Sazuna/UAT_keywords huggingface dataset:
On the Temporal Variability in the Magnetic Dichotomy of Late M Dwarf Stars. Rapidly rotating late M dwarfs are observed in two different branches of magnetic activity, although they operate in the same stellar parameter range. Current empirical evidence indicates that M dwarfs with spectral types ranging from M3/M4 to late-type M dwarfs, stellar masses smaller than 0.15 M⊙, and rotational periods shorter than 4 days display either a stable dipolar magnetic field or magnetic structures with significant time variability. The magnetic activity of fully convective M dwarfs is known to be regulated by a mechanism named the α2 dynamo. To further constrain the physics of this mechanism, we use a low-dimensional model for thermally driven magnetoconvection producing an α2 dynamo, specifically a modified magnetohydrodynamic shell model. Although the model neglects density stratification, it captures the essential nonlinear dynamics of an α2 dynamo. Therefore, the results should be interpreted in a qualitative sense, highlighting possible trends rather than providing direct quantitative predictions for fully convective stars. The model is validated by comparing the statistical properties of magnetic polarity reversals with paleomagnetic data, since the geodynamo provides the only natural α2 dynamo with sufficiently rich reversal statistics. Our findings reveal that increased convective heat transport correlates with more frequent magnetic-polarity reversals, resulting in enhanced magnetic variability. This suggests that the observed magnetic dichotomy in late M dwarfs could be interpreted in terms of differences in global heat transport efficiency. However, additional models and observations of M dwarfs are needed to further constrain this interpretation.

Keywords: M dwarf stars, Stellar convective zones, Stellar structures, Magnetohydrodynamics, Stellar magnetic fields, Stellar physics, Low mass stars
Estimation of Magnetic Fields from Synchrotron Emission: Numerical Tests. We use models of spectrally resolved cosmic-ray (CR) transport in TIGRESS MHD simulations of the local interstellar medium to produce synthetic synchrotron emission and to test, on scales from a few kiloparsecs down to ∼10 pc, the traditional estimate of magnetic field strength based on the assumption of equipartition between the magnetic and total CR energy densities. Our analysis shows that the traditional equipartition estimate works well at the kiloparsec scale of the simulation box, but breaks down at smaller scales. We find that the predicted magnetic field strength can be improved at small scales by assuming a constant CR energy density across each mock radio observation. The large-scale mean CR energy density can be estimated by assuming equipartition with the large-scale mean magnetic energy density, or as a function of additional observable quantities such as the star formation rate surface density or gas weight. In addition to estimating the magnetic field strength, we use synthetic polarized emission to create maps of the magnetic field direction. We find that the true magnetic field direction can be recovered well from the mock observations.

Keywords: Magnetohydrodynamical simulations, Magnetic fields, Interstellar medium, Cosmic rays
A Classification Scheme for X-Ray-bright Type Ia Supernova Remnants Based on Their Circumstellar Interaction. The parameter space for mass loss in Type Ia supernova (SN Ia) progenitors is large, with different progenitor scenarios favoring different mass-loss regimes. Here we focus on the impact that uniform and isotropic outflows have on the circumstellar environment of SN Ia progenitors. We vary mass-loss rate, wind velocity, and outflow duration, and evolve supernova remnant (SNR) models in this grid of circumstellar structures in order to compare the bulk properties of these models (ages, radii, and Fe Kα centroids and luminosities) to observations. We find that roughly 55% (7/13) of young X-ray-bright Type Ia SNRs in the Milky Way and the Large Magellanic Cloud had progenitors that did not substantially modify their surroundings on ∼parsec scales. This group includes SN Ia with a range of luminosities, and at least one likely product of a double-detonation explosion in a sub-Chandrasekhar white dwarf (WD). The other half of our sample can be divided into two distinct classes. A small subset of SNRs (∼15%, 2/13) have large radii and low Fe Kα centroids and are likely expanding into large cavities that might have been excavated by fast (∼1000 km s−1), sustained progenitor outflows. The majority of the SNRs that are expanding into a modified medium (∼30%, 4/13) show evidence for dense material, likely associated with slow (∼10 km s−1) progenitor outflows, possibly a byproduct of accretion processes in near-Chandrasekhar WDs spawned by younger stellar populations.

