Sazuna/UAT_keywords huggingface dataset:
Peering into the Black Box: Forward Modeling of the Uncertainty Budget of High-resolution Spectroscopy of Exoplanet Atmospheres. Ground-based high-resolution cross-correlation spectroscopy (HRCCS; R ≳ 15,000) is a powerful complement to space-based studies of exoplanet atmospheres. By resolving individual spectral lines, HRCCS can precisely measure chemical abundance ratios, directly constrain atmospheric dynamics, and robustly probe multidimensional physics. But the subtleties of HRCCS data sets—e.g., the lack of exoplanetary spectra visible by eye and the statistically complex process of telluric removal—can make interpreting them difficult. In this work, we seek to clarify the uncertainty budget of HRCCS with a forward-modeling approach. We present an HRCCS observation simulator, scope,5 5 https://github.com/arjunsavel/scope that incorporates spectral contributions from the exoplanet, star, tellurics, and instrument. This tool allows us to control the underlying data set, enabling controlled experimentation with complex HRCCS methods. Simulating a fiducial hot Jupiter data set (WASP-77Ab emission with IGRINS), we first confirm via multiple tests that the commonly used principal component analysis does not bias the planetary signal when few components are used. Furthermore, we demonstrate that mildly varying tellurics and moderate wavelength solution errors induce only mild decreases in HRCCS detection significance. However, limiting-case, strongly varying tellurics can bias the retrieved velocities and gas abundances. Additionally, in the low signal-to-noise ratio limit, constraints on gas abundances become highly non-Gaussian. Our investigation of the uncertainties and potential biases inherent in HRCCS data analysis enables greater confidence in scientific results from this maturing method. https://github.com/arjunsavel/scope

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Astronomy data modeling, Infrared spectroscopy, Radiative transfer simulations
SKYSURF. VI. The Impact of Thermal Variations of HST on Background Light Estimates. The SKYSURF project constrained extragalactic background light and diffuse light (DL) with the vast archive of Hubble Space Telescope (HST) images. Thermal emission from HST itself introduces an additional uncertain background and hinders accurate measurement of the DL level. Here, we use archival Wide Field Camera 3 (WFC3)/IR engineering data to investigate and model changes in the temperature of various components in HSTs optical path as a function of time (solar cycle) and time of the year (Earth–Sun distance). We also specifically investigate changes in temperature with HST's orbital phase and time since Earth occultation. We investigate possible correlations between HST component temperature and year, and temperature and month. The thermal background changes by less than one Kelvin in the WFC3 pickoff mirror, one of the most important contributors to the thermal background. We model these data to describe the impact that orbital phase, year, and time of year have on the HST and WFC3 component temperatures, and use this to derive the impact on the thermal dark signal and the resulting DL measurements. Based on this improved modeling, we provide new upper limits on the level of DL of 21, 32, and 25 nW m‑2 sr‑1 for F125W, F140W, and F160W. Additionally, by accounting for all known sources of measurement uncertainty, we report lower limits on the level of DL of 12, 20, and 2 nW m‑2 sr‑1 for F125W, F140W, and F160W.

Keywords: Optical astronomy, Hubble Space Telescope, Sky brightness, Zodiacal cloud, Cosmic background radiation
The James Webb Interferometer: Space-based Interferometric Detections of PDS 70 b and c at 4.8 μm. We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's aperture masking interferometric mode within NIRISS. Observing with the F480M filter centered at 4.8 μm, we simultaneously fit geometrical models to the outer disk and the two known planetary companions. We redetect the protoplanets PDS 70 b and c at a signal-to-noise ratio (SNR) of 14.7 and 7.0, respectively. Our photometry of both PDS 70 b and c provides tentative evidence of mid-IR circumplanetary disk emission through fitting spectral energy distribution models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of ~4, a position angle of  220‑15+10 °, and an unconstrained separation within ~200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5σ upper limit of 208 ± 10 μJy on the flux of the candidate PDS 70 d at 4.8 μm, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5σ contrast upper limit &gt;7 mag at separations greater than 110 mas. These are the deepest limits to date within ~250 mas at 4.8 μm and the first space-based interferometric observations of this system.

