Sazuna/UAT_keywords huggingface dataset:
UNIONS: The Ultraviolet Near-infrared Optical Northern Survey. The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada─France─Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain ugriz images of a core survey region of 6250 deg2 of the northern sky. The 10σ point source depth of the data, as measured within a 2″ diameter aperture, are [u, g, r, i, z] = [23.7, 24.5, 24.2, 23.8, 23.3] in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become a major ground-based legacy survey for the northern hemisphere for the next decade, and it provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the Euclid space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the Euclid point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for Euclid, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program.

Keywords: Weak gravitational lensing, Galactic archaeology, Sky surveys, Stellar streams
In-flight Performance of the IXPE Telescopes. We present a comprehensive characterization of the on-orbit imaging performance of the three telescopes on board the Imaging X-ray Polarimetry Explorer (IXPE). Each telescope comprises a Wolter-I mirror module assembly and a Gas Pixel Detector focal-plane detector unit. We analyze data from point-like X-ray sources and fit a composite point-spread function (PSF) model that we compare with ground calibrations. We study the dependence of the PSF parameters and of the angular resolution, in terms of half-power diameter (HPD), on the time and source counting rate. We find no significant secular evolution of PSF parameters or HPD over 30 months on orbit, with average HPDs of 26 .″ 1 ± 0 .″ 5 (Telescope 1), 32 .″ 1 ± 0 .″ 5 (Telescope 2), and 30 .″ 9 ± 0 .″ 6 (Telescope 3) and rate trends consistent with zero up to source counting rates of ∼60 cts s−1 in the 2─3 keV energy band for all three telescopes. We set a 99% C.L. upper limit of 4.4% on the optics-induced polarization in the PSF halo and find no measurable degradation of the polarization modulation factor in the wings versus the core due to misreconstructed photoelectron tracks. IXPE's imaging performance thus is consistent with the ≤30″ observatory requirement with high stability, ensuring robust spatially resolved polarization measurements for the mission's projected lifetime through 2030.

Keywords: Polarimetry, X-ray telescopes
Direct Spectroscopy of 51 Eridani b with JWST NIRSpec. We present high-contrast direct spectroscopy of the low-mass, cool exoplanet 51 Eridani b (2─4 MJup, ∼750 K) using JWST/NIRSpec in a fixed-slit configuration (F290LP/G395H, 3─5 μm, R ∼ 2700). A cross-correlation analysis between the continuum-subtracted data and atmospheric forward models indicates a detection of molecular signals of planetary origin at 4.8σ at the expected position and velocity of the planet. The detection of the planetary signal is driven primarily by molecular features from methane and carbon monoxide, providing the first direct confirmation of these two molecules coexisting in chemical disequilibrium in the atmosphere of 51 Eridani b. A new comprehensive atmospheric model analysis shows consistency between the ground-based IFU spectroscopy and the NIRSpec data, with the best-fit model parameters Teff = 800 −55.5+21.5  K,  logg  = 3.75 −0.37+0.09 , [M/H] = 0.7 −0.21+0.07 , C/O = 0.458 −0.09+0.08 ,  logKzz  = 3 −0.73+0.47 , RP = 1.36 −0.03+0.07  RJup, and fhole = 0.3 −0.07+0.10 , and the NIRSpec error bar inflation parameter  ê  = 1.74 −0.03+0.02 . We conclude with a discussion on the lessons learned between the fixed slit and IFU-based high contrast spectroscopic methods from our observing program, including some possibilities to improve the analysis method.

Keywords: High contrast spectroscopy, Exoplanet atmospheres
Machine Learning Techniques to Distinguish Giant Stars from Dwarf Stars Using Only Photometry—Pushing Redward. We present our photometric method, which combines Subaru/Hyper Suprime-Cam N B515, g-band, and i-band filters to distinguish giant stars in Local Group galaxies from Milky Way dwarf contamination. The N B515 filter is a narrowband filter that covers the MgI+MgH features at 5150 Å and is sensitive to stellar surface gravity. Using synthetic photometry derived from large empirical stellar spectral libraries, we model the N B515 filter's sensitivity to stellar atmospheric parameters and chemical abundances. Our results demonstrate that the N B515 filter effectively separates dwarfs from giants, even for the reddest and coolest M-type stars. To further enhance this separation, we develop machine learning models that improve the classification on the two-color (g − i, N B515 − g) diagram. We apply these models to photometric data from the Fornax dwarf spheroidal galaxy and two fields of M31, successfully identifying red giant branch stars in these galaxies.

