Sazuna/UAT_keywords huggingface dataset:
Asteroseismology of Carbon-deficient Red Giants: Merger Products of Hierarchical Triple Systems?. Carbon-deficient giants (CDGs) are a rare and chemically peculiar class of stars whose origins remain under active investigation. We present an asteroseismic analysis of the entire known CDG population, selecting 129 stars observed by Kepler, K2, and TESS to obtain seismic constraints. We detect solar-like oscillations in 43 CDGs. By measuring  νmax  and applying seismic scaling relations, we determine precise masses for these stars, finding that 79% are low mass (M ≲ 2 M⊙). The luminosity distribution is bimodal, and the CDGs separate into three chemically and evolutionarily distinct groups, characterized by clear trends in sodium and CNO abundances, α-element enhancement, and kinematics. We find that two of these groups are only distinguished by their initial α-element abundances, thus effectively reducing the number of groups to two. Lithium enrichment is common across all groups, linking CDGs to lithium-rich giants and suggesting a shared evolutionary origin. We find that the spectroscopic  logg  is systematically offset from seismic values. Group 1 CDG patterns are most consistent with formation through core He-flash mixing, while the more massive and more chemically processed Groups 2 and 2α likely formed through mergers involving helium white dwarfs, possibly in hierarchical triples. Pollution from asymptotic giant branch stars appears very unlikely, given the unchanged [C+N+O] abundance across all groups.

Keywords: Weak G band stars, Chemically peculiar giant stars, Binary stars, Stellar mergers, Stellar abundances, Low mass stars, Asteroseismology
Constraints on Diffuse X-Ray Emission from the TeV Halo Candidate HESS J1813-126. Extended regions of very high-energy γ-ray emission associated with middle-aged pulsars have been found by γ-ray observatories. These regions, called TeV halos or pulsar halos, are thought to be created when energetic electrons from a pulsar or pulsar wind nebula transport into the interstellar medium and undergo inverse Compton scattering with the cosmic microwave background radiation and the interstellar radiation field. The same electrons are expected to emit synchrotron emission in the X-ray band in the interstellar magnetic field. HESS J1813-126 is a pulsar halo candidate from which TeV γ-ray emission with extension 0 .° 21 and a hard E−2 spectrum is observed. We searched for the synchrotron component of this pulsar halo with Swift-X-Ray Telescope (XRT). In particular, we observed two fields within the region covered by HESS J1813-126 for 35 ks each and a region nearby as a background reference for 10 ks. We also analyzed 21 ks of archival Swift-XRT observations of PSR J1813-1246 and archival Swift-XRT observations of the nearby Galactic X-ray background. We find no evidence for excess X-ray emission from the two observations near HESS J1813-126 and place an upper limit differential flux of 2.18 × 10−3 and 2.02 × 10−3 keV−1 cm−2 s−1 at 1 keV, assuming a power-law spectrum in Fields 1 and 2. The archival differential flux upper limit is 3.36 × 10−3 keV−1 cm−2 s−1 at 1 keV. The nondetection implies that the magnetic field inside the halo is not significantly enhanced compared to the average Galactic magnetic field.

Keywords: Gamma-ray sources, X-ray astronomy, Pulsars
Turbulent Gas-rich Disks at High Redshift: Origin of Thick Stellar Disks Through 3D "Baryon Sloshing". In response to recent observations from JWST and Atacama Large Millimeter Array, we explore a new class of dynamically self-consistent models that mimics a plausible progenitor of the Milky Way over a wide range of disk gas fractions, fgas. The high gas surface densities encourage vigorous star formation, which in turn couples with the gas to drive turbulence. We show that this coupling through momentum recoil drives a random walk of the baryonic potential minimum with respect to total gravitational potential, Φtot(R, ϕ, z). The amplitude of the bulk motion depends on the feedback strength, which in turn is directly associated with fgas. At its most extreme, when gas is the sole contributor to the disk potential (fgas = 100%), the amplitude of the walk can reach up to R ≍ 5 kpc within Φtot. The disk dominates over dark matter (fdisk ≳ 50%) within Rs = 2.2Rdisk, where Rdisk is the exponential disk scale length. For a lower fdisk and/or fgas, the 3D sloshing amplitude and velocity are reduced. The combination of strong feedback and sloshing leads to the newly formed stars being dynamically heated and settling to a more spatially extended disk population. The 3D heating process is roughly isotropic but its effects are more noticeable in ∣z∣ due to the initial dynamical coldness of the star-forming disk. Such a disk has enhanced [α/Fe] stellar abundances and a vertical (but no radial) gradient in stellar age and metallicity, both consistent with the Milky Way's thick stellar disk.

Keywords: Galaxy chemical evolution, Galaxy dynamics, Milky Way dynamics, Galaxy disks, Galaxy evolution
Wakes from Companion Interactions in Type Ia Supernovae Nebular Emission Line Profiles. Thermonuclear supernovae (SNe) are the result of the nuclear transformation of carbon/oxygen white dwarfs (WDs) to the radioactive element 56Ni and intermediate mass elements like Ca, Ar, etc. Most progenitor scenarios involve a companion star that donates matter to the exploding WD, implying a fundamental prediction: the formation of a wake in the explosive ejecta as it runs into and moves past the companion star. This wake leaves an indelible imprint on the ejecta's density, velocity, and composition structure that remains fixed as the ejecta reaches homologous expansion. We simulate the interaction of the ejecta and Roche-lobe filling donor in a double degenerate double detonation Type Ia progenitor scenario and explore the detectability of this imprint in late-time nebular phase spectroscopy of Type Ia SNe under the assumption of local heating (t &gt; 200 days). At these times, the velocity profiles of forbidden emission lines reflect the velocity distribution of all of the ejecta and the critical electron density for that forbidden line. We explicitly calculate line shapes for the [Co III] 11.89 μm line that traces the initial 56Ni distribution and the [Ar III] 8.99 μm line, which traces a typical intermediate mass element. We predict the viewing angle dependence of the line shape, present a tool to quickly calculate optically thin line shapes for various 3D density─velocity profiles, and discuss JWST observations.

