Sazuna/UAT_keywords huggingface dataset:
Spectral Characterization of the Organic- and Methanol-rich Cliff-type Trans-Neptunian Objects. Trans-Neptunian objects (TNOs) harbor pristine materials from the early solar system. The James Webb Space Telescope offers major insights into the spectral classification of these small bodies. Among the three major spectral classes of TNOs, "cliff" types exhibit steep, red slopes from 0.7 to 1.2 μm, sheer reflectance drops from 2.65 to 2.85 μm, and deep 3 μm absorptions with low reflectance longward of the band. These types show more features associated with simple hydrocarbons and methanol than other TNO types. Cliff-type spectra show two further spectral subclasses (hereafter Cliff1 and Cliff2 types), with all cold-classical TNOs exhibiting Cliff2-type spectra. We apply radiative-transfer-based spectral modeling from 2.0 to 3.6 μm for 16 cliff-type TNOs to quantify compositions and investigate depth dependencies, which is crucial for understanding the cliff type's role in the outer solar system's development. We find mixtures of methanol, water, and tholins/organics are primarily responsible for the prototypical 3 μm region of cliff-type spectra, with methanol and tholins/organics being particularly suggestive of distant formation. Our models also demonstrate Cliff1 and Cliff2 types have distinct compositions of higher methanol and tholin/organic abundances, respectively. We find the Mors-Somnus binary system to be compositionally homogenous, consistent with a formation scenario that sampled a similar region in the protoplanetary disk (i.e., streaming instability). Object 2004 PG115 is compositionally distinct from the rest of the cliff types, suggesting some objects have compositions intermediate between cliff subclasses and major TNO classes. Observations with higher spectral resolution and signal-to-noise ratio are crucial for better understanding minor, often aliphatic components of cliff-type spectra.

Keywords: James Webb Space Telescope, Small Solar System bodies, Classical Kuiper belt objects, Trans-Neptunian objects
Efficient Exoplanet Imaging Simulations of the Habitable Worlds Observatory. Direct imaging simulations of starshades and other proposed mission concepts are needed to characterize planet detection performance and inform mission design trades. In order to assess the complementary role of a 60 m starshade for the Habitable Worlds Observatory (HWO), we develop the optical model of a starshade and simulate solar system imaging at 0° and 60° inclinations. The optical core throughput of a direct-imaging system is a key metric that governs exposure time and the potential exoplanetary yield of a mission. We use our optical model to evaluate core throughput, incorporating 6 m segmented and obscured telescope apertures, over the visible to near-infrared wavelength band (500─1000 nm). Accurate diffractive optical simulations of this form require many large Fourier transforms, with prohibitive run times, as both the starshade mask and telescope aperture require fine-scale spatial sampling. We introduce a Fourier sampling technique, the Bluestein fast Fourier transform (B-FFT), to efficiently simulate diffractive optics and enable high-fidelity simulations of core throughput. By characterizing sampling requirements and comparing B-FFTs computational complexity to standard Fourier methods (e.g., DFT, FFT), we demonstrate its efficiency in our optical pipeline. These methods are implemented in PyStarshade, an open-source Python package offering flexible diffraction tools and imaging simulations for starshades. Our results show the HWO starshade used with a segmented off-axis telescope aperture achieves an optimal core throughput measured within a photometric aperture of radius 0.7λ/D of 68%. With an additionally obscured aperture, a 66% core throughput is achieved.

