Sazuna/UAT_keywords huggingface dataset:
Spectral and Timing Properties of the Galactic X-Ray Transient Swift J1658.2-4242 Using Astrosat Observations. We present the X-ray timing and spectral analysis of the new Galactic X-ray transient Swift J1658.2-4242 observed with the Large Area X-ray Proportional Counter and Soft X-ray Telescope instruments on board Astrosat. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from ∼1.5 to ∼6.6 Hz along with distinct second harmonics and subharmonics. The QPO detected at ∼1.56 Hz drifts to a higher centroid frequency of ∼1.74 in the course of the observation, while the QPO detected at ∼6.6 Hz disappeared during hard flarings. The fractional rms at the QPO and the subharmonic frequencies increases with photon energy, while at the second harmonic frequencies the rms seems to be constant. In addition, we have observed soft time lag at QPO and subharmonic frequencies up to a timescale of ∼35 ms; however, at the second harmonic frequencies there is weak/zero time lag. We attempt spectral modeling of the broadband data in the 0.7-25 keV band using the doubly absorbed disk plus thermal Comptonization model. Based on the spectral and timing properties, we identified the source to be in the hard-intermediate state of black hole X-ray binaries. To quantitatively fit the energy- and frequency-dependent fractional rms and time lag, we use a single-zone fluctuation propagation model and discuss our results in the context of that model.

Keywords: Accretion, Black hole physics, X-ray binary stars, X-ray transient sources, X-ray sources, Stellar accretion disks
Propagation of Scatter-free Solar Energetic Electrons in a Meandering Interplanetary Magnetic Field. We investigate energetic electron transport in a meandering interplanetary magnetic field under the scatter-free regime. The meandering magnetic field is adopted from the Giacalone model in which a single parameter V rms is used to characterize how the interplanetary magnetic field deviates from the Parker field. The trajectories of energetic electrons are followed in this meandering field using test particle simulations. Ten thousand electrons are injected in the ecliptic plane and the path length distributions are obtained at distances 0.2, 0.5, 1.0, 2.0, and 3.0 au from the Sun for five different V rms, 0.3, 0.6, 1.0, 1.5, 2.0, and 2.5 km s-1. By generating 10,000 different realizations of the meandering field line, we also obtain the path length distribution of the field lines. Our simulations show that the path length distributions of the electrons and that of the field lines are different and the difference increases with V rms. When the V rms approaches zero, the field lines approach the Parker field, and the differences between particle path lengths and field path lengths are small but nonzero due to the gradient and curvature drifts. The path lengths for 1 MeV electrons do not differ much from those for 100 MeV electrons. Our results of the distribution of electron path length can be compared to the observations of Zhao et al. to set constraints on V rms. We also calculate both the longitudinal and latitudinal displacements from the source when electrons arrive at 1 au. This provides some basis for understanding simultaneous observations of impulsive events made at multiple spacecraft.

Keywords: Solar energetic particles, Solar flares, Interplanetary magnetic fields
Exploring Plasma Heating in the Current Sheet Region in a Three-dimensional Coronal Mass Ejection Simulation. We simulate a coronal mass ejection using a three-dimensional magnetohydrodynamic code that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The magnetic flux distribution at 1 R  s  is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. Transverse electric fields are applied near the polarity inversion line to introduce a transverse magnetic field, followed by the imposition of a converging flow to form and destabilize a flux rope, producing an eruption. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic effects, coronal heating, and ohmic heating. We find that ohmic heating is an important contributor to hot temperatures in the current sheet region early in the eruption, but in the late phase, adiabatic compression plays an important role in heating the plasma there. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process, producing a “thermal halo” and widening the region of high temperatures. We simulate emission from solar telescopes for this eruption and find that there is evidence for emission from heated plasma above the flare loops late in the eruption, when the adiabatic heating is the dominant heating term. These results provide an explanation for hot supra-arcade plasma sheets that are often observed in X-rays and extreme ultraviolet wavelengths during the decay phase of large flares.

