Sazuna/UAT_keywords huggingface dataset:
Influence of Ion-Neutral Damping on the Cosmic-Ray Streaming Instability: Magnetohydrodynamic Particle-in-cell Simulations. We explore the physics of the gyroresonant cosmic-ray streaming instability (CRSI) including the effects of ion-neutral (IN) damping. This is the main damping mechanism in (partially ionized) atomic and molecular gas, which are the primary components of the interstellar medium (ISM) by mass. Limitation of CRSI by IN damping is important in setting the amplitude of Alfvén waves that scatter cosmic rays (CRs) and control galactic-scale transport. Our study employs the magnetohydrodynamic (MHD)-particle-in-cell hybrid fluid-kinetic numerical technique to follow linear growth as well as post-linear and saturation phases. During the linear phase of the instability-where simulations and analytical theory are in good agreement-IN damping prevents wave growth at small and large wavelengths, with the unstable bandwidth lower for higher IN collision rates νin. Purely MHD effects during the post-linear phase extend the wave spectrum toward larger k. In the saturated state, the CR distribution evolves toward greater isotropy (lower streaming velocity) by scattering off of Alfvén waves excited by the instability. In the absence of low-k waves, CRs with sufficiently high momentum are not isotropized. The maximum wave amplitude and rate of isotropization of the distribution function decrease at higher νin. When the IN damping rate approaches the maximum growth rate of CRSI, wave growth and isotropization are suppressed. Implications of our results for CR transport in partially ionized ISM phases are discussed.

Keywords: Computational methods, Magnetic fields, Cosmic rays
Supernova 1987A: 3D Mixing and Light Curves for Explosion Models Based on Binary-merger Progenitors. Six binary-merger progenitors of supernova 1987A (SN 1987A) with properties close to those of the blue supergiant Sanduleak -69°202 are exploded by neutrino heating and evolved until long after shock breakout in 3D and continued for light-curve calculations in spherical symmetry. Our results confirm previous findings for single-star progenitors: (1) 3D neutrino-driven explosions with SN 1987A-like energies synthesize 56Ni masses consistent with the radioactive light-curve tail; (2) hydrodynamic models mix hydrogen inward to minimum velocities below 40 km s-1 compatible with spectral observations of SN 1987A; and (3) for given explosion energy the efficiency of outward radioactive 56Ni mixing depends mainly on high growth factors of Rayleigh-Taylor instabilities at the (C+O)/He and He/H composition interfaces and a weak interaction of fast plumes with the reverse shock occurring below the He/H interface. All binary-merger models possess presupernova radii matching the photometric radius of Sanduleak -69°202 and a structure of the outer layers allowing them to reproduce the observed initial luminosity peak in the first ~7 days. Models that mix about 0.5 M⊙ of hydrogen into the He-shell and exhibit strong outward mixing of 56Ni with maximum velocities exceeding the 3000 km s-1 observed for the bulk of ejected 56Ni have light-curve shapes in good agreement with the dome of the SN 1987A light curve. A comparative analysis of the best representatives of our 3D neutrino-driven explosion models of SN 1987A based on single-star and binary-merger progenitors reveals that only one binary model fulfills all observational constraints, except one.