Keywords: Local Group, Stellar populations, Galactic archaeology, Dwarf galaxies, Photometry, Narrow band photometry, Andromeda Galaxy, Galaxies
A Near-infrared Extinction and Reddening Map toward the Galactic Bulge Using UKIRT. The Galactic bulge is one of the most information-dense regions to study resolved stellar populations, variables, and transients, such as microlensing events. Studies toward the Galactic bulge are complicated by the large and variable extinction along the line of sight. We measure the near-infrared  AKS  extinction and E(H − KS) reddening in this region using H- and K-band photometry obtained with the 2017 UKIRT microlensing survey. We fit the apparent magnitude and color distribution of bright giants in the bulge to recover the apparent magnitude and color of Red Clump stars, which are known to be standard candles and crayons. We present  2'×2' resolution maps in UKIRT fields between −2 .° 15 ≤ l ≤ 2 .° 71 and −2 .° 69 ≤ b ≤ 2 .° 03 of the  AKS  extinction and the E(H − KS) reddening. We find large variations in the KS-band extinction and E(H − KS) reddening on all the scales we probe. We find that a constant, standard extinction law is a poor representation of the relationship between the extinction and reddening we measure in fields of different latitudes. These maps will be useful for understanding the near-infrared extinction law for sight lines close to the Galactic plane, as well as for final field selection for the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey.

Keywords: Red giant clump, Extinction, Interstellar reddening, Interstellar extinction, Near infrared astronomy
The Dynamical Environment within the Habitable Zone of the Gaia-4 and Gaia-5 Planetary Systems. Exoplanetary systems exhibit a broad range of architectures, which, in turn, enables a variety of dynamical environments. Many of the known planetary systems do not transit the host star, and so we measure the minimum masses of their planets, making it difficult to fully assess the dynamical environment within the system. Astrometry can resolve the mass ambiguity and thus allow a more complete dynamical analysis of systems to be conducted. Gaia-4 and Gaia-5 are two such systems, whose study with radial velocities and data from the Gaia mission revealed that each star harbors a massive planet on a highly eccentric orbit. In this work, we provide the results of a dynamical analysis of each system, including calculations of the Habitable Zone (HZ), from which we show that the presence of the known companions largely excludes the presence of planets within the HZ. We discuss the diagnostics of potential past planet─planet scattering events, and the occurrence of similar systems whereby a giant planet on an eccentric orbit can substantially disrupt the orbital integrity of terrestrial planets. These "wrecking ball" systems have an impact on the target selection for planned direct imaging missions that seek to identify potentially habitable environments.

Keywords: Exoplanet dynamics, Exoplanets, Exoplanet systems, Orbital evolution, Exoplanet astronomy, Keplerian orbit, Habitable zone, Habitable planets
The Influence of Tight Binaries on Protoplanetary Disk Masses. Binary systems are a common site of planet formation, despite the destructive effects of the binary on the disk. While surveys of planet-forming material have found diminished disk masses around binaries with medium separation (∼10─100 au), less is known about tight (&lt;10 au) binaries, where a significant circumbinary disk may escape the disruptive dynamical effects of the binary. We survey over 100 spectroscopic binaries in the Orion A region with the Atacama Large Millimeter/submillimeter Array (ALMA), detecting significant continuum emission among 21 of them with disk masses ranging from 1 to 100 M⊕. We find evidence of systematically lower disk masses among the binary sample when compared to single-star surveys, which may reflect a diminished planet-forming potential around tight binaries. The infrared excess fraction among the binary sample is comparable to that of single stars, although the tight binaries without significant ALMA emission display tentative evidence of weaker 3─5 μm excesses. The depletion of cold dust is difficult to explain by clearing alone, and the role of additional mechanisms needs to be explored. It may be the result of the formation pathway for these objects, systematic differences in intrinsic properties (e.g., opacity) or a bias in how the sample was constructed.

