Sazuna/UAT_keywords huggingface dataset:
Populations of Stellar-mass Black Holes from Binary Systems. In large and complicated stellar systems like galaxies, it is difficult to predict the number and characteristics of a black hole (BH) population. Such populations may be modeled as an aggregation of homogeneous (i.e., having uniform star formation history and the same initial chemical composition) stellar populations. Using realistic evolutionary models, we predict the abundances and properties of BHs formed from binaries in these environments. We show that the BH population will be dominated by single BHs originating from binary disruptions and stellar mergers. Furthermore, we discuss how BH populations are influenced by such factors as initial parameters, metallicity, initial mass function, and natal kick models. As an example application of our results, we estimate that about 26 microlensing events happen every year in the direction of the Galactic Bulge due to BHs in a survey like OGLE-IV. Our results may be used to perform in-depth studies related to realistic BH populations, such as observational predictions for space survey missions like Gaia or Einstein Probe. We prepared a publicly available database with the raw data from our simulations to be used for more in-depth studies.

Keywords: X-ray binary stars, Binary stars, Black holes, Stellar populations, Gravitational waves, Compact objects, Gravitational microlensing, Astrophysical black holes, Stellar evolution
Probing the Survival of Planetary Systems in Globular Clusters with Tidal Disruption Events. Among the growing list of confirmed exoplanets, the number of planets identified in dense star clusters remains sparse. Previous analyses have suggested that this may be due in part to dynamical interactions that can unbind planets from their host stars, limiting the survival of planetary systems in clusters. Thus, alternative detection strategies may be necessary to study planets in clusters that may no longer be bound to a host. Here, we use N-body models to explore the evolution of planetary systems in dense star clusters. Depending on various initial conditions, we show that 10%-50% of primordial planetary systems are broken through dynamical encounters over a cluster’s full lifetime, populating clusters with “free-floating” planets. Furthermore, a large number (30%-80%) of planets are ejected from their host cluster through strong dynamical encounters and/or tidal loss. Additionally, we show that planets naturally mix with stellar-mass black holes (BHs) in the cores of their host cluster. As a consequence, up to a few hundred planets will be tidally disrupted through close passages of BHs. We show that these BH-planet tidal disruption events (TDEs) occur in clusters at a rate of up to 10-5 yr-1 in a Milky-Way-type galaxy. In principle, these BH-planet TDEs may be detected by upcoming transient surveys such as the Large Synoptic Survey Telescope at a rate of a few events per year, although identification of these events may prove challenging. The observed rate of BH-planet TDEs could place new constraints upon the formation and survival of planetary systems and BHs in dense star clusters.

Keywords: Globular star clusters, Exoplanets, Stellar dynamics, Stellar mass black holes, Free floating planets
Dynamical Masses for the Triple System HD 28363 in the Hyades Cluster. The star HD 28363 in the Hyades cluster has been known for over a century as a visual binary with a period of 40 yr. The secondary is, in turn, a single-lined spectroscopic binary with a 21 day period. Here we report extensive spectroscopic monitoring of this hierarchical triple system that reveals the spectral lines of the third star for the first time. Combined with astrometric information, this makes it possible to determine the dynamical masses of all three stars. Only six other binaries in the Hyades have had their individual component masses determined dynamically. We infer the properties of the system by combining our radial-velocity measurements with visual observations, lunar occultation measurements, and with proper motions from the Hipparcos and Gaia missions that provide a constraint on the astrometric acceleration. We derive a mass of {1.341}-0.024+0.026 {M}⊙  for the visual primary, and 1.210 ± 0.021 and 0.781 ± 0.014 M ⊙ for the other two stars. These measurements along with those for the other six systems establish an empirical mass-luminosity relation in the Hyades that is in broad agreement with current models of stellar evolution for the known age and chemical composition of the cluster.

