Sazuna/UAT_keywords huggingface dataset:
Fitting the Shadows: Star Formation Scaling Relations in the Low Surface Brightness Regime. Classical low surface brightness (LSB) galaxies pose an important challenge to galaxy evolution models. While they are found to host large reservoirs of atomic hydrogen, they display low stellar and star formation surface densities. Global star formation scaling relations characterize trends in the star formation behaviour of galaxies; when used to compare populations or classes of galaxies, deviations in the observed trends can be used to probe predicted differences in physical conditions. In this work, we utilize the well-studied Star-forming Main Sequence and integrated Kennicutt─Schmidt Relations to characterize star formation in the LSB regime, and compare the observed trends to relations for normal star-forming galaxies. Using a comprehensive cross-matched sample of 277 LSB galaxies from the GALEX-SDSS-WISE Legacy Catalog Release 2 and the Arecibo Legacy Fast Arecibo L-band Feed Array Catalog, we gain an in-depth view of the star formation process in the LSB regime. H I-selected LSB galaxies follow very similar trends in atomic gas-to-stellar mass ratio and the star-forming main sequence to their high surface brightness counterparts. However, while LSB galaxies host comparably large atomic gas reservoirs, they prove to be largely inefficient in converting this gas to stars with a median depletion time tdep = ∼18 Gyr. These results are discussed in relation to previous studies, which find that LSB galaxies host low atomic gas densities and are largely deficient in molecular gas, which suggests that the faint appearance of LSB galaxies may be the result of physical conditions on the sub-kpc scale.

Keywords: Surveys, Galaxies, Scaling relations, Low surface brightness galaxies
Wide Binaries in an Ultra-faint Dwarf Galaxy: Discovery, Population Modeling, and A Nail in the Coffin of Primordial black hole Dark Matter. We report the discovery and characterization of a wide binary population in the ultrafaint dwarf galaxy Boötes I using deep JWST/NIRCam imaging. Our sample consists of 52 candidate binaries with projected separations of 7000─16,000 au and stellar masses from near the hydrogen-burning limit to the main-sequence turnoff (∼0.1─0.8 M⊙). By forward-modeling selection biases and chance alignments, we find that 1.25% ± 0.25% of Boötes I stars are members of wide binaries with separations beyond 5000 au. This fraction, along with the distributions of separations and mass ratios, matches that in the Solar neighborhood, suggesting that wide binary formation is largely insensitive to metallicity, even down to [Fe/H] ≍ −2.5. The observed truncation in the separation distribution near 16,000 au is well explained by stellar flyby disruptions. We also discuss how the binaries can be used to constrain the galaxy's dark matter properties. We show that our detection places new limits on primordial black hole dark matter, finding that compact objects with M ≳ 5 M⊙ cannot constitute more than ∼1% of the dark matter content. In contrast to previous work, we find that wide binaries are unlikely to provide robust constraints on the dark matter profile of ultrafaint galaxies given the uncertainties in the initial binary population, flyby disruptions, and contamination from chance alignments. These findings represent the most robust detection of wide binaries in an external galaxy to date, opening a new avenue for studying binary star formation and survival in extreme environments.

Keywords: Galaxy dark matter halos, Binary stars, Galaxy evolution, Wide binary stars, Dark matter
Wind Accretion in Massive Binaries Experiencing High Mass Loss Rates. I. Dependency on Mass Ratio and Orbital Period. We run numerical simulations to study high-power wind accretion in a massive binary system during a high mass loss event. The system consists of an evolved primary star with a zero age main sequence mass of M1 = 100 M⊙ and a hot secondary star with a mass ranging from M2 = 30─80 M⊙, orbiting in a circular orbits with periods between 455 and 1155 days. We initiate a weak eruption event with mass loss at a rate of 10−3 M⊙ yr−1 for 1.5 yr. During this event, a fraction of the mass lost by the primary is accreted onto the secondary, with the accretion rate being dependent on the orbital and stellar parameters. From the set of simulations, we derive an analytical relation describing the dependence of the mass accretion rate on the orbital period and stellar mass ratio. We also identify the transitional orbital period for which Roche lobe overflow begins to dominate over wind accretion. We find that accretion leads to a reduction in the effective temperature of the secondary star. However, the mass average accretion rate we obtain in the simulations is low enough for the secondary to remain in thermal equilibrium and avoid radial expansion.

