Sazuna/UAT_keywords huggingface dataset:
Semiempirical versus Theoretical Stellar Population Models: A Comparison with Star Clusters. Stellar population synthesis (SPS) models are a key tool for deriving the age, metallicity, radial velocity, and reddening of star clusters from their integrated spectra. Using a sample of 129 star clusters with high-quality spectra, we analyze the uncertainties associated with selecting an empirical versus a theoretical stellar spectral library in the SPS models. We find that the fits from the different models agree on the goodness-of-fit metrics and inferred reddening. However, the derived age and metallicity can be affected by the choice of the stellar library, with synthetic libraries tending to give lower age and metallicity, especially for spectra with low signal-to-noise ratio. Ages and reddening values from SSP-equivalent fits are consistent with the multipopulation fits; however, SSP-equivalent metallicities are affected by the coarse coverage of the SPS grid in [Fe/H]. When comparing the spectral fitting results with the literature, we find that (1) all models underestimate age for old and metal-poor systems, and (2) on average, SPS models based on synthetic stellar libraries better match the isochrone ages and metallicities from high-resolution stellar spectroscopy.

Keywords: Star clusters
The Second and Third Data Releases from the UKIRT Hemisphere Survey. This paper describes the second and third data releases (DR2 and DR3, respectively) from the ongoing United Kingdom Infrared Telescope Hemisphere Survey (UHS). DR2 is primarily comprised of the K-band portion of the UHS survey, and was released to the public on 2023 June 1. DR3 mainly includes the H-band portion of the survey, with a public release scheduled for September 2025. The H- and K-band data releases complement the previous J-band data release (DR1) from 2018. The survey covers approximately 12,700 square degrees between declinations of 0° and +60° and achieves median 5σ point source sensitivities of 19.0 mag and 18.0 mag (Vega) for H and K, respectively. The data releases include images and source catalogs, which include ∼581 million H-band detections and ∼461 million K-band detections. DR2 and DR3 also include merged catalogs, created by combining J- and K-band detections (DR2) and J-, H-, and K-band detections (DR3). The DR2 merged catalog has a total of ∼513 million sources, while the DR3 merged catalog contains ∼560 million sources.

Keywords: Astronomy databases, Infrared photometry, Near infrared astronomy
ABYSS. III. Observing Accretion Activity in Young Stars Through Empirical Veiling Measurements. Stellar accretion plays an important role in the early stages of stellar evolution, particularly in Classical T Tauri Stars (CTTSs). Accretion of a CTTS can be related to different physical parameters such as effective temperature (Teff), age, abundance of hydrogen, etc. We can infer how accretion works by examining it across different wavelength regions. Accretion can be traced using veiling, a parameter that measures how excess emission from accretion affects the photospheric spectrum of CTTS. In this study, we selected a sample of CTTSs, Weak-line T Tauri Stars, and field stars, observed as a part of the SDSS-V Milky Way Mapper using the Baryonic Oscillation Spectroscopic Survey spectrograph. We measured veiling for CTTSs through comparing them to theoretical spectra. Next, we assessed the effect of veiling on different stellar properties, including wavelength, Hα emission, effective temperature, and age. We investigated how veiling changes with these parameters and what the physical reasons behind the changes can be. Finally, we evaluated how our findings align with existing accretion shock models. This study highlights veiling as a critical diagnostic tool for understanding accretion in young stars.

