Sazuna/UAT_keywords huggingface dataset:
Cyclic Zoom: Multiscale GRMHD Modeling of Black Hole Accretion and Feedback. We present a "cyclic zoom" method to capture the dynamics of accretion flows onto black holes across a vast range of spatial and temporal scales in general relativistic magnetohydrodynamic (GRMHD) simulations. In this method, we cyclically zoom out (derefine) and zoom in (refine) the simulation domain while using a central mask region containing a careful treatment of the coarsened fluid variables to preserve the small-scale physics, in particular the magnetic field dynamics. The method can accelerate GRMHD simulations by ≳105 times for problems with large-scale separation. We demonstrate the validity of the technique using a series of tests, including spherically symmetric Bondi accretion, the Blandford–Znajek monopole, magnetized turbulent Bondi accretion, accretion of a magnetized rotating torus, and the long-term evolution of an accreting torus about both Schwarzschild and Kerr black holes. As applications, we simulate Bondi and rotating torus accretion onto black holes from galactic scales, covering an extremely large dynamic range. In Bondi accretion, the accretion rate is suppressed relative to the Bondi rate by  ∼(10rg/rB)1/2  with a feedback power of  ∼0.01Ṁc2  for vanishing spin and  ∼0.1Ṁc2  for spin a ≈ 0.9. In the long-term evolution of a rotating torus, the accretion rate decreases with time as  Ṁ∝t‑2  on timescales much longer than the viscous timescale, demonstrating that our method can capture not only quasi-steady problems but also secular evolution. Our new method likewise holds significant promise for applications to many other problems that need to cover vast spatial and temporal scales.

Keywords: Accretion, Supermassive black holes, Magnetohydrodynamics, Black holes, Bondi accretion, Computational methods, Active galactic nuclei, Astrophysical fluid dynamics, Magnetohydrodynamical simulations
Discovery of a Weak CN Spectral Absorption Feature in Red Supergiant Stars in the Andromeda (M31) and Triangulum (M33) Galaxies. Using Keck DEIMOS spectra of stars in the Andromeda (M31) and Triangulum (M33) galaxies, selected from the large multiband (near-ultraviolet, visible light, and near-infrared) Hubble Space Telescope surveys PHAT and PHATTER, respectively, we have identified a subset of stars that contain a previously unnoticed weak spectral absorption feature around 8000 Å (0.8 μm). This absorption feature appears to be associated with the cyanogen (CN) molecule. Strong CN spectral absorption is a standard feature of carbon stars, which are thought to be intermediate mass (2─3 M⊙) stars with C/O &gt; 1 in the thermally pulsating asymptotic giant branch phase of stellar evolution. However, the stars that are the focus of this paper are characterized by a weak version of this CN spectral absorption feature in a spectrum that is otherwise dominated by normal O-rich spectral absorption lines such as TiO and/or the Ca near-infrared triplet. We have dubbed these stars "weak CN" stars. We present an automated method for identifying weak CN stars in M31 and M33, and examine their photometric properties in relation to model isochrones and stellar tracks. We find that weak CN stars tend to be fairly localized in color─magnitude space, and appear to be red supergiant stars with masses ranging from 5 to 10 M⊙, overall lifetimes of about 40─50 Myr, and currently in the core He burning phase of stellar evolution.

Keywords: Carbon stars, Triangulum Galaxy, CN stars, Andromeda Galaxy, Stellar evolution
Cosmic-Ray-driven Galactic Winds with Resolved Interstellar Medium and Ion-neutral Damping. Feedback processes in galaxies dictate their structure and evolution. Baryons can be cycled through stars, which inject energy into the interstellar medium in supernova explosions, fueling multiphase galactic winds. Cosmic rays (CRs) accelerated at supernova remnants are an important component of feedback. CRs can effectively contribute to wind driving; however, their impact heavily depends on the assumed CR transport model. We run high-resolution "tallbox" simulations of a patch of a galactic disk using the moving mesh magnetohydrodynamics code AREPO, including varied CR implementations and the CRISP nonequilibrium thermochemistry model. We characterize the impact of CR feedback on star formation and multiphase outflows. While CR-driven winds are able to supply energy to a global-scale wind, a purely thermal wind loses most of its energy by the time it reaches 3 kpc above the disk midplane. We further find that the adopted CR transport model significantly affects the steady state of the wind. In the model with CR advection, streaming, diffusion, and nonlinear Landau damping, CRs provide very strong feedback. Additionally, accounting for ion-neutral damping (IND) decouples CRs from the cold ISM, which reduces the impact of CRs on the star formation rate. Nevertheless, CRs in this most realistic model are able to accelerate warm gas and levitate cool gas in the wind but have little effect on cold gas and hot gas. This model displays moderate mass loading and significant CR energy loading, demonstrating that IND does not prevent CRs from providing effective feedback.