Keywords: Binary stars, Eruptive variable stars, Massive stars, Stellar mass loss, Stellar winds
The Bimodal Distribution of Donor Stars in X-Ray Binaries. The classification of X-ray binaries into high- and low-mass types has historically lacked a unified, data-driven quantitative criterion, and large-scale statistical studies of the donor star population have been limited. In this work, we address this gap by compiling data for 3964 XRBs and deriving a plentiful set of physical parameters (mass, radius, age, and evolutionary stage) for a sub-sample of 288 donor stars using Gaia DR3 spectral data and stellar evolution models. We find a statistically bimodal distribution in the donor star parameters, which is characterized by a valley at approximately 3 M⊙ or 11,000 K. We uncover the physical mechanism behind this bimodality: a previously unreported "parallel tracks" phenomenon observed in the relationship between the donor's evolutionary stage and its fundamental parameters, such as luminosity and radius. These two tracks represent distinct main-sequence populations, and the valley between them corresponds to the sparsely populated pre- and post-main-sequence evolutionary phases.

Keywords: Low-mass x-ray binary stars, X-ray binary stars, High mass x-ray binary stars
The Role of the Convective Kissing Instability in Cataclysmic Variable Evolution. The convective kissing instability (CKI) is postulated to occur in low mass stars around the fully convective transition. Non-equilibrium 3He burning leads to the merging of core and envelope convective zones, which causes abrupt decreases in the stellar radius. It has been suggested by van Saders &amp; Pinsonneault that these effects may be relevant for cataclysmic variables (CVs). We have performed stellar evolution modeling to study the role of the CKI in CV evolution. We find that the CKI has no effect on normal CVs which evolve via magnetic braking and gravitational radiation above the period gap. CKI cycles either do not occur or are abruptly halted once mass transfer begins. If only gravitational radiation is considered, the CKI does occur. The abrupt radius changes can cause detachment phases which produce small period gaps with widths of a few minutes. We describe how the size of the period gaps is controlled by the 3He profiles of the secondaries. We also discuss how the results of this study apply to the evolution of strong field polars, where the magnetic field of the white dwarf is strong enough to suppress magnetic braking.

Keywords: Close binary stars, Cataclysmic variable stars, AM Herculis stars, Stellar evolution
Seeking Kinematic Association of Known FU Orionis Stars with Young Clusters in Cygnus. Kinematic studies of young stars and star clusters have increased our understanding of the process of star formation and evolution in the Milky Way. FU Orionis objects are a specific class of young stellar object notable for their extremely high disk-to-star accretion rates. We use parallax and proper motion information from the Gaia astrometric survey to study five known FU Ori stars towards the Cygnus clouds, in the distance range ∼500─900 pc, and seek evidence of their kinematic association with proximal stellar groups or clusters. We develop multiple search criteria within the Gaia data sets to look for nearby stellar aggregates and to reliably isolate their likely member stars. We show that V1057 Cygni and HBC 722 are kinematically consistent with the 3D locations as well as the inferred proper motion fields of the North America Nebula cluster. We show a similar association of V1515 Cygni with NGC 6914 in the Cygnus-X region, and of V2494 Cygni with stars in the dark cloud LDN 1003 and Braid Nebula. Further, we find that V1735 Cygni is consistent in both position and proper motion with the streamer structure of IC 5146, and we trace the streamer's similar proper motions to the main cluster. Color─magnitude diagrams of all identified clusters show the presence of pre-main-sequence populations, strengthening the likelihood of a physical association between the young FU Ori stars and their respective nearby clusters.