Keywords: Multiple stars, Fundamental parameters of stars, Radial velocity, Space astrometry, Spectroscopy, Stellar masses, Main sequence stars, Open star clusters, Visual binary stars
Kinetic Simulations of Nonrelativistic Perpendicular Shocks of Young Supernova Remnants. II. Influence of Shock-surfing Acceleration on Downstream Electron Spectra. We explore electron preacceleration at high-Mach-number nonrelativistic perpendicular shocks at, e.g., young supernova remnants, which are a prerequisite of further acceleration to very high energies via diffusive shock acceleration. Using fully kinetic particle-in-cell simulations of shocks and electron dynamics in them, we investigate the influence of shock-surfing acceleration (SSA) at the shock foot on the nonthermal population of electrons downstream of the shock. The SSA is followed by further energization at the shock ramp where the Weibel instability spawns a type of second-order Fermi acceleration. The combination of these two processes leads to the formation of a nonthermal electron population, but the importance of SSA becomes smaller for larger ion-to-electron mass ratios in the simulation. We discuss the resulting electron spectra and the relevance of our results to the physics of systems with real ion-to-electron mass ratios and fully three-dimensional behavior.

Keywords: Supernova remnants, Shocks, Interstellar medium, Space plasmas
Steepening of Cosmic-Ray Spectra in Shocks with Varying Magnetic Field Direction. Cosmic-ray (CR) spectra, both measured upon their arrival at the Earth’s atmosphere and inferred from the emission in supernova remnants (SNRs), appear to be significantly steeper than the “standard” diffusive shock acceleration (DSA) theory predicts. Although the reconstruction of the primary spectra introduces an additional steepening due to propagation effects, there is a growing consensus in the CR community that these corrections fall short to explain the newest high-precision data. Using 2D hybrid simulations, we investigate a new mechanism that may steepen the spectrum during the acceleration in SNR shocks. Most of the DSA treatments are limited to homogeneous shock environments. To investigate whether inhomogeneity effects can produce the necessary extra steepening, we assume that the magnetic field changes its angle along the shock front. The rationale behind this approach is the strong dependence of the DSA efficiency upon the field angle, θ Bn. Our results show that the variation of shock obliquity along its face results in a noticeable steepening of the DSA spectrum. Compared to simulations of quasi-parallel shocks, we observe an increase of the spectral index by Δq = 0.1-0.15. Possible extrapolation of the limited simulation results to more realistic SNR conditions are briefly considered.

Keywords: Galactic cosmic rays, Supernova remnants
An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124. We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system’s 2017-2018 giant outburst. The 1.2-10 keV energy spectrum of the source can be approximated with an absorbed cutoff power-law model. We detect strong, luminosity-dependent emission lines in the 6-7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex. An asymmetric broad-line profile, peaking at 6.67 keV, is possibly due to Doppler effects and gravitational redshift. The 1.2-79 keV broadband spectrum from Nuclear Spectroscopic Telescope Array (NuSTAR) and NICER observations at the outburst peak is well described by an absorbed cutoff power law plus multiple Gaussian lines and a blackbody component. Physical reflection models are also tested to probe the broad iron-line feature. Depending on the mass accretion rate, we found emission sites that are evolving from ∼5000 km to a range closer to the surface of the neutron star. Our findings are discussed in the framework of the accretion disk and its implication on the magnetic field, the presence of optically thick accretion curtain in the magnetosphere, jet emission, and the massive, ultrafast outflow expected at super-Eddington accretion rates. We do not detect any signatures of a cyclotron absorption line in the NICER or NuSTAR data.

Keywords: Accretion, Neutron stars, High mass x-ray binary stars, Pulsars
Molecular Cloud Distances Based on the MWISP CO Survey and Gaia DR2. We present a new method of calculating distances of molecular clouds in the Galactic plane, using CO observations and the Gaia DR2 parallax and G-band extinction (A  G ) measurements. Due to the complexity of dust environments in the Galactic plane, A  G  contains irregular variations, which are difficult to model. To overcome this, we propose that the A  G  of off-cloud stars (Gaia stars around molecular clouds) can be used as a baseline to calibrate the A  G  of on-cloud stars (Gaia stars toward molecular clouds), which removes the A  G  components that are unrelated to molecular clouds. The distance is subsequently inferred from the jump point in on-cloud A  G  with Bayesian analysis and Markov chain Monte Carlo (MCMC) sampling. We applied this baseline subtraction method to a 100 deg2 region (209.°75 ≤ l ≤ 219.°75, and | b| ≤slant 5^\circ ) in the third Galactic quadrant, which was mapped as part of the Milky Way Imaging Scroll Painting (MWISP) project, covering three CO isotopologue lines, and derived distances and masses for 11 molecular clouds, including the Maddalena molecular cloud and Sh 2-287. The results indicate that the distance of the Perseus Arm in this region is about 2.4 kpc and molecular clouds are present in the interarm regions.

