Sazuna/UAT_keywords huggingface dataset:
The Structure and Stability of Massive Hot White Dwarfs. We investigate the structure and stability against radial oscillations, pycnonuclear reactions, and inverse β-decay of hot white dwarfs. We consider the fluid matter to be made up of nucleons and electrons confined in a Wigner-Seitz cell surrounded by free photons. It is considered that the temperature depends on the mass density considering the presence of an isothermal core. We find that the temperature produces remarkable effects on the equilibrium and radial stability of white dwarfs. The stable equilibrium configuration results are compared with those for white dwarfs estimated from the Extreme Ultraviolet Explorer survey and the Sloan Digital Sky Survey. We derive masses, radii, and central temperatures for the most massive white dwarfs according to the surface gravity and effective temperature reported by the surveys. We note that these massive stars are in the mass region where general relativity effects are important. These stars are near the threshold of instabilities due to radial oscillations, pycnonuclear reactions, and inverse β-decay. Regarding the radial stability of these stars as a function of the temperature, we find that it decreases with the increment of central temperature. We also find that the maximum-mass point and the zero eigenfrequencies of the fundamental mode are determined at the same central energy density. Regarding low-temperature stars, pycnonuclear reactions occur in similar central energy densities, and the central energy density threshold for inverse β-decay is not modified. For Tc ≥ 1.0 × 108 [K], the onset of radial instability is attained before pycnonuclear reaction and inverse β-decay.

Keywords: White dwarf stars, Compact objects
Three-dimensional Multispecies Simulation of the Solar Wind Interaction with Mars Under Different Interplanetary Magnetic Field Orientations. Without the intrinsic magnetic field, the solar wind interaction with Mars can be significantly different from the interaction with Earth and other magnetized planets. In this paper, we investigate how a global configuration of the magnetic structures, consisting of the bow shock, the induced magnetosphere, and the magnetotail, is modulated by the interplanetary magnetic field (IMF) orientation. A 3D multispecies numerical model is established to simulate the interaction of solar wind with Mars under different IMF directions. The results show that the shock size including the subsolar distance and the terminator radius increases with Parker spiral angle, as is the same case with the magnetotail radius. The location and shape of the polarity reversal layer and inverse polarity reversal layer in the induced magnetotail are displaced to the y &lt; 0 sector for a nonzero flow-aligned IMF component, consistent with previous analytical solutions and observations. The responses of the Martian global magnetic configuration to the different IMF directions suggest that the external magnetic field plays an important role in the solar wind interaction with unmagnetized planets.

Keywords: Mars, Solar-planetary interactions, Magnetohydrodynamics
Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project. Through the Backyard Worlds: Planet 9 citizen science project, we have identified a wide-separation (~10', ~9900 au projected) substellar companion to the nearby (~17.5 pc), mid-M dwarf Ross 19. We have developed a new formalism for determining chance alignment probabilities based on the BANYAN Σ tool, and find a 100% probability that this is a physically associated pair. Through a detailed examination of Ross 19A, we find that the system is metal-poor ([Fe/H] = -0.40 ± 0.12) with an age of ${7.2}_{-3.6}^{+3.8}$ Gyr. Combining new and existing photometry and astrometry, we find that Ross 19B is one of the coldest known wide-separation companions, with a spectral type on the T/Y boundary, an effective temperature of ${500}_{-100}^{+115}$ K, and a mass in the range 15-40 MJup. This new, extremely cold benchmark companion is a compelling target for detailed characterization with future spectroscopic observations using facilities such as the Hubble Space Telescope or James Webb Space Telescope.

Keywords: Brown dwarfs, Low mass stars
Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915 NW with Velocity Decomposition of CO Rovibrational Absorption Lines. Understanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism. However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines (Δv = 0 →1, ΔJ = ±1) at λ ~ 4.67 μm observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy (R ~ 10,000) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately ~-160 km s-1, but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately ~+100 km s-1, which were attributed to the torus. The ratios of the velocity dispersions of each component led to those of the rotating radii around the black hole of Rrot,a: Rrot,b: Rrot,c ≈ 1: 5: 17, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with ${\sigma }_{V}\propto {R}_{\mathrm{rot}}^{-0.5}$ is assumed. Based on the kinetic temperature of components (a) and (b) of ~720 and ~25 K, respectively, estimated from the level population, the temperature gradient is ${T}_{\mathrm{kin}}\propto {R}_{\mathrm{rot}}^{-2.1}$ . Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient. * This research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.

