telescope WFC3 are used to determine the stellar light distribution. We perform fully triaxial Schwarzschild orbit modeling using the latest TriOS code and a Bayesian search in 6D galaxy model parameter space to determine NGC 2693's SMBH mass (M BH), stellar mass-to-light ratio, dark matter content, and intrinsic shape. We find ${M}_{\mathrm{BH}}=\left(1.7\pm 0.4\right)\times {10}^{9}\ {M}_{\odot }$ and a triaxial intrinsic shape with axis ratios p = b/a = 0.902 ± 0.009 and $q=c/a={0.721}_{-0.010}^{+0.011}$ , triaxiality parameter T = 0.39 ± 0.04. In comparison, the best-fit orbit model in the axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 prefer ${M}_{\mathrm{BH}}=\left(2.4\pm 0.6\right)\times {10}^{9}\ {M}_{\odot }$ and ${M}_{\mathrm{BH}}=\left(2.9\pm 0.3\right)\times {10}^{9}\ {M}_{\odot }$ , respectively. Neither model can account for the non-axisymmetric stellar velocity features present in the IFS data.

Keywords: Supermassive black holes, Galaxy dark matter halos, Galaxy dynamics, Early-type galaxies, Galaxy kinematics, Galaxy evolution, Galaxy masses, Galaxies
Multiphase ISM in the z = 5.7 Hyperluminous Starburst SPT 0346-52. With ΣSFR ~ 4200 M ⊙ yr-1 kpc-2, SPT 0346-52 (z = 5.7) is the most intensely star-forming galaxy discovered by the South Pole Telescope. In this paper, we expand on previous spatially resolved studies, using ALMA observations of dust continuum, [N II] 205 μm, [C II] 158 μm, [O I] 146 μm, and undetected [N II] 122 μm and [O I] 63 μm emission to study the multiphase interstellar medium (ISM) in SPT 0346-52. We use pixelated, visibility-based lens modeling to reconstruct the source-plane emission. We also model the source-plane emission using the photoionization code CLOUDY and find a supersolar metallicity system. We calculate T dust = 48.3 K and λ peak = 80 μm and see line deficits in all five lines. The ionized gas is less dense than comparable galaxies, with n  e  &lt; 32 cm-3, while ~20% of the [C II] 158 μm emission originates from the ionized phase of the ISM. We also calculate the masses of several phases of the ISM. We find that molecular gas dominates the mass of the ISM in SPT 0346-52, with the molecular gas mass ~4× higher than the neutral atomic gas mass and ~100× higher than the ionized gas mass.

Keywords: Starburst galaxies, High-redshift galaxies, Interstellar medium
Broadening and Redward Asymmetry of Hα Line Profiles Observed by LAMOST during a Stellar Flare on an M-type Star. Stellar flares are characterized by sudden enhancement of electromagnetic radiation in stellar atmospheres. So far, much of our understanding of stellar flares has come from photometric observations, from which plasma motions in flare regions could not be detected. From the spectroscopic data of LAMOST DR7, we have found one stellar flare that is characterized by an impulsive increase followed by a gradual decrease in the Hα line intensity on an M4-type star, and the total energy radiated through Hα is estimated to be of the order of 1033 erg. The Hα line appears to have a Voigt profile during the flare, which is likely caused by Stark pressure broadening due to the dramatic increase in electron density and/or opacity broadening due to the occurrence of strong nonthermal heating. Obvious enhancement has been identified in the red wing of the Hα line profile after the impulsive increase in the Hα line intensity. The red-wing enhancement corresponds to plasma moving away from the Earth at a velocity of 100-200 km s-1. According to our current knowledge of solar flares, this red-wing enhancement may originate from: (1) flare-driven coronal rain, (2) chromospheric condensation, or (3) a filament/prominence eruption either with nonradial backward propagation or with strong magnetic suppression. The total mass of the moving plasma is estimated to be of the order of 1015 kg.