Keywords: Interstellar molecules, Astrostatistics techniques, Interstellar clouds, Interstellar dust extinction
Thermodynamic Properties of Mirror Structures in the Magnetosheath: MMS Observations and Double-polytropic MHD Simulations. Mirror structures are manifested as a wave train of magnetic peaks and/or dips, which are anticorrelated with plasma density. The evolution behavior of the ion temperatures perpendicular and parallel to the local magnetic field, T ⊥ and T ∥, in the magnetic peaks and dips is rare to be theoretically studied. In this paper, the thermodynamic properties of mirror structures are investigated using two-dimensional magnetohydrodynamic simulations with double-polytropic laws. Two polytropic exponents, γ ∥ and γ ⊥, are used as parameters to describe various thermodynamic conditions in the anisotropic plasma—for example, γ ∥ = 1, γ ⊥ = 1 for double-isothermal and γ ∥ = 3, γ ⊥ = 2 for double-adiabatic. Using empirical values of γ ∥ = 1.14 and γ ⊥ = 0.94 for magnetosheath plasma, the variations of T ∥ and T ⊥ in the magnetic dips and peaks observed by the Magnetospheric Multiscale Mission in the Earth’s magnetosheath can be reproduced. This consistent result cannot be achieved by use of γ ∥ = 3, γ ⊥ = 2 and γ ∥ = 0.5, γ ⊥ = 2, where the latter exponents can lead to the same mirror instability threshold as kinetic theory. In magnetic dips, T ∥ is found to be increased for γ ∥ &gt; 1 but decreased for γ ∥ &lt; 1, while T ⊥ is decreased for γ ⊥ &gt; 1 but increased for γ ⊥ &lt; 1. For magnetic peaks, the variation features of T ∥ and T ⊥ are opposite to that of the magnetic dips. It is concluded that the thermodynamic properties of mirror structures are further from double-adiabatic but closer to double-isothermal conditions.

Keywords: Planetary magnetospheres, Magnetohydrodynamics, Heliosheath, Magnetohydrodynamical simulations
Stages of Reionization as Revealed by the Minkowski Functionals. We study the evolution of the hydrogen ionization field during the epoch of reionization (EoR) using seminumerical simulations. By calculating the Minkowski functionals (MFs) of the 21 cm brightness temperature field, which provides a quantitative description of topology of the neutral and ionized regions, we find that the reionization process can be divided into five stages, each with different topological structures, corresponding to isolated ionized regions (“bubbles”) connected ionized regions (“ionized fibers”) that percolate through the cosmic volume; a sponge-like configuration with intertwined neutral and ionized regions after the overlap of bubbles; connected neutral regions (“neutral fibers”), when the ionized region begins to surround the remaining neutral region; and isolated neutral regions (“islands”), before the whole space is ionized except for the rare dense clumps in galaxies and minihalos and the reionization process is completed. We use the MFs and the size statistics on the ionized or neutral regions to distinguish these different stages and find the neutral fractions at which the transitions of the different stages occur. At the later stages of reionization the neutral regions are more isolated than the ionized regions; this is the motivation for the island model description of reionization. We compare the late-stage topological evolution in the island model and the bubble model, showing that in the island model the neutral fibers are more easily broken into multiple pieces owing to the ionizing background.