Keywords: X-ray astronomy, Supernova remnants, Type Ia supernovae, Common envelope evolution, Supernovae
PSR J0952-0607: Tightening a Record-high Neutron Star Mass. We report on new orbit-minimum photometry and revised radial-velocity fitting that provide an improved measurement of the mass of the neutron star (NS) in pulsar PSR J0952−0607 at MNS = 2.35 ± 0.11 M⊙. With its fast spin and unusually low magnetic field, this NS has evidently experienced unusual evolution, likely connected with its high mass, which is now 2.5σ above that of the heaviest pulsar with a white dwarf companion, as measured by Shapiro delay techniques. By tightening the mass measurement, we also raise the maximum (commonly called Tolman─Oppenheimer─Volkoff) NS mass to MTOV &gt; 2.27 M⊙ (2.12 M⊙) at 1σ (3σ) confidence, which improves bounds on the dense-matter equation of state. While the statistical error decreases and systematic issues should be modest, uncertainties remain; we comment briefly on these factors and prospects for further improvement.

Keywords: Neutron stars
Genetic Algorithm for Inferring Model Parameters for Flux Transport Dynamo Simulation. The Sun exhibits an 11 yr cyclic variation, maintained by dynamo action in the solar interior. Mean-field flux transport dynamo models have successfully reproduced most of the features observed in solar cycles, while the model includes many free parameters, such as the speed of the meridional flow and the amplitude of the poloidal field generation. Inferring these free parameters is on demand because they correspond to the solar interior condition. We suggest a novel method for inferring the free parameters using a genetic algorithm. At each generation, we evaluate the fitness of our simulation against the observational data and optimize the parameters. We apply our method to the observed solar cycle data from 1723 to 2024 and successfully reproduce the observations from both qualitative and quantitative perspectives. We expect our method to be applicable to sunspot numbers, even those obtained from isotope data and historical documents, in the future, to better understand past solar interior dynamics.

Keywords: Solar cycle, Solar dynamo, Solar physics, Algorithms, Magnetohydrodynamical simulations
Beyond Extreme Burstiness: Evolving Star Formation Efficiency as the Key to Early Galaxy Abundance. JWST observations have revealed an overabundance of bright galaxies at z ≥ 9, creating apparent tensions with theoretical predictions within standard ΛCDM cosmology. We address this challenge using a semiempirical approach that connects dark matter halos to the observed UV luminosity through a physically motivated double power-law star formation efficiency (SFE) model as a function of the halo mass and redshift, and perform a joint Bayesian analysis of luminosity functions spanning z = 4─16 using combined Hubble Space Telescope and JWST data. Through systematic model comparison using information criteria (Akaike, Bayesian, and deviance information criteria), we identify the optimal framework requiring redshift evolution only in the low-mass slope parameter α(z) while maintaining other SFE parameters constant. Our best-fitting model achieves excellent agreement with observations using modest, constant UV scatter σUV = 0.32 dex─significantly lower than the ≳1.3 dex values suggested by previous studies for z &gt; 13. This reduced scatter requirement is compensated by strongly evolving star formation efficiency, with α increasing toward higher redshifts, indicating enhanced star formation in low-mass halos during the cosmic dawn. The model also successfully reproduces other important observational diagnostics, such as effective galaxy bias and cosmic star formation density, consistently across the full redshift range. Furthermore, model predictions are consistent up to a redshift of z ∼ 20. Our results demonstrate that JWST's early galaxy observations can be reconciled with standard cosmology through the interplay of modest stochasticity and evolving star formation physics, without invoking extreme burstiness or exotic mechanisms.