Keywords: FU Orionis stars, Stellar kinematics, Young star clusters, Young stellar objects, Star formation, Astrometry
Population Demographics of White Dwarf Binaries with Intermediate Separations: Gaia Constraints on post-AGB Mass Transfer. Astrometry from the Gaia mission has revealed a large population of white dwarf (WD) + main sequence (MS) binaries with periods of 100─1000 days. These systems have separations intermediate to predictions from standard binary evolution scenarios, challenging models of binary interaction and mass transfer. Because the selection function of Gaia astrometric catalogs is complex, the underlying population demographics of WD+MS binaries remain imperfectly understood. We present a forward-model of the AU-scale WD+MS binary population probed by Gaia that begins with a realistic binary population and incorporates a full model of Gaia mock observations and astrometric model fitting, as well as cuts employed in producing the Gaia astrometric catalog and selecting WD+MS binary candidates. We model the formation of AU-scale WD+MS binaries as the result of interaction when the WD progenitor is an AGB star. We test several models for the binaries' formation, including stable mass transfer with theoretically predicted stability criteria and two different formalisms for common envelope evolution. None of these models succeed in reproducing the observed component mass distributions or the absolute number of WD+MS binaries. The data are best reproduced by a model in which post-AGB binaries remain wide only if the accretor-to-donor mass ratio exceeds ∼0.4. Our model allows us to constrain the intrinsic population demographics of intermediate-separation WD+MS binaries. The inferred period distribution is close to flat, with  dN/dPorb∝Porb0.12 , while the WD mass distribution is sharply peaked at 0.6 M⊙. The model implies that ∼0.4% of solar-type stars have WD companions with periods of 100─1000 days.

Keywords: White dwarf stars, Binary stars, Astrometry
Variability of Central Stars of Planetary Nebulae with the Zwicky Transient Facility. II. Long-timescale Variables including Wide Binary and Late Thermal Pulse Candidates. In this second paper on our variability survey of central stars of planetary nebulae (CSPNe) using the Zwicky Transient Facility (ZTF), we report 11 long-timescale variables with variability timescales ranging from months to years. We also present preliminary analyses based on spectroscopic and/or photometric follow-up observations for six of them. Among them is NGC 6833, which shows a 980 days periodic variability with strange characteristics: "triangle-shaped" brightening in r, i, and WISE bands but almost coincidental shallow dips in the g-band. The most plausible explanation is a wide binary with the photometric period being the orbital period. Long-period near-sinusoidal variability was detected in two other systems, NGC 6905 and Kn 26, with periods of 700 days and 230 days, respectively, making them additional wide-binary candidates. The latter also shows a short period at 1.18 hr. We then present CTSS 2 and K 3-5, which show brightening and significant reddening over the whole ZTF baseline. A stellar model fit to the optical spectrum of CTSS 2 reveals it to be one of the youngest post-AGB CSPNe known. Both show high-density emission-line cores. We propose these to be late-thermal-pulse candidates, currently evolving towards the AGB phase. We then present recent HST/COS ultraviolet spectroscopy of the known wide-binary candidate LoTr 1, showing that the hot star is a spectroscopic twin of the extremely hot white dwarf in UCAC2 46706450. Similar to this object, LoTr 1 also has a fast rotating wide subgiant companion. We suggest that the long photometric period of 11 yr is the binary orbital period. Finally, we briefly discuss the ZTF light curves of the remaining variables, namely Tan 2, K 3-20, WHTZ 3, Kn J1857+3931, and IPHAS J1927+0814. With these examples, we present the effectiveness of the von Neumann statistics and Pearson Skew-based metric space in searching for long-timescale variables. *Based in part on observations obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians-Universität München, and Georg-August Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