Keywords: Core-collapse supernovae, Explosive nucleosynthesis, Supernova dynamics, Hydrodynamics
Nova-produced Common Envelope: Source of the Nonsolar Abundances and an Additional Frictional Angular Momentum Loss in Cataclysmic Variables. A substantial fraction of cataclysmic variables (CVs) reveal nonsolar abundances. A comprehensive list of CVs that includes those that have been examined for these abundances is given. Three possible sources of these nonsolar abundances on the secondary are accretion during the red giant common envelope phase, an evolved main-sequence secondary, and nova-processed material. Use of the secondary's cross section just on the escaping nova material to change the abundances of its convective region has been the killing objection for considering nova-processed material. The key element, ignored in other studies, is that a thermonuclear runaway on a white dwarf causes a strong propagating shock wave that not only ejects material but also produces a large amount of nonejected material that forms a common envelope. This nova-produced common envelope contains a large amount of nonsolar material. We demonstrate that the secondary has the capacity and time to reaccrete enough of this material to acquire a significant nonsolar convective region. This same envelope interacting with the binary will produce a frictional angular momentum loss, which can be the consequential angular momentum loss needed for the average CV white dwarf mass, the white dwarf mass accretion rates, the period minimum, the orbital period distribution, and the space density of CV problems. This interaction will decrease the orbital period, which can cause the recently observed sudden period decreases across nova eruptions. A simple, rapid evolutionary model of the secondary that includes the swept-up nova-produced material and the increasing convective region is developed and applied to individual CVs.

Keywords: Cataclysmic variable stars, Binary stars, Classical novae
The Black Hole Spin in GRS 1915+105, Revisited. We estimate the black hole spin parameter in GRS 1915+105 using the continuum-fitting method with revised mass and inclination constraints based on the very long baseline interferometric parallax measurement of the distance to this source. We fit Rossi X-ray Timing Explorer observations selected to be accretion-disk-dominated spectral states as described in McClintock et al. (2006) and Middleton et al. (2006), which previously gave discrepant spin estimates with this method. We find that, using the new system parameters, the spin in both data sets increased, providing a best-fit spin of a* = 0.86 for the Middleton et al. data and a poor fit for the McClintock et al. data set, which becomes pegged at the BHSPEC model limit of a* = 0.99. We explore the impact of the uncertainties in the system parameters, showing that the best-fit spin ranges from a* = 0.4 to 0.99 for the Middleton et al. data set and allows reasonable fits to the McClintock et al. data set with near-maximal spin for system distances greater than ~10 kpc. We discuss the uncertainties and implications of these estimates.

Keywords: Stellar accretion disks, Black hole physics, X-ray binary stars, Rotating black holes
Implications of Increased Central Mass Surface Densities for the Quenching of Low-mass Galaxies. We use the Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey data to study the relationship between quenching and the stellar mass surface density within the central radius of 1 kpc (Σ1) of low-mass galaxies (stellar mass M* ≲ 109.5 M⊙) at 0.5 ≤ z &lt; 1.5. Our sample is mass complete down to ~109 M⊙ at 0.5 ≤ z &lt; 1.0. We compare the mean Σ1 of star-forming galaxies (SFGs) and quenched galaxies (QGs) at the same redshift and M*. We find that low-mass QGs have a higher Σ1 than low-mass SFGs, similar to galaxies above 1010 M⊙. The difference of Σ1 between QGs and SFGs increases slightly with M* at M* ≲ 1010 M⊙ and decreases with M* at M* ≳ 1010 M⊙. The turnover mass is consistent with the mass where quenching mechanisms transition from internal to environmental quenching. At 0.5 ≤ z &lt; 1.0, we find that Σ1 of galaxies increases by about 0.25 dex in the green valley (i.e., the transition region from star forming to fully quenched), regardless of their M*. Using the observed specific star formation rate gradient in the literature as a constraint, we estimate that the quenching timescale (i.e., time spent in the transition) of low-mass galaxies is a few (~4) Gyr at 0.5 ≤ z &lt; 1.0. The mechanisms responsible for quenching need to gradually quench star formation in an outside-in way, i.e., preferentially ceasing star formation in outskirts of galaxies while maintaining their central star formation to increase Σ1. An interesting and intriguing result is the similarity of the growth of Σ1 in the green valley between low-mass and massive galaxies, which suggests that the role of internal processes in quenching low-mass galaxies is a question worthy of further investigation.