Keywords: Stellar coronal mass ejections, Time domain astronomy, Stellar flares, Spectroscopy, Late-type dwarf stars
Gravitational Microlensing Rates in Milky Way Globular Clusters. Many recent observational and theoretical studies suggest that globular clusters (GCs) host compact object populations large enough to play dominant roles in their overall dynamical evolution. Yet direct detection, particularly of black holes and neutron stars, remains rare and limited to special cases, such as when these objects reside in close binaries with bright companions. Here we examine the potential of microlensing detections to further constrain these dark populations. Based on state-of-the-art GC models from the CMC Cluster Catalog, we estimate the microlensing event rates for black holes, neutron stars, white dwarfs (WDs), and, for comparison, also for M dwarfs in Milky Way GCs, as well as the effects of different initial conditions on these rates. Among compact objects, we find that WDs dominate the microlensing rates, simply because they largely dominate by numbers. We show that microlensing detections are in general more likely in GCs with higher initial densities, especially in clusters that undergo core collapse. We also estimate microlensing rates in the specific cases of M22 and 47 Tuc using our best-fitting models for these GCs. Because their positions on the sky lie near the rich stellar backgrounds of the Galactic bulge and the Small Magellanic Cloud, respectively, these clusters are among the Galactic GCs best suited for dedicated microlensing surveys. The upcoming 10 yr survey with the Rubin Observatory may be ideal for detecting lensing events in GCs.

Keywords: Globular star clusters, Gravitational lensing, N-body simulations, Compact objects
Central Black Hole Mass in the Distant Tidal Disruption Event Candidate of Swift J2058.4+0516. In this article, the central black hole (BH) mass in the distant tidal disruption event (TDE) of Swift J2058.4+0516, the second candidate of relativistic jet birth related to a TDE, is estimated. Swift J2058.4+0516 has quite different BH masses estimated through different indirect methods in the literature. Therefore, it is necessary and interesting to determine the central BH mass in Swift J2058.4+0516 by another independent method. Here, based on the theoretical TDE model applied to describe the long-term time-dependent X-ray variabilities of Swift J2058.4+0516, the central BH mass can be well determined to be around ${1.05}_{-0.29}^{+0.39}\times {10}^{5}{M}_{\odot }$ , after considering the suggested intrinsic beaming effects from such relativistic jets tightly related to TDEs. Moreover, Swift J2058.4+0516 is a unique object in the space of BH masses versus energy transfer efficiencies of the reported TDE candidates, providing interesting clues to detect and/or anticipate candidates of relativistic TDEs that cause the birth of relativistic jets.

Keywords: Supermassive black holes, Tidal disruption, Active galaxies, Active galactic nuclei
A Study on the X-Ray Pulse Profile and Spectrum of the Crab Pulsar Using NICER and Insight-HXMT's Observations. We analyze the energy dependence of the X-ray pulse profile and the phase-resolved spectra (PRS) of the Crab pulsar using observations from the Neutron star Interior Composition Explorer (NICER) and the Hard X-ray Modulation Telescope (Insight-HXMT). We parameterize the pulse profiles and quantify the evolution of these parameters in the broad energy band of 0.4-250 keV. A log-parabola function is used to fit the PRS in 2-250 keV, and the curvature of the spectrum, i.e., the evolution of the photon index with energy, as represented by the parameter β of the log-parabola model, also changes with phase. The relation of β and phase has two turning points slightly later than those of the pulse intensity profile, where the values of β are the lowest, suggesting that the energy-loss rate of the particles is the lowest in the corresponding regions. A three-segment broken-power-law model is also used to fit those PRS. The differences between the hard spectral index and the soft ones have a distribution similar to that of β, confirming the fitting results of the log-parabola model, while the broken energies are generally higher in the region bridging the two pulses. We find anticorrelations between the spectral indices and the curvature of the log-parabola model fitting and a similar anticorrelation between the spectral indices and broken energies of the broken-power-law model fitting, suggesting a scenario where the highest-energy particles are produced in regions where radiation energy loss is strongest.