Keywords: High contrast techniques, Exoplanets, Fast Fourier transform, Astronomy software, Astronomical optics, Direct imaging, Exoplanet detection methods, Habitable planets, Astronomical simulations
The Hubble Ultracool Multiplicity (HUM) Survey. I. Characterizing Sensitivity to Companions at Subdiffraction Limit Separations with Hubble Space Telescope Wide Field Camera 3/IR. We characterize the sensitivity of a double point-spread function (PSF) fitting algorithm—employing empirical, position-dependent PSF models—for detecting companions using the infrared channel of the Wide Field Camera 3 (WFC3)/IR on the Hubble Space Telescope (HST). The observed separation distribution of known brown dwarf (BD) binaries is potentially biased toward separations larger than the angular resolution limits of current imaging techniques. Previous analyses suffer from incompleteness at separations &lt;2λ/D; our aim is to probe within this limit to identify previously missed companions. We evaluate the performance of our technique on artificial data across eight WFC3/IR filters and a broad range of signal-to-noise ratios (S/N), determining our ability to accurately recover injected companions and identifying the region of parameter space where false positive fits are likely. Here, we demonstrate the capability of this technique to recover companions at subpixel separations on the WFC3/IR detector—below the diffraction limit in multiple filters. For F160W at a typical S/N of 75, we resolve companions separated by 0.8 pixels (104 mas, 0.759λ/D) at 1.5 mag contrast with ≥90% confidence. We achieve the closest angular resolution for any detection method with WFC3/IR imaging to date. Compared to previous BD multiplicity surveys with WFC3/IR, we achieve a 2.5× improvement in separation sensitivity at contrasts of 0─3 mag in F127M. We have demonstrated that applying our improved technique to archival HST images of field BDs will thus probe down to separations of 1 au, in one of the largest high-angular-resolution surveys of such objects to date.

Keywords: Brown dwarfs, Binary stars, Surveys, Hubble Space Telescope, Direct imaging, High angular resolution
The AGEL Survey Data Release 2: A Gravitational Lens Sample for Galaxy Evolution and Cosmology. The ASTRO 3D Galaxy Evolution with Lenses (AGEL) Survey is an ongoing effort to spectroscopically confirm a diverse sample of gravitational lenses with high spatial resolution imaging, to facilitate a broad range of science outcomes. The AGEL systems span single galaxy-scale deflectors to groups and clusters, and include rare targets such as galaxy-scale lenses with multiple sources, lensed quiescent galaxies, and Einstein rings. We build on the 68 systems presented in Tran et al. (AGEL data release 1) to present a total of 139 lenses, and high-resolution Hubble Space Telescope images for 167 lenses from three programs (including one ongoing). Lens candidates were originally identified by convolutional neural networks in the Dark Energy Camera Legacy Survey imaging fields, and of the targets with follow-up spectroscopy, we find a high (96%) success rate. Compared with other spectroscopic lens samples, AGEL lenses tend to have both higher redshift deflectors and sources. We briefly discuss the common causes of false-positive candidates, and suggest strategies for mitigating false-positives in next-generation lens searches. Lastly, we present the newly measured redshifts for six (five confirmed strong lenses, one probable) galaxy-scale double-source plane lenses, targets which are useful for cosmological analyses. With next-generation telescopes and surveys such as Euclid, Vera Rubin's Legacy Survey of Space and Time, Keck Observatory's KAPA program, and 4MOST's 4SLSLS surveys on the horizon, the AGEL survey represents a pathfinder for refining automated candidate search methods and identifying and triaging candidates for follow-up based on scientific potential.

Keywords: Cosmology, Redshift surveys, Gravitational lensing, Galaxy evolution
An Updated Efficient Galaxy Morphology Classification Model Based on ConvNeXt Encoding with UMAP Dimensionality Reduction. We present an enhanced unsupervised machine learning (UML) module within our previous USmorph classification framework featuring two components: (1) hierarchical feature extraction via a pretrained ConvNeXt convolutional neural network with transfer learning, and (2) nonlinear manifold learning using uniform manifold approximation and projection (UMAP) for topology-aware dimensionality reduction. This dual-stage design enables efficient knowledge transfer from large-scale visual datasets while preserving morphological pattern geometry through UMAP's neighborhood preservation. We apply the upgraded UML on I-band images of 99,806 COSMOS galaxies at redshift 0.2 &lt; z &lt; 1.2 (to ensure rest-frame optical morphology) with Imag &lt; 25. The predefined cluster number is optimized to 20 (reduced from 50 in the original framework), achieving significant computational savings. The 20 algorithmically identified clusters are merged into five physical morphology types. About 51% of galaxies (50,056) were successfully classified. To assess classification effectiveness, we tested morphological parameters for massive galaxies with M* &gt; 109M⊙. Our classification results align well with galaxy evolution theory. This improved algorithm significantly enhances galaxy morphology classification efficiency, making it suitable for large-scale sky surveys such as those planned with the China Space Station Telescope.

