Sazuna/UAT_keywords huggingface dataset:
Every Data Point Counts: Stellar Flares as a Case Study of Atmosphere-aided Studies of Transients in the LSST Era. Due to their short timescale, stellar flares are a challenging target for the most modern synoptic sky surveys. The upcoming Vera C. Rubin Legacy Survey of Space and Time (LSST), a project designed to collect more data than any precursor survey, is unlikely to detect flares with more than one data point in its main survey. We developed a methodology to enable LSST studies of stellar flares, with a focus on flare temperature and temperature evolution, which remain poorly constrained compared to flare morphology. By leveraging the sensitivity expected from the Rubin system, differential chromatic refraction (DCR) can be used to constrain flare temperature from a single-epoch detection, which will enable statistical studies of flare temperatures and constrain models of the physical processes behind flare emission using the unprecedentedly high volume of data produced by Rubin over the 10 yr LSST. We model the refraction effect as a function of the atmospheric column density, photometric filter, and temperature of the flare, and show that flare temperatures at or above ∼4000 K can be constrained by a single g-band observation at air mass X ≳ 1.2, given the minimum specified requirement on the single-visit relative astrometric accuracy of LSST, and that a surprisingly large number of LSST observations are in fact likely be conducted at X ≳ 1.2, in spite of image quality requirements pushing the survey to preferentially low X. Having failed to measure flare DCR in LSST precursor surveys, we make recommendations on survey design and data products that enable these studies in LSST and other future surveys.

Keywords: Astronomical methods, Atmospheric refraction, Sky surveys, Red dwarf flare stars
USmorph: An Updated Framework of Automatic Classification of Galaxy Morphologies and Its Application to Galaxies in the COSMOS Field. Morphological classification conveys abundant information on the formation, evolution, and environment of galaxies. In this work, we refine a two-step galaxy morphological classification framework (USmorph), which employs a combination of unsupervised machine-learning and supervised machine-learning techniques, along with a self-consistent and robust data-preprocessing step. The updated method is applied to galaxies with I mag &lt; 25 at 0.2 &lt; z &lt; 1.2 in the COSMOS field. Based on their Hubble Space Telescope/Advanced Camera for Survey I-band images, we classify them into five distinct morphological types: spherical (SPH, 15,200), early-type disk (17,369), late-type disk (21,143), irregular disk (IRR, 28,965), and unclassified (UNC, 17,129). In addition, we have conducted both parametric and nonparametric morphological measurements. For galaxies with stellar masses exceeding 109 M ☉, a gradual increase in effective radius from SPHs to IRRs is observed, accompanied by a decrease in the Sérsic index. Nonparametric morphologies reveal distinct distributions of galaxies across the Gini‑M 20 and C‑A parameter spaces for different categories. Moreover, different categories exhibit significant dissimilarity in their G 2 and Ψ distributions. We find morphology to be strongly correlated with redshift and stellar mass. The consistency of these classification results with expected correlations among multiple parameters underscores the validity and reliability of our classification method, rendering it a valuable tool for future studies.

Keywords: Astrostatistics techniques, Galaxy structure, Astronomy data analysis
A Sample of Am and Ap Candidates from LAMOST DR10 (v1.0) Based on the Ensemble Regression Model. Large samples of Am and Ap stars are helpful in studying the interplay between phenomena like atomic diffusion, magnetic fields, and stellar rotation in stellar astrophysics. Existing samples of Am and Ap stars, mostly obtained from spectral data with a signal-to-noise ratio in the g band (S/Ng) greater than 50, can benefit from expansion by exploring spectra with lower S/Ng. Therefore, this paper proposes an ensemble regression model applicable to spectra with a minimum S/Ng of 30. Using the model, we identify 21,361 Am candidates, of which 11,614 are new, and 6182 Ap candidates, of which 4978 are new, from LAMOST DR10. The Am sample size has increased by 60% and the Ap sample size has increased by 180% compared to the previous sample. In terms of effective temperature (T eff), the Am candidates range mainly from 6000 to 8500 K, while the Ap candidates range from 6000 to 11,700 K. The surface gravity ( ) distributions for Am and Ap candidates differ in the range of 3.25–4.75 dex. The number of Am candidates increases stepwise, in contrast to the relatively uniform distribution of Ap candidates across the entire surface gravity range. Regarding metallicity ([Fe/H]), Am candidates typically range from ‑0.75 to 0.38 dex, peaking near 0 dex, while Ap candidates are distributed from ‑1.38 to 0.38 dex, with a peak near ‑0.5 dex.