Keywords: Protoplanetary disks, Exoplanets
Structural Parameters of the Thin Disk Population from Evolved Stars in the Solar Neighborhood. This study investigates the structural parameters of the thin-disk population by analyzing the spatial distribution of evolved stars in the solar neighborhood. From the Gaia Data Release 3 database, about 39.1 million stars within 1 kpc and with relative parallax errors σϖ/ϖ ≤ 0.10 were selected. The photometric data was corrected for extinction using a Galactic dust map. The sample was refined by considering the color–magnitude region   associated with evolved stars, applying a stricter parallax error limit of σϖ/ϖ ≤ 0.02, and yielding 671,600 stars. The star sample was divided into 36 regions based on their Galactic coordinates, with evolved stars in the absolute magnitude range of ‑1 &lt; MG (mag) ≤ 4 further split into five one-unit magnitude intervals. This led to 180 subgroups whose space-density profiles were modeled using a single-component Galaxy model. The analysis shows that the space densities are in agreement with the literature and that the scale heights vary with 200 &lt; H (pc) &lt; 600 interval to their absolute magnitudes. Red clump stars in the solar neighborhood were also estimated to have a scale height of 295 ± 10 pc. These findings indicate that evolved stars with bright absolute magnitudes originate from the evolution of the early spectral-type stars with short scale height, while fainter ones come from the evolution of the intermediate spectral-type stars with large scale height, suggesting that variations in scale height reflect the contribution of Galactic evolution processes.

Keywords: Milky Way disk, Galaxy structure, Solar neighborhood
Minute-cadence Observations of the LAMOST Fields with the TMTS. VI. Physical Parameters of Contact Binaries. With the development of wide-field surveys, a large amount of data on short-period W UMa contact binaries have been obtained. Continuous and uninterrupted light curves as well as high-resolution spectroscopic data are crucial in determining the absolute physical parameters. Targets with both TMTS light curves and LAMOST medium-resolution spectra were selected. The absolute physical parameters were inferred with the W-D code for 10 systems, all of them are W-type shallow or medium contact binaries. The O'Connell effect observed in the light curves can be explained by adding a spot on the primary or secondary component in the models. According to O − C analysis, the orbital periods exhibit a long-term increasing or decreasing trend, among which J0132, J1300, and J1402 show periodic variations that may be attributed to the presence of a third body or magnetic activity cycles. Spectral subtraction analysis revealed that the equivalent width of Hα indicates strong magnetic activity in J0047, J0305, J0638, and J1402. Among the 10 selected binary systems, except for J0132 and J0913, the more massive components are found to be main-sequence stars while the less massive components have evolved off the main sequence. In J0132, both components are in the main sequence, whereas both components of J0913 lie above the terminal-age main sequence. Based on the relationship between orbital angular momentum and total mass for these two systems, as well as their low fill-out factors, it is possible that these two systems are newly formed contact binaries, having recently evolved from the detached configuration.

Keywords: Starspots, Late-type stars, Close binary stars, Star formation, Contact binary stars, Stellar evolution
Disk in the Circumstellar Envelope of Carbon Mira V Cygni. Asymptotic giant branch (AGB) stars are the primary source of dust and complex molecules in the interstellar medium. The determination of outflow parameters is often hindered by the unknown geometry of the circumstellar environment, creating a demand for high-angular resolution observations. We use our near-infrared spectra and photometry of the carbon AGB star V Cyg, along with literature data, to construct its spectral energy distribution over a wide range of wavelengths. The dust envelope responsible for the infrared excess was also resolved in scattered polarized light at angular scales of 50─80 mas using differential speckle polarimetry. We present an interpretation of the thermal and scattered radiation of the dust using models of a spherical dusty outflow (Mdust = 5.3 × 10−7 M⊙) and an inclined equatorial density enhancement, either in the form of a disk (Mdust = 7.6 × 10−3 M⊕) or a torus (Mdust = 5.7 × 10−3 M⊕), which material is concentrated at stellocentric distances less than 25 au. The dust material consists of amorphous carbon and SiC, with 84% of the dust being amorphous carbon. Dust particle radii range from 5 to 950 nm and follow a power law with an exponent of −3.5. Modeling the envelope allowed us to improve the accuracy of stellar luminosity estimations: 21,000L⊙ and 8300L⊙ at maximum and minimum brightness, respectively. The relation between the disk and the high water content in the envelope is also discussed.