Keywords: High resolution spectroscopy, Molecular gas, Infrared astronomy, Active galactic nuclei, Ultraluminous infrared galaxies
On the Importance of Wave-Planet Interactions for the Migration of Two Super-Earths Embedded in a Protoplanetary Disk. We investigate a repulsion mechanism between two low-mass planets migrating in a protoplanetary disk, for which the relative migration switches from convergent to divergent. This mechanism invokes density waves emitted by one planet transferring angular momentum to the coorbital region of the other and then directly to it through the horseshoe drag. We formulate simple analytical estimates, which indicate when the repulsion mechanism is effective. One condition for a planet to be repelled is that it forms a partial gap in the disk and another is that this should contain enough material to support angular momentum exchange with it. Using two-dimensional hydrodynamical simulations, we obtain divergent migration of two super-Earths embedded in a protoplanetary disk because of repulsion between them and verify these conditions. To investigate the importance of resonant interaction, we study the migration of planet pairs near first-order commensurabilities. It appears that proximity to resonance is significant but not essential. In this context we find repulsion still occurs when the gravitational interaction between the planets is removed, suggesting the importance of angular momentum transfer through waves excited by another planet. This may occur through the scattering of coorbital material (the horseshoe drag), or material orbiting close by. Our results indicate that if conditions favor the repulsion between two planets described above, we expect to observe planet pairs with their period ratios greater, often only slightly greater, than resonant values or possibly rarity of commensurability.

Keywords: Planetary system formation, Exoplanet evolution, Exoplanet dynamics
Core-collapse Supernovae: From Neutrino-driven 1D Explosions to Light Curves and Spectra. We present bolometric and broadband light curves and spectra for a suite of core-collapse supernova models exploded self-consistently in spherical symmetry within the PUSH framework. We analyze broad trends in these light curves and categorize them based on morphology. We find that these morphological categories relate simply to the progenitor radius and mass of the hydrogen envelope. We present a proof-of-concept sensitive-variable analysis, indicating that an important determining factor in the properties of a light curve within a given category is 56Ni mass. We follow spectra from the photospheric to the nebular phase. These spectra show characteristic iron-line blanketing at short wavelengths and Doppler-shifted Fe II and Ti II absorption lines. To enable this analysis, we develop a first-of-its-kind pipeline from a massive progenitor model, through a self-consistent explosion in spherical symmetry, to electromagnetic counterparts. This opens the door to more detailed analyses of the collective properties of these observables. We provide a machine-readable database of our light curves and spectra online at go.ncsu.edu/astrodata.

Keywords: Type Ic supernovae, Light curve classification , Core-collapse supernovae, High energy astrophysics, Type II supernovae, Light curves, Type Ib supernovae, Transient sources, Time domain astronomy, Radiative transfer, Radiative transfer simulations
Gamma Rays from Fast Black-hole Winds. Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersion of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this work we use data from the Fermi Large Area Telescope to search for the γ-ray emission from galaxies with an ultrafast outflow (UFO): a fast (v ~ 0.1 c), highly ionized outflow, detected in absorption at hard X-rays in several nearby active galactic nuclei (AGN). Adopting a sensitive stacking analysis we are able to detect the average γ-ray emission from these galaxies and exclude that it is due to processes other than UFOs. Moreover, our analysis shows that the γ-ray luminosity scales with the AGN bolometric luminosity and that these outflows transfer ~0.04% of their mechanical power to γ-rays. Interpreting the observed γ-ray emission as produced by cosmic rays (CRs) accelerated at the shock front, we find that the γ-ray emission may attest to the onset of the wind-host interaction and that these outflows can energize charged particles up to the transition region between galactic and extragalactic CRs.

Keywords: Galactic winds, Active galactic nuclei, Gamma-rays
Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. II. Statistics. Angular momentum is a key property regulating star formation and evolution. However, the physics driving the distribution of the stellar rotation rates of early-type main-sequence stars is as yet poorly understood. Using our catalog of 40,034 early-type stars with homogeneous $v\sin i$ parameters, we review the statistical properties of their stellar rotation rates. We discuss the importance of possible contaminants, including binaries and chemically peculiar stars. Upon correction for projection effects and rectification of the error distribution, we derive the distributions of our sample's equatorial rotation velocities, which show a clear dependence on stellar mass. Stars with masses less than 2.5 M⊙ exhibit a unimodal distribution, with the peak velocity ratio increasing as stellar mass increases. A bimodal rotation distribution, composed of two branches of slowly and rapidly rotating stars, emerges for more massive stars (M &gt; 2.5 M⊙). For stars more massive than 3.0 M⊙, the gap between the bifurcated branches becomes prominent. For the first time, we find that metal-poor ([M/H] &lt; -0.2 dex) stars only exhibit a single branch of slow rotators, while metal-rich ([M/H] &gt; 0.2 dex) stars clearly show two branches. The difference could be attributed to unexpectedly high spin-down rates and/or in part strong magnetic fields in the metal-poor subsample.