Keywords: Spectroscopic binary stars, Binary stars, Protoplanetary disks
Eclipse Depth Variations in Seven Eclipsing Binaries as Observed by KELT and TESS. A set of eclipsing binary systems exhibit a changing inclination over time due to the gravitational influence of a third stellar companion. These changing inclinations manifest in photometric observations over time as eclipse depth variations. To detect changing eclipse depths, it is advantageous to have a long time baseline of observations, which can be attained by combining data from multiple surveys. We collect ground-based photometry from the Kilodegree Extremely Little Telescope and space-based photometry from the Transiting Exoplanet Survey Satellite (TESS) for seven known changing-inclination eclipsing binaries: HS Hya, RW Per, IU Aur, AH Cep, SV Gem, V685 Cen, and SS Lac. We measure eclipse depth variations and eclipse timing variations in six systems; SS Lac no longer eclipses. As of observations presented here from TESS Sector 35, eclipses are no longer visible in HS Hya (as noted in J. R. A. Davenport et al. 2021). SV Gem, previously believed to have stopped eclipsing, exhibits eclipse-like features across all years of observation, as well as evidence of the negative "O'Connell Effect." We also present high-resolution speckle imaging from Gemini-North, Gemini-South, and the NESSI instrument on the WIYN telescope for RW Per, AH Cep, SV Gem, and SS Lac, none of which revealed a third companion. Speckle imaging of IU Aur from NESSI revealed the presence of a third companion at an angular separation of ∼0 .″ 14; we report the details of this detection.

Keywords: Eclipsing binary stars, Binary stars
Hα Emission among Evolved FGKM Stars: A Compendium from the Literature. Emission in the wings of the Hα line among late-type giant stars occurs as a consequence of conditions in their chromospheres. Data from the literature have been used to document the incidence of Hα emission among Population I giant stars as a function of position in various color─magnitude diagrams (CMDs), including infrared versions that plot  MKs  versus (J − Ks) and (V − Ks). Population I and metal-poor Population II red giants are compared with regard to certain characteristics of Hα emission. In the case of stars with emission, both observed photometry and photometry corrected for interstellar reddening are considered. Population I and II giants having Hα emission are found to share a number of phenomena: (a) they occupy similar regions of the visual and infrared CMDs; (b) the emission in the blue and red wings is often of unequal strength, suggestive of mass motions in the chromosphere; (c) there are indications of time variability for a few stars that have been observed on multiple occasions; (d) red giants of both Population I and II having Hα emission are often long-period or semiregular variables; and (e) a subset of them, but by no means all, evince circumstellar dust. While some giants with Hα emission are pulsating red variables that have formed dusty circumstellar envelopes, others may be in prior phases of evolution where pulsations have commenced, which is restructuring the chromosphere and producing outflows, but has not yet generated the conditions needed for dust formation at higher circumstellar altitudes.

Keywords: Hertzsprung Russell diagram, Stellar chromospheres, Circumstellar dust, Red giant stars
Extending the [C/N]─Age Calibration: Using Globular Clusters to Explore Older and Metal-poor Populations. In the coming years, detailed chemical abundances from large-scale high-resolution spectroscopic surveys will become available for vast numbers of stars across the Milky Way. Previous work has suggested that abundance ratios from these spectra can allow us to estimate ages from a large number of stars. These data will be leveraged to calibrate chemical clocks to age-date field stars, as reliable stellar ages remain elusive. In this work, we extended our empirical relationship between stellar age and their carbon-to-nitrogen ([C/N]) abundance ratio for evolved stars to older and more metal-poor stars by combining the original open cluster calibration sample and four globular clusters: 47 Tuc, M 71, M 4, and M 5. With this extension, [C/N] can be used as a chemical clock for evolved field stars to investigate not only regions within the metal-rich disk but also more metal-poor regions of our Galaxy. We have established the [C/N]─age relationship for Apache Point Observatory Galactic Evolution Experiment (APOGEE) DR17 red giant stars, which have experienced the first dredge-up but have not yet undergone any extramixing, in clusters usable for ages between  8.62≤log(Age[yr])≤10.13  and for metallicities of −1.2 ≤ [Fe/H] ≤ +0.3. This relationship can be uniformly applied to these stars within the APOGEE DR17 sample. This measured [C/N]─age APOGEE DR17 relationship is also shown to be consistent with stellar ages derived from asteroseismic results of APOKASC and APO-K2.

