Sazuna/UAT_keywords huggingface dataset:
Mapping the Milky Way with Gaia BP/RP Spectra. III. The First Medium-resolution Follow-up Spectroscopy of Metal-poor Stars<SUP></SUP>. The Gaia BP/RP spectra provide an excellent opportunity to search for extremely metal-poor (EMP; [M/H] ≤ ─3.0) stars. In this study, we assess the potential of our Gaia BP/RP-based candidate catalog, vetting newly identified EMP candidates with higher-resolution follow-up observations. The candidates are selected based on the metallicity derived from BP/RP spectra and the goodness of fit. Fifteen candidates were observed with the Intermediate Dispersion Spectrograph (IDS) on the Isaac Newton Telescope to validate the sample. We analyzed the data with 1D local thermodynamic equilibrium models and assessed the reliability of the [C/Fe] estimates. Three well-studied metal-poor stars are included as a sanity check. For most targets, the metallicities estimated from IDS data agree well with those derived from BP/RP spectra. Five of these stars are EMP stars (four of them are newly identified), including two with [M/H] ≤ ─3.5, one of which is a carbon-enhanced metal-poor star. Reliable [C/Fe] estimates are obtained for eight stars. The efficiency in detecting EMP candidates (as eight candidates with [M/H] ≤ ─3.0 yielding five EMP stars) is estimated to be  63−24+19%  at a 68% confidence level, which is comparable to or higher than that of the Pristine-Gaia synthetic metallicity catalogue (38%), highlighting the potential of our method. *Termed medium resolution in this context, contrasting with the lower resolution of Gaia BP/RP spectra.

Keywords: Stellar abundances, CEMP stars, Metallicity, Population II stars
Analysis of Six Long-period Low-mass Eclipsing Binaries. The radius inflation is predominantly observed in short-period, low-mass stellar systems, while being rarely detected in long-period binaries. Using Transiting Exoplanet Survey Satellite photometric and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey data, we conducted a detailed photometric and spectroscopic analysis of six long-period (P &gt; 7 days) detached eclipsing binaries: TIC 17303250, TIC 196817076, TIC 219488423, TIC 252991035, TIC 344753509, and TIC 72696540. Our results indicate that the first five systems are composed of low-mass stars (M ≤ 0.8M⊙), while TIC 72696540 is likely composed of subgiant stars with M1 = 1.267 ± 0.011M⊙, R1 = 2.365 ± 0.043R⊙, and M2 = 1.281 ± 0.011M⊙, R2 = 2.517 ± 0.035R⊙. Their large radii are solely due to their evolutionary stage. Apart from TIC 72696540, none of the components of these systems displays a clear Li I λ6708 line. Under the assumption of binary rotational synchronization, the rotational velocities of these low-mass stars are found to be less than 8 km s−1, which is the upper limit related to the LAMOST-MRS resolution. Notably, however, significant radius inflation is evident in the systems TIC 17303250, TIC 344753509, and TIC 252991035. Their radii exceed the predictions of the 12 Gyr isochrones. A positive correlation between radius inflation and metallicity is evident in four of the five low-mass stars, with TIC 196817076 being the sole exception. These results suggest that metallicity may play a significant role in causing radius inflation.

Keywords: Eclipsing binary stars, Low mass stars, Late-type dwarf stars, Spectroscopic binary stars
Identification of Galactic H I Counterpart of the Large [O III] Emission Structure 1<inline-formula> <mml:math><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>°</mml:mtext></mml:mrow></mml:mover></mml:math> </inline-formula>2 Southeast of M31. Strottner─Drechsler─Sainty Object 1 (SDSO1) is a faint [O III] emission nebula spanning 1 .°5 , discovered southeast of M31. In previous surveys, no counterpart has been observed across radio, infrared, UV, and X-ray wavelengths, thus complicating distance determination. Utilizing the M31 H I survey with the Five-hundred-meter Aperture Spherical radio Telescope, we identified an atomic gas structure associated with SDSO1. This potential neutral gas counterpart includes three strips spatially aligned with the [O III] emission arcs. The H I structure has a velocity between −79 and −45 km s−1 with respect to the local standard of rest. It angularly extends to  2.°9 , surpassing SDSO1 in size. Several structures around the H I counterpart share similar velocities, hinting at a link between the H I counterpart and the Galactic disk's large-scale structure. The combined analysis of the three-dimensional dust map and the reddening─distance relations for these H I strips and their nearby H I structures suggests a distance of 2.0 ± 0.2 kpc. The mass of the H I counterpart is calculated to be 614M⊙. All of these results collectively demonstrate that SDSO1 is most likely a structure in the Milky Way rather than one associated with M31.