Keywords: Galaxy structure, Galaxy classification systems
The Diversity of Cold Worlds: Age and Characterization of the Exoplanet COCONUTS-2 b. Studying cold brown dwarfs is key to understanding the diverse characteristics of cold giant exoplanets atmospheres. COCONUTS-2 is a wide binary system composed of a T9 brown dwarf and an M3 star, which presents a unique opportunity to characterize a cold benchmark brown dwarf. As part of a JWST program to study the range of physical and atmospheric properties of the coldest brown dwarfs, we obtained NIRSpec G395H spectra (R ∼ 2700, 2.87−5.13 μm) and MIRI F1000W, F1280W, and F1800W photometry for COCONUTS-2 b. In this work, we find a 99% probability of the system belonging to the Corona of Ursa Major moving group (414 ± 23 Myr) using BANYAN Σ and its full kinematics. We also reestimate the astrometry of COCONUTS-2b using the MIRI data. We support this membership with a comparison of the rotation period, metallicity, and C/O ratio of the group with those of the COCONUTS-2 system. We also calculate its bolometric luminosity, which, combined with our age estimation, allows us to derive its mass, effective temperature, surface gravity, and radius with high precision. As a result of our analysis, we support the conclusion that COCONUTS-2 b is a planetary-mass object (7.5 ± 0.4 MJup), which was likely formed via the same mechanism as stars. In addition we compare the JWST spectrum to another object in the sample, J082507.35+280548.5 (0825+2805), a Y0.5 brown dwarf, which is a candidate member of the same moving group, but has a lower mass (3.7 ± 0.2 MJup). We identify absorption feature differences, which could indicate that 0825+2805 has stronger vertical mixing.

Keywords: Brown dwarfs, Stellar ages, Young star clusters, Low mass stars, Exoplanet formation, Exoplanet atmospheres, T dwarfs
Data-driven Informative Priors for Bayesian Inference with Quasiperiodic Data. Bayesian computational strategies for inference can be inefficient in approximating the posterior distribution in models that exhibit some form of periodicity. This is because the probability mass of the marginal posterior distribution of the parameter representing the period is usually highly concentrated in a very small region of the parameter space. Therefore, it is necessary to provide as much information as possible to the inference method through the parameter prior distribution. We intend to show that it is possible to construct a prior distribution from the data by fitting a Gaussian process (GP) with a periodic kernel. More specifically, we want to show that it is possible to approximate the marginal posterior distribution of the hyperparameter corresponding to the period in the kernel. Subsequently, this distribution can be used as a prior distribution for the inference method. We use an adaptive importance sampling method to approximate the posterior distribution of the hyperparameters of the GP. Then, we use the marginal posterior distribution of the hyperparameter related to the periodicity in order to construct a prior distribution for the period of the parametric model. This workflow is empirical Bayes, implemented as a modular (cut) transfer of a GP posterior for the period to the parametric model. We applied the proposed methodology to both synthetic and real data. We approximated the posterior distribution of the period of the GP kernel and then passed it forward as a posterior-as-prior with no feedback. Finally, we analyzed its impact on the marginal posterior distribution.

Keywords: Bayesian statistics, Monte Carlo methods, Gaussian Processes regression, Radial velocity, Rapid stellar oscillations, Prior distribution
An Oasis in the Brown Dwarf Desert: Confirmation of Two Low-mass Transiting Brown Dwarfs Discovered by TESS. As the intermediate-mass siblings of stars and planets, brown dwarfs (BDs) are vital to study for a better understanding of how objects change across the planet-to-star mass range. Here, we report two low-mass transiting BD systems discovered by TESS, TOI-4776 (TIC 196286578) and TOI-5422 (TI 80611440), located in an underpopulated region of the BD mass─period space. These two systems have comparable masses but different ages. The younger and larger BD is TOI-4776 b with  32.3−1.7+1.8MJup  and 1.01 ± 0.05 RJup, orbiting a late-F star about  4.7−2.5+3.1  Gyr old in an ∼10.41 day period. The older TOI-5422 b has  28.0−1.2+1.6MJup  and 0.81 ± 0.03 RJup in an ∼5.38 day orbit around a subgiant star about  7.6−2.6+2.5  Gyr old. Compared with substellar mass─radius evolution models, TOI-4776 b has an inflated radius. In contrast, TOI-5422 b is slightly "underluminous" with respect to model predictions, which is not commonly seen in the BD population. In addition, TOI-5422 shows apparent photometric modulations with a rotation period of 10.8 ± 0.5 days found by rotation analysis, and the stellar inclination angle is obtained to be  I⋆=76−12+10  deg. Therefore, it is likely that TOI-5422 b is spinning up the host star and its orbit is aligned with the stellar spin axis.

