Sazuna/UAT_keywords huggingface dataset:
Additional Evidence for the Existence of a Primordial Disk System. The origin of very metal-poor (VMP; [Fe/H] ≤ ‑2.0) stars on planar orbits has been the subject of great attention since their first discovery. However, prior to the release of the Gaia BP/RP (XP) spectra and large photometric samples such as SkyMapper, SAGES, J-PLUS, and S-PLUS, most studies have been limited due to their small sample sizes or strong selection effects. Here, we crossmatch photometric metallicities derived from Gaia XP synthetic photometry and geometric distances from Bailer-Jones et al., and select 12,000 VMP stars (1604 dwarfs and 10,396 giants) with available high-quality astrometry. After calculating dynamical parameter estimates using AGAMA, we employ the nonnegative matrix factorization technique to the vϕ distribution across bins in  Zmax  (the maximum height above or below the Galactic plane during the stellar orbit). We find three primary populations of the selected VMP stars: halo, disk system, and the Gaia Sausage/Enceladus structure. The fraction of disk-like stars decreases with increasing  Zmax  (as expected), although it is still ∼20% for stars with  Zmax ∼ 3 kpc. Similar results emerge from the application of the Hayden criterion, which separates stellar populations on the basis of their orbital inclination angles relative to the Galactic plane. We argue that such high fractions of disk-like stars indicate that they are an independent component, rather than originating solely from Galactic building blocks or heating by minor mergers. We suggest that most of these VMP stars are members of the hypothesized "primordial" disk.

Keywords: Milky Way formation, Galactic archaeology, Milky Way dynamics, Milky Way disk, Milky Way evolution, Milky Way Galaxy
X-Ray Reflection Spectroscopy with Improved Calculations of the Emission Angle. The reflection spectrum produced by a cold medium illuminated by X-ray photons is not isotropic and its shape depends on the emission angle. In the reflection spectrum of an accretion disk of a black hole, the value of the emission angle changes over the disk and, in general, is different from the value of the inclination angle of the disk because of the light bending in the strong gravitational field of the black hole. Current reflection models make some approximations, as calculating a reflection spectrum taking the correct emission angle at every point of the disk into account would be too time-consuming and make the model too slow to analyze observations. In a recent paper, we showed that these approximations are unsuitable to fit high-quality black hole spectra expected from the next generation of X-ray missions. Here, we present a reflection model with improved calculations of the emission angle that solves this problem.

Keywords: X-ray astronomy, Relativistic disks, X-ray sources, Astrophysical black holes
The HETDEX Survey: Probing Neutral Hydrogen in the Circumgalactic Medium of ∼88,000 Lyα Emitters. We explore the neutral hydrogen (H I) gas around 1.9 &lt; z &lt; 3.5 Lyman alpha emitters (LAEs) from the Hobby─Eberly Telescope Dark Energy Experiment using faint Lyα absorption. This absorption is the result of H I in the halo of the LAE scattering Lyα photons from the integrated light of background galaxies along the line of sight. We stack millions of spectra from regions around ∼88,000 LAEs, in order to focus on the physics of the gas at large radii. The extensive number of fiber spectra contributing to the stacks ensures a sufficient signal-to-noise ratio to detect the faint Lyα absorption, which would otherwise be buried within the noise. We detect absorption out to a projected ∼350 kpc around an average LAE at z ∼ 2.5. We use these results to create an empirical radial Wλ(Lyα) profile around LAEs. Comparison with numerical simulations reveals a profile similar to the empirical one within this region. Compared to previous studies, the profile is similar but modestly higher. We also outline a simple physical picture motivated by the observed trends in the data. We plan to quantify this radial profile as a function of redshift, local density, and Lyα luminosity, to explore the relationship between LAE environments and H I distribution.