Keywords: Magnetohydrodynamics, Galaxy winds, Interstellar medium, Cosmic rays
A New LISA-detectable Type Ia Supernova Progenitor in the Southern Sky: SMSS J1138−5139. We present the discovery and analysis of a nearby eclipsing ultracompact accreting binary SMSS J1138−5139, the first well-constrained LISA-detectable Type Ia supernova progenitor. Our time-series optical spectroscopy identifies its orbital period through radial velocity monitoring at  Porb,RV=27.682minutes , twice the photometric period seen in 2 minute cadence data from TESS Sector 37. We model our optical spectroscopy together with new simultaneous multiband time-series photometry from Gemini to place constraints on the binary parameters. Our light-curve modeling finds that SMSS J1138−5139 contains an M2 = 0.25 ± 0.01 M⊙ pre-white-dwarf donor with a massive M1 = 1.02 ± 0.05 M⊙ white dwarf accretor at orbital inclination  i=88.∘6±0.∘1 . Based on our photometrically derived system parameters, we expect that gravitational-wave radiation will drive SMSS J1138−5139 to a merger within τ = 5.7 ± 0.3 Myr and result in a Type Ia supernova. Even without a direct merger event, the component masses of SMSS J1138−5139 and active hydrogen accretion suggest that eventual helium accretion will likely also trigger a Type Ia supernova explosion through the dynamically driven double-degenerate double-detonation (D6) channel. We expect LISA to detect the gravitational-wave emission from SMSS J1138−5139 with a signal-to-noise ratio of 7─10 after a 48 month mission.

Keywords: Subdwarf stars, White dwarf stars, Interacting binary stars, Gravitational wave sources, Eclipsing binary stars
A Gravitational-wave-detectable Candidate Type Ia Supernova Progenitor. Type Ia supernovae (SNe Ia), critical for studying cosmic expansion, arise from thermonuclear explosions of white dwarfs, but their precise progenitor pathways remain unclear. Growing evidence supports the "double-degenerate scenario," where two white dwarfs interact. The absence of nondegenerate companions capable of explaining the observed SN Ia rate, along with observations of hypervelocity white dwarfs, interpreted as surviving companions of such systems, provide compelling evidence for this scenario. Upcoming millihertz gravitational-wave observatories like the Laser Interferometer Space Antenna (LISA) are expected to detect thousands of double-degenerate systems, though the most compact known candidate SN Ia progenitors produce marginally detectable signals. Here, we report observations of ATLAS J1138-5139, a binary white dwarf system with an orbital period of just 28 minutes. Our analysis reveals a 1 M☉ carbon─oxygen white dwarf accreting from a high-entropy helium-core white dwarf. Given its mass, the accreting carbon─oxygen white dwarf is poised to trigger a typical-luminosity SN Ia within a few million years, to evolve into a stably transferring AM Canum Venaticorum (or AM CVn) system, or undergo a merger into a massive white dwarf. ATLAS J1138-5139 provides a rare opportunity to calibrate binary evolution models by directly comparing observed orbital parameters and mass-transfer rates closer to merger than any known SN Ia progenitor. Its compact orbit ensures detectability by LISA, demonstrating the potential of millihertz gravitational-wave observatories to reveal a population of SN Ia progenitors on a Galactic scale, paving the way for multimessenger studies offering insights into the origins of these cosmologically significant explosions.