Keywords: Circumstellar envelopes, Mira variable stars, Infrared spectroscopy, Speckle interferometry
LAMOST Reveals Long-lived Protoplanetary Disks. While both observations and theories demonstrate that protoplanetary disks are not expected to live much longer than ∼10 Myr, several examples of prolonged disks have been observed in the past. In this work, we perform a systematic search for aged young stellar objects still surrounded by protoplanetary disks in the M-star catalog from the LAMOST archive. We identify 14 sources older than 10 Myr, still surrounded by protoplanetary disks and with ongoing accretion activities, significantly improving the census of the category known as the Peter Pan disks. The stellar parameters, variability, and accretion properties of these objects, as well as their spatial distribution, are investigated. Nearly all of these objects are distributed far away from nearby associations and star-forming regions but show evidence of being members of open clusters. Investigating the correlation between mass accretion rates and stellar masses, we find that these long-lived disks accrete at systematically lower levels, compared to their younger counterparts with similar stellar masses. Studying the evolution of mass accretion rates with stellar ages, we find that these aged disks follow a similar trend to young ones.

Keywords: Young stellar objects, Protoplanetary disks, Spectral energy distribution, Circumstellar disks, Stellar accretion disks, Hertzsprung Russell diagram
JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-776 b. We present two transit observations of the ∼520 K, 1.85 R⊕, 4.0 M⊕ super-Earth TOI-776 b with JWST NIRSpec/G395H, resulting in a 2.8–5.2 μm transmission spectrum. Producing reductions using the ExoTiC-JEDI and Eureka! pipelines, we obtain a median transit depth precision of 34 ppm for both visits and both reductions in spectroscopic channels 30 pixels wide (∼0.02 μm). We find that our independent reductions produce consistent transmission spectra; however, each visit shows differing overall structure. For both reductions, a flat line is preferred for Visit 1 while a flat line with an offset between the NRS1 and NRS2 detectors is preferred for Visit 2; however, we are able to correct for this offset during our modeling analysis following methods outlined in previous works. Using PICASO forward models, we can rule out metallicities up to at least 100× solar with an opaque pressure of 10‑3 bars to ≥3σ in all cases; however, the exact lower limit varies between the visits, with Visit 1 ruling out ≲100× solar while the lower limits for Visit 2 extend beyond ∼350× solar. Our results add to the growing list of super-Earth atmospheric constraints by JWST, which provide critical insight into the diversity and challenges of characterizing terrestrial planets.

Keywords: Exoplanet atmospheric composition , Infrared spectroscopy, Exoplanet atmospheres, Exoplanets
Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of Old Globular Clusters in the Large Magellanic Cloud. How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca─CN─CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly first-generation-dominated populational number ratio of n(FG):n(SG) = 61:39(±4), where FG and SG denote the first and second generations, respectively. Both the FG and SG have similar cumulative radial distributions, consistent with the idea that NGC 2257 is dynamically old. We obtain [Fe/H]hk = −1.78 ± 0.00 dex(σ = 0.05 dex), and our metallicity is ∼0.2 dex larger than that from the high-resolution spectroscopy by others, due to their significantly lower temperatures by ∼−200 K. The NGC 2257 FG shows a somewhat larger metallicity variation than the SG, the first detection of such a phenomenon in an old LMC GC, similar to Galactic GCs with MPs, strongly suggesting that it is a general characteristic of GCs with MPs. Interestingly, the NGC 2257 SG does not show a helium enhancement compared to the FG. Our results for the Galactic normal GCs exhibit that the degree of carbon and nitrogen variations is tightly correlated with the GC mass, while NGC 2257 exhibits slightly smaller variations in its mass. We show that old LMC GCs follow the same trends as the Galactic normal GCs in the ∆WCF336W,F438W,F814W, NFG/Ntot, and   domains. Our result indicates that the environment of the host galaxy did not play a major role in the formation and evolution of GC MPs.