Keywords: Am stars, Ap stars, Chemically peculiar stars
Sample and Statistical Analysis on NEOWISE Variability of ATLASGAL Sources. This study focuses on the analysis of mid-infrared variability in a sample of high-mass young stellar objects (YSOs) associated with the cataloged sources from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The Near-Earth Object Wide-field Infrared Survey Explorer Reactivation Mission (NEOWISE) database was used to explore the long-term mid-infrared variability of these high-mass YSOs at a half-year scale. After matching with NEOWISE photometric measurements, a total of 2230 ATLASGAL sources were selected for the variability analysis, out of which 717 were identified as variables. The derived proportions of variables at different evolutionary stages show that the variability rate of high-mass YSOs is highest during the YSO stage and decreases with evolution toward the H II region stage, resembling the behavior of low-mass YSOs. The variables can be classified into six types based on their light curves, divided into two categories: secular (linear, sin, sin+linear) and stochastic variables (burst, drop, and irregular). The magnitude–color variations observed in ∼160 secular variables can be mainly divided into "bluer when brighter/redder when dimming" and "redder when brighter/bluer when dimming," likely originating from changes in accretion rate or the effect of extinction due to obscuration. Moreover, several episodic accretion candidates were selected for further observational studies.

Keywords: Massive stars, Young stellar objects, Variable stars, Protostars, Infrared photometry
A Catalog of Early-type Runaway Stars from LAMOST DR8. Runaway stars are OB-type stars ejected from their birthplace with large peculiar velocities. The leading hypothesis addressed in their formation includes the supernova ejection mechanism and the dynamic ejection scenario. Identification of runaway populations is the first step to investigating their formation and evolution. Here we present our work of searching for Galactic runaway candidate stars from the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) Medium Resolution Survey Data Release 8 (DR8) database. After studying the kinematic properties for a collection of 4432 early-type stars, predominantly B-type stars, using radial velocity measurements from LAMOST DR8 and astrometric solutions made by Gaia Data Release 3, we identified 229 runaway candidate stars. They span a wide distribution in projected rotational velocities. We investigated the Galactic spatial distribution of the runaway population and noticed that most of them likely reside within the Galactic thin disk. Based upon analyzing the Doppler shifts of the candidate stars, we found two binary runaway candidates displaying velocity variations with estimated orbital periods of 40 and 61 days.

Keywords: Surveys, Early-type stars, Runaway stars, Catalogs
Numerical Modeling of Energetic Charged-particle Transport with SPECTRUM Software: General Approach and Artificial Effects due to Field Discretization. Test-particle simulations are an important tool for magnetospheric and heliophysics research. In this paper, we present the Space Plasma and Energetic Charged particle TRansport on Unstructured Meshes (SPECTRUM) software as a novel tool for performing these types of simulations in arbitrary astrophysical environments, specified either analytically or numerically (i.e., on a grid). We discuss and benchmark SPECTRUM's interface with meshed magnetohydrodynamic backgrounds, including output from the Block Adaptive Tree Solar-wind Roe-type Upwind Scheme (BATS-R-US) code. We also investigate the effects of field discretization on both deterministic and stochastic particle motion, with emphasis on space science applications, concluding that the discretization error typically enhances the diffusive behavior of the ensemble.

Keywords: Monte Carlo methods, Heliosphere, Distributed computing, Cosmic rays
Multiobject Spectroscopy of Galaxy Clusters at z ∼ 0.95 in the Ultra Deep Survey Field with Different Star Formation Properties and Large-scale Environments. While galaxy clusters are dominated by quiescent galaxies in the local Universe, they show a wide range in quiescent galaxy fraction (QF) at higher redshifts. Here we present the discovery of two galaxy clusters at z ∼ 0.95 with contrasting QFs despite having similar masses (log (M 200/M ⊙) ∼ 14) and spectra and redshifts of 29 galaxies in these clusters and 76 galaxies in the surrounding area. The clusters are found in the Ultra Deep Survey field and confirmed through multiobject spectroscopic observation using the Inamori Magellan Areal Camera and Spectrograph on the Magellan telescope. The two clusters exhibit QFs of and , respectively. Analysis of large-scale structures (LSSs) surrounding these clusters finds that properties of these clusters are consistent with the anticorrelation trend between the QF and the extent of surrounding LSS, found in Lee et al., which can be interpreted as a result of the replenishment of young, star-forming galaxies keeping the QF low when galaxy clusters are accompanied by rich surrounding environments.