Keywords: Young stellar objects
Deep Reinforcement Learning for Efficient Scheduling of Ground-based Astronomical Observations. Ground-based astronomical observations face inherent challenges from weather changes, target visibility window constraints, and observational requirements. Enhancing the efficiency and effectiveness of telescope operations has long been a key objective for many observatories because of the high cost of observational resources. In this study, we formalize observation scheduling as a time-dependent combinatorial optimization problem. To achieve this, we implement a pointer network with temporal attention that is capable of planning observations while accounting for time-varying factors such as moonlight interference, target altitude, and air mass, which impact the exposure time and image quality. To support the training of the deep neural network, we propose a scoring mechanism to evaluate the effectiveness of the observations, which is optimized through a refined REINFORCE algorithm with a baseline. Furthermore, an exposure time calculator and an equipment kinematic model are incorporated to dynamically estimate the time costs during the decision-making process. The simulation results demonstrated that the trained model significantly outperformed both manual scheduling and a greedy algorithm in terms of theoretical reward scores and the total number of scheduled targets. Observation experiments conducted using a dual-telescope system at Muztaga observatory further validated the superiority of our approach, demonstrating a 45.8% enhancement in the total signal-to-noise ratio across all observed targets and a 24.1% increase in the number of completed tasks under the same observing conditions.

Keywords: Observational astronomy, Optical observation, Neural networks, Astronomical techniques, Ground-based astronomy
A Massive Yellow Supergiant in the Far Outer Disk of M31: Evidence for in Situ Massive Star Formation beyond the Optical Radius. While massive stars are known to shape galactic ecosystems, their formation has long been assumed to require the high-density environments of inner galactic disks. This paradigm is challenged by mounting evidence of young massive stars in extended galaxy outskirts, yet direct confirmation of in situ massive star formation in such extreme low-density environments remains scarce. Here, we present the discovery of LAMOST J0048+4154, a massive yellow supergiant situated at a deprojected galactocentric distance of ∼34 kpc in M31, making it the most distant massive star confirmed in this galaxy. Through spectroscopic and photometric analyses, we classify J0048+4154 as an F5–F8I supergiant with an effective temperature of  6357‑118+121  K and a luminosity of  logL/L⊙=5.00‑0.06+0.06 , corresponding to an ∼18 M⊙ progenitor and an age of ∼10 Myr. FAST H I observations reveal close spatial and kinematic alignment between the star and a faint H I external arm, suggesting in situ formation in a region of low gas density. The presence of other UV-bright, early-type stars in the vicinity further supports low-level recent star formation in M31's very outer disk. These findings challenge the prevailing assumption that massive star formation is confined to inner disks or classical star-forming regions and underscore the need to reexamine the role of spiral galaxy outskirts in fueling and sustaining star formation. J0048+4154 thereby expands our understanding of the extent of M31's young stellar component and exemplifies how outer disks may harbor conditions conducive to forming massive stars despite low-density environments.

Keywords: Star formation, Massive stars, Andromeda Galaxy, F supergiant stars
Reidentification of Redshifts of SDSS Galaxies Overlapped with Galactic Objects. This work presents a catalog of reidentified redshifts of 853 galaxies for which the redshifts of overlapping foreground objects were registered in the Sloan Digital Sky Survey (SDSS) DR16 Database. We examined SDSS DR16 spectra of the candidates contaminated by foreground Galactic stars and reidentified their galaxy redshift features, such as Hα and other emission lines or absorption lines. Comparisons of redshifts measured at neighboring fibers, previous SDSS fits, and other published literature showed that our reidentification of redshift would be accurate to within 0.001. For the redshift range, 0 &lt; z &lt; 0.35, at least 0.1% of galaxies overlap with Galactic stars, and SDSS DR16 assigns the redshift of the foreground object, not the galaxies.

Keywords: Galaxies, Redshift surveys, Catalogs
Resolving the Unresolved: Using NESSI to Search for Unresolved Companions in Low-mass Disk Wide Binaries. Stellar systems consisting of three or more stars are not an uncommon occurrence in the Galaxy. Nearly 50% of solar-type wide binaries with separations &gt;1000 au are actually higher-order multiples with one component being a close binary. Additionally, the higher-order multiplicity fraction appears to be correlated with the physical separation of the widest component. These facts have motivated some of our current theories behind how the widest stellar systems formed, which can have separations on the order of or larger than protostellar cores. However, it is unclear if the correlation between wide binary separation and higher-order multiplicity extends to low-mass binaries. We present initial results of an ongoing speckle imaging survey of nearby low-mass wide binaries. We find an overall higher-order multiplicity fraction for our sample of 42.0% ± 10.9%. If we include systems where Gaia indicates that a companion is likely present, this fraction increases to 62.0% ± 14.2%. This is consistent with previous results from both higher-mass stars and a previous result for low-mass wide binaries. However, we do not detect the expected increase in higher-order multiplicity fraction with separation, as was seen with previous studies. We briefly explore why higher-order multiplicity statistics could be different in low-mass stars, and what the significance might be for models of wide binary formation.