Keywords: Post-asymptotic giant branch stars, Binary stars, Light curves, Planetary nebulae nuclei, Planetary nebulae, Wide binary stars
Radial Velocity Strategies for the Orbital Refinement of Exoplanet Direct Imaging Targets. Many potential direct imaging candidates suffer from large orbital period uncertainties, leading to challenges in accurate predictions of future orbital positions and imprecise direct imaging measurements of planetary parameters. To improve the precision in orbital properties, precursor radial velocity (RV) follow-up observations for selected candidates are essential. This study examines the impact of three variables on the orbital period uncertainties of long-period giant planets: the number of future observations, the temporal gap between past and future data, and the temporal coverage of upcoming observations. Our simulations indicate that the orbital phases at which future RV observations are acquired play a significant role in reducing period uncertainties. Additionally, observing too frequently within a given time frame adds limited value to the program once a certain number of observations has been achieved. The temporal gap proves to be the most important factor when there is no strict end time to the observing campaign. However, if a strict end time is set, starting observations earlier yields improved reductions in orbital period uncertainty. These insights offer practical guidance for planning efficient RV follow-up campaigns to maximize the science yield of future space-based direct imaging missions.

Keywords: Radial velocity, Astronomical techniques, Astronomical methods, Exoplanets
HWO Target Stars and Systems: A Prioritized Community List of Potential Stellar Targets for the Habitable Worlds Observatory's ExoEarth Survey. The HWO Target Stars and Systems 2025 (TSS25) list is a community-developed catalog of potential stellar targets for the Habitable Worlds Observatory (HWO) in its survey to directly image Earth-sized planets in the habitable zone. The TSS25 list categorizes potential HWO targets into priority tiers based on their likelihood to be surveyed and the necessity of obtaining observations of their stellar properties prior to the launch of the mission. This target list builds upon previous efforts to identify direct imaging targets and incorporates the results of multiple yield calculations assessing the science return of current design concepts for HWO. The TSS25 list identifies a sample of target stars that have a high probability to be observed by HWO (Tiers 1 and 2), independent of assumptions about the mission's final architecture. These stars should be the focus of community precursor science efforts in order to mitigate risks and maximize the science output of HWO. This target list is publicly available and is a living catalog that will be continually updated leading up to the mission.

Keywords: Stellar properties, Exoplanets, Direct imaging, Planet hosting stars, Habitable planets
Three Binary-source Binary-lens Microlensing Events from the 2024 Microlensing Campaign. We investigated microlensing events detected by the Optical Gravitational Lensing Experiment (OGLE) and Korea Microlensing Telescope Network surveys during the 2024 observing season, focusing on those that exhibit very complex anomaly features. Through this analysis, we found that the light curves of three events including OGLE-2024-BLG-0657, KMT-2024-BLG-2017, and KMT-2024-BLG-2480 cannot be readily interpreted using standard three-body lensing models such as a binary lens with a single source (2L1S) or a single lens with a binary source (1L2S). In this work we present detailed analyses of these events to uncover the nature of their anomalous features. An initial analysis using 2L1S modeling of the light curves showed that while it was difficult to simultaneously explain all of the multiple anomaly features, the main anomaly feature could be accounted for. Based on this model, we conducted four-body modeling that includes an additional lens or source. Through this approach, we found that the complex anomalies observed in the three events could be explained by a 2L2S model, in which both the lens and the source are binaries. Analysis of the color and magnitude revealed that the source is a binary system consisting of G- and K-type main sequence stars for OGLE-2024-BLG-0657, two K-type main sequence stars for KMT-2024-BLG-2017, and a K-type star with an early G-type main sequence companion for KMT-2024-BLG-2480. A Bayesian analysis incorporating constraints from the lensing observables indicates that the lenses in KMT-2024-BLG-2017 and KMT-2024-BLG-2480 are likely binary systems of low-mass stars located in the Galactic bulge, whereas the lens system OGLE-2024-BLG-0657L is likely a binary composed of two stellar remnants situated in the Galactic disk.

