Sazuna/UAT_keywords huggingface dataset:
JWST 1.5 μm and 4.8 μm Photometry of Y Dwarfs. Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric data set of Y dwarfs: 23 were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and three using NIRISS with the F480M filter. We present an F480M versus F150W – F480M color–magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by S. A. Beiler et al. For one target, WISEA J083011.95+283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W – F480M = 9.62 mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum, which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low mass and young. We update the resolved photometry for the close binary system WISE J033605.05–014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83–071442.5, with Teff ≲ 300 K, however the F150W – F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by J. D. Kirkpatrick et al. and F. Marocco et al.

Keywords: Stellar atmospheres, Brown dwarfs, Space astrometry, Infrared photometry
Study of Self-lensing/Eclipsing Signals in Edge-on Double White-dwarf Systems. Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by the observer. Here, we study the characterization and detection of these signals. In common DWDs, the Einstein radii have similar orders of magnitude to the radii of the white dwarfs (WDs), and the projected source and lens radii normalized to the Einstein radius (ρ⋆ and ρl) are ∼1. Both of them are reduced with the orbital period and the lens mass. If ρl ≃ 1 the lensing-induced minor image is always blocked by the lens, which results in lower magnification factors. If ρl ≲ 1, and in transit events, the finite-lens effects decrease the light curves' width. When ρl ≳ 1 (which happens for close DWDs consisting of a low-mass WD and a massive one) deep or complete eclipses dominate over lensing effects. The self-lensing signals are maximal for massive DWDs in wide orbits. We study the detectability of lensing/eclipsing signals in edge-on DWDs in observations by NASA's Transiting Exoplanet Survey Satellite (TESS), the Vera Rubin Observatory Large Synoptic Survey Telescope (LSST), and the Nancy Grace Roman Space Telescope. We simulate stellar light curves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency is maximal for extremely low-mass WDs in close orbits, and the numbers of DWDs within 100 pc and an observing cone with detectable lensing/eclipsing signals in one observing window of 27.4 days for TESS and 62 days for Roman are ∼1 and &lt;1, respectively. Detecting these signals by LSST is barely possible because of its long cadence.

Keywords: Eclipses, Monte Carlo methods, Compact binary stars, Gravitational lensing, Compact objects
Water in Protoplanetary Disks with JWST-MIRI: Spectral Excitation Atlas and Radial Distribution from Temperature Diagnostic Diagrams and Doppler Mapping. This work aims at providing fundamental general tools for the analysis of water spectra as observed in protoplanetary disks with JWST-MIRI. We analyze 25 high-quality spectra from the JDISC Survey reduced with asteroid calibrators as presented in K. M. Pontoppidan et al. (2024). First, we present a spectral atlas to illustrate the clustering of H2O transitions from different upper-level energies (Eu) and identify single (unblended) transitions that provide the most reliable measurements. With that, we demonstrate two important excitation effects: the opacity saturation of ortho-para line pairs that overlap, and the subthermal excitation of excitation of v = 1–1 lines scattered across the v = 0–0 rotational band. Second, we define a shorter list of fundamental lines spanning Eu = 1500–6000 K to develop simple line-ratio diagnostic diagrams for the radial temperature distribution of water in inner disks, which are interpreted using discrete temperature components and power-law radial gradients. Third, we report the detection of disk-rotation Doppler broadening of molecular lines, which confirms the radial distribution of water emission including, for the first time, the radially extended ≈170–220 K reservoir close to the snowline. The combination of measured line ratios and broadening suggests that drift-dominated disks have shallower temperature gradients with an extended cooler disk surface enriched by ice sublimation. We also report the first detection of an H2O-rich inner disk wind from narrow blueshifted absorption in the ro-vibrational lines. We summarize these findings and tools into a general recipe to make the study of water in planet-forming regions reliable, effective, and sustainable for samples of &gt;100 disks.