Keywords: Observational astronomy, Stellar astronomy, Multiple stars, Wide binary stars
Ages of Large Magellanic Cloud Star Clusters with Gemini Multi-Object Spectrograph Integrated Spectroscopy: Systematic Comparison of Available Tools. We present the first systematic analysis comparing the ages, reddening, and radial velocities of star clusters using two widely used tools: STARLIGHT and Analyzer of Spectra for Age Determination (A.S.A.D). Both tools utilize the full integrated spectrum fitting technique but they use different approaches in calculating the parameters. We find that there is a good agreement between the parameters derived by the two tools and confirm that both tools provide consistent results with the literature parameters obtained from resolved photometry. We note that for optimal age and reddening estimates, observed integrated spectra should have signal-to-noise ratio (S/N) &gt; 10 when using A.S.A.D and the combination of the single stellar populations should be added linearly (not using logarithmic values) when using STARLIGHT. We also show that the deviation of the radial velocity estimates between the two tools depends on the S/N of the observed integrated spectrum and demonstrate that when varying the metallicity, the age estimates of STARLIGHT are not affected significantly, while the results of A.S.A.D are generally underestimated. As more observational data become available through modern instruments, the strengths and limitations of each available automated tool need to be taken in consideration when interpreting their results.

Keywords: Magellanic Clouds, Spectroscopy, Star clusters
A Short History of (Orbital) Decay: Roman's Prospects for Detecting Dying Planets. The Roman Space Telescope Galactic Bulge Time Domain Survey (GBTDS) is expected to detect ∼105 transiting planets. Many of these planets will have short orbital periods and are thus susceptible to tidal decay. We use a catalog of simulated transiting planet detections to predict the yield of orbital decay detections in the Roman GBTDS. Assuming a constant stellar tidal dissipation factor,  Q*' , of 106, we predict ∼5─10 detections. We additionally consider an empirical period-dependent parameterization of  Q*'∝P−3  and find a substantially suppressed yield. We conclude that Roman will provide constraints on the rate of planet engulfment in the Galaxy and probe the physics of tidal dissipation in stars.

Keywords: Surveys, Exoplanet tides, Transits, Exoplanets
Finding New Hot Subdwarf Stars in SDSS Images. Hot subdwarf stars, located at the end of the blue horizontal branch, have a burning helium core, and are crucial for studying stellar structure. Currently, the number of known hot subdwarf star is relatively small. Many studies apply machine learning classification to search for hot subdwarf stars based on high quality spectra. With the accumulated image data in the digital sky surveys, we proposed the Hot Subdwarf Detector (HsdDet), a novel multiscale object detection algorithm designed to directly locate hot subdwarf stars' coordinates in Sloan Digital Sky Survey (SDSS) images. We applied the HsdDet algorithm to some photometric images of SDSS, and detected 29,695 candidates, whose reduced proper motions are primarily concentrated between 5 and 20 mas yr‑1. Most of the candidates have distances of 1.5 ∼ 7.5 kpc, while some candidates can be as far as 20 kpc or even more. Candidates' colors are ‑2.5 &lt; u ‑ g &lt; 2.0, ‑3.5 &lt; g ‑ r &lt; 2.0, ‑2.5 &lt; r ‑ i &lt; 2.5, and ‑3.0 &lt; i ‑ z &lt; 3.0. We crossmatched the candidates catalog with Large Sky Area Multi-Object Fiber Spectroscopic Telescope and obtained 3823 spectra. The confidence measures the probability of a candidate being a hot subdwarf star. With the confidence threshold being 0.5, 263 new hot subdwarf stars were confirmed by the spectral fitting method, and the purity is 6.9%. When we set confidence threshold at 0.9, the purity is 13.5%. We discussed the selection bias in the search region and released the hot subdwarf stars catalog. These results have the potential to expand the population of hot subdwarf stars.