Keywords: Gravitational microlensing
Long-term Trends of Precipitable Water Vapor and Temperature at the Delingha Observatory. Long-term variations in precipitable water vapor (PWV) and temperature are critical for ground-based astronomical observations at infrared, millimeter, and sub-millimeter wavelengths. This study presents a comprehensive 40 yr analysis (1984─2023) of atmospheric conditions at the Delingha Observatory on the northeastern Tibetan Plateau, based on ERA5 reanalysis and in situ measurements. The site exhibits a median PWV of 3.96 mm, with PWV remaining below 6.00 mm for approximately 63% of the time. The median temperature is 2.32°C, with a median nighttime variation amplitude of 11.97°C. Both PWV and temperature exhibit strong seasonal cycles, with highest values typically observed in summer (peaking in July) and lowest in winter (January). Statistically significant long-term trends are observed, with annual mean PWV increasing by +0.24 mm decade−1 and temperature rising by +0.42°C decade−1. Furthermore, the observed correlations suggest that PWV is significantly modulated by the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO), while temperature also shows significant correlations with the El Niño-outhern Oscillation, in addition to the NAO and PDO, with phase lags ranging from 0 to 11 months. These findings highlight the importance of incorporating climate diagnostics into long-term planning for telescope scheduling and site management.

Keywords: Nonparametric hypothesis tests, Earth atmosphere, Observatories, Astronomical instrumentation, Time series analysis
Identification of Blue Straggler Stars Based on MultiScale Dilation and Attention Mechanisms. Blue straggler stars (BSSs) serve as vital tracers for investigating the dynamics and evolution of stellar systems, owing to their relatively higher luminosities and effective temperatures. However, traditional manual or semi-automated approaches to identifying BSSs are significantly constrained when processing large-scale astronomical data sets. Additionally, there is a notable absence of publicly available spectral data sets for BSSs, posing a challenge for research in this area. To address these issues, we initially construct spectral data sets for BSSs across various signal-to-noise ratio (SNR) thresholds. Furthermore, we propose an automated and efficient network called MDA-Net, which is based on Multiscale Dilation and Attention mechanisms for the BSS identification. The MDA-Net architecture integrates a MultiScale Dilated Large Kernel Convolution Block (MSDLC) and a Channel Group self-Attention Block (CGA). The MSDLC Block incorporates long and short convolution submodules with varying dilation rates to extract sufficient features across diverse receptive fields. Meanwhile, the CGA Block computes inter-channel attention scores, allowing the model to automatically focus on critical features. Experimental results demonstrate that MDA-Net consistently achieves the highest F1-score for the BSS category in all data sets with varying SNRs, reaching 85.79% even in low-SNR threshold data sets, 1.78% higher than the best baseline model. Notably, it reaches an impressive 90.22% when SNR &gt; 30. Extensive experiments indicate the superior performance and robustness of MDA-Net. These advancements offer a promising approach for further exploring the physical characteristics and dynamical behaviors of BSSs.

Keywords: Celestial objects catalogs, Stellar spectral types, Classification, Neural networks
Aligned, Multiple-transient Events in the First Palomar Sky Survey. Old, digitized astronomical images taken before the human spacefaring age offer a rare glimpse of the sky before the era of artificial satellites. In this paper, we present the first optical searches for artificial objects with high specular reflections near the Earth. We follow the method proposed in Villarroel et al. and use a transient sample drawn from Solano et al. We use images from the First Palomar Sky Survey to search for multiple (within a plate exposure) transients that, in addition to being point-like, are aligned along a narrow band. We provide a shortlist of the most promising candidate alignments, including one with ∼3.9σ statistical significance. These aligned transients remain difficult to explain with known phenomena, even if rare optical ghosting producing point-like sources cannot be fully excluded at present. We explore remaining possibilities, including fast reflections from highly reflective objects in geosynchronous orbit, or emissions from artificial sources high above Earth's atmosphere. We also find a highly significant (∼22σ) deficit of POSS-I transients within Earth's shadow when compared with the theoretical hemispheric shadow coverage at 42,164 km altitude. The deficit is still present though at reduced significance (∼7.6σ) when a more realistic plate-based coverage is considered. This study should be viewed as an initial exploration into the potential of archival photographic surveys to reveal transient phenomena, and we hope it motivates more systematic searches across historical data sets.

Keywords: Surveys, Search for extraterrestrial intelligence, Transient detection, Solar system astronomy