Keywords: Eclipsing binary stars, White dwarf stars, Type Ia supernovae, Compact binary stars
Hydroxylated Mg-rich Amorphous Silicates as Catalysts for Molecular Hydrogen Formation in the Interstellar Medium. We present results from an experimental study on the interaction of atomic deuterium with magnesium-rich amorphous enstatite- and forsterite-type silicates. Infrared spectroscopy was used to examine the process. During deuterium atom exposure, deuteroxyl group formation was observed. The cross section for OD group formation, estimated from the OD stretching band intensity with D atom fluence, is σf,OD = 4.2 × 10‑18 cm2 for both silicates. HD (D2) molecules form via D atom abstraction of chemisorbed H (D) atoms from OH (OD) groups, with a cross section of  σf,D2  = 7.0 × 10‑18 cm2. Quantum-chemical calculations on enstatite and forsterite amorphous nanoclusters were used to analyze chemisorption and abstraction energies of hydrogen atoms. The formation of OH groups on forsterite is barrierless, while enstatite has a small energy barrier. H2 abstraction from hydroxyl groups is barrierless in both silicates. The results support our interpretation of IR spectral changes during D atom exposure as addition and exchange reactions, with catalytic molecular deuterium formation. These findings, obtained at 300 K, are relevant to astrophysical environments like photodissociation regions and interstellar clouds at lower temperatures. Amorphous silicates, like carbon grains, undergo hydrogenation in the diffuse interstellar medium due to interactions with atomic hydrogen and UV photons. The detection of these components on comet 67P/Churyumov–Gerasimenko connects primitive solar system objects to interstellar dust, offering new insights into their evolution.

Keywords: Astrochemistry
Sgr A* Spin and Mass Estimates through the Detection of Multiple Extremely Large Mass Ratio Inspirals. We analyze the parameter estimation accuracy that can be achieved for the mass and spin of Sgr A*, the supermassive black hole in our Galactic center, by detecting multiple extremely large mass ratio inspirals (XMRIs). XMRIs are formed by brown dwarfs inspiraling into a supermassive black hole, thus emitting gravitational waves (GWs) inside the detection band of future space-based detectors such as LISA and TianQin. Theoretical estimates suggest the presence of approximately 10 XMRIs emitting detectable GWs, making them some of the most promising candidates for space-based GW detectors. Our analysis indicates that even if individual sources have low signal-to-noise ratios (SNRs; ≈10), high-precision parameter estimates can still be achieved by detecting multiple sources. In this case, the accuracy of the parameter estimates increases by approximately 1–2 orders of magnitude at least. Moreover, by analyzing a small sample of 400 initial conditions for XMRIs formed in the Galactic center, we estimate that almost 80% of the detectable XMRIs orbiting Sgr A* will have eccentricities between 0.43 and 0.95 and an SNR ∈ [10, 100]. The remaining ∼20% of the sources have an SNR ∈ [100, 1000] and eccentricities ranging from 0.25 to 0.92. Additionally, some XMRIs with high SNRs are far from being circular. These loud sources with SNR ≈ 1000 can have eccentricities as high as e ≈ 0.7; although their detection chances are low, representing ≲2% of the detectable sources, their presence is not ruled out.

Keywords: Milky Way Galaxy physics, Black hole physics, Supermassive black holes, Gravitational waves
Regarding the Detection of Interstellar C<SUB>4</SUB> and C<SUB>5</SUB> Molecules. Analysis of very high signal-to-noise ratio (S/N) spectra of reddened stars allowed us to determine an upper limit (UL) of the column density N(C4). We developed a robust calibration of the N(C4) based on the C4 gas-phase spectrum profile at 3789 Å. The UL of the column density can be calculated using the equation NUL(C4) = 8.963 × 1015/(S/N), where S/N is in the wavelength range ∼3790 Å. Nondetection of this molecule was confirmed in stars exhibiting a high abundance of C2 and C3 molecules. According to our calibration, assuming an optimistic estimate of the ratio  N(C3)N(C4)  = 10, even for the star HD 147889 with the highest known to date column density of C3, the S/N required for detecting the C4 molecule is about 12,000 per pixel, which is a challenging task. Despite this tough conclusion regarding the possibility of detecting the interstellar molecule C4, we also tried to find a link between known lines of C5 at 4975 and 5109 Å and weak interstellar features. The expected C5 4975 Å feature coincides well with weak diffuse interstellar band (DIB) 4975, while the search for the 5109 Å C5 band is badly conditioned by the overlap with a broad spectral feature, which is a blend of stellar and interstellar lines. However, we found a rather good correlation between the equivalent width of DIB 4975 and N(C2), making the search for C5 not hopeless. If DIB 4975 is formed by C5, its column density is only 2 times lower than that of C3.