Keywords: Galaxy environments, Large-scale structure of the universe, Galaxy pairs, Neutral hydrogen clouds, Galactic and extragalactic astronomy, Circumgalactic medium, Lyman-alpha galaxies
Stellar Models Also Limit Exoplanet Atmosphere Studies in Emission. Stellar contamination has long been recognized as a major bottleneck in transmission spectroscopy, limiting our ability to accurately characterize exoplanet atmospheres—particularly for terrestrial worlds. In response, significant observational efforts have shifted toward emission spectroscopy as a potentially more robust alternative, exemplified by initiatives such as the 500 hr JWST Rocky Worlds Director's Discretionary Time program. However, the extent to which emission spectroscopy may be affected by stellar effects remains mostly unexplored, in stark contrast with the extensive exploration and mitigation work for transmission spectroscopy. In this study, we assess the impact of imperfect knowledge of stellar spectra on exoplanet atmospheric retrievals from emission spectroscopy. At 12.8 μm, none of the considered bare surface types—basalt, ultramafic, Fe oxidized, and granitoid—can be reliably distinguished when accounting for the 3σ model precision between SPHINX and PHOENIX. At 15.0 μm, only the granitoid surface is distinguishable from all others above this threshold. These results show that stellar model uncertainty alone substantially limits our ability to constrain surface composition from photometric data, even before including other sources of uncertainty, such as stellar radius. Also, we find that current 15 μm eclipse depth estimations using different stellar models introduce a 60 ppm difference for M8 and 20 ppm for M5 stars. This model discrepancy leads to a degeneracy in retrieved planetary albedos and weakens constraints on the presence of an atmosphere. We therefore recommend that future JWST secondary eclipse observations systematically include stellar mid-IR spectroscopy to mitigate these uncertainties.

Keywords: M dwarf stars, Infrared spectroscopy, Exoplanet systems, Exoplanet astronomy, Exoplanet surfaces
Radiative Flux from a High-resolution Atmospheric Dynamics Simulation of a Hot Jupiter for JWST and Ariel. We present medium-wave (∼0.5–13 μm) radiative flux distributions and spectra derived from high-resolution atmospheric dynamics simulations of an exoplanet, WASP-121 b. This planet serves to illustrate several important features. Assuming different chemical compositions for its atmosphere (e.g., H2/He only and Z ∈ {1, 12} times solar metallicity), the outgoing radiative flux is computed using full radiative transfer that folds in the James Webb Space Telescope (JWST) and Ariel instrument characteristics. We find that the observed variability depends strongly on the assumed chemistry and the instrument wavelength range, hence the probed altitude of the atmosphere. With H2/He only, the flux and variability originate near the 105 Pa level; with solar and higher metallicity, the ∼103 Pa level is probed, and the variability is distinguishably reduced. Our calculations show that JWST and Ariel have the sensitivity to capture the atmospheric variability of exoplanets like WASP-121 b, depending on the metallicity—both in repeated eclipse and phase-curve observations.

Keywords: Hydrodynamical simulations, Exoplanets, Hydrodynamics, Exoplanet atmospheric dynamics, Hot Jupiters, Exoplanet atmospheric variability, Planetary atmospheres, Planetary climates, Exoplanet atmospheres
Time-integrated Polarizations of the GRB X-Ray Flares. Despite decades of studies, the energy dissipation mechanism of the X-ray flares in the afterglow phase of gamma-ray bursts (GRBs) is still debated. If the jet is dominated by the Poynting flux, there would be a large-scale ordered magnetic field in it, and the X-ray flares might be powered by the magnetic reconnection process. However, if the jet is dynamical energy dominated and the magnetic field is random, the X-ray flares may be generated by the internal shocks of the cold outflow or by the synchrotron emission escaping from the hot plasma. Polarization is very sensitive to the magnetic field configuration in the radiation region; hence, it can be used as a probe of the magnetic field and the corresponding energy dissipation mechanism in the radiation region. In this paper, the magnetic reconnection model, the internal shock model, and the photosphere model are all described by a simple parametric model to study the time-integrated polarizations of the GRB X-ray flares. We found the time-integrated polarization degree of the GRB X-ray flares would concentrate on high values for the magnetic reconnection process and around zero for the internal shock or the photosphere origin. The influences of the parameters on the time-integrated polarizations are also discussed. Therefore, the statistical properties of the polarizations obtained by the dedicated polarization detector, Low-energy Polarimetry Detector on board POLAR-2, would make a distinction of the energy dissipation processes in the radiation region of the GRB X-ray flares.