Keywords: Interstellar atomic gas, Neutral hydrogen clouds, Interstellar dust extinction, Interstellar clouds, Interstellar medium, Andromeda Galaxy
Multi-band Spectral and Astrometric Characterization of the HIP 99770 b Planet with SCExAO/CHARIS and Gaia<SUP></SUP>. We present and analyze follow-up, higher resolution (R ∼ 70) H and K band integral field spectroscopy of the superjovian exoplanet HIP 99770 b with SCExAO/CHARIS. Our new data recover the companion at a high SNR in both bandpasses and more than double the astrometric baseline for its orbital motion. Jointly modeling HIP 99770 b's position and the star's astrometry from Hipparcos and Gaia yields orbital parameters consistent with those from the discovery paper, albeit with smaller errors, and a slight preference for a smaller semimajor axis (∼15.7─15.8 au) and a larger eccentricity (∼0.28─0.29), disfavoring a circular orbit. We revise its dynamical mass slightly downwards to 15.0 −4.4+4.5  MJup for a flat prior and 13.1 −5.2+4.8  MJup for a more standard log-uniform mass prior, where the inclusion of its relative radial-velocity measurement is primarily responsible for these changes. We find consistent results for HIP 99770 b's dynamical mass, including recent VLTI/GRAVITY astrometry, albeit with a slightly smaller, better constrained eccentricity of e ∼ 0.22 −0.13+0.10 . HIP 99770 b is a ∼1300 K object at the L/T transition with a gravity intermediate between that of the HR 8799 planets and older, more massive field brown dwarfs with similar temperatures but with hints of equilibrium chemistry. HIP 99770 b is particularly well suited for spectroscopic follow-up with Roman Coronagraph Instrument during the technology demonstration phase at 730 nm to further constrain its metallicity and chemistry; JWST thermal infrared observations could likewise explore the planet's carbon chemistry, metallicity, and clouds. *Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: Direct imaging, Astrometry, Exoplanet atmospheres
A Wavelength-aware Unsupervised Learning Approach for Large, Multicolor, Photometric Surveys. Observational astronomy has undergone a significant transformation driven by large-scale surveys such as the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey, the Sloan Digital Sky Survey, and the Gaia Mission. These programs yield large, complex data sets that pose significant challenges for conventional analysis methods, and as a result many different machine learning techniques are being tested and deployed. We introduce a new approach to analyzing multiband photometry by using a long short-term memory autoencoder. This model provides input-dependent reweighting of the passbands on a star-by-star basis, enabling it to encode patterns present in the stars' spectral energy distributions (SEDs) into a two-dimensional latent space. We showcase this by using Pan-STARRS grizy mean magnitudes, and we use globular clusters, labels from SIMBAD, Gaia Data Release 3 parallaxes, and PanSTARRS images to aid our analysis and understanding of the latent space. For 3,112,259 stars in an annulus around the North Galactic Cap, 99.51% have their full SED shape reconstructed—that is, the absolute difference between the observed and the model-predicted magnitude in every band—within five-hundredths of a magnitude. We show that the model likely denoises photometric data, potentially improving the quality of measurements. Lastly, we show that the detection of rare stellar types can be performed by analyzing poorly reconstructed photometry.

