Sazuna/UAT_keywords huggingface dataset:
Counting the Unseen. II. Tidal Disruption Event Rates in Nearby Galaxies with REPTiDE. Tidal disruption events (TDEs) are a class of transients that occur when a star is destroyed by the tides of a massive black hole (MBH). Their rates encode valuable MBH demographic information, but this can only be extracted if accurate TDE rate predictions are available for comparisons with observed rates. In this work, we present a new, observer-friendly Python package called REPTiDE, which implements a standard loss-cone model for computing TDE rates given a stellar density distribution and an MBH mass. We apply this software to a representative sample of 91 nearby galaxies over a wide range of stellar masses with high-resolution nuclear density measurements from C. H. Hannah et al. We measure per-galaxy TDE rates ranging between 10‑7.7 and 10‑2.9 yr–1 and find that the sample-averaged rates agree well with observations. We find a turnover in the TDE rate as a function of both galaxy stellar mass and black hole mass, with the peak rates being observed in galaxies at a galaxy mass of 109.5 M⊙ and a black hole mass of 106.5 M⊙. Despite the lower TDE rates inferred for intermediate-mass black holes, we find that they have gained a higher fraction of their mass through TDEs when compared to higher-mass black holes. This growth of lower-mass black holes through TDEs can enable us to place interesting constraints on their spins; we find maximum spins of a• ≈ 0.9 for black holes with masses below ∼105.5 M⊙.

Keywords: Intermediate-mass black holes, Supermassive black holes, Black holes, Tidal disruption, Stellar dynamics, Galaxy nuclei, Star clusters
Gamma-Ray Burst Jets in Circumstellar Material: Dynamics, Breakout, and Diversity of Transients. Recent observations indicate that stripped-envelope core-collapse supernovae are often surrounded by dense circumstellar material (CSM). Motivated by this, we develop an analytic model to systematically study the dynamics of long gamma-ray burst (LGRB) jet propagation in various CSM environments. We derive a general expression for the jet head velocity (βh) and breakout time (tb) valid across Newtonian, relativistic, and intermediate regimes, accounting for a previously unrecognized dependence on 1 ‑ βh. Our results highlight a fundamental distinction between jet propagation in massive stars, where βh ≪ 1, and in extended CSM, where 1 ‑ βh ≪ 1. We establish an analytic success/failure criterion for jets and express it in terms of jet and CSM parameters, revealing a strong dependence on CSM radius. To quantify the relativistic nature of the jet-cocoon system, we introduce the energy-weighted proper velocity  Γβ¯ . We identify three possible jet outcomes—(a) successful jets ( Γβ¯∼10-100 ), (b) barely failed jets ( Γβ¯∼1 ), and (c) completely failed jets ( Γβ¯∼0.1 )—and constrain their respective jet/CSM parameter spaces. We show that, in (b) and (c), large CSM radii can result in luminous fast blue optical transients via cocoon cooling emission. This theoretical framework provides a basis for future observational and theoretical studies to understand the link between LGRBs, intermediate GRBs, low-luminosity LGRBs, and their environments.

Keywords: Type Ic supernovae, Gamma-ray bursts, Hydrodynamics, Core-collapse supernovae, High energy astrophysics, Relativistic jets, Transient sources, Circumstellar matter
Comparing Grid Model Fitting Methodologies for Low-temperature Atmospheres: Markov Chain Monte Carlo versus Random Forest Retrieval. The atmospheres of low-temperature stars, brown dwarfs, and exoplanets are challenging to model due to strong molecular features and complex gas and condensate chemistry. Self-consistent atmosphere models are commonly used for spectral fitting, but computational limits restrict the production of finely sampled multidimensional parameter grids, necessitating interpolation methods to infer precise parameters and uncertainties. Here, we compare two grid model fitting approaches: a Markov Chain Monte Carlo (MCMC) algorithm interpolating across spectral fluxes, and a random forest retrieval (RFR) algorithm trained on a grid model set. We test these with three low-temperature model grids—Sonora Diamondback, Sonora Elf Owl, and Spectral ANalog of Dwarfs (SAND)—and a sample of 11 L and T dwarf companions to FGKM stars with known distances, compositions, and ages. Diamondback models are optimal for early- and mid-type L dwarfs, Elf Owl for mid and late T dwarfs, and SAND for young L dwarfs and L/T transition objects. The MCMC approach yields higher fit quality and more precise parameters, though best-fit parameters are generally consistent between approaches. RFR analysis is orders of magnitude faster after training. Both approaches yield mixed results when comparing fit parameters to expected values based on the primary (metallicity and surface gravity) or evolutionary models (temperature and radius). We propose modeling low-temperature spectra efficiently by first fitting multiple model sets using RFR, followed by a more accurate MCMC assessment, to accelerate improved grid development.