Keywords: Galaxy clusters, Large-scale structure of the universe, High-redshift galaxy clusters, Galaxy evolution, Cosmic web, High-redshift galaxies
Complex Network View of the Sun's Magnetic Patches. I. Identification. Solar and stellar magnetic patches (i.e., magnetic fluxes that reach the surface from the interior) are believed to be the primary sources of a star's atmospheric conditions. Here, we apply the complex network approach and investigate its efficacy in the identification of these features. For this purpose, we use the line-of-sight magnetograms provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We construct the magnetic network following a specific visibility graph condition between pairs of pixels with opposite polarities and search for possible links between these regions. The complex network facilitates the construction of node degrees and PageRank images, and applying the downhill algorithm to node-degree images allows for the grouping of pixels into features corresponding to one-to-one matches with magnetogram patches. This approach promisingly serves to identify the nontrivial morphological structure of the magnetic patches for small and large sizes. We observe that the changes in the features of the node-degree images effectively correspond to the cospatial magnetic patches over time. Through visual assessment, we estimate an average false-negative error rate of approximately 1% in identifying small-scale features (one or two pixels in size).

Keywords: The Sun, Solar active regions
CO Observations of Early-mid Stage Major Mergers in the MaNGA Survey. We present a study of the molecular gas in early-mid stage major mergers, with a sample of 43 major-merger galaxy pairs selected from the Mapping Nearby Galaxies at Apache Point Observatory survey and a control sample of 195 isolated galaxies selected from the xCOLD GASS survey. Adopting kinematic asymmetry as a new effective indicator to describe the merger stage, we aim to study the role of molecular gas in the merger-induced star formation enhancement along the merger sequence of galaxy pairs. We obtain the molecular gas properties from CO observations with the James Clerk Maxwell Telescope, Institut de Radioastronomie Milimetrique 30 m telescope, and the MaNGA-ARO Survey of CO Targets survey. Using these data, we investigate the differences in molecular gas fraction ( ), star formation rate (SFR), star formation efficiency (SFE), molecular-to-atomic gas ratio ( /M H I ), total gas fraction (f gas), and the SFE of total gas (SFEgas) between the pair and control samples. In the full pair sample, our results suggest the of paired galaxies is significantly enhanced, while the SFE is comparable to that of isolated galaxies. We detect significantly increased and /M H I  in paired galaxies at the pericenter stage, indicating an accelerated transition from atomic gas to molecular gas due to interactions. Our results indicate that the elevation of plays a major role in the enhancement of global SFR in paired galaxies at the pericenter stage, while the contribution of enhanced SFE in specific regions requires further explorations through spatially resolved observations of a larger sample spanning a wide range of merger stages.

Keywords: Star formation, Molecular gas, Galaxy pairs, Galaxy mergers
The R2D2 Deep Neural Network Series Paradigm for Fast Precision Imaging in Radio Astronomy. Radio-interferometric imaging entails solving high-resolution high-dynamic-range inverse problems from large data volumes. Recent image reconstruction techniques grounded in optimization theory have demonstrated remarkable capability for imaging precision, well beyond CLEAN's capability. These range from advanced proximal algorithms propelled by handcrafted regularization operators, such as the SARA family, to hybrid plug-and-play (PnP) algorithms propelled by learned regularization denoisers, such as AIRI. Optimization and PnP structures are however highly iterative, which hinders their ability to handle the extreme data sizes expected from future instruments. To address this scalability challenge, we introduce a novel deep-learning approach, dubbed "Residual-to-Residual DNN series for high-Dynamic-range imaging" or in short R2D2. R2D2's reconstruction is formed as a series of residual images, iteratively estimated as outputs of deep neural networks (DNNs) taking the previous iteration's image estimate and associated data residual as inputs. It thus takes a hybrid structure between a PnP algorithm and a learned version of the matching pursuit algorithm that underpins CLEAN. We present a comprehensive study of our approach, featuring its multiple incarnations distinguished by their DNN architectures. We provide a detailed description of its training process, targeting a telescope-specific approach. R2D2's capability to deliver high precision is demonstrated in simulation, across a variety of image and observation settings using the Very Large Array. Its reconstruction speed is also demonstrated: with only a few iterations required to clean data residuals at dynamic ranges up to 105, R2D2 opens the door to fast precision imaging. R2D2 codes are available in the BASPLib (https://basp-group.github.io/BASPLib/) library on GitHub.