Keywords: Non-Gaussianity, Reionization, Voids, Large-scale structure of the universe
Tidal Disruption Events, Main-sequence Extreme-mass Ratio Inspirals, and Binary Star Disruptions in Galactic Nuclei. The Galactic Center has been under intense scrutiny in recent years thanks to pioneering missions aiming to measure the gas and star dynamics near the supermassive black hole (SMBH) and to find the gravitational-wave (GW) signatures of inspiraling stellar black holes. In the crowded environment of galactic nuclei, the two-body interactions alter the distribution of stars on long timescales, making them drift in energy and angular momentum. We present a simplified analytical treatment of the scattering processes in galactic stellar nuclei, assuming all stars have the same mass. We have discussed how the interplay between two-body relaxation and GW emission modifies the slope of the inner stellar cusp within the SMBH sphere of influence, and calculated the rates of tidal disruption events (TDEs) and main-sequence extreme-mass ratio inspirals (MS-EMRIs) of stars that are tidally disrupted by the SMBH. We find that typically the ratio of the TDE and MS-EMRI rates is the square of the ratio of the tidal and Schwarzschild radii. For our Galaxy, this implies that the rate of MS-EMRIs is just about a percent of the TDE rate. We then consider the role of stars injected on highly eccentric orbits in the vicinity of the SMBH due to the Hills binary disruption mechanism, and show that the MS-EMRI rate can almost approach the TDE rate if the binary fraction at the SMBH influence radius is close to unity. Finally, we discuss how physical stellar collisions affect a large area of phase space.

Keywords: Supermassive black holes, Binary stars, Black holes, High energy astrophysics, Tidal disruption
Effects of ϕ-meson on the EOS, Maximum Masses, and Radii of Hyperon Stars. The relativistic mean field (RMF) model is considered as one of the best methods to study the nuclear system that has a high degree of isospin asymmetry and baryon density. In the present contribution, we take 25 well-known parameter sets of the RMF model to discuss the parametric dependence of the neutron and hyperon star properties. Various properties of the canonical star are discussed and only a few parameter sets are found to satisfy both the astrophysical and nuclear matter constraints. We add both ϕ and σ* strange mesons to the σ-ω-ρ model. Effects of the ϕ-meson on the equation of state and maximum mass of the hyperon star are discussed in detail. ϕ-meson affects the threshold density of hyperon production and pushes the hyperon production to a higher density. Effects of the hyperon-meson coupling constants on the maximum mass-radius profile and strangeness content of the hyperon star are discussed in the σ-ω-ρ-ϕ-σ* model.

Keywords: Neutron stars, Nuclear astrophysics, Neutron star cores, Compact objects
Structural and Evolutionary Diagnostics from Asteroseismic Phase Functions. In the asymptotic parameterization of mode frequencies, the phase function ∊(ν) completely specifies the detailed structure of the frequency eigenvalues. In practice, however, this function of frequency is reduced to a single scalar ∊, defined, particularly by observers, as the intercept of a least-squares fit to the frequencies against radial order, or via the central value of this function. The procedure by which this is done is not unique. We derive a few simple expressions relating various observational estimators of ∊ for radial modes to each other, and to the underlying theoretical object. In particular we demonstrate that a “reduced” functional parameterization is both insensitive to mis-estimations of ∆ν, and easy to evaluate locally in terms of both observational and theoretical quantities. It has been shown previously that such a local definition of ∊ can distinguish between stars on the ascending part of the red giant branch and those in the red clump. We find that this sensitivity to evolutionary stage arises from differences in the local frequency derivative of the underlying phase function, a consequence of differences in internal structure. By constructing an H-R-like diagram out of purely seismic observables, we provide a unified view of the Kepler asteroseismic sample, as well as the initial results from TESS. We investigate how various astrophysical quantities and modeling parameters affect the morphology of isochrones on this seismic diagram. We also show that ∊ can be used as an independent input when deriving stellar parameters from global asteroseismic quantities.