Keywords: Galaxy formation, Quenched galaxies, Galaxy environments, Galaxy structure, Galaxy physics, Dwarf galaxies, Galaxy evolution, Extragalactic astronomy, Galaxy quenching
Could Switchbacks Originate in the Lower Solar Atmosphere? II. Propagation of Switchbacks in the Solar Corona. The magnetic switchbacks observed recently by the Parker Solar Probe have raised the question about their nature and origin. One of the competing theories of their origin is the interchange reconnection in the solar corona. In this scenario, switchbacks are generated at the reconnection site between open and closed magnetic fields, and are either advected by an upflow or propagate as waves into the solar wind. In this paper we test the wave hypothesis, numerically modeling the propagation of a switchback, modeled as an embedded Alfvén wave packet of constant magnetic field magnitude, through the gravitationally stratified solar corona with different degrees of background magnetic field expansion. While switchbacks propagating in a uniform medium with no gravity are relatively stable, as reported previously, we find that gravitational stratification together with the expansion of the magnetic field act in multiple ways to deform the switchbacks. These include WKB effects, which depend on the degree of magnetic field expansion, and also finite-amplitude effects, such as the symmetry breaking between nonlinear advection and the Lorentz force. In a straight or radially expanding magnetic field the propagating switchbacks unfold into waves that cause minimal magnetic field deflections, while a super-radially expanding magnetic field aids in maintaining strong deflections. Other important effects are the mass uplift the propagating switchbacks induce and the reconnection and drainage of plasmoids contained within the switchbacks. In the Appendix, we examine a series of setups with different switchback configurations and parameters, which broaden the scope of our study.

Keywords: Magnetohydrodynamics, Solar wind, Nonlinear regression, Solar coronal waves, Alfven waves
Star Formation in Nuclear Rings with the TIGRESS Framework. Nuclear rings are sites of intense star formation at the centers of barred galaxies. To understand what determines the structure and star formation rate (SFR; ${\dot{M}}_{\mathrm{SF}}$ ) of nuclear rings, we run semi-global, hydrodynamic simulations of nuclear rings subject to constant mass inflow rates ${\dot{M}}_{\mathrm{in}}$ . We adopt the TIGRESS framework of Kim &amp; Ostriker to handle radiative heating and cooling, star formation, and related supernova (SN) feedback. We find that the SN feedback is never strong enough to destroy the ring or quench star formation everywhere in the ring. Under the constant ${\dot{M}}_{\mathrm{in}}$ , the ring star formation is very steady and persistent, with the SFR exhibiting only mild temporal fluctuations. The ring SFR is tightly correlated with the inflow rate as ${\dot{M}}_{\mathrm{SF}}\approx 0.8{\dot{M}}_{\mathrm{in}}$ , for a range of ${\dot{M}}_{\mathrm{in}}=0.125-8\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . Within the ring, vertical dynamical equilibrium is maintained, with the midplane pressure (powered by SN feedback) balancing the weight of the overlying gas. The SFR surface density is correlated nearly linearly with the midplane pressure, as predicted by the pressure-regulated, feedback-modulated star formation theory. Based on our results, we argue that the ring SFR is causally controlled by ${\dot{M}}_{\mathrm{in}}$ , while the ring gas mass adapts to the SFR to maintain the vertical dynamical equilibrium under the gravitational field arising from both gas and stars.

Keywords: AGN host galaxies, Hydrodynamical simulations, Starburst galaxies, Galactic center, Stellar feedback, Disk galaxies, Star formation, Galaxy winds, Interstellar medium, Galaxy circumnuclear disk, Barred spiral galaxies, Superbubbles
On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances. We provide the largest and most homogeneous sample of α-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t ≥ 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3 dex in iron abundance (-3.00 ≤ [Fe/H] ≤ 0.24). We found that field RRLs are ~0.3 dex more α poor than typical halo tracers in the metal-rich regime ([Fe/H] ≥ -1.2), while in the metal-poor regime ([Fe/H] ≤ -2.2) they seem to be on average ~0.1 dex more α enhanced. This is the first time that the depletion in α elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [α/Fe] trend between α-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between α-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies. These results are supported by similar elemental abundances for 46 field horizontal branch stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy. * Based on observations obtained with the du Pont telescope at Las Campanas Observatory, operated by Carnegie Institution for Science. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere.