Keywords: Stellar photometry, Astroinformatics, Sky surveys, Multi-color photometry, Classification, Neural networks, Astronomy data analysis, Nonlinear regression, Outlier detection, Stellar colors, Clustering, Interdisciplinary astronomy
CSST Slitless Spectra: Target Detection and Classification with Yolo. Addressing the spatial uncertainty and spectral blending challenges in China Space Station Telescope slitless spectroscopy, we present a deep learning-driven, end-to-end framework based on the You Only Look Once (YOLO) models. This approach directly detects, classifies, and analyzes spectral traces from raw 2D images, bypassing traditional, error-accumulating pipelines. YOLOv5 effectively detects both compact zero-order and extended first-order traces, even in highly crowded fields. Building on this, YOLO11 integrates source classification (star/galaxy) and discrete astrophysical parameter estimation (e.g., redshift bins), showcasing complete spectral trace analysis without other manual preprocessing. Our framework processes large images rapidly, learning spectral─spatial features holistically to minimize errors. We achieve high trace detection precision (YOLOv5) and demonstrate successful quasar identification and binned redshift estimation (YOLO11). This study establishes machine learning as a paradigm shift in slitless spectroscopy, unifying detection, classification, and preliminary parameter estimation in a scalable system. Future research will concentrate on direct, continuous prediction of astrophysical parameters from raw spectral traces.

Keywords: Detection, Space telescopes, Astronomical methods
K2-18b Does Not Meet the Standards of Evidence for Life. K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable debate, primarily around arguments that their absorption features are not uniquely identifiable. Here, we consider all five questions from the astrobiology standards of evidence framework, starting with the following: Have we detected an authentic signal? To answer this, we analyzed publicly available JWST observations of K2-18b using independent data reduction and spectral retrieval methodologies. Our comprehensive set of reductions demonstrates that the MIRI transit spectrum is highly susceptible to unresolved instrumental systematics. Applying different wavelength binning schemes yields a potpourri of planet spectra that then lead to a wide assortment of atmospheric interpretations. Consequently, we offer recommendations to help minimize this previously underappreciated instrument systematic in future MIRI reductions of any exoplanet. While the MIRI binning scheme adopted by N. Madhusudhan et al. (2025) favors the presence of DMS/DMDS in K2-18b, we find that 87.5% of retrievals using our preferred MIRI binning scheme do not. When considering the full 0.7─12 μm transit spectrum, we confirm the detection of CH4 and favor CO2 and find the presence of DMS and C2H4 to be interchangeable. Moreover, we find that the tentative presence of large features in the MIRI transit spectrum is in tension with the more robust, yet smaller, features observed in the near-IR. We conclude that red noise—rather than an astrophysical signal—plagues the mid-IR data, and there is, as yet, no statistically significant evidence for biosignatures in the atmosphere of K2-18b.

Keywords: Exoplanet atmospheric composition , Exoplanets, Astronomy data analysis, Biosignatures, Habitable planets, Exoplanet atmospheres
Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. III. Detectability of Giant Exomoons of Wide-separation Giant Planets. The Nancy Grace Roman Space Telescope (Roman) will conduct a Galactic Exoplanet Survey to discover bound and free-floating exoplanets using gravitational microlensing. Roman should be sensitive to lenses with mass down to ∼0.02 M⊕, or roughly the mass of Ganymede. Thus, the detection of moons with masses similar to the giant moons in our solar system is possible with Roman. Measuring the demographics of exomoons will provide constraints on both moon and planet formation. We conduct simulations of Roman microlensing events to determine the effects of exomoons on microlensing light curves, and whether these effects are detectable with Roman. We focus on giant planets from 30 M⊕ to 10 MJup on orbits from 0.3 to 30 au, and assume that each planet is orbited by a moon with moon─planet mass ratio from 10−4 to 10−2 and separation from 0.1 to 0.5 planet Hill radii. We find that Roman is sensitive to exomoons, although the number of expected detections is only on the order of one over the duration of the survey, unless exomoons are more common or massive than we assumed. We argue that changes in the survey strategy, in particular focusing on a few fields with higher cadence, may allow for the detection of more exomoons with Roman. Regardless, the ability to detect exomoons reinforces the need to develop robust methods for modeling triple lens microlensing events to fully utilize the capabilities of Roman.