Keywords: Stellar ages, Abundance ratios, Chemical abundances, Open star clusters, Galactic abundances
Metallicity Regulates Planet Formation across All Masses. The role of stellar metallicity in shaping planetary systems is central to our understanding of planet formation. While the core accretion paradigm is widely accepted as the dominant mechanism for forming low- and intermediate-mass planets, the origin of the most massive planets remains debated, with gravitational instability often invoked to explain their existence. In this study, we analyze the dependence of planet formation on metallicity using the total heavy-element mass fraction (Z), which is a proxy for the composition of the protoplanetary disk inferred from stellar photospheres. We show that even the most massive planets form preferentially in metal-rich environments. Z correlates not only with the presence of planets, but also with planetary system multiplicity and total planetary mass. The most massive planets are found in the most metal-rich environments, and in agreement with core-accretion theory, only the upper end of the planetary mass distribution shows a clear positive correlation with metallicity. These findings suggest that the chemical enrichment of protoplanetary disks plays a central role in shaping the full spectrum of planetary masses.

Keywords: Stellar abundances, Exoplanet formation, Exoplanet systems, Exoplanets
An Earthlike Density for the Temperate Earth-sized Planet GJ 12 b. While JWST has provided us with the opportunity to probe the atmospheres of potentially habitable planets, observations of the TRAPPIST-1 system have shown us that active stars severely complicate efforts at studying their planets. GJ 12 b is a newly discovered temperate (Teq ≍ 300 K), Earth-sized (Rp = 0.96 ± 0.05 R⊕) planet orbiting an inactive M dwarf that might be a good alternate to the TRAPPIST-1 planets for atmospheric characterization. In this paper, we use MAROON-X radial velocities to measure a mass of 0.70 ± 0.10 M⊕ for GJ 12 b. We also recover a planetary eccentricity of 0.24, but there is no strong evidence that the planet has an eccentric orbit. GJ 12 b's mass results in a planetary density comparable to or less dense than that of Earth, possibly indicating the presence of water or a low bulk iron mass fraction. With its low mass, GJ 12 b is likely within reach of JWST transmission spectroscopy observations, making it an excellent target for determining the location of the cosmic shoreline. Its low mass may mean that the planet could have trouble retaining its primary atmosphere during the star's active pre-main-sequence phase. However, if it has a heightened eccentricity, it may be able to sustain a secondary atmosphere through tidally induced volcanism.

Keywords: M dwarf stars, Radial velocity
Kepler-1624b Has No Significant Transit Timing Variations. It is relatively rare for gas giant planets to have resonant or near-resonant companions, but these systems are particularly useful for constraining planet formation and migration models. In this study, we examine Kepler-1624b, a sub-Saturn orbiting an M dwarf that was previously found to exhibit transit timing variations (TTVs) with an amplitude of approximately 2 minutes, suggesting the presence of a nearby nontransiting companion. We reanalyze the transits from archival Kepler data and extend the TTV baseline by 11 yr by combining TESS data with three new ground-based transit observations from Palomar and Las Cumbres Observatories. We jointly fit these datasets and find that the TTV amplitude is significantly weaker in our updated analysis. We calculate the Bayes factor for a one-planet versus two-planet model and find that the one-planet model is preferred. Our results highlight the need for careful analysis of systems with relatively low amplitude TTV signals that are identified in large automated catalogs.