Keywords: High resolution spectroscopy, Pulsating variable stars, RR Lyrae variable stars, Milky Way stellar halo, Spectroscopy
Convectively Coupled Equatorial Trapped Waves in Stars and Planets. In this paper, we have studied convectively coupled equatorially trapped waves in rotating stars, with and without magnetic fields. The equatorial trapped hydrodynamic and magnetohydrodynamic Poincaré, Rossby, mixed Rossby-Poincaré, and Kelvin waves were identified. The effects of stratification and nontraditional Coriolis force terms have been investigated. When the flow is strongly stratified, the wave frequencies of the convectively coupled model are almost the same as those of a shallow-water model. However, when the flow is weakly stratified, the wave frequencies are constrained by the buoyancy frequency. The nontraditional Coriolis terms affect the widths and phases of the equatorial waves. The width increases with an increasing nontraditional Coriolis parameter. Phase shift occurs when the nontraditional Coriolis parameter is included. The magnetic effect is significant when the magnetic field is strong. We have applied the model in the solar atmosphere and solar tachocline to explain the Rieger-type periodicities. For the solar atmosphere, when the magnetic effect is taken into account, we find that the magnetic field should be smaller than 5 G in the solar photosphere. Otherwise, the Rieger-type periodicities can only be attributed to long Rossby waves. For the solar tachocline, we find that magnetic field of the solar tachocline should be smaller than 50 kG to observe the 160 day Rieger period. In addition, we find that the effect of the nontraditional Coriolis terms is not obvious in the solar photosphere, but its effect on the tachocline is significant.

Keywords: Stellar interiors, Internal waves, Solar atmosphere, Hydrodynamics, Stellar rotation, Planetary interior
A New Window into Planet Formation and Migration: Refractory-to-Volatile Elemental Ratios in Ultra-hot Jupiters. A primary goal of exoplanet characterization is to use a planet's current composition to understand how that planet formed. For example, the C/O ratio has long been recognized as carrying important information on the chemistry of volatile species. Refractory elements, like Fe, Mg, and Si, are usually not considered in this conversation because they condense into solids like Fe(s) or MgSiO3 and would be removed from the observable, gaseous atmosphere in exoplanets cooler than about 2000 K. However, planets hotter than about 2000 K, called ultra-hot Jupiters (UHJs), are warm enough to largely avoid the condensation of refractory species. In this paper, we explore the insight that the measurement of refractory abundances can provide into a planet's origins. Through refractory-to-volatile elemental abundance ratios, we can estimate a planet's atmospheric rock-to-ice fraction and constrain planet formation and migration scenarios. We first relate a planet's present-day refractory-to-volatile ratio to its rock-to-ice ratio from formation using various compositional models for the rocky and icy components of the protoplanetary disk. We discuss potential confounding factors like the sequestration of heavy metals in the core and condensation. We then show such a measurement using atmospheric retrievals of the low-resolution UV-IR transmission spectrum of WASP-121b with PETRA, from which we estimate a refractory-to-volatile ratio of 5.0 ${}_{-2.7}^{+6.0}\,\times $ solar and a rock-to-ice ratio greater than 2/3. This result is consistent with significant atmospheric enrichment by rocky planetismals. Lastly, we discuss the rich future potential for measuring refractory-to-volatile ratios in UHJs with the arrival of the James Webb Space Telescope and by combining observations at low and high resolution.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheres, Spectroscopy, Exoplanet formation, Planet formation
Ultradense Gas Tracked by Unshifted Broad Absorption Lines in a Quasar. We present a detailed analysis of the broad absorption line system in the quasar SDSS J122017.06+454941.1, which are clearly detected in hydrogen Lyman series and metal lines, such as C IV, Si IV, Si III, Al III, and C II, with a similar velocity as that of the broad emission lines. We reliably measured the column densities of H I, Al III, and C II, and obtained a low limit to Si IV and Si III. With the help of the photoionization simulations, we found that the absorption gas has a hydrogen number density nH ≈ 1011.03 cm-3 and a hydrogen column density NH ≈ 1021.0 cm-2, and is exposed to the radiation with an ionization parameter U ≈ 10-1.25, and thus located the absorber at ~0.3 pc from the central supermassive black hole, remarkably similar to the radius of the broad-line region (BLR; 0.17-0.84 pc as estimated by the luminosity-radius relation) of the quasar. It is likely that our line of sight may happen to intercept the low-column part of the BLR with a high density similar to that of the inferred value of the absorber. We suggest that detection of Al III absorption line doublet in moderate quality quasar spectra could be a good indicator of dense gases, provided that the neutral hydrogen column density of the absorber is $15.4\lesssim \mathrm{log}\,{N}_{{\rm{H}}{\rm\small{I}}}\,({\mathrm{cm}}^{-2})\lesssim 16.5$ .