Keywords: Globular star clusters, Hertzsprung Russell diagram, Stellar populations, Chemical abundances, Large Magellanic Cloud, Red giant stars, Population II stars, Stellar evolution
Mind the Gap. II. The Near-UV Fluxes of M Dwarfs. Because of the continuous variations in mass, metallicity, and opacity, dwarf stars are distributed along the main sequence on optical and near-IR color–magnitude diagrams following a smooth polynomial. In this study, utilizing a catalog of crossmatched Galaxy Evolution Explorer (GALEX) and Gaia sources, we identify two distinct populations of M dwarfs in the near-UV (NUV) band on the MNUV versus MG diagram. We also reveal a pronounced increase in the number of stars exhibiting high NUV fluxes near the spectral type M2 or MG ~ 9.4, coinciding with the H2 formation in the atmosphere that improves the energy transportation at the surface. This suggests that certain yet-to-be-understood stellar mechanisms drive heightened activity in the NUV band around the effective temperatures of M2 and later types of M dwarfs. Through examination of archival Hubble Space Telescope spectra, we show that Fe II line forests at ~2400 Å and 2800 Å dominate the spectral features in the GALEX NUV bandpass, contributing to the observed excess fluxes at a given mass between the two populations. Additionally, our investigation indicates that fast rotators and young stars likely increase in brightness in the NUV band, but not all stars with bright NUV fluxes are fast rotators or young stars.

Keywords: M dwarf stars, Stellar structures, Stellar chromospheres, Ultraviolet photometry, Main sequence stars
Resolving Pleiades Binary Stars with Gaia and Speckle Interferometric Observations. The Pleiades is the most prominent open star cluster visible from Earth and an important benchmark for simple stellar populations unified by common origin, age, and distance. Binary stars are its essential ingredient, yet their contribution remains uncertain due to heavy observational biases. A resolved multiplicity survey was conducted for a magnitude-limited G &lt; 15mag sample of 423 potential cluster members, including sources with poorly fitted astrometric solutions in Gaia DR3. Speckle interferometric observations at the 2.5 m telescope of the Sternberg Astronomical Institute, Moscow State University observatory were combined with Gaia data, enabling the identification of 61 resolved binary or multiple systems within the 0 04–10″ (5–1350 au) separation range. With speckle observations, we discovered 21 components in 20 systems. The existence of a Merope (23 Tau) companion is confirmed after several previous unsuccessful attempts. We show that the Gaia multipeak fraction is a strong predictor of subarcsecond multiplicity, as all sources with ipd_frac_multi_peak &gt; 4% are successfully resolved. We found that 10% of Pleiades stars have a companion with a mass ratio q &gt; 0.5 within the projected separation of 27 &lt; s &lt; 1350 au, and confirm a deficit of wide binaries with s &gt; 300 au. An observed dearth of wide pairs with a large mass ratio (q &gt; 0.55) may imprint the transition from hard to soft binaries regime at the early stages of cluster evolution. The total binary fraction for q &gt; 0.5 systems is extrapolated to be around 25%.