Keywords: Gravitational microlensing exoplanet detection, Natural satellites (Extrasolar), Exoplanets
Exploring Giant Barium Stars:<SUP>12</SUP>C/<SUP>13</SUP>C Ratio and Elemental Abundances of Carbon, Nitrogen, and Oxygen. Barium (Ba) stars belong to binary systems that underwent mass-transfer events. As a consequence, their envelopes were enriched with material synthesized in the interiors of their evolved companions via slow neutron-capture nucleosynthesis, the s-process. As postinteracting binaries, Ba stars figure as powerful tracers of the s-process. In this study, we conduct a classical local thermodynamic equilibrium analysis for a sample of 180 Ba giant stars to find complementary insights for the s-process, in form of elemental abundances of carbon, nitrogen, and oxygen, as well as the 12C/13C ratio. We found carbon abundances systematically larger than those observed in normal giants, with [C/Fe] ratios ranging within from −0.30 to +0.60 dex. As expected, the [C/Fe] ratios increase for lower metallicity regimes and are strongly correlated with the average s-process abundances. Nitrogen abundances have a flat behavior around [N/Fe] ∼ +0.50 dex and are moderately correlated with sodium abundances. Except for HD 107541, the entire sample shows C/O &lt; 1. We found 12C/13C &lt; 20 for ∼80% of the sampled stars and 12C/13C &gt; 60 for three objects. *The program stars were observed under the programs ID 079.A-9200(A), 080.A-9206(A), 081.A-9203(A), 082.A-9200(A), 083.A-9206(A), 084.A-9205(A), and 085.A-9202(A), under agreement between Observatório Nacional (Brazil) and European Southern Observatory (ESO).

Keywords: Stellar abundances, Asymptotic giant branch stars, Stellar nucleosynthesis, Chemically peculiar giant stars
The New SDSS 2.5 m Telescope Wide-field Corrector for SDSS-V. SDSS-V is the fifth generation of the Sloan Digital Sky Survey and is an ambitious follow-up to a project that has been producing ground-breaking science for more than two decades. SDSS-V uses two dedicated 2.5 m telescopes—the SDSS telescope at Apache Point Observatory in New Mexico and the du Pont telescope at Las Campanas Observatory in Chile—feeding the BOSS and APOGEE spectrographs at each site. These survey machines generate multiobject, all-sky spectroscopy in the optical and near-infrared in support of primary science programs. The new wide-field corrector for the SDSS 2.5 m telescope is one of several major infrastructure upgrades undertaken for SDSS-V, necessitated by the replacement of the legacy fiber plug plate system with a new robotic Focal Plane System (FPS), which places different requirements on the focal characteristics of the telescope. The original two-element corrector produced a focal surface that was nontelecentric and suffered from axial color, throughput, and image quality issues when used in the H band with the APOGEE spectrograph. We have designed and built a three-element fused silica corrector that addresses the optical shortcomings in relation to the FPS. This paper discusses the optical and optomechanical design details of the new wide-field corrector, provides a detailed description of the assembly, integration, and test effort, and concludes with a description of the commissioning effort and on-sky performance.

Keywords: Astronomical instrumentation, Spectroscopy, Wide-field telescopes
Primordial Black Holes as Coma Cluster Dark Matter and the Unresolved γ-Ray Background. If 0.1% of the dark matter (DM) in the Coma cluster is primordial black holes of mass between 1 and 100 × 10−19 M⊙, then the GeV radiation from the cluster may be Hawking radiation. Dark Energy Survey has mapped the DM in the largest weak lensing maps so far produced. A correlation between the unresolved γ-ray background and large scale structure has been noted. This correlation might find a natural explanation if some of the DM is evaporating primordial black holes, but no correlation is seen. We draw attention to a cluster of Coma-like x-ray clusters, Draco X, at redshift 0.12.

Keywords: Cosmology, Cold dark matter, Galaxy clusters, Primordial black holes
Detection of a Deeply Embedded Protocluster Candidate in NGC 602 with JWST. JWST NIRCam and MIRI photometry of NGC 602, a low-metallicity young star cluster in the Small Magellanic Cloud, reveals an extended mid-infrared bright emission feature designated as MZS-1. This feature is prominent between 10 and 25.5 μm, but is extremely faint at 7.7 μm and entirely undetected at shorter wavelengths. MZS-1 exhibits an elliptical morphology with a major axis of approximately 8″ and a minor axis of about 4″. Its elongated shape and multiple emission peaks in the two-dimensional flux map suggest a group of deeply embedded sources with blackbody-like temperatures ranging from 100 K to 140 K. Spectral energy distribution fitting using the T. P. Robitaille (2017) model grids identifies these sources as Stage I young stellar objects (YSOs) with masses below ∼3 M⊙ and total stellar mass of the protocluster ≍∼300 M⊙ (based on Salpeter IMF). The low YSO masses are consistent with their absence in Spitzer-based catalogs due to sensitivity limits. By revealing a deeply embedded, low-mass protocluster invisible in previous surveys, this work highlights JWST's unparalleled resolution and sensitivity in uncovering the earliest stages of low-mass cluster formation in the metal-poor regime.