Keywords: Early-type stars, Stellar properties, Astronomy data analysis, Stellar rotation, Stellar evolution
Time Evolution of a System of Particles Obeying Coulomb's Law and the High-speed Rollover of Suprathermal Tails in the Solar Wind. In this article, we show through a series of rigorous mathematical steps, starting with Liouville's equation and solving it for the case of two protons using the method of characteristics, that a velocity distribution function, f(u), is formed that exhibits a power law, f ∝ uγ, where γ is -9/2, and an exponential-type rollover at large speeds, providing a potential explanation for the observations of suprathermal ions in the solar wind. The solution is valid for all times and all background conditions, though the power law does at some point merge with the core of the distribution. When it does so, a final distribution is found that agrees with overall energy conservation. Analytical approximations to the solution are discussed, along with explanations for the various phases that the solution undergoes.

Keywords: Solar energetic particles
Reconciling the 16.35-day Period of FRB 20180916B with Jet Precession. A repeating fast radio burst (FRB), FRB 20180916B (hereafter FRB 180916), was reported to have a 16.35-day period. This period might be related to a precession period. In this paper, we investigate two precession models to explain the periodic activity of FRB 180916. In both models, the radio emission of FRB 180916 is produced by a precessing jet. For the first disk-driven jet precession model, an extremely low viscous parameter (i.e., the dimensionless viscosity parameter α ≲ 10-8) is required to explain the precession of FRB 180916, which implies its implausibility. For the second tidal-force-driven jet precession model, we consider that a compact binary consists of a neutron star/black hole and a white dwarf; the white dwarf fills its Roche lobe, and mass transfer occurs. Due to the misalignment between the disk and orbital plane, the tidal force of the white dwarf can drive jet precession. We show that the relevant precession periods are several days to hundreds of days, depending on the specific accretion rates and component masses. The duration of FRB 180916 generation in the binary with extremely high accretion rate will be several thousand years.

Keywords: Jets, White dwarf stars, Compact binary stars, Stellar accretion disks, Radio transient sources
The X-Ray Binary Population in the Galactic Center Revealed through Multi-decade Observations. We present an investigation of the quiescent and transient X-ray binaries (XRBs) of the Galactic Center (GC). We extended our Chandra analysis of the non-thermal X-ray sources, located in the central parsec, from Hailey et al. (2018), using an additional 4.6 Msec of ACIS-S data obtained in 2012-2018. The individual Chandra spectra of the 12 sources fit to an absorbed power-law model with a mean photon index Γ ≈ 2 and show no Fe emission lines. Long-term variability was detected from nine of them, confirming that a majority are quiescent XRBs. Frequent X-ray monitoring of the GC revealed that the 12 non-thermal X-ray sources, as well as four X-ray transients have shown at most a single outburst over the last two decades. They are distinct from the six known neutron star LMXBs in the GC, which have all undergone multiple outbursts with ≲ 5 year recurrence time on average. Based on the outburst history data of the broader population of X-ray transients, we conclude that the 16 sources represent a population of ~240-630 tightly bound BH-LMXBs with ~4-12 hr orbital periods, consistent with the stellar/binary dynamics modeling in the vicinity of Sgr A*. The distribution of the 16 BH-LMXB candidates is disk-like (at 87% CL) and aligned with the nuclear star cluster. Our results have implications for XRB formation and the rate of gravitational wave events in other galactic nuclei.

Keywords: Low-mass x-ray binary stars, X-ray transient sources, Galactic center, Stellar mass black holes
Constraining Scalar-tensor Theories Using Neutron Star-Black Hole Gravitational Wave Events. With the continuous upgrade of detectors, greater numbers of gravitational wave (GW) events have been captured by the LIGO Scientific Collaboration and Virgo Collaboration (LVC), which offer a new avenue to test general relativity and explore the nature of gravity. Although various model-independent tests have been performed by LVC in previous works, it is still interesting to ask what constraints can be placed on specific models by current GW observations. In this work, we focus on three models of scalar-tensor theories, the Brans-Dicke theory (BD), the theory with scalarization phenomena proposed by Damour and Esposito-Farèse (DEF), and screened modified gravity (SMG). Of the four possible neutron star-black hole events that have occurred so far, we use two of them to place constraints. The other two are excluded in this work because of possible unphysical deviations. We consider the inspiral range with the cutoff frequency at the innermost stable circular orbit and add a modification of dipole radiation into the waveform template. The scalar charges of neutron stars in the dipole term are derived by solving the Tolman-Oppenheimer-Volkoff equations for different equations of state. The constraints are obtained by performing the full Bayesian inference with the help of the open source software Bilby. The results show that the constraints given by GWs are comparable to those given by pulsar timing experiments for DEF theory, but are not competitive with the current solar system constraints for BD and SMG theories.