Keywords: Interstellar molecules, Interstellar line absorption, Diffuse interstellar bands
A Be Star + He Star Binary as an Indicator of a Binary Mass Transfer Phase. The rapid rotation of Be stars is supposed to mainly originate from binary evolution. In recent years, more and more Be stars with helium (He) star companions have been discovered, which provides a significant opportunity to study binary interaction physics. In this work, we perform binary population synthesis with an updated binary mass transfer stability criterion and try to understand the details of mass transfer processes by constructing a series of Be star + He star (BeHe) binary populations. We found that the simulations and the observations can be divided into two groups according to the masses of components, corresponding to the two distinct evolutionary processes during the mass transfer. In particular, we found that the mass ratios of BeHe binaries may be taken as a probe of the initial mass ratios of the primordial binaries. Moreover, the results suggest that a higher mass transfer efficiency (≳0.5) supports the observations better. The simulations predicted too many Be star binaries experiencing case B mass transfer, which conflicts with the observations. The reason is due to either observational selection effects or unclear physical factors.

Keywords: Mass ratio, Be stars, Binary stars, Stellar evolution
Total Power and Low-energy Cutoff Time Evolution of Solar Flare Accelerated Electrons Using X-Ray Observations and Warm-target Model. A primary characteristic of solar flares is the efficient acceleration of electrons to nonthermal deka-keV energies. While hard X-ray (HXR) observation of bremsstrahlung emission serves as the key diagnostic of these electrons. In this study, we investigate the time evolution of flare-accelerated electrons using the warm-target model. This model, unlike the commonly used cold-target model, can determine the low-energy cutoff in the nonthermal electron distribution, so that the energetics of nonthermal electrons can be deduced more accurately. Here, we examine the time-evolution of nonthermal electrons in flares well-observed by the Reuven Ramaty High Resolution Solar Spectroscopic Imager and the Solar Orbiter spacecraft (using the Spectrometer/Telescope for Imaging X-rays instrument). Using spectroscopic and imaging HXR observations, the time evolution of the low-energy cutoff of the accelerated electron distribution, the total power of nonthermal electrons, total rate of nonthermal electrons, and excess thermal emission measure from the nonthermal electrons are investigated. We find that the time profile of the low-energy cutoff of the accelerated electron distribution shows a high-low-high trend around the HXR bursts of flares, while the time evolution of the total rate of injected electrons shows a low-high-low behavior. Although the total power of nonthermal electrons is sensitive to the cutoff energy, the temporal variation of the flare power follows the temporal variation of the acceleration rate. We further find that the highest contribution of the excess thermal emission measure coming from thermalization of injected electrons takes place around the HXR peak.

Keywords: Solar flares, Solar physics, Solar x-ray flares, Solar activity, Active solar corona
The Structure and Evolution of a High-mass Stellar Merger in the Hertzsprung Gap. Post-main-sequence binary mergers are a common evolutionary pathway for massive stars, but the effects of merging on the long-term structure and evolution of the resulting star are a matter of active debate. Furthermore, the way in which merger products are modeled in 1D is not uniform. We present the evolution of an 11 M⊙ and 6.6 M⊙ binary on an 11 days orbit that merges while the primary is crossing the Hertzsprung gap. We construct the merger product either by rapidly accreting the secondary onto the surface of the primary or by injecting material from the secondary deeper into the primary via entropy sorting. We then evolve them to carbon ignition, comparing their interior structures at this stage. We find that all merger products experience an extended blue supergiant phase and have undermassive helium cores and low carbon mass fractions compared to single and stripped stars. However, the evolution of central density, temperature, and composition in the entropy-sorted model is distinct from those of the rapid-accretion models.