Keywords: Young stellar objects
An Interpretable AI Framework to Disentangle Self-interacting and Cold Dark Matter in Galaxy Clusters: The CKAN Approach. Convolutional neural networks have shown their ability to differentiate between self-interacting dark matter (SIDM) and cold dark matter on galaxy cluster scales. However, their large parameter counts and "black-box" nature make it difficult to assess whether their decisions adhere to physical principles. To address this issue, we have built a convolutional Kolmogorov─Arnold network (CKAN) that reduces parameter count and enhances interpretability, and propose a novel analytical framework to understand the network's decision-making process. With this framework, we leverage our network to qualitatively assess the offset between the dark matter distribution center and the galaxy cluster center, as well as the size of heating regions in different models. These findings are consistent with current theoretical predictions and show the reliability and interpretability of our network. By combining network interpretability with unseen test results, we also estimate that for SIDM in galaxy clusters, the minimum cross section (σ/m)th required to reliably identify its collisional nature falls between 0.1 and 0.3 cm2 g−1. Moreover, CKAN maintains robust performance under simulated JWST and Euclid noise, highlighting its promise for application to forthcoming observational surveys.

Keywords: Galaxy dark matter halos, Neural networks
The NEID Earth Twin Survey. III. Survey Performance after Three Years on Sky. The NEID Earth Twin Survey (NETS) has been delivering a rich set of precise radial velocity (RV) measurements for 41 bright, nearby main-sequence stars. Here, we describe the status of the survey after 3 yr on sky, and we present the full set of RV measurements and accompanying stellar activity indicators. We discuss intermediate survey diagnostics, including calibration of the known RV zero-point offset introduced following the Contreras fire in 2022 and the identification of an undiagnosed and previously unknown zero-point offset in 2021. An analysis of our data set using RVSearch demonstrates that for these target stars, NEID is independently sensitive to nearly all known planets with periods shorter than the NETS observing baseline. We also highlight a number of newly detected RV signals, which present exciting opportunities for future investigations.

Keywords: Exoplanet astronomy, Exoplanet detection methods, Radial velocity, Surveys
Extreme Starlight Polarization Efficiency toward ζ Ophiuchi: A Case for Line-of-sight Foreground Subtraction. Despite the pervasive nature of interstellar dust and its impact on nearly all observations, most dust corrections employ line-of-sight averages over large angular scales. This neglects real variations on small angular and distance scales from discrete components of the interstellar medium (ISM). We use V-band polarimetry, public dust maps, and Gaia Data Release 3 distances of 25 stars along a 50' radius sight line toward the O9.5IV star ζ Ophiuchi (d ≍ 182 pc) to examine both dust and magnetic structures over the range d = 36─1176 pc and angular scales of &lt;1°. Polarization and reddening data indicate two discrete dust populations having different magnetic field orientations along the sight line, one at d ≃ 86─127 pc and another at d ≃ 252─287 pc. After removal of the foreground, the more distant component exhibits alignment in polarization angle with 12 μm polycyclic aromatic hydrocarbon (PAH) striations seen in the field. This more distant dust population exhibits evidence of extreme starlight polarization efficiency, with an average of 14.1% mag−1, greater than the canonical Serkowski limit of 9% mag−1. The spatial coincidence with the PAH striations indicates the PAH-emitting grains and those responsible for the high polarization efficiency may be components of the same dust population. We find no evidence that ζ Oph's radiative influence affects the polarizing or reddening properties of the surrounding dust. Our study demonstrates that accurate distance-based foreground subtraction is vital to properly understanding superimposed dust and the magnetic field components in the ISM.

Keywords: Interstellar dust, Interstellar dust extinction, Interstellar magnetic fields, Starlight polarization, Interstellar reddening