Keywords: Brown dwarfs, L dwarfs, Random Forests, Stellar atmospheres, T dwarfs
Asteroseismology of WD J004917.14−252556.81, the Most Massive Pulsating White Dwarf. We present extensive follow-up time-series photometry of WD J0049−2525, the most massive pulsating white dwarf currently known, with Teff = 13,020 K and  logg=9.34  cm s−2. The discovery observations detected only two significant pulsation modes. Here, we report the detection of 13 significant pulsation modes ranging from 170 to 258 s based on 11 nights of observations with the New Technology Telescope, Gemini, and Apache Point Observatory telescopes. We use these 13 modes to perform asteroseismology and find that the best-fitting models (under the assumption of an ONe core composition) have M⋆ ≍ 1.29M⊙, a surface hydrogen layer mass of  log(MH/M⋆)≲−7.5 , and a crystallized core fraction of &gt;99%. An analysis of the period spacing also strongly suggests a very high mass. The asteroseismic distance derived is in good agreement with the distance provided by Gaia. We also find tentative evidence of a rotation period of 0.3 or 0.67 days. This analysis provides the first look at the interior of a ∼1.3 M⊙ white dwarf.

Keywords: White dwarf stars, Asteroseismology, Pulsation modes, ZZ Ceti stars
Coronal Magnetometry with EUV Permitted Lines. A major challenge in solar physics is to obtain empirical information on the magnetic field of the million-degree plasma of the solar corona. To this end, we need observables of the solar radiation sensitive to the coronal magnetic field. The most familiar observables are the polarization signals of visible and near-infrared forbidden lines of highly ionized species and some ultraviolet permitted lines, like hydrogen Lyα. While the coronal radiation in these spectral lines can only be detected for off-limb lines of sight, the coronal radiation from permitted extreme ultraviolet (EUV) lines can be observed also on the solar disk. These coronal lines are mainly collisionally excited, but it has been pointed out that some permitted EUV lines can actually be linearly polarized if their lower level carries atomic alignment, and that their linear polarization is sensitive to the orientation of the coronal magnetic field . Here we theoretically investigate the linear polarization in permitted EUV lines of a variety of ions: Fe X, Fe XI, Fe XIII, Fe XIV, Si IX, and Si X. To this end, we have developed a numerical code, which we have applied to investigate the linear polarization and magnetic sensitivity of many permitted EUV lines in a one-dimensional model of the solar corona, providing a list of the most promising lines to be further investigated for polarimetry with future space telescopes. Our next step will be to extend this work by using state-of-the-art three-dimensional coronal models.

Keywords: Extreme ultraviolet astronomy, Spectropolarimetry, Solar corona
Effective Viscosity in the Intracluster Medium During Magnetic Field Amplification via Turbulent Dynamo. Galaxy clusters, the largest gravitationally bound structures, host a hot, diffuse plasma with poorly understood viscosity and magnetic field amplification. Astrophysical plasmas are often modeled with magnetohydrodynamics (MHD), but low collision rates in environments such as the intracluster medium (ICM) hinder thermodynamic equilibrium, causing pressure anisotropies and high viscosity. High-β plasmas, dominated by thermal pressure, are prone to instabilities (e.g., firehose or mirror) that limit anisotropy, reduce viscosity, and enable small-scale dynamo-driven magnetic amplification. This study examines viscosity evolution in the ICM during turbulent magnetic field amplification. We performed 3D MHD simulations of forced turbulence with an initially weak, uniform magnetic field. Using the Chew–Goldberger–Low (CGL)-MHD framework, we incorporate anisotropic pressure dynamics and instability-driven anisotropy limitation. We analyze effective viscosity and dynamo evolution, comparing results with Braginskii-MHD and uniform-viscosity MHD. Our results show that viscosity decreases over time, allowing magnetic field amplification to saturation levels similar to nonviscous MHD. Viscosity distribution becomes bimodal, reflecting (i) collisional values and (ii) turbulence-dominated values proportional to 1 × 10‑4LturbUturb in unstable regions. At saturation, 60% of plasma retains collisional viscosity. Braginskii-MHD reproduces similar magnetic amplification and viscosity structures. However, uniform-viscosity MHD, where viscosity equals the mean saturated CGL-MHD value, fails to capture the turbulence inertial range. These findings highlight the need for anisotropic viscosity models in studying ICM processes such as magnetic topology, cosmic ray transport, and active galactic nucleus-driven shocks. Moreover, our CGL-MHD and Braginskii-MHD models match the Coma cluster density fluctuation spectrum, reinforcing its weakly collisional nature.

