Sazuna/UAT_keywords huggingface dataset:
Advective Accretion onto a Nonspherical Accretor in White Dwarf and Neutron Star Binaries: A New Scenario of Shock Formation. Numerous studies on hydrodynamics of the Keplerian as well as the sub-Keplerian accretion disk around a compact object (e.g., white dwarf (WD), neutron star (NS), or a black hole) have attempted to explain the observed UV, soft, and hard X-ray spectra. Although, when the compact object (e.g., a WD or an NS) has a finite surface, its rapid rotation, the stellar magnetic field could cause deformation of the spherical symmetry. Earlier studies on the Keplerian disk showed that a deviation from the spherical symmetry of the compact object could affect the observed light curve and spectra at high frequencies. Here, we have explored the effect of the nonspherical nature of a compact object on the hydrodynamics of an optically thin, geometrically thick sub-Keplerian advective flow. We find that due to the nonspherical shape of the central accretor, there is a possibility to trigger Rankine-Hugoniot shock in the sub-Keplerian advective flow close to the accretor without considering any general relativistic effect or presence of the hard surface of the star. Our results are more relevant for accretion onto a WD as hardly any general relativistic effect will come into the picture. We propose that some observational features, e.g., high significance of fitting the spectra with multi-temperature plasma models rather than single-temperature models, and variable efficiency of X-ray emission (X-ray luminosity in comparison with the optical and UV luminosity of the disk) in nonmagnetic cataclysmic variables can be explained by the presence of a shock in the sub-Keplerian advective flow.

Keywords: Accretion, High energy astrophysics, White dwarf stars, Shocks, Cataclysmic variable stars
Resolved Dwarf Galaxy Searches within  5 Mpc with the Vera Rubin Observatory and Subaru Hyper Suprime-Cam. We present a preview of the faint dwarf galaxy discoveries that will be possible with the Vera C. Rubin Observatory and Subaru Hyper Suprime-Cam in the next decade. In this work, we combine deep ground-based images from the Panoramic Imaging Survey of Centaurus and Sculptor and extensive image simulations to investigate the recovery of faint, resolved dwarf galaxies in the Local Volume with a matched-filter technique. We adopt three fiducial distances (1.5, 3.5, and 5 Mpc) and quantitatively evaluate the effects on dwarf detection of varied stellar backgrounds, ellipticity, and Milky Way foreground contamination and extinction. We show that our matched-filter method is powerful for identifying both compact and extended systems, and near-future surveys will be able to probe at least ~4.5 mag below the tip of the red giant branch (TRGB) for a distance of up to 1.5 Mpc and ~2 mag below the TRGB at 5 Mpc. This will push the discovery frontier for resolved dwarf galaxies to fainter magnitudes, lower surface brightnesses, and larger distances. Our simulations show the secure census of dwarf galaxies down to MV ≈ -5, -7, and -8 will soon be within reach, out to 1.5, 3.5, and 5 Mpc, respectively, allowing us to quantify the statistical fluctuations in satellite abundances around hosts and parse environmental effects as a function of host properties. * This paper includes data gathered with the 6.5 m Magellan Telescope at Las Campanas Observatory, Chile.

Keywords: Cosmology, Local Group, Dwarf galaxies, Photometry, Galaxies
The Nickel Mass Distribution of Stripped-envelope Supernovae: Implications for Additional Power Sources. We perform a systematic study of the 56Ni mass (MNi) of 27 stripped-envelope supernovae (SESNe) by modeling their light-curve tails, highlighting that use of "Arnett's rule" overestimates MNi for SESNe by a factor of ~2. Recently, Khatami &amp; Kasen presented a new model relating the peak time (tp) and luminosity (Lp) of a radioactively powered supernova to its MNi that addresses several limitations of Arnett-like models, but depends on a dimensionless parameter, β. Using observed tp, Lp, and tail-measured MNi values for 27 SESNe, we observationally calibrate β for the first time. Despite scatter, we demonstrate that the model of Khatami &amp; Kasen with empirically calibrated β values provides significantly improved measurements of MNi when only photospheric data are available. However, these observationally constrained β values are systematically lower than those inferred from numerical simulations, primarily because the observed sample has significantly higher (0.2-0.4 dex) Lp for a given MNi. While effects due to composition, mixing, and asymmetry can increase Lp none can explain the systematically low β values. However, the discrepancy can be alleviated if ~7%-50% of Lp for the observed sample comes from sources other than radioactive decay. Either shock cooling or magnetar spin-down could provide the requisite luminosity. Finally, we find that even with our improved measurements, the MNi values of SESNe are still a factor of ~3 larger than those of hydrogen-rich Type II SNe, indicating that these supernovae are inherently different in terms of the initial mass distributions of their progenitors or their explosion mechanisms.