Keywords: Cosmology, James Webb Space Telescope, High-redshift galaxies, Galaxies
A Flux-limited Sample of Dusty Star-forming Galaxies from the Atacama Cosmology Telescope: Physical Properties and the Case for Multiplicity. We report the modeling of the millimeter and far-infrared (FIR) spectral energy distributions (SEDs) of 71 dusty star-forming galaxies (DSFGs) selected by the Atacama Cosmology Telescope (ACT) with a 5σ flux density limit of 8 mJy at 220 GHz (1.4 mm). All sources were cross-identified with Herschel surveys at 500, 350, and 250 μm, and 19 of our sources were observed with the Submillimeter Array (SMA). A probabilistic cataloging (PCAT) algorithm favors multiple unresolved flux components in the Herschel data for the majority of ACT-selected DSFGs. We compare the derived physical properties of the DSFGs obtained from modeling the flux densities with those from similar studies of DSFG populations. We find the median, 16th, and 84th percentiles for the following SED model parameters: redshift  zphot=3.3−0.6+0.7 , apparent size  μd=5.2−2.4+0.9kpc , apparent dust mass  log10(μMd/M⊙)=9.14−0.04+0.12 , and cutoff temperature  Tc=35.6−1.6+4.8K  for a power-law distribution, and the corresponding apparent FIR luminosity  log10(μLIR/L⊙)=13.6−0.3+0.2 , where μ is the lensing magnification. While many of the properties broadly agree with those of samples of primarily lensed DSFGs, we exercise caution in interpreting them. ACT's lower flux limit, the PCAT decomposition, and the SMA observations all suggest that some fraction of these DSFGs are likely to be unlensed and possibly multiples. The SMA data indicate that at least 14 out of 19 sources are such, either via "missing" flux in comparison to the model or detection of additional sources in the fields. Additional high-resolution follow-up and redshift determination are needed to better understand this flux-limited sample of DSFGs.

Keywords: Millimeter astronomy, Interferometry, Spectral energy distribution, Luminous infrared galaxies
JWST's PEARLS: Temperatures of Nine Highly Magnified Stars in a Galaxy at Redshift 0.94 and Simulated Stellar Population Dependence on Stellar Metallicity and the Initial Mass Function. We present stellar atmosphere modeling of JWST NIRCam photometry of nine highly magnified individual stars in a single galaxy at redshift z = 0.94 known as the Warhol arc, which is strongly lensed by the galaxy cluster MACS J0416. Seven of these transients were identified by Yan et al. The nine sources are likely red supergiants with temperatures Teff ≍ 4000 K. We present new long-slit spectroscopy of the Warhol arc acquired with Keck I telescope and the Large Binocular Telescope, and use these data to help constrain the arc's oxygen abundance to be  12+log(O/H)=8.45±0.08 . A microlensing simulation is performed on synthetic stellar populations using a range of stellar metallicities and initial mass function (IMF) slopes. The temperature distribution of the simulated detectable stars is sensitive to the choice of stellar metallicity, and setting the stellar metallicity equal to the arc's nebular metallicity ( log(Z*/Z⊙)=−0.24 ) produces a simulated temperature distribution that is consistent with the observations, while lower stellar metallicities ( log(Z*/Z⊙)&lt;─0.75 ) produce simulated temperatures that are inconsistent with the observations. The expected detection rate is strongly anticorrelated with the IMF slope for α &gt; 1.2. For the canonical IMF slope α = 2.35, the simulation yields expected transient detection rates that agree with the observed detection rates in the Hubble Space Telescope Flashlights filters, but overpredicts the detection rate by a factor of ∼3─12 (&lt;2σ tension) in the JWST filters. The simulated detection rate is sensitive to the choice of stellar metallicity, with lower metallicities ( log(Z*/Z⊙)&lt;─0.75 ) yielding a significantly lower simulated detection rate that further reduces the modest tension with the observations.

Keywords: Massive stars, Gravitational lensing, Initial mass function
Deep Chandra X-Ray Observations of A2029: The Merger History of a Relaxed, Strong Cool Core Cluster. We present results from very deep (485 ks) Chandra X-ray observations of the relaxed, cool core cluster A2029 (z = 0.0767). A2029 hosts one of the longest, most continuous sloshing spirals ever observed, which we find extends nearly 600 kpc from the cluster core. In addition to providing detailed views of the sloshing spiral, imaging and spectroscopic analysis reveals intracluster medium (ICM) substructure related to the merger history, including a broad "splash" of cooler gas and a potential merger shock. The radio lobes of the central WAT source show evidence of alignment with the sloshing motions, consistent with ICM bulk flow, rather than host-galaxy motion, as the primary driver of lobe bending. Comparison to a 1:10 mass-ratio off-axis merger simulation indicates that the observed ICM structures are relics of a second core passage of a subcluster ∼4 Gyr after the start of the merger, where the "splash" feature is revealed to be a wake of cool gas trailing behind the subcluster. Overall, our results suggest that A2029 is still settling from past interactions—showing that even the initially most relaxed-looking clusters can be hiding a rich history of dynamical activity.