Keywords: Astronomy data analysis, Astronomical object identification, Subdwarf stars, Astrostatistics
Technosignature Searches with Real-time Alert Brokers. We present an exploration of technosignature research that is possible using real-time alert brokers from surveys such as the Zwicky Transient Facility (ZTF) and the upcoming Legacy Survey of Space and Time (LSST). Nine alert brokers currently stream up to one million alerts each night from ZTF, and LSST is projected to increase this volume by an order of magnitude. While these brokers are primarily designed to facilitate real-time follow-up of explosive transients such as supernovae, they offer a unique platform to discover rare forms of variability from nearby stars in real time, which is crucial for follow-up and characterization. We evaluate the capability for both spatial and temporal search for extraterrestrial intelligence (SETI) methods using the currently available brokers, and present examples of technosignature searches using ZTF alert and archival data. We have deployed optical SETI techniques, such as planetary transit zone geometries and the SETI Ellipsoid. We have also developed a search for novel high-amplitude stellar dippers, and present a workflow that integrates features available directly through the brokers, as well as postprocessing steps that build on the existing capabilities. Though the SETI methods that alert brokers can execute are currently limited, we provide suggestions that may enhance future technosignature and anomaly searches in the era of the Vera C. Rubin Observatory.

Keywords: Technosignatures, Sky surveys, Variable stars
SDSS-V Milky Way Mapper (MWM): ASPCAP Stellar Parameters and Abundances in SDSS-V Data Release 19. The goal of this paper is to describe the science verification of Milky Way Mapper (MWM) APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) data products published in Data Release 19 (DR19) of the fifth phase of the Sloan Digital Sky Survey (SDSS-V). We compare MWM ASPCAP atmospheric parameters Teff, log g, 24 abundances of 21 elements (carbon, nitrogen, and oxygen have multiple sources for deriving their abundance values) and their uncertainties determined from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph spectra with those of the literature and evaluate their accuracy and precision. We also test the zero-point calibration of the vrad derived by the APOGEE Data Reduction Pipeline. This data release contains ASPCAP parameters for 964,989 stars, including all APOGEE-2 targets expanded with new observations of 336,511 stars from the Apache Point Observatory observed until 2023 July 4. Overall, the new Teff values show excellent agreement with the IRFM scale, while the surface gravities exhibit slight systematic offsets compared to asteroseisimic gravities. The estimated precision of Teff is between 50 and 70 K for giants and 70–100 K for dwarfs, while surface gravities are measured with a precision of 0.07–0.09 dex for giants. We achieve an estimated precision of 0.02–0.04 dex for multiple elements, including metallicity, α, Mg, and Si, while the precision of at least 10 elements is better than 0.1 dex.

Keywords: High resolution spectroscopy
Sorcha: Optimized Solar System Ephemeris Generation. Sorcha is a solar system survey simulator built for the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) and future large-scale wide-field surveys. Over the 10 yr survey, the LSST is expected to collect roughly a billion observations of minor planets. The task of a solar system survey simulator is to take a set of input objects (described by orbits and physical properties) and determine what a real or hypothetical survey would have discovered. Existing survey simulators have a computational bottleneck in determining which input objects lie in each survey field, making them infeasible for LSST data scales. Sorcha can swiftly, efficiently, and accurately calculate the on-sky positions for sets of millions of input orbits and surveys with millions of visits, identifying which exposures these objects cross, in order for later stages of the software to make detailed estimates of the apparent magnitude and detectability of those input small bodies. In this paper, we provide the full details of the algorithm and software behind Sorcha's ephemeris generator. Like many of Sorcha's components, its ephemeris generator can be easily used for other surveys.