Keywords: Infrared spectroscopy, Molecular spectroscopy, Classical T Tauri stars, Young stellar objects, Pre-main sequence stars, Star formation, Protoplanetary disks, Circumstellar disks, Exoplanet formation, Planet formation
TESS Hunt for Young and Maturing Exoplanets (THYME). XII. A Young Mini-Neptune on the Upper Edge of the Radius Valley in the Hyades Cluster. We present the discovery and characterization of TOI-4364b, a young mini-Neptune in the tidal tails of the Hyades cluster, identified through TESS transit observations and ground-based follow-up photometry. The planet orbits a bright M dwarf (K = 9.1 mag) at a distance of 44 pc, with an orbital period of 5.42 days and an equilibrium temperature of   K. The host star's well-constrained age of 710 Myr makes TOI-4364b an exceptional target for studying early planetary evolution around low-mass stars. We determined a planetary radius of  , indicating that this planet is situated near the upper edge of the radius valley. This suggests that the planet retains a modest H/He envelope. As a result, TOI-4364b provides a unique opportunity to explore the transition between rocky super-Earths and gas-rich mini-Neptunes at the early stages of evolution. Its radius, which may still evolve as a result of ongoing atmospheric cooling, contraction, and photoevaporation, further enhances its significance for understanding planetary development. Furthermore, TOI-4364b's moderately high transmission spectroscopy metric of 44.2 positions it as a viable candidate for atmospheric characterization with instruments such as JWST. This target has the potential to offer crucial insights into atmospheric retention and loss in young planetary systems.

Keywords: Exoplanet astronomy, Exoplanet evolution, Stellar rotation, Exoplanet detection methods, Transit photometry, Exoplanet atmospheres
Improving Radial Velocities by Marginalizing over Stars and Sky: Achieving 30 m s<SUP>‑1</SUP> RV Precision for APOGEE in the Plate Era. The radial velocity catalog from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) is unique in its simultaneously large volume and high precision as a result of its decade-long survey duration, multiplexing (600 fibers), and spectral resolution of R ∼ 22,500. However, previous data reductions of APOGEE have not fully realized the potential radial velocity (RV) precision of the instrument. Here we present an RV catalog based on a new reduction of all 2.6 million visits of APOGEE DR17 and validate it against improved estimates for the theoretical RV performance. The core ideas of the new reduction are the simultaneous modeling of all components in the spectra, rather than a separate subtraction of point estimates for the sky, and a marginalization over stellar types, rather than a grid search for an optimum. We show that this catalog, when restricted to RVs measured with the same fiber, achieves noise-limited precision down to 30 m s‑1 and delivers well-calibrated uncertainties. We also introduce a general method for calibrating fiber-to-fiber constant RV offsets and demonstrate its importance for high RV precision work in multifiber spectrographs. After calibration, we achieve 47 m s‑1 RV precision on the combined catalog with RVs measured with different fibers. This degradation in precision relative to measurements with only a single fiber suggests that refining line spread function models should be a focus in the Sloan Digital Sky Survey V to improve the fiber-unified RV catalog.

Keywords: Catalogs, Radial velocity, Astronomy data reduction, Atmospheric effects
Evidence of Truly Young High-α Dwarf Stars. The existence of high-α stars with inferred ages &lt;6 Gyr has been confirmed recently with large spectroscopic and photometric surveys. However, stellar mergers or binary interactions can induce properties associated with young ages, such as high mass, rapid rotation, or high activity, even in old populations. Literature studies have confirmed that at least some of these apparently young stars are old merger products. However, none have ruled out the possibility of genuinely young high-α stars. Because cool GKM dwarfs spin down, rapid rotation can be used to indicate youth. In this paper, we provide strong evidence that truly young high-α stars exist by studying high-α rotators in the Kepler and K2 field with abundance measurements from GALAH and APOGEE. After excluding close binaries using radial velocity (RV) measurements from Gaia DR3 and multiepoch RVs from APOGEE, we find a total of 32 high-α rapid rotators with periods ∼10–30 days, 14 of which have lithium measurements from GALAH, indicating that they have not gone through past mass transfer or stellar merger events. We identify 10 young high-α candidates with no signs of merger-induced mixing or close companions. One clear example is a G dwarf with a measurable rotation and an age of &lt;5 Gyr that is likely a single star with multiple RV measurements from APOGEE, has significant lithium detection from GALAH (A(Li) = 1.79), and has no signs of planet engulfment.