Keywords: X-ray stars, Pulsars
The Extremely Buried Nucleus of IRAS 17208-0014 Observed at Submillimeter and Near-infrared Wavelengths. The ultraluminous infrared galaxy IRAS 17208-0014 is a late-stage merger that hosts a buried active galactic nucleus (AGN). To investigate its nuclear structure, we performed high-spatial-resolution ( ~ 0.″04 ~ 32 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 9 (~450 μm or ~660 GHz), along with near-infrared AKARI spectroscopy in 2.5-5.0 μm. The Band 9 dust continuum peaks at the AGN location, and toward this position CO(J = 6 - 5) and CS(J = 14 - 13) are detected in absorption. Comparison with nonlocal thermal equilibrium calculations indicates that, within the central beam (r ~ 20 pc), there exists a concentrated component that is dense (107 cm-3) and warm (&gt;200 K) and has a large column density ( ${N}_{{{\rm{H}}}_{2}}\gt {10}^{23}\,{\mathrm{cm}}^{-2}$ ). The AKARI spectrum shows deep and broad CO rovibrational absorption at 4.67 μm. Its band profile is well reproduced with a similarly dense and large column but hotter (~1000 K) gas. The region observed through absorption in the near-infrared is highly likely in the nuclear direction, as in the submillimeter, but with a narrower beam including a region closer to the nucleus. The central component is considered to possess a hot structure where vibrationally excited HCN emission originates. The most plausible heating source for the gas is X-rays from the AGN. The AKARI spectrum does not show other AGN signs in 2.5-4 μm, but this absence may be usual for AGNs buried in a hot mid-infrared core. Further, based on our ALMA observations, we relate the various nuclear structures of IRAS 17208-0014 that have been proposed in the literature.

Keywords: Active galactic nuclei, Galaxy mergers, Spectroscopy, Ultraluminous infrared galaxies, Interferometry
Variability Timescales of Hα on Active Mid-to-late M dwarfs. We present a study of the variation timescales of the chromospheric activity indicator Hα on a sample of 13 fully convective, active mid-to-late M stars with masses between 0.1 and 0.3 solar masses. Our goal was to determine the dominant variability timescale and, by inference, a possible mechanism responsible for the variation. We gathered 10 or more high-resolution spectra each of 10 stars using the TRES spectrograph at times chosen to span all phases of stellar rotation, as determined from photometric data from the MEarth Observatories. All stars varied in their Hα emission. For nine of these stars, we found no correlation between Hα and rotational phase, indicating that constant emission from fixed magnetic structures, such as star spots and plage, are unlikely to be the dominant source of Hα emission variability. In contrast, one star, G 7-34, shows a clear relationship between Hα and stellar rotational phase. Intriguingly, we found that this star is a member of the AB Doradus moving group and hence has the young age of 149 Myr. High-cadence spectroscopic observations of three additional stars revealed that they are variable on timescales ranging from 20 to 45 minutes, which we posit may be due to flaring behavior. For one star, GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in Hα emission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in Hα on the timescales we observe and thus may be the dominant source of Hα variability on active fully convective M dwarfs.

Keywords: M dwarf stars, Stellar rotation, Stellar flares, Stellar activity
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b. We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate.

Keywords: Gravitational wave astronomy, Gamma-ray bursts, Gravitational waves, Gravitational wave detectors
Minidisk Accretion onto Spinning Black Hole Binaries: Quasi-periodicities and Outflows. We perform a full 3D general relativistic magnetohydrodynamical (GRMHD) simulation of an equal-mass, spinning, binary black hole approaching merger, surrounded by a circumbinary disk and with a minidisk around each black hole. For this purpose, we evolve the ideal GRMHD equations on top of an approximated spacetime for the binary that is valid in every position of space, including the black hole horizons, during the inspiral regime. We use relaxed initial data for the circumbinary disk from a previous long-term simulation, where the accretion is dominated by a m = 1 overdensity called the lump. We compare our new spinning simulation with a previous non-spinning run, studying how spin influences the minidisk properties. We analyze the accretion from the inner edge of the lump to the black hole, focusing on the angular momentum budget of the fluid around the minidisks. We find that minidisks in the spinning case have more mass over a cycle than the non-spinning case. However, in both cases we find that most of the mass received by the black holes is delivered by the direct plunging of material from the lump. We also analyze the morphology and variability of the electromagnetic fluxes, and we find they share the same periodicities of the accretion rate. In the spinning case, we find that the outflows are stronger than the non-spinning case. Our results will be useful to understand and produce realistic synthetic light curves and spectra, which can be used in future observations.

Keywords: Supermassive black holes, Jets, Compact objects, Magnetohydrodynamical simulations