Keywords: Starlight polarization, Gamma-ray bursts, Magnetic fields
AT 2019aalc: A Bowen Fluorescence Flare with a Precursor Flare in an Active Galactic Nucleus. AT 2019aalc is a peculiar sequence of highly variable emission events observed towards the nucleus of the broad-line active galactic nucleus (AGN) SDSS J152416.66+045119.0. The system exhibited two distinct UV-optical flares (the first detected in 2019, the second one in 2023). Spectra obtained following the detection of the second flare revealed prominent Bowen fluorescence (BF) and high-ionization coronal emission lines, which were much weaker, if at all detectable, in a spectrum taken following the first flare. We present and analyze a large set of multi-wavelength, multi-epoch data for this source, with particular emphasis on optical spectroscopic monitoring conducted with the Las Cumbres Observatory network. During the relatively slow dimming that followed the second optical flare, the UV-optical light curve shows a sequence of minor rebrightening events, while the BF and the coronal lines vary (roughly) in tandem with these "bumps" in the broadband light curve. Most of the observed behavior of AT 2019aalc links it to the growing class of BF flares while setting it apart from canonical tidal disruption events. However, AT 2019aalc has some outstanding peculiarities, including two short flares seen in its soft X-ray light-curve during the dimming phase of the second optical flare, and which do not seem to be linked to the emission line variations. We discuss the optical and X-ray properties of the source and possible scenarios of the origin of the flare, in particular radiation pressure instabilities in the (preexisting) AGN accretion disk.

Keywords: Accretion, Time domain astronomy, Active galactic nuclei, Transient sources
Thermodynamic Constraints on Solar Wind Radial Profiles. In this paper, we use thermodynamics to develop the radial density profile of the solar wind, which is described by kappa distributions. First, we show the connection of kappa distributions with polytropic processes, emphasizing the two "paths"—i.e., a kappa distribution of particle energies designates a polytropic relationship among the plasma moments, and, conversely, a polytropic relationship among plasma moments designates a kappa distribution of particle energies. We consider a radially dependent bulk speed and the various Hamiltonian terms for the solar wind. This generalizes earlier approaches that allowed for only a simple radially dependent potential energy and a constant bulk speed. Then, we study the profiles of density and other thermodynamic parameters and show how these can be used to determine unmeasured or missing solar wind parameters. As a proof of concept, an example analysis is performed to determine the magnetic field magnitude from observations of the plasma moments and validated with Voyager observations.

Keywords: Space plasmas, Plasma astrophysics, Heliosphere, Plasma physics
A 3D Nonequilibrium Ionization Model of a Shock Wave in the Low Corona. I. Extreme-ultraviolet Emission and Inefficient Electron Heating. Shocks in the low corona are best observed in the extreme ultraviolet (EUV); however, time-dependent ionization in the postshock region is generally incompatible with the otherwise straightforward plasma diagnostics typically applied to EUV imaging data. As a result, these rich data are largely underutilized. In this work, we present our approach to modeling the evolving EUV emission from coronal shocks, including nonequilibrium ionization (NEI) effects in the shocked plasma. Our framework combines (1) a 3D reconstruction of the shock geometry and kinematics derived from Solar Dynamics Observatory Atmospheric Imaging Assembly and STEREO-A/EUVI imaging, with (2) a simulated MHD snapshot of the pre-eruption corona built from magnetogram data, to solve Rankine–Hugoniot jump conditions. We then (3) track the density, temperature, and ionization history of the expanding 3D downstream region from which we generate synthetic postshock EUV light curves. We model the 2010 June 13 coronal mass ejection and shock wave using this framework, where we find that NEI is necessary to replicate the observed time-dependent EUV signal. This is especially true for the observed AIA 193 Å and 211 Å shock emission given that the predicted postshock temperatures would result in little Fe XII and Fe XIV. Moreover, the EUV model is highly sensitive to the postshock electron-to-ion temperature ratio (Te/Tp). We find that the data are well described by the model and broadly prefer lower Te/Tp &lt; 1, suggesting inefficient electron heating throughout most of the shock structure.