Keywords: Supernovae, Core-collapse supernovae
The Missing Link? Discovery of Pulsations in the Nitrogen-rich PG 1159 Star PG 1144+005. Up to 98% of all single stars will eventually become white dwarfs-stars that link the history and future evolution of the Galaxy, and whose previous evolution is engraved in their interiors. Those interiors can be studied using asteroseismology, utilizing stellar pulsations as seismic waves. The pulsational instability strips of DA and DB white dwarf stars are pure, allowing for the important generalization that their interior structure represents that of all DA and DB white dwarfs. This is not the case for the hottest pulsating white dwarfs, the GW Vir stars: only about 50% of white dwarfs in this domain pulsate. Several explanations for the impurity of the GW Vir instability strip have been proposed, based on different elemental abundances, metallicity, and helium content. Surprisingly, there is a dichotomy that only stars rich in nitrogen, which by itself cannot cause pulsation driving, pulsate-the only previous exception being the nitrogen-rich nonpulsator PG 1144+005. Here, we report the discovery of pulsations in PG 1144+005 based on new observations. We identified four frequency regions: 40, 55, 97, and 112 day-1 with low and variable amplitudes of about 3-6 mmag and therefore confirm the nitrogen dichotomy. As nitrogen is a trace element revealing the previous occurrence of a very late thermal pulse (VLTP) in hot white dwarf stars, we speculate that it is this VLTP that provides the interior structure required to make a GW Vir pulsator.

Keywords: Stellar pulsations, Pulsating variable stars, PG 1159 stars, Non-radial pulsations, Stellar evolution
The Discovery of the Largest Gas Filament in Our Galaxy, or a New Spiral Arm?. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we detect a giant H I filamentary structure in the sky region of 307°7 &lt; α &lt; 311°0 and 40°9 &lt; δ &lt; 43°4. The structure has a velocity range of -170 to -130 km s-1, and a mean velocity of -150 km s-1, putting it at a Galactocentric distance of 22 kpc. The H I structure, which we name Cattail, has a length of 1.1 kpc, which so far appears to be the furthest and largest giant filament in the Galaxy. Its mass is calculated to be 6.5 × 104 M⊙ and the linear mass density is 60 M⊙ pc-1. Its width is 207 pc, corresponding to an aspect ratio of 5:1. Cattail possesses a small velocity gradient (0.02 km s-1 pc-1) along its major axis. Together with the HI4PI data, we find that Cattail could be even longer, up to 5 kpc. We also identify another new elongated structure as the extension into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far behind the OSC arm. The question about how such a huge filament is produced at this extreme Galactic location remains open. Alternatively, Cattail might be part of a new arm beyond the OSC arm, though it is puzzling that the structure does not fully follow the warp of the Galactic disk.

Keywords: Interstellar filaments, Interstellar atomic gas
Touching the Stars: Using High-resolution 3D Printing to Visualize Stellar Nurseries. Owing to their intricate variable density architecture, and as a principal site of star formation, molecular clouds represent one of the most functionally significant, yet least understood features of our universe. To unravel the intrinsic structural complexity of molecular clouds, here we leverage the power of high-resolution bitmap-based three-dimensional (3D) printing, which provides the opportunity to visualize astrophysical structures in a way that uniquely taps into the human brain's ability to recognize patterns suppressed in 2D representations. Using a new suite of nine simulations, each representing different physical extremes in the turbulent interstellar medium, as our source data, our workflow permits the unambiguous visualization of features in the 3D-printed models, such as quasi-planar structures, that are frequently obscured in traditional renderings and animations. Our bitmap-based 3D printing approach thus faithfully reproduces the subtle density gradient distribution within molecular clouds in a tangible, intuitive, and visually stunning manner. While laying the groundwork for the intuitive analysis of other structurally complex astronomical data sets, our 3D-printed models also serve as valuable tools in educational and public outreach endeavors.