Keywords: Open star clusters, Visual binary stars, Speckle interferometry
CDN-Net: Faint Celestial Target Detection Based on Densely Nested Hierarchical Network. The detection of celestial objects in ground-based wide-field optical telescope images serves as the foundational step for subsequent celestial analysis tasks. Existing methods for astronomical target detection have not addressed the challenges posed by a high dynamic range, faintness of targets, and an inaccurate supervision map. This paper presents a faint celestial target detection framework named the Celestial Densely Nested Network (CDN-Net). First, a hierarchical bit-depth decomposition strategy is designed to address high dynamic range astronomical FITS images, ensuring effective representation of faint targets. Second, a densely nested hierarchical network is introduced to extract high-resolution features of these faint astronomical targets. Lastly, a soft segmentation map, along with the corresponding loss, is proposed to guide the network's focus toward faint targets. Experiments were conducted on both simulated and real data sets, separately comprising 2560 images and 24,087 images, respectively, to evaluate the performance of CDN-Net. Compared to six existing methods, CDN-Net achieves superior precision, recall, and F1 score, especially for faint targets with signal-to-noise ratios below 3. Additionally, comparisons with star catalogs validate the effectiveness of CDN-Net. The code for this work is available at https://github.com/AeroFirefly/CDN-Net.

Keywords: Detection, Convolutional neural networks, Astronomy image processing
TOI-6038 A b: A Dense Sub-Saturn in the Transition Regime between the Neptunian Ridge and Savanna. We present the discovery and characterization of a sub-Saturn exoplanet, TOI-6038 A b, using the PARAS-2 spectrograph. The planet orbits a bright (mV = 9.9), metal-rich late F-type star, TOI-6038 A, with Teff = 6110 ± 100 K,  , and   dex. The system also contains a wide-orbit binary companion, TOI-6038 B, an early K-type star at a projected separation of ≈3217 au. We combined radial velocity data from PARAS-2 with photometric data from the Transiting Exoplanet Survey Satellite for joint modeling. TOI-6038 A b has a mass of   and a radius of  , orbiting in a circular orbit with a period of   days. Internal structure modeling suggests that ≈74% of the planet's mass is composed of dense materials, such as rock and iron, forming a core, while the remaining mass consists of a low-density H/He envelope. TOI-6038 A b lies at the transition regime between the recently identified Neptunian ridge and savanna. Having a density of  , TOI-6038 A b is compatible with the population of dense ridge planets (ρP ≃ 1.5–2.0 g cm‑3), which have been proposed to have reached their close-in locations through high-eccentricity tidal migration (HEM). First-order estimates suggest that the secular perturbations induced by TOI-6038 B may be insufficient to drive the HEM of TOI-6038 A b. Therefore, it is not clear whether HEM driven by a still undetected companion or early disk-driven migration brought TOI-6038 A b to its present-day close-in orbit. Interestingly, its bright host star makes TOI-6038 A b a prime target for atmospheric escape and orbital architecture observations, which will help us to better understand its overall evolution.

Keywords: Exoplanet dynamics, Exoplanet systems, Extrasolar gaseous planets, Wide binary stars, Radial velocity, Transit photometry
starkiller: Subtracting Stars and Other Sources from IFU Spectroscopic Data Through Forward Modeling. We present starkiller, an open-source Python package for forward-modeling flux retrieval from integral field unit (IFU) spectrograph data cubes. starkiller simultaneously provides stellar spectral classification, relative velocity, and line-of-sight extinction for all sources in a catalog, alongside a source-subtracted data cube. It performs synthetic difference imaging by simulating all catalog sources in the field of view, using the catalog for positions and fluxes to scale stellar models, independent of the data cube. This differencing method is particularly powerful for subtracting both point sources and trailed or even streaked sources from extended astronomical objects. We demonstrate starkiller's effectiveness in improving observations of extended sources in dense stellar fields for Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE) observations of comets, asteroids, and nebulae. We also show that starkiller can treat satellite-impacted VLT/MUSE observations. The package could be applied to tasks as varied as dust extinction in clusters and stellar variability; the stellar modeling using Gaia fluxes is provided as a standalone function. The techniques can be expanded to imagers and to other IFUs.

Keywords: Open source software, Small Solar System bodies, Extended radiation sources, Artificial satellites, Interstellar objects, Interdisciplinary astronomy