Keywords: Stellar oscillations, Computational methods, Asteroseismology
Evolutionary Models for R Coronae Borealis Stars. We use Modules for Experiments in Stellar Astrophysics (MESA) to construct stellar evolution models that reach a hydrogen-deficient, carbon-rich giant phase like the R Coronae Borealis (R CrB) stars. These models use opacities from OPAL and ÆSOPUS that cover the conditions in the cool, H-deficient, CNO-enhanced envelopes of these stars. We compare models that begin from homogeneous He stars with models constructed to reproduce the remnant structure shortly after the merger of a He and a CO white dwarf (WD). We emphasize that models originating from merger scenarios have a thermal reconfiguration phase that can last up to ≈ 1 {kyr} post-merger, suggesting some galactic objects should be in this phase. We illustrate the important role of mass loss in setting the lifetimes of the R CrB stars. Using asymptotic giant branch-like mass-loss prescriptions, models with CO WD primaries ≲ 0.7{M}⊙  typically leave the R CrB phase with total masses ≈ 0.6{--}0.7{M}⊙ , roughly independent of their total mass immediately post-merger. This implies that the descendants of the R CrB stars may have a relatively narrow range in mass and luminosity as extreme He stars and a relatively narrow range in mass as single WDs.

Keywords: R Coronae Borealis variable stars, Stellar evolution
Integrated Spectra of Milky Way Globular Clusters. Integrated spectra of Milky Way globular clusters (GCs) are reproduced by computing synthetic spectra taking into account individual element abundances. Five clusters were selected from their location in the Galactic bulge, for which integrated spectra were available in the WiFeS Atlas of Galactic Globular Cluster Spectra project. Our aim is to further study the oldest GCs located in the Galactic bulge, with a metallicity in the range -1.6 &lt; [Fe/H] &lt; -0.7. We also include the halo cluster NGC 6752 for comparison purposes. We reproduce the full spectra in the range 4500-9000 Å available in these observed spectra, as well as individual lines of Na, Mg, Al, Si, Ca, Ti, Ba, and Eu. We report a list of lines that are suitable for abundance derivation, and by adopting these abundances, we are able to fit the damping parameters that define the wings of strong lines of well-known triplets of Mg I and Ca II. Finally, the effect of multiple stellar populations through enhanced Na abundances is tested.

Keywords: Globular star clusters, Stellar populations, Galactic bulge, Galaxy abundances, Stellar atmospheres
TESS Asteroseismology of the Known Red-giant Host Stars HD 212771 and HD 203949. The Transiting Exoplanet Survey Satellite (TESS) is performing a near all-sky survey for planets that transit bright stars. In addition, its excellent photometric precision enables asteroseismology of solar-type and red-giant stars, which exhibit convection-driven, solar-like oscillations. Simulations predict that TESS will detect solar-like oscillations in nearly 100 stars already known to host planets. In this paper, we present an asteroseismic analysis of the known red-giant host stars HD 212771 and HD 203949, both systems having a long-period planet detected through radial velocities. These are the first detections of oscillations in previously known exoplanet-host stars by TESS, further showcasing the mission’s potential to conduct asteroseismology of red-giant stars. We estimate the fundamental properties of both stars through a grid-based modeling approach that uses global asteroseismic parameters as input. We discuss the evolutionary state of HD 203949 in depth and note the large discrepancy between its asteroseismic mass (M * = 1.23 ± 0.15 M ☉ if on the red-giant branch or M * = 1.00 ± 0.16 M ☉ if in the clump) and the mass quoted in the discovery paper (M * = 2.1 ± 0.1 M ☉), implying a change &gt;30% in the planet’s mass. Assuming HD 203949 to be in the clump, we investigate the planet’s past orbital evolution and discuss how it could have avoided engulfment at the tip of the red-giant branch. Finally, HD 212771 was observed by K2 during its Campaign 3, thus allowing for a preliminary comparison of the asteroseismic performances of TESS and K2. We estimate the ratio of the observed oscillation amplitudes for this star to be {A}\max {TESS}/{A}\max K2=0.75+/- 0.14, consistent with the expected ratio of ∼0.85 due to the redder bandpass of TESS.

Keywords: Asteroseismology, Exoplanets, Evolved stars