Keywords: Giant molecular clouds, Astronomy data visualization, Interstellar medium
Core Mass Function of a Single Giant Molecular Cloud Complex with  10,000 Cores. Similarity in shape between the initial mass function (IMF) and the core mass functions (CMFs) in star-forming regions prompts the idea that the IMF originates from the CMF through a self-similar core-to-star mass mapping process. To accurately determine the shape of the CMF, we create a sample of 8431 cores with the dust continuum maps of the Cygnus X giant molecular cloud complex, and design a procedure for deriving the CMF considering the mass uncertainty, binning uncertainty, sample incompleteness, and the statistical errors. The resultant CMF coincides well with the IMF for core masses from a few M⊙ to the highest masses of 1300 M⊙ with a power-law of ${dN}/{dM}\propto {M}^{-2.30\pm 0.04}$ , but does not present an obvious flattened turnover in the low-mass range as the IMF does. More detailed inspection reveals that the slope of the CMF steepens with increasing mass. Given the numerous high-mass star-forming activities of Cygnus X, this is in stark contrast with the existing top-heavy CMFs found in high-mass star-forming clumps. We also find that the similarity between the IMF and the mass function of cloud structures is not unique at core scales, but can be seen for cloud structures of up to several parsec scales. Finally, our SMA observations toward a subset of the cores do not present evidence for the self-similar mapping. The latter two results indicate that the shape of the IMF may not be directly inherited from the CMF.

Keywords: Molecular gas, Star forming regions, Dense interstellar clouds, Stellar mass functions, Dust continuum emission
Periodic Activities of Repeating Fast Radio Bursts from Be/X-Ray Binary Systems. The frequency-dependent periodic active window of the fast radio burst FRB 180916.J0158+65 (FRB 180916B) was observed recently. In this letter, we propose that a Be/X-ray binary (BeXRB) system, which is composed of a neutron star (NS) and a Be star with a circumstellar disk, might be the source of a repeating FRB with periodic activities, and we apply this model to explain the activity window of FRB 180916B. The interaction between the NS magnetosphere and the accreted material results in evolution of the spin period and the centrifugal force of the NS, leading to the change of the stress in the NS crust. When the stress of the crust reaches the critical value, a starquake occurs and further produces FRBs. The interval between starquakes is estimated to be a few days, which is smaller than the active window of FRB 180916B. When the NS moves out of the disk of the Be star, the interval between starquakes becomes much longer than the orbital period, which corresponds to the nonactive phase. In this model, due to the absorption of the disk of the Be star, a frequency-dependent active window would appear for the FRBs, which is consistent with the observed properties of FRB 180916B. And the contribution of the dispersion measure from the disk of the Be star is small. In addition, the location of FRB 180916B in the host galaxy is consistent with a BeXRB system.

Keywords: Accretion, High mass x-ray binary stars, Pulsars, Be stars, Radio transient sources
Two Steps Forward and One Step Sideways: The Propagation of Relativistic Jets in Realistic Binary Neutron Star Merger Ejecta. The association of GRB170817A with GW170817 has confirmed the long-standing hypothesis that binary neutron star (BNS) mergers are the progenitors of at least some short gamma-ray bursts (SGRBs). This connection has ushered in an era in which broadband observations of SGRBs, together with measurements of the time delay between the gravitational waves and the electromagnetic radiation, allow for probing the properties of the emitting outflow and its engine to an unprecedented detail. Because the structure of the radiating outflow is molded by the interaction of a relativistic jet with the binary ejecta, it is of paramount importance to study the system in a realistic setting. Here we present a three-dimensional hydrodynamic simulation of a relativistic jet propagating in the ejecta of a BNS merger, which were computed with a general relativistic magnetohydrodynamic simulation. We find that the jet's centroid oscillates around the axis of the system, due to inhomogeneities encountered in the propagation. These oscillations allow the jet to find the path of least resistance and travel faster than an identical jet in smooth ejecta. In our setup the breakout time is ~0.6 s, which is comparable to the expected central engine duration in SGRBs and possibly a non-negligible fraction of the total delay between the gravitational and gamma-ray signals. Our simulation also shows that energy is carried in roughly equal amounts by the jet and by the cocoon, and that about 20% of the injected energy is transferred to the ejecta via mechanical work.