Keywords: Galaxy clusters, Cooling flows, High energy astrophysics, Radio active galactic nuclei, Intracluster medium, Radio sources
Photometric Redshift Estimation Using Scaled Ensemble Learning. The development of the state-of-the-art telescopic systems capable of performing expansive sky surveys such as the Sloan Digital Sky Survey, Euclid, and the Rubin Observatory's Legacy Survey of Space and Time (LSST) has significantly advanced efforts to refine cosmological models. These advances offer deeper insight into persistent challenges in astrophysics and our understanding of the Universe's evolution. A critical component of this progress is the reliable estimation of photometric redshifts (Pz). To improve the precision and efficiency of such estimations, the application of machine learning (ML) techniques to large-scale astronomical datasets has become essential. This study presents a new ensemble-based ML framework aimed at predicting Pz for faint galaxies and higher redshift ranges, relying solely on optical (grizy) photometric data. The proposed architecture integrates several learning algorithms, including gradient boosting machine, extreme gradient boosting, k-nearest neighbors, and artificial neural networks, within a scaled ensemble structure. By using bagged input data, the ensemble approach delivers improved predictive performance compared to stand-alone models. The framework demonstrates consistent accuracy in estimating redshifts, maintaining strong performance up to z ∼ 4. The model is validated using publicly available data from the Hyper Suprime-Cam Strategic Survey Program by the Subaru Telescope. Our results show marked improvements in the precision and reliability of Pz estimation. Furthermore, this approach closely adheres to—and in certain instances exceeds—the benchmarks specified in the LSST Science Requirements Document. Evaluation metrics include catastrophic outlier, bias, and rms.

Keywords: High-redshift galaxies, Redshift surveys, Galaxies, Neural networks
Rotational Spectra and Search for Aromatic Imines: 9-iminofluorene and Benzophenone Imine. Interstellar detections of several cyano derivatives of large polycyclic aromatic hydrocarbons (PAHs) have now been achieved, enabled by accurate laboratory measurements of their microwave rotational spectra. These results highlight the continued promise of other N-containing unsaturated PAHs, such as aromatic imines, as candidates for future laboratory studies and astronomical searches. In this work, we present broadband spectroscopic measurements of 9-iminofluorene and benzophenone imine in the 6─18 GHz band. These measurements yield accurate rotational, centrifugal distortion, and 14N quadrupole coupling constants for both molecules. Using these experimentally-derived constants, we attempted a search for both molecules in the cold molecular cloud TMC-1 using observations from the Green Bank Telescope. Neither of these two ketimines was detected above the current noise level, establishing upper limits for their column densities of 5.1 × 1012 cm−2 for 9-iminofluorene and 1.3 × 1013 cm−2 for benzophenone imine. We also attempted a search for phenylmethanimine (both E/Z isomers) as the simplest aromatic aldimine, but neither was detected in TMC-1. To provide insight into these nondetections, we propose and evaluate different formation pathways using respective potential energy surfaces as determined by high-precision quantum chemical calculations. The result suggests the presence of an entrance barrier to forming the intermediate species, potentially explaining the low abundance.

Keywords: Interstellar molecules, Polycyclic aromatic hydrocarbons, Rotational spectroscopy, Cavity-enhanced Fourier-transform, Molecular clouds, Microwave spectroscopy, Astrochemistry, Reaction rates, Interstellar medium, Radio astronomy
Energetic Particles from Quasi-separatrix Layers and Current Sheets at the Sun. Quasi-separatrix layers (QSLs) at the Sun are created in regions where channels of open magnetic flux have footpoints near regions of large-scale closed magnetic flux. These regions show rapid changes in curvature and field strength. Numerical simulations of a relaxed coronal magnetic field and solar wind using the Magnetohydrodynamic Algorithm outside a Sphere model coupled to the Energetic Particle Radiation Environment Module model indicate common sources of energetic particles over broad longitudinal distributions in the background solar wind. These regions accelerate energetic particles from QSLs and current sheets. Here, we develop an analytical framework to describe the acceleration of energetic particles due to the magnetic field changes within and near separatrix layers. The reduced field strength near the separatrix layer drives magnetic field magnitude changes that accelerate energetic particles in the presence of plasma flow along the structure. Separatrix layers are prone to magnetic reconnection, creating fluctuations in the field that propagate out from the Sun, and release material previously contained within closed magnetic field structures, which are often rich in heavy ions and 3He ions. Thus, we present a model of energetic particles accelerated from separatrix layers in the corona. Our results provide a plausible source for seed populations near the Sun.