Keywords: Galaxy formation, Stellar ages, Galaxy chemical evolution, Galaxy dynamics, Galaxy abundances, Stellar rotation
Exoplanet Ephemerides Change Observations (ExoEcho). I. Transit Timing Analysis of 37 Exoplanets Using HST/WFC3 Data. The ExoEcho project is designed to study the photodynamics of exoplanets by leveraging high-precision transit timing data from ground- and space-based telescopes. Some exoplanets are experiencing orbital decay, and transit timing variation (TTV) is a useful technique to study their orbital period variations. In this study, we have obtained transit middle-time data from the Hubble Space Telescope observations for 37 short-period exoplanets, most of which are hot Jupiters. To search for potential long- and short-term orbital period variations within the sample, we conduct TTV model fitting using both linear and quadratic ephemeris models. Our analysis identifies two hot Jupiters experiencing strong periodic decays. Given the old age of the host stars of the hot Jupiter population, our findings call for a scenario where HJs are continuously being destructed and created. Our study demonstrates the importance of incorporating high-precision transit timing data to TTV study in the future.

Keywords: Exoplanet astronomy, Hubble Space Telescope, Transit photometry, Transit timing variation method
A Differentiable Binary Microlensing Model Using Adaptive Contour Integration Method. We present microlux, which is a Jax-based code that can compute the binary microlensing light curve and its derivatives both efficiently and accurately. The key feature of microlux is the implementation of a modified version of the adaptive sampling algorithm that was originally proposed by V. Bozza to account for the finite-source effect most efficiently. The efficiency and accuracy of microlux have been verified across the relevant parameter space for binary microlensing. As a differentiable code, microlux makes it possible to apply gradient-based algorithms to the search and posterior estimation of the microlensing modeling. As an example, we use microlux to model a real microlensing event and infer the model posterior via both Fisher information matrix and Hamiltonian Monte Carlo, neither of which would have been possible without access to accurate model gradients.

Keywords: Gravitational microlensing, Markov chain Monte Carlo, Algorithms, Binary lens microlensing
Bioverse: Giant Magellan Telescope and Extremely Large Telescope Direct Imaging and High-resolution Spectroscopy Assessment—Surveying Exo-Earth O<SUB>2</SUB> and Testing the Habitable Zone Oxygen Hypothesis. Biosignature detection in the atmospheres of Earth-like exoplanets is one of the most significant and ambitious goals for astronomy, astrobiology, and humanity. Molecular oxygen is among the strongest indicators of life on Earth, but it will be extremely difficult to detect via transmission spectroscopy. We used the Bioverse statistical framework to assess the ability to probe Earth-like O2 levels on hypothetical nearby habitable zone exo-Earth candidates (EECs) using direct imaging and high-resolution spectroscopy on the Giant Magellan Telescope (GMT) and the Extremely Large Telescope (ELT). Assuming continued improvement in instruments and data processing, our analysis highlights the best-case scenarios. Earth-like O2 levels could be probed on up to ∼7 and ∼19 EECs orbiting bright M dwarfs within 20 pc in a hypothetical 10 yr survey on the GMT and ELT, respectively. Four known super-Earth candidates, including Proxima Centauri b, could be probed for O2 within about 1 week of observations on the ELT and a few months on the GMT. We also assessed the ability of the ELT to test the habitable zone oxygen hypothesis—that habitable zone Earth-sized planets are more likely to have O2—within a 10 yr survey using Bioverse. Testing this hypothesis requires either ∼one-half of the EECs to have O2 or ∼one-third if η⊕ is large. A Northern Hemisphere large-aperture telescope, such as the Thirty Meter Telescope, would expand the target star pool by about 25%, reduce the time to probe biosignatures on individual targets, and provide an additional independent check on potential biosignature detections.