Keywords: Computational methods, Aperture synthesis, Astronomy image processing, Neural networks
Microlensing Optical Depth and Event Rate toward the Large Magellanic Cloud Based on 20 yr of OGLE Observations. Measurements of the microlensing optical depth and event rate toward the Large Magellanic Cloud (LMC) can be used to probe the distribution and mass function of compact objects in the direction toward that galaxy—in the Milky Way disk, the Milky Way dark matter halo, and the LMC itself. The previous measurements, based on small statistical samples of events, found that the optical depth is an order of magnitude smaller than that expected from the entire dark matter halo in the form of compact objects. However, these previous studies were not sensitive to long-duration events with Einstein timescales longer than 2.5–3 yr, which are expected from massive (10–100 M ⊙) and intermediate-mass (102–105 M ⊙) black holes. Such events would have been missed by the previous studies and would not have been taken into account in calculations of the optical depth. Here, we present the analysis of nearly 20 yr long photometric monitoring of 78.7 million stars in the LMC by the Optical Gravitational Lensing Experiment (OGLE) from 2001 through 2020. We describe the observing setup, the construction of the 20 yr OGLE data set, the methods used for searching for microlensing events in the light-curve data, and the calculation of the event detection efficiency. In total, we find 16 microlensing events (13 using an automated pipeline and three with manual searches), all of which have timescales shorter than 1 yr. We use a sample of 13 events to measure the microlensing optical depth toward the LMC τ = (0.121 ± 0.037) × 10‑7 and the event rate Γ = (0.74 ± 0.25) × 10‑7 yr‑1 star‑1. These numbers are consistent with lensing by stars in the Milky Way disk and the LMC itself, and they demonstrate that massive and intermediate-mass black holes cannot comprise a significant fraction of the dark matter.

Keywords: Milky Way dark matter halo, Intermediate-mass black holes, Large Magellanic Cloud, Gravitational microlensing, Dark matter, Primordial black holes
T-ReX: The Tarantula—Revealed by X-Rays. The Tarantula Nebula (30 Doradus, 30 Dor) is the most important star-forming complex in the Local Group, offering a microscope on starburst astrophysics. At its heart lies the exceptionally rich young stellar cluster R136, containing the most massive stars known. Stellar winds and supernovae have carved 30 Dor into an amazing display of arcs, pillars, and bubbles. We present first results and advanced data-processing products from the 2 Ms Chandra X-ray Visionary Project, "The Tarantula—Revealed by X-rays" (T-ReX). The 3615 point sources in the T-ReX catalog include massive stars, compact objects, binaries, bright pre-main-sequence stars, and compact young stellar (sub)clusters in 30 Dor. After removing point sources and excluding the exceptionally bright supernova remnant N157B (30 Dor B), the global diffuse X-ray maps reveal hot plasma structures resolved at 1–10 pc scales, with an absorption-corrected total-band (0.5–7 keV) X-ray luminosity of 2.110 × 1037 erg s‑1. Spatially resolved spectral modeling provides evidence for emission lines enhanced by charge-exchange processes at the interfaces. We identify a candidate for the oldest X-ray pulsar detected to date in 30 Dor, PSR J0538-6902, inside a newly resolved arcuate X-ray wind nebula, the Manta Ray. The long temporal baseline of T-ReX allowed monitoring of dozens of massive stars, several showing periodic variability tied to binary orbital periods, and captured strong flares from at least three low-mass Galactic foreground stars.