Keywords: Solar coronal mass ejection shocks, Shocks, Solar extreme ultraviolet emission
Multiwavelength Constraints on Dust Dynamics and Size Evolution in Protoplanetary Disk Rings. I. Method. Observations with the Atacama Large Millimeter/submillimeter Array and the Jansky Very Large Array have revealed many dust rings in protoplanetary disks, often interpreted as dust traps at gas pressure bumps. Previous studies have typically modeled these rings by assuming a single dust species in drift–diffusion equilibrium, neglecting dust size evolution resulting from coagulation and fragmentation. In this work, we perform numerical simulations that incorporate both dust-gas dynamics (drift and diffusion) and dust size evolution. Our results show that the radial distributions of different dust species (up to the fragmentation limit) are nearly identical in the dust ring, as dust growth dominates over drift and diffusion (e.g., with a typical dust-to-gas ratio of ϵ ∼ 10‑2). Building on this finding, we develop a comprehensive, self-consistent analytical theory that describes the dust ring structure while explicitly accounting for size evolution effects. Our model provides a unified framework for interpreting multiwavelength observations by linking the physical dust distribution to the observed ring properties, thus laying the foundation for future observational modeling.

Keywords: Hydrodynamical simulations, Gas-to-dust ratio, Dust continuum emission, Protoplanetary disks, Exoplanet formation
Rotation Signatures of TESS B-type Stars: Enlarging the Sample. Massive stars are essential for the evolution and chemical enrichment of the universe, yet their structure and evolution remain poorly understood. This study aims to expand the sample of B-type stars with known rotation periods by analyzing NASA's Transiting Exoplanet Survey Satellite (TESS) light curves (LCs). The analysis encompasses 373 B-type stars observed with 2 minute cadence LCs from TESS, employing a manifold approach that integrates three techniques: the Fast Fourier Transform, the Lomb─Scargle periodogram, and wavelet analysis. Rotational periods were identified for 14 new B-type stars in the TESS data, while periods for 16 previously studied targets were confirmed based on literature data. Among the remaining 343 stars, as a byproduct of our analysis, we have identified 36 pulsating candidates, seven with binary signatures, and 48 hot subdwarf (sdB) candidates. Integrating these three techniques offers a robust method for separating stellar rotation from other sources of variability in the LCs, such as pulsation, binarity, and sdB. Finally, the rotational periodicities identified in this study could provide valuable constraints for refining stellar evolution models, particularly those that include rotation and advancing asteroseismic analyses of massive stars.

Keywords: Stellar photometry, Stellar rotation, B stars, Variable stars
Survivors and Zombies: The Quenching and Disruption of Satellites Around Milky Way Analogs. It is necessary to understand the full accretion history of the Milky Way in order to contextualize the properties of observed Milky Way satellite galaxies and the stellar halo. This paper compares the dynamical properties and star formation histories of surviving and disrupted satellites around Milky Way–like galaxies using the D.C. JUSTICE LEAGUE suite of very high-resolution cosmological zoom-in simulations of Milky Way analogs and their halo environments. We analyze the full census of galaxies accreted within the past 12 Gyr, including both surviving satellites at z = 0, and dwarf galaxies that disrupted and merged with the host prior to z = 0. Our simulations successfully reproduce the trends in M*‑[Fe/H]‑[α/Fe] observed in surviving Milky Way satellites and disrupted stellar streams, indicating earlier star formation for disrupted progenitors. We find the likelihood and timescales for quenching and disruption are strongly correlated with the mass and time of infall. In particular, none of the galaxies accreted more than 12 Gyr ago survived, and only 20% of all accreted galaxies with M* &gt; 108 M⊙ survive. Additionally, satellites with highly radial trajectories are more likely to quench and disrupt. Disruption proceeds quickly for ≥106 M⊙satellites accreted 10–12 Gyr ago, often on timescales similar to the ∼300 Myr snapshot spacing. For high-mass satellites, the disruption timescale is faster than the quenching timescale. As a result, 92% of disrupted galaxies remain star forming up until disruption. In contrast, ultrafaint dwarfs (UFDs) tend to quench prior to accretion, and 94% of UFDs accreted up to 12 Gyr ago survive at z = 0.