Keywords: Galaxy clusters, Plasma astrophysics, Intracluster medium, Magnetic fields, Magnetohydrodynamical simulations
Evolutionary Period Changes for 25 X-Ray Binaries and the Measurement of an Empirical Universal Law for Angular Momentum Loss in Accreting Binaries. I measure and collect timings of phase markers (like eclipse times) for the orbits of 25 X-ray binaries (XRBs) so as to calculate the steady evolutionary period change ( Ṗ ). I combine these with my observed  Ṗ  measures from 52 cataclysmic variables (CVs). Further, I subtract out the contributions from gravitational radiation ( ṖGR ) and mass transfer ( Ṗmt ), deriving the period change from the residual unknown angular momentum loss ( ṖAML  =  Ṗ – ṖGR – Ṗmt ). I have  ṖAML  measures for 77 XRBs and CVs, with these being direct measures of the driver of binary evolution. The venerable magnetic braking model of binary evolution has its most fundamental predictions tested, with most systems having predictions wrong by over 1 order of magnitude. Other proposed mechanisms to explain the angular momentum loss (AML) also fail, so we are left with no known mechanism that dominates the AML. An alternative path to the AML law is empirical, where my  ṖAML  measures are fitted to a power law involving the fundamental binary properties. With this, the dominant AML law for systems with orbital periods (P) from 0.13–1.0 day is  ṖAML=‑1500×10‑12P1.29Mprim2.75Mcomp‑1.00Ṁ‑80.43 , in appropriate units. Similar AML laws for binaries below the period gap and for binaries with P &gt; 1.0 day are derived. These three AML laws are of good accuracy and are the best representations of the actual evolution for all 77 XRBs and CVs of all classes, so the three taken together can be called "universal."

Keywords: X-ray binary stars, Multiple star evolution, High mass x-ray binary stars, Orbital evolution, Hz Herculis x-ray binary stars, Low-mass x-ray binary stars, Cataclysmic variable stars, X-ray novae, Classical novae, Stellar evolution
Rethinking Habitability Using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy. We present a comprehensive study of formaldehyde (H2CO) absorption and radio recombination line (H110α) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey, observed using the Nanshan 25 m radio telescope. H2CO was detected in 88 sources (40.93%) with 59 being new detections, while H110α emission was found in only 11 sources (5.12%), all coincident with H2CO absorption. There exists a correlation of H2CO fluxes with millimeter fluxes below a 3 Jy threshold and an increased dispersion above it, suggesting the sub-cosmic microwave background cooling of H2CO. Cross-matching with kinematic distance catalogs revealed H2CO spanning galactocentric distances from 0.216 to 10.769 kpc, with column densities ranging from 7.82 × 1011 to 6.69 × 1014 cm‑2. A significant inverse correlation was observed between H2CO detection fraction and galactocentric distance, suggesting enhanced star-forming activity closer to the Galactic Center. These findings challenge traditional Galactic Habitable Zone (GHZ) models by demonstrating the presence of biogenic precursors in the inner Galaxy, shielded within dense molecular clouds. Our results underscore the importance of incorporating chemical tracers such as H2CO, alongside physical constraints to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.