Keywords: Active galactic nuclei, Quasars, Broad-absorption line quasar
Properties of Interplanetary Fast Shocks Close to the Martian Environment. Magnetic field and plasma measurements from the Mars Atmosphere and Volatile EvolutioN mission in orbit around Mars are analyzed for interplanetary fast shock properties and drivers from 2014 October to 2018 November. We identified 52 fast shocks, including 39 fast forward (FF) shocks and 13 fast reverse (FR) shocks. Most (79%) of the FF shocks are driven by stream interaction regions (SIRs) with only a few cases being driven by interplanetary coronal mass ejections, and all of the FR shocks are driven by SIRs. A total of 92% of the identified shocks are quasi-perpendicular shocks. On average, the shock strengths of SIR-driven forward and reverse shocks are comparable, and they are greater than that of ICME-driven forward shocks. The shock strengths show no systematic dependence on the shock locations relative to the Martian bow shock. We find no evidence that the shock shapes are affected by Mars and its bow shock as an obstacle in the propagating medium. The results can help us understand the nature of interplanetary shocks propagating in different environments.

Keywords: Interplanetary shocks, Heliosphere, Mars, Solar wind, Shocks
Line-tied Boundary Conditions Can Cause Resonant Absorption Models to Generate Unphysically Large Boundary Layers. This paper uses linear magnetohydrodynamics to model resonant absorption in coronal plasma with a Cartesian coordinate system. We impose line-tied boundary conditions and tilt the background magnetic field to be oblique to the transition region. Halberstadt &amp; Goedbloed, Goedbloed &amp; Halberstadt, and Arregui et al. show that line-tied boundary conditions cause their resonant absorption models to produce steep boundary layers/evanescent fast waves. We aim to study the importance of boundary layers and assess their significance in a solar context. We calculate solutions in a model where we impose line-tied boundary conditions and compare this with a model where we include the chromosphere instead. Results are calculated analytically and then verified numerically. We show that line-tied boundary conditions can cause the model to overestimate the boundary layers' amplitude significantly. If the fast waves can propagate in the chromosphere, then the line-tied model accurately predicts the boundary layers' amplitude. However, if the fast waves are evanescent, then the boundary layers' size is reduced significantly, and the line-tied model overestimates their amplitude. This leads to the counterintuitive result that length scales tangential to the transition region can play an essential role in determining line-tied boundary conditions' validity. The results suggest that line-tied boundary conditions can cause the model to generate unphysically large boundary layers. However, researchers may wish to continue to use them in their models for their simplicity and ability to significantly reduce computation time if they understand and are aware of their flaws.

Keywords: Solar atmosphere, Magnetohydrodynamics, Analytical mathematics, Solar physics, Alfven waves, Solar corona, Solar coronal waves, Solar oscillations, Magnetohydrodynamical simulations