Keywords: Tidal disruption, Dwarf galaxies, Galaxy evolution, Galaxy quenching, Milky Way evolution, Astronomical simulations
Testing a New Star Formation History Model from Principal Component Analysis to Facilitate Spectral Synthesis Modeling. The spectrum of a galaxy is a complicated convolution of many properties of the galaxy, such as the star formation history (SFH), initial mass function, and metallicity. Inferring galaxy properties from the observed spectrum via spectral synthesis modeling is thus challenging. In particular, a simple yet flexible model for the SFH is required to obtain unbiased inferences. In this paper, we use SFHs from the IllustrisTNG and EAGLE simulations to test SFH models in terms of their capability of describing the simulated SFHs and the spectra generated from them. In addition to some commonly used SFH models (Γ, τ, and nonparametric), we also examine a model developed from principal component analysis (PCA), trained by a set of SFHs from IllustrisTNG. We find that when using the first five principal components (eigenhistories), the PCA-based models can achieve a good balance between simplicity and accuracy. Among the models tested, the PCA-based model provides high flexibility, by capturing diverse and complex simulated SFHs. To accurately reproduce spectra generated from the simulated SFHs, it is necessary to have a degree of freedom to describe the most recent SFH (e.g., a step function covering the age of 0–0.3 Gyr). Overall, the PCA+step model performs well in capturing the diversity of SFHs and reproducing the associated spectra, suggesting it is a promising and reliable approach for spectral synthesis modeling.

Keywords: Galaxy evolution, Astronomical models, Star formation, Galaxy stellar content
Validating an Atmospheric Absorption Model through Solar Instrumentation on Sounding Rockets. Extreme-ultraviolet and X-ray data taken from suborbital sounding rocket platforms are affected by atmospheric absorption. The absorption correction factor varies with time, launch location, launch profile, and atmospheric conditions. This discussion is the first application of our spherical shell model for computing atmospheric absorption features. We find good agreement between the predicted and observed absorption in the first two flights of the High-resolution Coronal Imager sounding rocket instrument. We also find that the model agrees with the near-negligible absorption found at the longer wavelengths observed with the Marshall Grazing Incidence X-ray Spectrometer X-ray spectra. We now intend to explore the results from past and future missions, apply this model with greater confidence, and uncover novel insights.

Keywords: Theoretical models, Earth atmosphere, Experimental data, Solar x-ray emission, Coronagraphic imaging, Spectroscopy, Atmospheric effects
Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d. The nearby TRAPPIST-1 system, with its seven small rocky planets orbiting a late-type M8 star, offers an unprecedented opportunity to search for secondary atmospheres on temperate terrestrial worlds. In particular, the 0.8 R⊕TRAPPIST-1 d lies at the edge of the habitable zone (Teq,A=0.3 = 262 K). Here we present the first 0.6–5.2 μm NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500–1000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within ±100–150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM's sensitivity to CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (&gt;3σ). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 to further reject high mean molecular weight compositions analogous to a haze-free Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (&gt;95% confidence). If TRAPPIST-1 d retains an atmosphere, it is likely extremely thin or contains high-altitude aerosols, with water cloud formation at the terminator predicted by 3D global climate models. Alternatively, if TRAPPIST-1 d is airless, our evolutionary models indicate that TRAPPIST-1 b, c, and d must have formed with ≲4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g.

Keywords: Extrasolar rocky planets, M dwarf stars, Starspots, Exoplanets, Stellar activity, Transmission spectroscopy, Stellar faculae, Habitable planets, Exoplanet atmospheres