Keywords: Radio spectroscopy, Star forming regions, Habitable zone, Pre-biotic astrochemistry
Modeling of Two Low-amplitude Radially Pulsating δ Scuti Stars: KIC 12602250 and KIC 5768203. In this research, we conducted systematic photometric, spectroscopic, and theoretical modeling analyses of two δ Scuti stars—KIC 12602250 and KIC 5768203—that pulsate only in radial modes. We collected their relevant photometric and spectroscopic parameters from multiple catalogs and estimated the absolute luminosities of both stars. Using high-precision time-series data from Kepler and TESS, we performed in-depth analysis of the periodic modulation in pulsation frequency phases, successfully determining the orbital periods and companion mass distribution ranges for these binary systems. Additionally, we thoroughly investigated the temporal evolution characteristics of pulsation periods and amplitudes. Based on calculations using Modules for Experiments in Stellar Astrophysics stellar evolution models, we determined that KIC 12602250 has a mass of  M=1.66‑0.07+0.05M⊙  with metallicity  Z=0.039‑0.010+0.018  and is currently in the main-sequence evolutionary stage. For KIC 5768203, we derived precise parameters through rigorous constraints: mass M = 2.09 ± 0.01M⊙, metallicity Z = 0.024 ± 0.003, and radius R = 3.19 ± 0.01R⊙. Theoretical models reveal that this star has already crossed the first main-sequence turn-off point and entered the late-main-sequence evolutionary stage. Through comparative studies with typical High Amplitude δ Scuti stars, we believe that the primary reason for the low radial pulsation amplitudes in these two stars likely stems from their specific evolutionary states.

Keywords: Multi-periodic variable stars, Delta Scuti variable stars, Pulsating variable stars
Nonparallel Wave Propagation in an Asymmetric Magnetic Slab. Theoretical and numerical analyses of the behavior of magnetohydrodynamic (MHD) waves in solar atmospheric structures have a vital role in understanding the plasma dynamics of the Sun. Magneto-helioseismology is indebted to the insight gained from simple magnetic slab structures accompanied by varying conditions within the slab and its environment. This paper builds on the existing literature on these structures by presenting an analytical approach to deriving the dispersion relation for MHD wave propagation in a nonparallel case. Analogous to the parallel case, a plethora of modes emerges that can be classified into quasi-kink or quasi-sausage, body or surface, as well as fast or slow waves. The slab itself can be viewed as thin or wide similarly to previous works, however due to the nonparallel condition it can also be categorised as short or long in the direction of the tilt of the wavevector. This is the analog of the thin or wide slab classification in the parallel direction, expanding our established knowledge regarding propagating MHD waves in magnetic slabs. The variance of the wavenumber along the nonparallel dimension brings to light a number of intriguing features, such as modes changing character with variation of the angle of the wavevector while the propagation speed remains the same. Further new information is provided by the newly derived classification limits, u±, which act as a form of generalised Alfvén and sound speeds in the dispersion relation.

Keywords: Solar atmosphere, Magnetohydrodynamics, Quiet solar chromosphere, Helioseismology, Solar physics, Solar coronal waves, Solar magnetic fields, Quiet solar corona, Solar oscillations
The Structural and Kinematical Properties of NGC 5634, a Globular Cluster Associated with the Sagittarius Dwarf Galaxy?. We investigate the origin of NGC 5634 through a comprehensive analysis of its morphology, kinematics, and dynamics. Utilizing data from the DESI Legacy Survey, we refined its fundamental parameters (age τ = 12.8 ± 0.3 Gyr, metallicity [Fe/H] = ‑1.8 ± 0.1 dex, distance modulus dm = 17.0 ± 0.1 mag) and constructed a matched-filter template based on the combination of these parameters to search for extra-tidal structures. However, no significant features were detected above a 3σ signal-to-noise threshold, which limits our ability to further investigate the association between NGC 5634 and the Sagittarius (Sgr) stream based on morphological evidence. Incorporating GAIA data, we further examine the orbital path of NGC 5634. We found that its orbit only briefly intersects with the Sgr stream and diverges significantly over long-term integrations. This behavior contrasts with that of confirmed Sgr-associated clusters, whose orbits remain closely aligned with the stream throughout their orbital evolution. Additionally, NGC 5634 exhibits a relatively shorter semimajor axis and smaller apocenter and pericenter distances compared to Sgr clusters. These orbital characteristics are more consistent with clusters associated with the Gaia–Sausage–Enceladus (GSE) or the Helmi streams. From a dynamical perspective, in the Lz–E space, NGC 5634 is also distinctly different from Sgr clusters and aligns more closely with the GSE and Helmi regions. Taken together, these findings do not support a strong connection between NGC 5634 and the Sgr dSph, but instead suggest a potential association with another progenitor system, such as GSE or Helmi stream. Nevertheless, further evidence is needed to definitively establish its origin.