Keywords: Ephemerides, Sky surveys, Small Solar System bodies, N-body simulations
Predictions of the LSST Solar System Yield: Discovery Rates and Characterizations of Centaurs. The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will start by the end of 2025 and operate for 10 yr, offering billions of observations of the southern night sky. One of its main science goals is to create an inventory of the solar system, allowing for a more detailed understanding of small-body populations, including the Centaurs, which will benefit from the survey's high cadence and depth. In this paper, we establish the first discovery limits for Centaurs throughout the LSST's decade-long operation using the best available dynamical models. Using the survey simulator Sorcha, we predict a roughly 7-fold increase in Centaurs in the Minor Planet Center (MPC) database, reaching ∼1200–2000 (dependent on definition) by the end of the survey—about 50% of which are expected within the first 2 yr. Approximately 30–50 Centaurs will be observed twice as frequently, as they fall within one of the LSST's Deep Drilling Fields (DDF) for on average only up to 2 months. Outside of the DDFs, Centaurs will receive ∼200 observations across the ugrizy filter range, facilitating searches for cometary-like activity through point-spread function extension analysis, as well as fitting light curves and phase curves for color determination. Regardless of definition, over 200 Centaurs will achieve high-quality color measurements across at least three filters in the LSST's six filters. These observations will also provide over 300 well-defined phase curves in the griz bands, improving absolute magnitude measurements to a precision of 0.2 mag.

Keywords: Small Solar System bodies, Sky surveys, Centaur group
Predictions of the LSST Solar System Yield: Near-Earth Objects, Main Belt Asteroids, Jupiter Trojans, and Trans-Neptunian Objects. The NSF-DOE Vera C. Rubin Observatory is a new 8m-class survey facility presently being commissioned in Chile, expected to begin the 10 yr long Legacy Survey of Space and Time (LSST) by the end of 2025. Using the purpose-built Sorcha survey simulator, and near-final observing cadence, we perform the first high-fidelity simulation of LSST's solar system catalog for key small body populations. We show that the final LSST catalog will deliver over 1.1 billion observations of small bodies and raise the number of known objects to 1.27E5 near-Earth objects, 5.09E6 main belt asteroids, 1.09E5 Jupiter Trojans, and 3.70E4 trans-Neptunian objects. These represent 4×‑9× more objects than are presently known in each class, making LSST the largest source of data for small body science in this and the following decade. We characterize the measurements available for these populations, including orbits, griz colors, and light curves, and point out science opportunities they open. Importantly, we show that ∼70% of the main asteroid belt and more distant populations will be discovered in the first 2 yr of the survey, making high-impact solar system science possible from very early on. We make our simulated LSST catalog publicly available, allowing researchers to test their methods on an up-to-date, representative, full-scale simulation of LSST data.

Keywords: Open source software, Sky surveys, Small Solar System bodies, Astronomy software, Surveys
Sorcha: A Solar System Survey Simulator for the Legacy Survey of Space and Time. The upcoming Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory is expected to revolutionize solar system astronomy. Unprecedented in scale, this 10 yr wide-field survey will collect billions of observations and discover a predicted ∼5 million new solar system objects. Like all astronomical surveys, its results will be affected by a complex system of intertwined detection biases. Survey simulators have long been used to forward-model the effects of these biases on a given population, allowing for a direct comparison to real discoveries. However, the scale and tremendous scope of the LSST requires the development of new tools. In this paper we present Sorcha, an open-source survey simulator written in Python . Designed with the scale of LSST in mind, Sorcha is a comprehensive survey simulator to cover all solar system small-body populations. Its flexible, modular design allows Sorcha to be easily adapted to other surveys by the user. The simulator is built to run both locally and on high-performance computing clusters, allowing for repeated simulation of millions to billions of objects (both real and synthetic).

Keywords: Astronomical simulations, Small Solar System bodies, Astronomy software, Solar system astronomy