Keywords: Solar activity, Solar coronal mass ejections, Solar magnetic reconnection, Magnetohydrodynamical simulations
[C I](1-0) and [C I](2-1) in Resolved Local Galaxies. We present resolved [C I] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from J up = 1 to 7 to interpret what phase of the interstellar medium the [C I] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4-3) and [C I](2-1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [C I] and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the [C I](1-0) line is clearly dominated by the low-excitation component. We determine [C I] to molecular mass conversion factors for both the [C I](1-0) and [C I](2-1) lines, with mean values of α [C I](1-0) = 7.3 M ⊙ K-1 km-1 s pc-2 and α [C I](2-1) = 34 M ⊙ K-1 km-1 s pc-2 with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of {α }[{{C}{{I}}](1{--}0)} to {α }CO} (derived using the CO(2-1) line) suggests that [C I](1-0) may be just as good a tracer of cold molecular gas as CO(2-1) in galaxies of this type. On the other hand, the wider spread of α [C I](2-1) and the tight relation found between [C I](2-1) and CO(4-3) suggest that much of the [C I](2-1) emission may originate in warmer molecular gas. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Keywords: Disk galaxies, Interstellar atomic gas
Type Ia Supernovae Are Excellent Standard Candles in the Near-infrared. We analyze a set of 89 type Ia supernovae (SNe Ia) that have both optical and near-infrared (NIR) photometry to derive distances and construct low-redshift (z ≤ 0.04) Hubble diagrams. We construct mean light curve (LC) templates using a hierarchical Bayesian model. We explore both Gaussian process (GP) and template methods for fitting the LCs and estimating distances, while including peculiar-velocity and photometric uncertainties. For the 56 SNe Ia with both optical and NIR observations near maximum light, the GP method yields a NIR-only Hubble-diagram with a root mean square (rms) of 0.117 +/- 0.014 mag when referenced to the NIR maxima. For each NIR band, a comparable GP method rms is obtained when referencing to NIR-max or B-max. Using NIR LC templates referenced to B-max yields a larger rms value of 0.138 +/- 0.014 mag. Fitting the corresponding optical data using standard LC fitters that use LC shape and color corrections yields larger rms values of 0.179 ± 0.018 mag with SALT2 and 0.174 +/- 0.021 mag with SNooPy. Applying our GP method to subsets of SNe Ia NIR LCs at NIR maximum light, even without corrections for LC shape, color, or host-galaxy dust reddening, provides smaller rms in the inferred distances, at the ∼2.3-4.1σ level, than standard optical methods that correct for those effects. Our ongoing RAISIN program on the Hubble Space Telescope will exploit this promising infrared approach to limit systematic errors when measuring the expansion history of the universe in order to constrain dark energy.

Keywords: Cosmology, Optical observation, Distance measure, Type Ia supernovae, Photometry, Infrared photometry
Massive-star Formation via the Collapse of Subvirial and Virialized Turbulent Massive Cores. Similar to their low-mass counterparts, massive stars likely form via the collapse of prestellar molecular cores. Recent observations suggest that most massive cores are subvirial (i.e., not supported by turbulence) and therefore are likely unstable to gravitational collapse. Here we perform radiation-hydrodynamic simulations to follow the collapse of turbulent massive prestellar cores with subvirial and virialized initial conditions to explore how their dynamic state affects the formation of massive stars and core fragmentation into companion stars. We find that subvirial cores undergo rapid monolithic collapse, resulting in higher accretion rates at early times as compared to the collapse of virialized cores that have the same physical properties. In contrast, we find that virialized cores undergo a slower, gradual collapse and significant turbulent fragmentation at early times, resulting in numerous companion stars. In the absence of strong magnetic fields and protostellar outflows, we find that the faster growth rate of massive stars that are born out of subvirial cores leads to an increase in the radiative heating of the core, thereby further suppressing fragmentation at early times when turbulent fragmentation occurs for virialized cores. Regardless of initial condition, we find that the massive accretion disks that form around massive stars dominant the accretion flow onto the star at late times and eventually become gravitationally unstable and fragment to form companion stars at late times.

Keywords: Massive stars, Computational methods, Star formation, Astrophysical fluid dynamics
Eclipsing Binaries in the Open Cluster Ruprecht 147. II. Epic 219568666. We report our spectroscopic monitoring of the detached, grazing, and slightly eccentric 12 day double-lined eclipsing binary EPIC 219568666 in the old nearby open cluster Ruprecht 147. This is the second eclipsing system to be analyzed in this cluster, following our earlier study of EPIC 219394517. Our analysis of the radial velocities combined with the light curve from the K2 mission yields absolute masses and radii for EPIC 219568666 of M 1 = 1.121 ± 0.013 M ⊙ and R 1 = 1.1779 ± 0.0070 R ⊙ for the F8 primary and M 2 = 0.7334 ± 0.0050 M ⊙ and R 2 = 0.640 ± 0.017 R ⊙ for the faint secondary. Comparison with current stellar evolution models calculated for the known metallicity of the cluster points to a primary star that is oversized, as is often seen in active M dwarfs, but this seems rather unlikely for a star of its mass and with a low level of activity. Instead, we suspect a subtle bias in the radius ratio inferred from the photometry, despite our best efforts to avoid it, which may be related to the presence of spots on one or both stars. The radius sum for the binary, which bypasses this possible problem, indicates an age of 2.76 ± 0.61 Gyr, which is in good agreement with a similar estimate from the binary in our earlier study.