Keywords: Solar magnetic reconnection, Solar energetic particles, Solar coronal loops, Solar wind, Solar magnetic fields, Solar corona
The Velocity Dispersion Profile of Nine Open Clusters in the Solar Neighborhood. We analyze the velocity dispersion profiles of nine open clusters in the solar neighborhood using kinematic data from Gaia DR 3, aiming to identify potential dynamical signatures of stellar-mass black holes through a comparison of theoretical and observed dispersion profiles. The selected clusters include LP 2373 gp4, NGC 1980, NGC 2451A, NGC 2516, NGC 3532, NGC 6475, UBC 7, Praesepe, and Pleiades. We refine the center positions of the clusters with the Meanshift algorithm. Using the Markov Chain Monte Carlo method, we calculate the velocity dispersion for each cluster and construct 1D velocity dispersion profiles. NGC 2516, NGC 3532, and NGC 6475 show potential central cusps in their radial velocity dispersion profiles, which may indicate the presence of stellar-mass black holes. LP 2373 gp4, NGC 6475, and Praesepe all display a negative correlation between velocity dispersion and stellar mass, indicating these clusters are approaching energy equipartition or expanding. NGC 2516 and NGC 3532 exhibit a positive dependence between velocity dispersion and stellar mass, which may be attributed to the preferential ejection of massive stars following dynamical interactions involving binaries or black holes. These two clusters are the only two that are dynamical, not relaxed, and are closest to virial equilibrium. We compare the observations with N-body simulations of star clusters. A comparison of observed and simulated velocity dispersion profiles reveals that NGC 2516 and NGC 3532 exhibit lower proper motion dispersions than model clusters. Better agreement with the observed profiles is achieved for model clusters with larger ages. This suggests that the observed clusters may have undergone rapid dynamical evolution. Our results suggest that NGC 2516 and NGC 3532 may host at least two stellar-mass black holes each.

Keywords: Open star clusters, Dynamical evolution, Star clusters
Multiphase State Transitions and Thermal−Tidal Decoupling in the AM CVn−Type Star V803 Cen. AM CVn systems are ultracompact, short-period binaries emitting multimessenger signals and showing both normal outbursts and superoutbursts. They serve as ideal laboratories for studying accretion physics under extreme conditions and for testing the disk instability model (DIM) and thermal−tidal instability (TTI) framework. Here we report the detection of 10 new minor outbursts for the AM CVn−type system V803 Cen by TESS. Positive superhumps (PSHs) are discovered across multiple evolutionary phases, providing direct evidence of decoupled tidal and thermal instabilities. Notably, transient PSHs appear during the initial rise of normal outbursts and fade as the outburst progresses—contrary to predictions from both the DIM (which expects the disk radius to increase during rise) and the TTI (which predicts that PSHs should not disappear once the disk has surpassed the 3:1 resonance radius and continues to expand). During the high state, we reveal multiphase transitions through a superoutburst, dip, cycling state (∼13.5─14.5 mag), and stable standstill (∼13.5 mag). This stable standstill is found for the first time, suggesting that the accretion disk variability is more complex than simple oscillations during the standstill-like states, offering new insights into the physics of disk evolution. While superoutburst and supercycle durations remain stable, high-state durations range from tens to hundreds of days, suggesting additional disk replenishment mechanisms beyond supercycle accumulation. We suggest enhanced mass transfer due to variable irradiation of the secondary as the primary driver. The complex variations in V803 Cen likely arise from coupled processes including DIM, TTI in low mass ratio systems, modulated mass transfer fluctuations, and irradiation-enhanced mass transfer.

Keywords: AM Canum Venaticorum stars, Dwarf novae, Z Camelopardalis stars, SU Ursae Majoris stars, Cataclysmic variable stars