Keywords: Exoplanet dynamics, Transits, Exoplanets, Transit timing variation method, Exoplanet detection methods
Investigating the Effects of Point Source Injection Strategies on KMTNet Real/Bogus Classification. Recently, machine learning-based real/bogus (RB) classifiers have demonstrated effectiveness in filtering out artifacts and identifying genuine transients in real-time astronomical surveys. However, the rarity of transient events and the extensive human labeling required for a large number of samples pose significant challenges in constructing training data sets for RB classification. Given these challenges, point source injection techniques, which inject simulated point sources into optical images, provide a promising solution. This paper presents the first detailed comparison of different point source injection strategies and their effects on classification performance within a simulation-to-reality framework. To this end, we first construct various training data sets based on random injection (RI), near galaxy injection (NGI), and a combined approach by using the Korea Microlensing Telescope Network data sets. Subsequently, we train convolutional neural networks on simulated cutout samples and evaluate them on real, imbalanced data sets from gravitational wave follow-up observations for GW190814 and S230518h. Extensive experimental results show that RI excels at asteroid detection and bogus filtering but underperforms on transients occurring near galaxies (e.g., supernovae). In contrast, NGI is effective for detecting transients near galaxies but tends to misclassify variable stars as transients, resulting in a high false positive rate. The combined approach effectively handles these trade-offs, thereby balancing between detection rate and false positive rate. Our results emphasize the importance of point source injection strategy in developing robust RB classifiers for transient (or multimessenger) follow-up campaigns.

Keywords: Convolutional neural networks, Transient detection, Astronomy image processing
The PRime-focus Infrared Microlensing Experiment (PRIME): First Results. We present the description of the instruments and the first results of the PRime-focus Infrared Microlensing Experiment (PRIME). PRIME is the first dedicated near-infrared (NIR) microlensing survey telescope, and is located at the South African Astronomical Observatory in Sutherland, South Africa. Among its class, it offers one of the widest fields of view in the NIR regime. PRIME's main goals are (1) to study planetary formation by measuring the frequency and mass function of planets. In particular, we compare results from the central Galactic bulge (GB), accessible only in the NIR by PRIME, with those from the outer GB by optical surveys. (2) To conduct concurrent observations with NASA's Nancy Grace Roman Space Telescope. Due to the different lines of sight between the ground and space, we detect slight variations in light curves, known as "space-based parallax." This effect allows us to measure the mass of lens systems and their distance from the Earth. It is the only method to measure the mass of free-floating planets down to Earth mass. We began the GB survey in 2024 February and analyzed images through 2025 June 1, identifying 486 microlensing candidates and over a thousand variable stars, including Mira variables, which are useful for studying the Galactic structure. We issue real-time alerts for follow-up observations, supporting exoplanet searches and the chemical evolution studies in the GB. During the off-bulge season, we conduct an all-sky grid survey and target-of-opportunity observations of transients, including gravitational-wave events, γ-ray bursts, and other science.

Keywords: Gravitational microlensing exoplanet detection, Galactic bulge
Binary-lens Microlensing Degeneracy: Impact on Planetary Sensitivity and Mass-ratio Function. Gravitational microlensing is a unique method for discovering cold planets across a broad mass range. Reliable statistics of the microlensing planets require accurate sensitivity estimates. However, the impact of the degeneracies in binary-lens single-source (2L1S) models that affect many actual planet detections is often omitted in sensitivity estimates, leading to potential self-inconsistency of the statistics studies. In this work, we evaluate the effect of the 2L1S degeneracies on planetary sensitivity by simulating a series of typical microlensing events and comprehensively replicating a realistic planet detection pipeline, including the anomaly identification, global 2L1S model search, and degenerate model comparison. We find that for a pure-survey statistical sample, the 2L1S degeneracies reduce the overall planetary sensitivity by 5%─10%, with the effect increasing at higher planet-host mass ratios. This bias leads to an underestimation of planet occurrence rates and a flattening of the inferred mass-ratio function slope. This effect will be critical for upcoming space-based microlensing surveys like the Roman or Earth 2.0 missions, which are expected to discover  O(103)  planets. We also discuss the computational challenges and propose potential approaches for future applications.

Keywords: Gravitational microlensing, Exoplanet detection methods, Gravitational microlensing exoplanet detection