Keywords: Stellar ages, Fundamental parameters of stars, Light curves, Stellar evolutionary models, Eclipsing binary stars, Open star clusters
Influence of Density Dependence of Symmetry Energy in Hot and Dense Matter for Supernova Simulations. We study the influence of density-dependent symmetry energy at high densities in simulations of core-collapse supernovae, black hole formation, and proto-neutron star cooling by extending the relativistic mean field (RMF) theory used for the Shen equation-of-state (EOS) table. We adopt the extended RMF theory to examine the density dependence of the symmetry energy with a small value of the slope parameter L, while the original properties of the symmetric nuclear matter are unchanged. In order to assess matter effects at high densities, we perform numerical simulations of gravitational collapse of massive stars adopting the EOS table at high densities beyond 1014 g cm-3 with the small L value, which is in accord with the experimental and observational constraints, and compare them with the results obtained by using the Shen EOS. Numerical results for 11.2 and 15 M ⊙ stars exhibit minor effects around the core bounce and in the following evolution for 200 ms. Numerical results for 40 and 50 M ⊙ stars reveal a shorter duration toward the black hole formation with a smaller maximum mass for the small-L case. Numerical simulations of proto-neutron star cooling over 10 s through neutrino emissions demonstrate increasing effects of the symmetry energy at high densities. Neutrino cooling drastically proceeds in a relatively long timescale with high luminosities and average energies with the small symmetry energy. Evolution toward the cold neutron star is affected because of the different behavior of neutron-rich matter, while supernova dynamics around core bounce remains similar in less neutron-rich environments.

Keywords: Neutron stars, Supernova neutrinos, Black holes, Core-collapse supernovae, Compact objects
Mapping Spatial Variations of H I Turbulent Properties in the Small and Large Magellanic Cloud. We developed methods for mapping spatial variations of the spatial power spectrum (SPS) and structure function slopes, with the goal of connecting the statistical properties of neutral hydrogen (H I) with the turbulent drivers. The new methods were applied to the H I observations of the Small and Large Magellanic Clouds (SMC and LMC). In the case of the SMC, we find highly uniform turbulent properties of H I, with no evidence for local enhancements of turbulence due to stellar feedback. These properties could be caused by a significant turbulent driving on large scales. Alternatively, the significant line-of-sight depth of the SMC could be masking out localized regions with a steeper SPS slope caused by stellar feedback. In contrast to the SMC, the LMC H I shows a large diversity in terms of its turbulent properties. Across most of the LMC, the small-scale SPS slope is steeper than the large-scale slope due to the presence of the H I disk. On small spatial scales, we find several areas of localized steepening of the SPS slope around major H II regions, with the 30 Doradus region being the most prominent. This is in agreement with predictions from numerical simulations, which suggest a steepening of the SPS slope due to stellar feedback that erodes and destroys interstellar clouds. We also find a localized steepening of the large-scale SPS slope in the outskirts of the LMC. This is likely caused by the flaring of the H I disk, or alternatively, by ram-pressure stripping of the LMC disk due to the interactions with the surrounding halo gas.

Keywords: Interstellar medium, Magellanic Clouds, Neutral hydrogen clouds, Interstellar atomic gas
Star Formation Histories of the LEGUS Dwarf Galaxies. III. The Nonbursty Nature of 23 Star-forming Dwarf Galaxies. We derive the recent star formation histories (SFHs) of 23 active dwarf galaxies using Hubble Space Telescope observations from the Legacy Extragalactic UV Survey. We apply a color-magnitude diagram (CMD) fitting technique using two independent sets of stellar models, PARSEC-COLIBRI and MIST. Despite the nonnegligible recent activity, none of the 23 star-forming dwarfs show enhancements in the last 100 Myr larger than three times the 100 Myr average. The unweighted mean of the individual SFHs in the last 100 Myr is also consistent with a rather constant activity, irrespective of the atomic gas fraction. We confirm previous results that for dwarf galaxies, the CMD-based average star formation rates (SFRs) are generally higher than the FUV-based SFRs. For half of the sample, the 60 Myr average CMD-based SFR is more than two times the FUV SFR. In contrast, we find remarkable agreement between the 10 Myr average CMD-based SFR and the Hα-based SFR. Finally, using core helium-burning stars of intermediate mass, we study the pattern of star formation spatial progression over the past 60 Myr and speculate on the possible triggers and connections of the star formation activity with the environment in which these galaxies live. Approximately half of our galaxies show spatial progression of star formation in the last 60 Myr and/or very recent diffuse and off-center activity compared to RGB stars. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555.