Keywords: Neutron stars, Gamma-ray bursts, Relativistic jets
A Universal Cloud Composition on the Nightsides of Hot Jupiters. The day and nightside temperatures of hot Jupiters are diagnostics of heat transport processes in their atmospheres. Recent observations have shown that the nightsides of hot Jupiters are a nearly constant 1100 K for a wide range of equilibrium temperatures (Teq), lower than those predicted by 3D global circulation models. Here we investigate the impact of nightside clouds on the observed nightside temperatures of hot Jupiters using an aerosol microphysics model. We find that silicates dominate the cloud composition, forming an optically thick cloud deck on the nightsides of all hot Jupiters with Teq ≤ 2100 K. The observed nightside temperature is thus controlled by the optical depth profile of the silicate cloud with respect to the temperature-pressure profile. As nightside temperatures increase with Teq, the silicate cloud is pushed upward, forcing observations to probe cooler altitudes. The cloud vertical extent remains fairly constant due to competing impacts of increasing vertical mixing strength with Teq and higher rates of sedimentation at higher altitudes. These effects, combined with the intrinsically subtle increase of the nightside temperature with Teq due to decreasing radiative timescale at higher instellation levels, lead to low, constant nightside photospheric temperatures consistent with observations. Our results suggest a drastic reduction in the day-night temperature contrast when nightside clouds dissipate, with the nightside emission spectra transitioning from featureless to feature-rich. We also predict that cloud absorption features in the nightside emission spectra of hot Jupiters should reach ≥100 ppm, potentially observable with the James Webb Space Telescope.

Keywords: Exoplanet atmospheric composition , Atmospheric clouds, Hot Jupiters, Planetary atmospheres, Exoplanet atmospheres
No Large Dependence of Planet Frequency on Galactocentric Distance. Gravitational microlensing is currently the only technique that helps study the Galactic distribution of planets as a function of distance from the Galactic center. The Galactic location of a lens system can be uniquely determined only when at least two of the three quantities that determine the mass-distance relations are measured. However, even if only one mass-distance relation can be obtained, a large sample of microlensing events can be used to statistically discuss the Galactic distribution of the lenses. In this study, we extract the Galactic distribution of planetary systems from the distribution of the lens-source proper motion, μrel, for a given Einstein radius crossing time, tE, measured for the 28 planetary events in the statistical sample by Suzuki et al. Because microlensing is randomly caused by stars in our Galaxy, the observational distribution can be predicted using a Galactic model. We incorporate the planet-hosting probability, ${P}_{\mathrm{host}}\propto {M}_{{\rm{L}}}^{m}{R}_{{\rm{L}}}^{r}$ , into a Galactic model for random-selected stars, where ML is the lens mass (~host mass), and RL is the Galactocentric distance. By comparing the observed distribution with the model-predicted μrel distribution for a given tE at various combinations of (m, r), we obtain an estimate r = 0.2 ± 0.4 under a plausible uniform prior for m of 0 &lt; m &lt; 2. This indicates that the dependence of the planet frequency on the Galactocentric distance is not large, and suggests that the Galactic bulge does have planets.

Keywords: Gravitational microlensing, Galactic bulge, Milky Way Galaxy, Exoplanets
APOGEE-2S Discovery of Light- and Heavy-element Abundance Correlations in the Bulge Globular Cluster NGC 6380. We derive abundance ratios for nine stars in the relatively high-metallicity bulge globular cluster NGC 6380. We find a mean cluster metallicity between [Fe/H] = -0.80 and -0.73, with no clear evidence for a variation in iron abundances beyond the observational errors. Stars with strongly enhanced [N/Fe] abundance ratios populate the cluster and are anticorrelated with [C/Fe], trends that are considered a signal of the multiple-population phenomenon in this cluster. We detect an apparent intrinsic star-to-star spread (≳0.27 dex) in the slow neutron-capture process element (s-element) Ce II. Moreover, the [Ce/Fe] abundance ratio exhibits a likely correlation with [N/Fe], and a somewhat weaker correlation with [Al/Fe]. If confirmed, NGC 6380 could be the first high-metallicity globular cluster where a N-Ce correlation is detected. Furthermore, this correlation suggests that Ce may also be an element involved in the multiple-population phenomenon. Currently, a consensus interpretation for the origin of the this apparent N-Ce correlation in high-metallicity clusters is lacking. We tentatively suggest that it could be reproduced by different channels-low-mass asymptotic giant branch stars in the high-metallicity regime or fast-rotating massive stars ("spinstars"), due to the rotational mixing. It may also be the cumulative effect of several pollution events including the occurrence of peculiar stars. Our findings should guide stellar nucleosynthesis models, in order to understand the reasons for its apparent exclusivity in relatively high-metallicity globular clusters.