Keywords: Globular star clusters, Stellar structures, Milky Way Galaxy
SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks. Short large-amplitude magnetic structures (SLAMS) are frequently detected during spacecraft crossings over Earth's bow shock. We investigate the existence of such structures at astrophysical shocks, where they could result from the steepening of cosmic-ray (CR) driven waves. Using kinetic particle-in-cell simulations, we study the growth of SLAMS and the appearance of associated transient shocks in the upstream region of parallel, nonrelativistic, high-Mach-number collisionless shocks. We find that high-energy CRs significantly enhance the transverse magnetic field within SLAMS, producing highly inclined field lines. As SLAMS are advected toward the shock, these field lines form an intermittent superluminal configuration that traps magnetized electrons at fast shocks. Due to their oscillatory nature, SLAMS are periodically separated by subluminal gaps with lower transverse magnetic field strength. In these regions, electrons diffuse and accelerate by bouncing between the shock and the approaching SLAMS' region through a mechanism that we call quasi-periodic shock acceleration (QSA). We analytically derive the distribution of electrons accelerated via QSA, f(p) ∼ p[‑4.7,‑5.7], which agrees well with the simulation spectra. We find that the electron power law remains steep until the end of our longest runs, providing a possible explanation for the steep electron spectra observed at least up to GeV energies in young and fast supernova remnants.

Keywords: Supernova remnants, Interstellar medium, Shocks, Astronomical simulations, Cosmic rays
Bright Bursts with Submillisecond Structures of FRB 20230607A in a Highly Magnetized Environment. We report the observations of a repeating FRB 20230607A for 15.6 hr spanning 16 months using the Five-hundred-meter Aperture Spherical Radio Telescope with the detection of 565 bursts. We present three bright bursts with detailed temporal/spectral structures. We also report that one burst carries a narrow component with a width of only 0.3 ms, which is surrounded by broader components. This suggests that repeaters can make both narrow and broad components in one burst. With the narrow spike, we precisely measure the dispersion measure of 362.85 ± 0.15 pc cm‑3 and the Faraday rotation measures (RMs) of ‑12249.0 ± 1.5 rad m‑2. We also analyze the statistical distribution of the burst parameters, including waiting times, temporal widths, central frequencies and frequency widths, fluences and energies, all showing typical distributions of known active repeaters. In particular, most bursts show narrow spectra with Δν/ν0 = 0.125 ± 0.001. This fact, together with the narrow 0.3 ms spike, strongly suggests a magnetospheric origin of the FRB emission. Based on a predicted correlation between RM and the luminosity of a persistent radio source (PRS) by Yang et al., we predict that the PRS should have a specific luminosity of the order of 1029 erg s‑1 Hz‑1 and encourage a search for such a PRS.

Keywords: Radio transient sources
Spectroastrometry and Reverberation Mapping of Active Galactic Nuclei. II. Measuring Geometric Distances and Black Hole Masses of Four Nearby Quasars. The geometric distances of active galactic nuclei (AGNs) are challenging to measure because of their exceptionally compact structure, yet vast cosmic distances. A combination of spectroastrometry and reverberation mapping (SARM) of broad-line regions (BLRs) constitutes a novel means to probe the geometric distance of AGNs, which has recently become practically feasible owing to successful interferometric observations with the Very Large Telescope Interferometer/GRAVITY. Here, we perform SARM analysis of four nearby quasars: Mrk 509, PDS 456, 3C 273, and NGC 3783. Results for the former two are reported for the first time, and the latter two are revisited using our improved BLR dynamical modeling that includes the radial-dependent responsivity of BLRs. This allows us to self-consistently account for the emissivity weighting of the BLR in spectroastrometry and responsivity weighting in reverberation mapping. We obtain angular-diameter distances of the four quasars, from which we derive a Hubble constant of  H0=69−10+12kms−1Mpc−1 . Although this constitutes a large uncertainty for a measurement of H0, it is anticipated that the precision will improve to a competitive level once a greater number of AGNs are accessible following the upgrade of GRAVITY in the near future. From SARM analysis, the black hole masses of the four quasars are also measured with the statistical uncertainty ranging from 0.06 to 0.23 dex, consistent with the correlations between black hole masses and properties of the host bulges.

Keywords: Supermassive black holes, Reverberation mapping, Active galactic nuclei, Quasars