Keywords: Dwarf irregular galaxies, Blue loop, Massive stars, Dwarf galaxies, Stellar evolutionary models, Star formation, Interacting galaxies
Unbiased Differential Size Evolution and the Inside-out Growth of Galaxies in the Deep CANDELS GOODS Fields at 1 ≤ z ≤ 7. We present a size analysis of a sample of ∼49,000 galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Survey GOODS North and South fields, using redshift-independent relative surface-brightness metrics to determine an unbiased measure of the differential size evolution of galaxies at 1 ≤ z ≤ 7. We introduce a novel method of removing foreground objects from distant galaxy (z &gt; 3) images that makes use of the Lyman break at 912 Å, in what we call “2D Lyman-break imaging.” The images used are in the rest-frame optical at z &lt; 3 and progressively bluer bands at z &gt; 3. They are therefore subject to K-correction and cosmological dimming effects, which are tested and corrected for. We separately consider a mass-selected sample (with masses in the range 109 M ⊙ ≤ M * ≤ 1010.5 M ⊙) and a number-density-selected sample (using a constant number density of n = 1 × 10-4Mpc-3). Instead of utilizing the commonly used, but potentially biased, effective radii for size measurements, we measure the redshift-independent Petrosian radius, defined by the parameter η, for each galaxy for three values of η, and use this as a proxy for size. The evolution of the measured radii can be described by a power law of the form R Petr = α(1+z) β  kpc where β &lt; 0. We find that the outer radius increases more rapidly, suggesting that as a galaxy grows, mass is added to its outer regions via an inside-out growth. This growth is stronger for the number-density-selected sample, with a growth rate of nearly three in the outer radii compared to the inner. We test and confirm these results using a series of image simulations.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution, Galaxies
Metallicity Structure in the Milky Way Disk Revealed by Galactic H II Regions. The metallicity structure of the Milky Way disk stems from the chemodynamical evolutionary history of the Galaxy. We use the National Radio Astronomy Observatory Karl G. Jansky Very Large Array to observe ∼8-10 GHz hydrogen radio recombination line and radio-continuum emission toward 82 Galactic H II regions. We use these data to derive the electron temperatures and metallicities for these nebulae. Since collisionally excited lines from metals (e.g., oxygen, nitrogen) are the dominant cooling mechanism in H II regions, the nebular metallicity can be inferred from the electron temperature. Including previous single-dish studies, there are now 167 nebulae with radio-determined electron temperature and either parallax or kinematic distance determinations. The interferometric electron temperatures are systematically 10% larger than those found in previous single-dish studies, likely due to incorrect data analysis strategies, optical depth effects, and/or the observation of different gas by the interferometer. By combining the interferometer and single-dish samples, we find an oxygen abundance gradient across the Milky Way disk with a slope of -0.052 ± 0.004 dex kpc-1. We also find significant azimuthal structure in the metallicity distribution. The slope of the oxygen gradient varies by a factor of ∼2 when Galactocentric azimuths near ∼30° are compared with those near ∼100°. This azimuthal structure is consistent with simulations of Galactic chemodynamical evolution influenced by spiral arms.

Keywords: Surveys, Milky Way Galaxy, Interstellar medium, Nebulae
Spectroscopy of the Young Stellar Association Price-Whelan 1: Origin in the Magellanic Leading Arm and Constraints on the Milky Way Hot Halo. We report spectroscopic measurements of stars in the recently discovered young stellar association Price-Whelan 1 (PW 1), which was found in the vicinity of the Leading Arm (LA) of the Magellanic Stream (MS). We obtained Magellan+MIKE high-resolution spectra of the 28 brightest stars in PW 1 and used The Cannon to determine their stellar parameters. We find that the mean metallicity of PW 1 is [Fe/H] = -1.23 with a small scatter of 0.06 dex and the mean RV is {V}hel} = 276.7 {km} {{{s}}}-1 with a dispersion of 11.0 {km} {{{s}}}-1. Our results are consistent in {\text{}}{T}eff}, {log}g, and [Fe/H] with the young and metal-poor characteristics (116 Myr and [Fe/H] = -1.1) determined for PW 1 from our discovery paper. We find a strong correlation between the spatial pattern of the PW 1 stars and the LA II gas with an offset of -10.°15 in {L}MS} and +1.°55 in {B}MS}. The similarity in metallicity, velocity, and spatial patterns indicates that PW 1 likely originated in LA II. We find that the spatial and kinematic separation between LA II and PW 1 can be explained by ram pressure from Milky Way (MW) gas. Using orbit integrations that account for the LMC and MW halo and outer disk gas, we constrain the halo gas density at the orbital pericenter of PW 1 to be {{\boldsymbol{n}}}halo}(17 {kpc})={2.7}-2.0+3.4× {10}-3 {atoms} {cm}}-3 and the disk gas density at the midplane at 20 {kpc} to be {{\boldsymbol{n}}}disk}(20 {kpc},0)={6.0}-2.0+1.5× {10}-2 {atoms} {cm}}-3. We, therefore, conclude that PW 1 formed from the LA II of the MS, making it a powerful constraint on the MW-Magellanic interaction.

Keywords: High resolution spectroscopy, Open star clusters, Magellanic Stream, Halo stars