Keywords: Brown dwarfs, Substellar companion stars, Photometry, Radial velocity, Transit photometry
Searching for Transit Timing Variations in Young Transiting Systems. The discovery of young (&lt;800 Myr) transiting planets has provided a new avenue to explore how planets form and evolve over their lifetimes. Mass measurements for these planets would be invaluable, but radial velocity surveys of young systems are often overwhelmed by stellar activity. Transit timing variations (TTVs) offer an alternative route to measure masses that are less impacted by signals from the host star. Here we search for candidate TTVs in a sample of 39 young systems hosting 53 transiting planets using data from Kepler, K2, and TESS. We recover previously reported TTVs for 11 planets, including those in V1298 Tau, TOI-2076, Kepler-51, and TOI-1227, and identify new candidate TTVs for four planets (DS Tuc Ab, HD 63433 b, K2-101 b, and Kepler-1643 b). In total, 28.3% ± 6.2% of the young planets in our sample show evidence of TTVs, which is higher than the rate from Kepler on mostly older systems (7.3% ± 0.6%). Accounting for differences in data coverage and quality between Kepler and TESS only increases this difference (&gt;4σ), although differences in methodology make a totally fair comparison challenging. We show that spots have a weak-to-negligible impact on our results, and similarly cannot explain the higher TTV fraction. Longer-term monitoring will be required to validate these TTVs as planetary in nature and confirm the high TTV rate. While the candidate TTV signals detected here are sparsely sampled, our work provides a clear priority list for additional ground-based observations, and for multiplanet TTVs, to measure the masses and eccentricities of these planets.

Keywords: Timing variation methods, Transit photometry, Transit timing variation method, Exoplanets
Segmented-Polynomial-fitting Least Squares (SPLS): An Optimized Algorithm to Find Earth Twins. Detecting Earth twins remains challenging because their shallow, long-period transits are difficult to distinguish from background noise. Motivated by the challenge, we developed Segmented-Polynomial-fitting Least Squares (SPLS), a new algorithm that simultaneously fits planetary transits and background trends using a segmented double polynomial model. Prior to signal detection, the optimal polynomial order for the trend component is selected using Bayes factor-based model comparison. During the periodogram search, the Signal Detection Efficiency metric is used to assess signal significance. The algorithm is accelerated by a three-step approximation and nonlinear parameter sampling tailored to SPLS. We compare the performance of SPLS with traditional detrending-detection approaches across different orbital periods, signal-to-noise ratios (SNR), planet radii, and stellar noise levels on an injection─recovery test. When detecting signals with periods between 10 and 480 days and SNRs below 9, SPLS achieves at least a 22.6% higher true positive rate than other methods at the same 10% false positive rate. Using the threshold determined from the Receiver Operating Characteristic curve analysis, our method also recovers the most true signals while yielding the fewest false positives among all injected samples, and reaches a 97% recovery fraction in Kepler confirmed single-planet systems. The tests demonstrate that SPLS improves the detection of transiting planets, particularly for low-SNR, long-period signals. It offers the potential for finding Earth twins in future applications to data from Kepler, TESS, and upcoming PLATO and Earth 2.0 missions.

Keywords: Light curves, Astronomy data analysis, Period search , Exoplanet detection methods, Transit photometry, Time series analysis
On-sky Demonstration of Second-stage Wave-front Control with a Photonic Lantern. Ground-based direct imaging of exoplanets at high contrast requires precise correction of atmospheric turbulence using adaptive optics (AO). The planet-to-star contrast ratio at small angular separations from the host star is often limited by non-common-path aberrations (NCPAs) that are seen only in the science plane. The photonic lantern (PL) can be used to sense aberrations at the final science imaging plane. This enables a two-stage wave-front control architecture, in which the first-stage wave-front sensor senses atmospheric turbulence and the PL senses NCPAs and other aberrations not seen by the first stage. We demonstrate closed-loop control of residual wave-front errors using a nondispersed PL after first-stage AO correction on the Shane 3 m telescope at Lick Observatory. Our results show that nondispersed PLs can be used for second-stage wave-front sensing, enabling performance improvements via minimally invasive retrofits to existing AO systems.