Keywords: Bayesian statistics, Exoplanets, Astronomical simulations, Exoplanet systems, Astrobiology, Parametric hypothesis tests, Biosignatures, Habitable zone, Habitable planets, Exoplanet atmospheres
New Stellar Parameters, Metallicities, and Elemental Abundance Ratios for 311 Metal-poor Stars. We present equivalent widths, improved model atmosphere parameters, and revised abundances for 14 species of 11 elements derived from high-resolution optical spectroscopy of 311 metal-poor stars. All of these stars had their parameters previously published by Roederer et al. We use color─Teff relationships calibrated for Gaia and 2MASS photometry to calculate improved effective temperatures (Teff). We calculate log of surface gravity (log g) values using measurements derived from Gaia parallaxes and other fundamental stellar properties. We perform a standard LTE abundance analysis using MARCS model atmospheres and the MOOG line analysis software to rederive microturbulence velocity parameters, metallicities, and abundances based on O I, Na I, Mg I, Si I, K I, Ca I, Ti I, Ti II, Cr I, Cr II, Fe I, Fe II, Ni I, and Zn I lines using previously measured equivalent widths. On average, the new Teff values are 310 K warmer, the new log g values are higher by 0.64 dex, and the new [Fe/H] values are higher by 0.26 dex. We apply NLTE corrections to the abundances derived from O I, Na I, Mg I, Si I, K I, Fe I, and Fe II lines. Our sample contains 6 stars with [Fe/H] &lt; −3.5, 28 stars with [Fe/H] &lt; −3.0, and 113 stars with [Fe/H] &lt; −2.5. Our revised abundances for these 311 stars are now in better agreement with those derived by previous studies of smaller samples of metal-poor stars in the Milky Way.

Keywords: Stellar astronomy, Population II stars, Stellar abundances, Nucleosynthesis
Variations of Absolute Source Positions Determined from Quad-band VLBI Observations. Active galactic nuclei (AGNs) observed with the very long baseline interferometry (VLBI) technique are used as fiducial references on the sky to precisely measure the shape and orientation of the Earth. Their positions form a celestial reference frame that plays an important role in both astronomy and geodesy. This study investigates the accuracy and stability of the positions of the AGNs that are measured by simultaneous VLBI observations at 3.3, 5.5, 6.6, and 10.5 GHz. Based on position time series from dedicated geodetic solutions, we characterize the observed source position variations and identify the possible factors causing such variations. We find that the primary contributor is source structure for sources above 20° decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20° decl. The position time series are further explored to derive more realistic uncertainties for the quad-band positions. Significant position offsets with respect to the positions at 2.2/8.6 GHz are found for 15% of the sources. For 6% of the sources, the offsets are larger than 0.8 mas. The source structure may be divided into two parts: the invisible structure (within the beam size) and the visible structure (on larger scales). The latter causes closure delays enlarging postfit delay residuals in geodetic solutions, whereas the former causes source position changes. Such position changes will contribute significantly to the offsets between radio and optical positions. Overall, this work highlights the necessity to have a specific quad-band catalog for processing operational quad-band observations.

Keywords: Active galactic nuclei, Equatorial coordinate system
A Comprehensive Catalog of Emission-line Nebulae, Star Clusters, and Supergiants in M31 from the LAMOST Spectroscopic Survey. Spectroscopic observations of various tracers in nearby galaxies, such as Andromeda (M31), play a crucial role in identifying and classifying individual stellar populations and nebular objects, thereby enhancing our understanding of galactic composition, environment, and dynamics, as well as stellar evolution. While the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey of M31 has produced extensive data sets, a comprehensive catalog of emission-line nebulae, star clusters, and supergiants is yet to be completed. In this paper, we present a final catalog of 384 emission-line nebulae, 380 star clusters, and 375 supergiants and candidates in M31, as carefully selected and identified from the LAMOST spectroscopic database. These objects were classified using a random forest algorithm, followed by thorough visual examinations of their spectral characteristics, as well as morphologies revealed by archive images. For emission-line nebulae, we measured radial velocities and relative fluxes of emission lines, enabling further classification of planetary nebulae and H II regions. Additionally, we identified 245 emission-line nebulae in M33. This work lays the data foundation for the study of M31 and offers valuable tracers to investigate M31's structure and evolution.