Keywords: Non-standard theories of gravity, Gravitational waves
Star Formation Triggered by Shocks. Star formation can be triggered by compression from shock waves. In this study, we investigated the interaction of hydrodynamic shocks with Bonnor-Ebert spheres using 3D hydrodynamical simulations with self-gravity. Our simulations indicated that the cloud evolution primarily depends on two parameters: shock speed and initial cloud radius. Stronger shocks can compress clouds more efficiently, and when the central region becomes gravitationally unstable, a shock triggers cloud contraction. However, if it is excessively strong, it shreds the cloud more violently and the cloud is destroyed. From simple theoretical considerations, we derived the condition of triggered gravitational collapse, which agreed with the simulation results. Introducing sink particles, we followed the further evolution after star formation. Since stronger shocks tend to shred the cloud material more efficiently, the stronger the shock is, the smaller the final (asymptotic) masses of the stars formed (i.e., sink particles) become. In addition, shocks accelerate clouds, promoting mixing of shock-accelerated interstellar medium gas. As a result, the separation between sink particles and shocked clouds center and their relative speeds increase over time. We also investigated the effect of cloud turbulence on shock-cloud interaction. We observed that cloud turbulence prevents rapid cloud contraction; thus, turbulent clouds are destroyed more rapidly than thermally supported clouds. Therefore, the masses of stars formed become smaller. Our simulations provide a general guide to the evolutionary process of dense cores and Bok globules impacted by shocks.

Keywords: Shocks, Star formation, Molecular clouds
A Pixon-based Method for Reverberation-mapping Analysis in Active Galactic Nuclei. We present an alternative method for reconstructing a velocity-delay map in reverberation mapping (RM) based on the pixon algorithm initially proposed for image reconstruction by Pina. The pixon algorithm allows for a variable pixon basis to adjust resolution of each image pixel according to the information content in that pixel, which therefore enables the algorithm to make the best possible use of measured data. The final optimal pixon basis functions would be those that minimize the number of pixons while still providing acceptable descriptions to data within the accuracy allowed by noises. We adapt the pixon algorithm to RM analysis and develop a generic framework to implement the algorithm. Simulation tests and comparisons with the widely used maximum entropy method demonstrate the feasibility and high performance of our pixon-based RM analysis. This paper serves as an introduction to the framework and the application to velocity-unresolved RM. An extension to velocity-resolved cases will be presented in a companion paper.

Keywords: Reverberation mapping, Active galactic nuclei, Algorithms, Quasars
Statistical Properties of Electron-scale Magnetic Peaks in the Solar Wind at 1 au. Energy cascade from magnetohydrodynamic to kinetic scales can create many coherent structures in the turbulent astrophysical plasma environment, such as magnetic holes and magnetic peaks. Knowing the properties of each coherent structure is critical to better understand the process of the energy cascade. Recently, electron-scale magnetic peaks (ESMPs) are revealed to exist in the solar wind at 1 au. Here, we investigate the properties of the ESMPs upstream of the terrestrial bow shock based on observations of the Magnetospheric Multiscale spacecraft. We regard an isolated ESMP or a train of ESMPs as an ESMP event, and 204 ESMPs or 32 ESMP events are found. Both the durations and cross-section sizes of the ESMPs obey log-normal distributions. The median duration and cross-section size are ~0.25 s and ~0.33 ion gyroradius, respectively. The ESMP event with an average occurrence rate of ~8.8 events per day tends to occur during the weak interplanetary magnetic field strength or the slow solar wind. We also find that the ion foreshock is an important source of the ESMP events, and a small part of the ESMP events originates from the upstream pristine solar wind. Although only 12 out of 204 ESMPs have bipolar electron velocities, we suggest that the electron vortex is an essential feature for the stable ESMP. The generation mechanism of the ESMPs is unclear; nevertheless, finding out the origin of the electron vortex in the ion foreshock might help to reveal their generation mechanism.

Keywords: Solar wind, Interplanetary magnetic fields