Keywords: Massive stars, Stellar mergers
Investigating Turbulence Effects on Magnetic Reconnection Rates through 3D Resistive Magnetohydrodynamic Simulations. We investigate the impact of turbulence on magnetic reconnection through high-resolution 3D magnetohydrodynamic (MHD) simulations, spanning Lundquist numbers from S = 103 to 106. Building on the A. Lazarian &amp; E. T. Vishniac theory, which asserts reconnection rate independence from ohmic resistivity, we introduce small-scale perturbations until t = 0.1 tA. Even after the perturbations cease, turbulence persists, resulting in sustained high reconnection rates of Vrec/VA ∼ 0.03–0.08. These rates exceed those generated by resistive tearing modes (plasmoid chain) in 2D and 3D MHD simulations by factors of 5–6. Our findings match observations in solar phenomena and previous 3D MHD global simulations of solar flares, accretion flows, and relativistic jets. The simulations show a steady-state fast reconnection rate compatible with the full development of turbulence in the system, demonstrating the robustness of the process in turbulent environments. We confirm reconnection rate independence from the Lundquist number, supporting Lazarian and Vishniac's theory of fast turbulent reconnection. Additionally, we find a mild dependence of Vrec on the plasma–β parameter, decreasing from 0.036 to 0.028 (in Alfvén units) as β increases from 2.0 to 64.0 for simulations with a Lundquist number of 105. Lastly, we explore the magnetic Prandtl number's (Prm = ν/η) influence on the reconnection rate and find it negligible during the turbulent regime across the range tested, from Prm = 1 to 60.

Keywords: Magnetohydrodynamics
Observational Properties of Thermal Emission from Relativistic Jets Embedded in Active Galactic Nucleus Disks. Relativistic jets can be produced within the accretion disk of an active galactic nucleus (AGN), leading to distinct thermal emission as they propagate through a dense disk environment. In this paper, we present a comprehensive study of the dynamical evolution of jets embedded in an AGN disk and their associated observational properties, focusing on scenarios in which jets either successfully break out of the disk or become choked. By modeling the jet-cocoon system propagation, we calculate the thermal emission contributions from the jet-head shock breakout, disk-cocoon, and jet-cocoon components. Our results reveal that soft X-ray flares are the most prominent observable signatures, with a duration ranging from O(102) s to O(105) s, occasionally exhibiting double-peaked light curves, whereas UV/optical flares are detectable only for powerful jets, persisting for several days to tens of days. This thermal emission serves as a critical electromagnetic counterpart to jet-producing events and provides insights into jet dynamics and AGN disk properties. Our findings highlight the importance of multiwavelength follow-up observations to establish a diagnostic paradigm for candidate electromagnetic counterpart identification of AGN-embedded events and to distinguish thermal flares from AGN background variability.

Keywords: Accretion, Relativistic jets, Active galactic nuclei
A Fast, Analytic Empirical Model of the Gaia Data Release 3 Astrometric Orbit Catalog Selection Function. In 2022 June, the Gaia mission released a catalog of astrometric orbital solutions for 168,065 binary systems, by far the largest such catalog to date. The catalog's selection function is difficult to characterize because of choices made in its construction. Understanding the catalog's selection function is required to model and interpret its contents. We use a combination of analytic and empirical prescriptions to construct a function that computes the probability that a binary with a given set of properties would have been published in the Gaia Data Release 3 astrometric orbit catalog. This is a complementary approach to the more accurate but significantly more computationally expensive approach of El-Badry et al. We also construct a binary population synthesis model to validate our characterization of the selection function, finding good agreement with the actual Gaia NSS catalog, with the exception of the orbital eccentricity distribution. The NSS catalog suggests high-eccentricity orbits are relatively uncommon at intermediate periods 100 ≲ Porb ≲ 1000 days. As an example application of the selection function, we estimate the Gaia DR3 detection probabilities of the star + BH binaries Gaia BH1 and BH2, and find them to be 0.38 and 0.27, respectively. Compared to the values obtained by detailed modeling in El-Badry et al., the probabilities are identical for BH1, and within a factor of 2 for BH2. We also estimate the population of Sun-like star + BH binaries in the Galaxy to be ∼3000 for 100 &lt; Porb &lt; 400 days, &lt;800 for 400 &lt; Porb &lt; 1000 days, and &lt;12,000 for 1000 &lt; Porb &lt; 1500 days.

Keywords: Binary stars, Stellar mass black holes, Gaia