Keywords: Catalogs, Triangulum Galaxy, Planetary nebulae, H II regions, Supergiant stars, Andromeda Galaxy, Galaxies, Star clusters
HD 206893 B at High Spectral Resolution with the Keck Planet Imager and Characterizer. We present an atmospheric characterization and orbital analysis of HD 206893 B, an exceptionally red, L/T-transition substellar companion in a multiplanetary system, via Keck Planet Imager and Characterizer (KPIC) high-resolution (R ∼ 35,000) K-band spectroscopy. Using PHOENIX atmospheric models in a forward-model framework that fits the spectrum of the companion and diffracted starlight simultaneously, we detect HD 206893 B at &gt;8σ significance via cross correlation in two epochs. We find an effective temperature for the companion of 1634  K and a   of 4.55 . Only accounting for statistical uncertainties, we measure the carbon-oxygen ratio (C/O) of this companion to be 0.57 ± 0.02, or near-solar while assuming solar metallicity. The C/O ratio we measure fits the tentative trend of &gt;4 MJup companions having near-solar C/O ratios while less massive companions have greater-than-solar C/O ratios. Using substellar evolution models, we find an age of 112  Myr, a mass of 22.7  MJup, and a radius of 1.11 ± 0.03 RJup for this companion. We also use KPIC radial velocity data to fit the orbit of HD 206893 B and analyze the orbital stability of this system. We find that the orbital stability is relatively independent of the mass of HD 206893 B, and favors an orbital configuration where B and its interior planetary companion, HD 206893 c, are coplanar. The measured C/O ratio coupled with the current architecture of the system cannot rule out the core accretion scenario, nor the disk fragmentation scenario regarding the formation pathway of HD 206893 B.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Exoplanet atmospheric dynamics, Exoplanet formation, High contrast spectroscopy
MOMOS: The Multi-Object MKID Optical Spectrometer Simulator and Data Reduction Package. The Multi-Object MKID Optical Spectrometer (MOMOS) is a proposed visible wavelength spectrograph that uses microwave kinetic inductance detectors (MKIDs) targeting an initial resolving power of 3500 for up to five fiber inputs. With their modest wavelength-resolving abilities, MKIDs take the place of both the cross disperser and detector in the spectrograph. MKIDs lack read noise and dark current enabling noiseless post-observation rebinning and characterization of faint objects, as well as time-resolved photon-counting spectroscopy. This work presents a MOMOS simulator customizable for different MOMOS configurations. Treating simulator products as inputs, an algorithm was developed and implemented in the MOMOS data reduction package to calibrate and extract spectra.

Keywords: Astronomical detectors, Spectrometers, Astronomical instrumentation
Long-term X-Ray Variability on the Benchmark YSO HL Tau. HL Tau is one of the most well-studied Class I young stellar objects (YSOs), including frequent observations at near- and mid-infrared, (sub)millimeter, and X-ray wavelengths. We present the results of an X-ray variability monitoring campaign with XMM-Newton in 2020 and X-ray grating spectroscopy from Chandra/HETGS in 2018. We find that the X-ray spectrum of HL Tau is consistently hot (with characteristic plasma temperatures T ≳ 30 MK) over 31 epochs spanning 20 yr, which is consistent in temperature with most Class I YSOs. The high-resolution HETG spectrum indicates the presence of some cooler plasma. We characterize the variability of the star across the 31 observations and find a subset of observations with significant variability on a ∼21-day timescale in the observed count rate and flux. We discuss the possible origins of this variability and identify further observations that would better constrain the nature of the changes.

Keywords: Stellar x-ray flares, Young stellar objects, Pre-main sequence stars, Protoplanetary disks, Stellar accretion disks, Single x-ray stars