Keywords: Astronomical instrumentation, Adaptive optics
Variable X-Ray Emission of the Planet Hosting T Tauri Star CI Tau. We report results of Chandra X-ray observations of CI Tau, a young magnetically active classical T Tauri star for which previous studies have reported periodic variability attributed to a massive planet in a short-period orbit. CI Tau was clearly detected by Chandra in four separate observations acquired in late 2023. The X-ray emission was steady in the first two observations with a characteristic plasma temperature kT ≍ 2 keV (≍23 MK) and X-ray luminosity log Lx = 29.74 erg s−1. During each of the last two observations obtained two weeks later the count rate increased slowly and the X-ray plasma temperature was much higher but remained nearly steady at kT ≍ 4─5 keV (≍46─58 MK) and peak luminosity log Lx = 30.5 erg s−1. Such variable X-ray emission in T Tauri stars accompanied by high plasma temperatures is a signature of magnetic activity, consistent with the known presence of a strong magnetic field in CI Tau. We summarize the variable X-ray emission properties of CI Tau within the framework of T Tauri stars of similar mid-K spectral type, identify possible variability mechanisms, and assess the effects of stellar X-ray irradiation on the claimed planet.

Keywords: X-ray astronomy, Star-planet interactions, Classical T Tauri stars
Orbital Eccentricities Suggest a Gradual Transition from Giant Planets to Brown Dwarfs. To date, hundreds of substellar objects with masses between 1 and 80 MJup have been detected orbiting main-sequence stars. The current convention uses the deuterium-burning limit, Mc ≍ 13 MJup to divide this population between giant planets and brown dwarfs. However, this classification heuristic is largely divorced from any formation physics and may not accurately reflect the astrophysical nature of these objects. Previous work has suggested that a transition from "planet-like" to "brown-dwarf-like" characteristics occurs somewhere in the range 1─10MJup, but precise the crossover mass and whether the transition is gradual or abrupt remains unknown. Here, we explore how the occurrence rate, host star metallicity, and orbital eccentricities vary as a function of mass in a sample of 70 Doppler-detected substellar objects (0.8 &lt; Mc/MJup &lt; 80) from the California Legacy Survey. Our population consists of objects near and beyond the water ice line (1 &lt; a/AU &lt; 10), providing valuable clues to the details of giant planet formation physics at a location in the protostellar disk where planet formation efficiency is thought to be enhanced. We find that occurrence rate, host star metallicity, and orbital eccentricity all change gradually across the mass range under consideration, suggesting that "bottom-up" core accretion mechanisms and "top-down" gravitational instability mechanisms produce objects that overlap in mass. The observed eccentricity distributions could arise either from different formation channels or from postformation dynamical interactions between massive substellar objects.

Keywords: Brown dwarfs, Bayesian statistics, Eccentricity, Exoplanets
Photometric Observations and Analysis of Active Asteroid (62412) 2000 SY178. The active asteroid (62412) 2000 SY178 is a C-type object located in the outer main belt and was first reported to exhibit a dust tail in 2014 May. Before and after its recent perihelion, we carried out long-term observations of 2000 SY178 with the Lijiang 2.4 m telescope between 2024 January 15 and 2025 May 13 to detect its activity and physical properties. In our research, the absolute magnitude was determined to be H = 14.02 ± 0.31 mag, which is consistent with the value of H = 14.07 ± 0.24 mag observed during the 2014 active event. Using this magnitude, we derived the effective radius of 2000 SY178 as re = 3.95 ± 0.05 km. We modeled the light curves of 2000 SY178 with the Cellinoid shape model and derived its six axis ratios as a1 = 1.0 ± 0.0000, a2 = 1.3695 ± 0.0093, b1 = 1.6748 ± 0.0076, b2 = 1.6691 ± 0.0080, c1 = 2.0267 ± 0.0093, and c2 = 0.0324 ± 0.0023. Assuming 2000 SY178 is a strengthless rubble pile, its current rotation period of 3.328 hr exceeds the critical limit for rotational stability, suggesting that the observed activity 1is likely triggered by rotational destabilization.

Keywords: Light curves, Asteroid rotation, Asteroids, Photometry