Keywords: Globular star clusters, Stellar abundances
Reimagining the Water Snowline. Water is a molecule that is tightly related to many facets of star and planet formation. Water's abundance and distribution, especially the location of its snowline has thus been the subject of much study. While water is seen to be abundant in the inner region of protoplanetary disks in infrared spectroscopy, detections of water in the disk in the submillimeter are rare, with only one detection toward AS 205. Here we put the multitude of nondetections and the single detection into context of recent physicochemical models. We find that the 321.2257 GHz (102,9-93,6) line detection toward AS 205 is inconsistent with a normal inner disk temperature structure and that the observed line must be masing. Furthermore, the emitting area derived from the line width, together with published analyses on water in disks around T-Tauri stars implies that the water snowline in the disk surface is at the same location as the snowline in the midplane. We propose that this is caused by vertical mixing continuously sequestering water from the warm surface layers into the cold disk midplane.

Keywords: Submillimeter astronomy, Protoplanetary disks, Chemical abundances, Astrochemistry
Brightness Temperature Constraints on Coherent Processes in Magnetospheres of Neutron Stars. We discuss constraints that the observed brightness temperatures impose on coherent processes in pulsars and fast radio bursts, and in particular on the hypothesis of coherent curvature emission by bunches. We estimate the peak brightness temperature that a bunch of charge Ze can produce via synchrotron and/or curvature emission as kBT ~ (Ze)2/λ, where λ is the typical emitted wavelength. We demonstrate that the bunch's electrostatic energy required to produce observed brightness temperature is prohibitively high, of the order of the total bulk energy. We compare corresponding requirements for the free-electron laser mechanism and find that in that case the constraints are more easily satisfied.

Keywords: Radio transient sources, Radio bursts, Pulsars
Predicting Spectral Parameters in the Backscattering-dominated Model for the Prompt Phase of GRBs. We present new results of the backscattering-dominated prompt emission model in which the photons generated through pair annihilation at the center of a gamma-ray burst (GRB) are backscattered through Compton scattering by an outflowing stellar cork. Using a Comptonized pair annihilation spectrum accompanied by bremsstrahlung radiation for seed photons, we show that the obtained spectra produce a low-energy photon index in the range α ~ -1.95 to -1.1, steeper high-energy slopes β ~ -3.5 to -2.4, and spectral peak energies approximately a few KeV to a few tens of MeV. These findings are consistent with the values covered in GRB prompt phase observations.

Keywords: Theoretical models, Gamma-ray bursts, Relativistic jets, High energy astrophysics
Measurements of the Magnetic Field Strengths at the Bases of Stellar Coronae Using the Magnetic-field-induced Transition Theory. Measurements of the magnetic field in the stellar coronae are extremely difficult. Recently, it was proposed that the magnetic-field-induced transition (MIT) of the Fe X 257 Å line can be used to measure the coronal magnetic field of the Sun. We performed forward modeling with a series of global stellar magnetohydrodynamics models to investigate the possibility of extending this method to other late-type stars. We first synthesized the emissions of several Fe X lines for each stellar model, then calculated the magnetic field strengths using the intensity ratios of Fe X 257 Å to several other Fe X lines based on the MIT theory. Finally, we compared the derived field strengths with those in the models, and concluded that this method can be used to measure at least the magnetic field strengths at the coronal bases of stars with a mean surface magnetic flux density about one order of magnitude higher than that of the Sun. Our investigation suggests the need for an extreme ultraviolet spectrometer to perform routine measurements of the stellar coronal magnetic field.

Keywords: Magnetohydrodynamics, Stellar coronae, Stellar magnetic fields