Keywords: Early-type stars, High energy astrophysics, Star formation, Interstellar medium, H II regions, Superbubbles
TESS Light Curves of Cataclysmic Variables. IV. A Synoptic View of Eclipsing Old Novae and Novalike Variables. Based mainly on the months-long 2 minutes time-resolution light curves observed by the Transiting Exoplanet Survey Telescope (TESS) space mission of 48 eclipsing old novae and novalike variables (commonly referred to as NLs) selected from the Ritter &amp; Kolb catalog, a synoptic view of some basic properties of these systems is provided. The supraorbital variations exhibit a large diversity of behavior. Data taken from the literature and many additional eclipse epochs measured in the TESS and in AAVSO light curves are used to update the orbital ephemerides of 21 targets. The large majority of these suffer period variations which defy current theoretical understanding. Orbital waveforms are constructed and, if possible, their variation over time is studied, revealing some common characteristics but also substantial differences between individual systems. The dependence of the eclipse depth on the out-of-eclipse flux reveals that in all systems a fraction of the light source responsible for the out-of-eclipse variations escapes eclipse and is probably located in the outer disk regions. In systems exhibiting superhumps, both eclipse width and epoch are modulated with the accretion disk precession period. This suggests an expansion and contraction of the eclipsed light source, as well as a periodic shift of its light center as a function of the accretion disk precession phase. The dependence of the orbital and superhump waveforms on the disk precession phase is also examined but does not lead to a consistent picture. Two cataclysmic variables are newly identified as eclipsing. Attention is drawn to specific peculiarities in some of the target stars.

Keywords: Eclipsing binary stars, Nova-like variable stars, Cataclysmic variable stars, Novae
Multimode δ Sct stars from the Zwicky Transient Facility Survey. We obtain the largest catalog of multimode δ Sct stars in the northern sky to date using the Zwicky Transient Facility (ZTF) Data Release 20. The catalog includes 2254 objects, of which 2181 are new to our study. Among these multimode δ Sct stars, 2142 objects are double-mode δ Sct, while 109 objects are triple-mode δ Sct and three are quadruple-mode δ Sct. By analyzing the light curves in the r and g bands of the ZTF, we determine the basic parameters of multimode δ Sct stars, including the periods and amplitudes. Periods are checked by comparison with the Optical Gravitational Lensing Experiment catalog of double-mode δ Sct stars. On the Petersen diagram, multimode δ Sct stars form six sequences. We find that in Galactic coordinates, the periods of 1O/F double-mode δ Sct stars at high latitudes are shorter than those of 1O/F double-mode δ Sct stars in the disk, due to metallicity variations. In the future, our catalog can be used to establish the period–luminosity relation and the period–metallicity relation of double-mode δ Sct stars, and to study the Galactic structure.

Keywords: Periodic variable stars, Delta Scuti variable stars, Astronomy databases, Pulsating variable stars, Distance indicators, Stellar oscillations
Stellar X-Ray Activity and Habitability Revealed by the ROSAT Sky Survey. Using the homogeneous X-ray catalog from ROSAT observations, we conducted a comprehensive investigation into stellar X-ray activity–rotation relations for both single and binary stars. Generally, the relation for single stars consists of two distinct regions: a weak decay region, indicating a continued dependence of the magnetic dynamo on stellar rotation rather than a saturation regime with constant activity, and a rapid decay region, where X-ray activity is strongly correlated with the Rossby number. Detailed analysis reveals more fine structures within the relation: in the extremely fast-rotating regime, a decrease in X-ray activity was observed with increasing rotation rate, referred to as supersaturation, while in the extremely slow-rotating region, the relation flattens, mainly due to the scattering of F stars. This scattering may result from intrinsic variability in stellar activities over one stellar cycle or the presence of different dynamo mechanisms. Binaries exhibit a similar relation to that of single stars while the limited sample size prevented the identification of fine structures in the relation for binaries. We calculated the mass-loss rates of planetary atmospheres triggered by X-ray emissions from host stars. Our findings indicate that for an Earthlike planet within the stellar habitable zone, it would easily lose its entire primordial H/He envelope (equating to about 1% of the planetary mass).

Keywords: Late-type stars, Stellar activity, Stellar rotation, Habitable zone, X-ray stars