Keywords: White dwarf stars, Hypervelocity stars, Type Ia supernovae, Binary stars
Lost Sisters Found: TESS and Gaia Reveal a Dissolving Pleiades Complex. Most star clusters dissolve into the Galaxy over tens to hundreds of millions of years after they form. While recent Gaia studies have honed our view of cluster dispersal, the exact chronology of which star formation events begat which star cluster remnants remains unclear. This problem is acute after 100 Myr, when cluster remnants have spread over hundreds of parsecs and most age estimates for main-sequence stars are too imprecise to link the stars to their birth events. Here we develop a Bayesian framework that combines TESS stellar rotation rates with Gaia kinematics to identify diffuse remnants of open clusters. We apply our method to the Pleiades, which previous studies have noted shows kinematic similarities to other nearby young stellar groups. We find that the Pleiades constitutes the bound core of a much larger, coeval structure that contains multiple known clusters distributed over 600 pc. We refer to this structure as the Greater Pleiades Complex. On the basis of uniform ages, coherent space velocities, detailed elemental abundances, and traceback histories, we conclude that most stars in this complex originated from the same giant molecular cloud. This work establishes a scalable approach for tracing the genealogies of nearby clusters and further cements the Pleiades as a cornerstone of stellar astrophysics. We aim to apply this methodology to other associations as part of the upcoming TESS All-Sky Rotation Survey.

Keywords: Open star clusters, Stellar rotation, Young star clusters, Stellar evolution
Modeling the Excitation, Propagation, and Damping of Quasiperiodic Fast Magnetosonic Waves in Realistic Coronal Active Region Magnetic Field Structures. Quasiperiodic fast propagating (QFP) magnetosonic waves have been discovered in the solar corona in the extreme ultraviolet (EUV) since the launch of the Solar Dynamics Observatory (SDO) spacecraft more than a decade ago. The QFP waves are associated with flares and coronal mass ejections, providing information on flare pulsations as well as on the magnetic field by MHD wave seismology. Previous models of QFP waves primarily used idealized magnetic active region (AR) structures. However, more realistic AR numerical models are needed to improve the application of coronal seismology to observations of waves in coronal structures. Here, we extend the previous models by including a realistic magnetic configuration based on an observed coronal AR in a case study using AR 11166, observed on 2011 March 10 by the SDO Atmospheric Imaging Assembly, using potential field extrapolation of the photospheric magnetic field with realistic gravitationally stratified density structure and typical coronal temperature in our resistive 3D MHD model. We aim at reproducing the observed QFP properties, such as directionality, propagation, reflection, nonlinearity, and damping of these waves. We model various forms of excitation of QFPs through time-dependent boundary conditions and localized pulses at the base of the corona. We produce synthetic emission measure maps from the 3D MHD modeling results to facilitate comparison to EUV observations. We find that the present, more realistic model provides better qualitative agreement with observations compared to previous idealized models, improving the study of QFP wave excitation, propagation, and damping in coronal ARs, with potential applications to coronal seismology.

Keywords: Solar coronal transients, Magnetohydrodynamics, Solar coronal waves, Active solar corona, Solar coronal seismology, Magnetohydrodynamical simulations
Constraining the Mass Loss and the Kinetic Energy of Stellar Coronal Mass Ejections with Solar Far-ultraviolet Flares. Stellar eruptive events, such as flares and coronal mass ejections (CMEs), can affect planetary habitability by disturbing the stability of their atmospheres. For instance, strong stellar flares and CMEs can trigger atmospheric escape and, in extreme cases, may strip away the atmosphere completely. While stellar flares have been observed and explored at a wide range of wavelengths, the physical properties of stellar CMEs remain unconstrained due to the difficulty in observing them. In this context, the Sun provides our only window on the potential characteristics of CMEs on Sun-like stars. A correlation between solar X-ray flare peak flux and the mass of flare-associated solar CMEs has been reported using solar data collected during Solar Cycle 23. Here, we build upon that work. We extend the correlation into the far-UV (FUV), where stellar flares are, and will continue to be, routinely detected with existing and future FUV observatories by incorporating data spanning two entire Solar Cycles (23 and 24; 1996─2019). Using three different space missions (CMEs from Large Angle Spectrometric Coronagraph/Solar and Heliospheric Observatory, X-ray flare events from X-ray Spectrometer/GOES, and FUV flares from Atmospheric Imaging Assembly/Solar Dynamics Observatory), we report a correlation between FUV flare peak flux and energy centered at 1600 Å and mass, kinetic energy, and linear speed of flare-associated CMEs. These empirical relations enable estimates of CME masses and kinetic energies from FUV flares on Sun-like stars. While direct stellar CME detections remain elusive, the correlations derived here are likely applicable to Sun-like stars and provide a working framework for evaluating exoplanet atmospheric erosion.

Keywords: Stellar flares, Solar flares, Solar coronal mass ejections, Stellar coronal mass ejections
Magnetic Dip Found in a Quiescent Prominence Foot via Observation and Simulation. Solar prominences (or filaments) are cooler and denser plasma suspended in the much hotter and rarefied solar corona. When viewed on the solar disk, filament barbs or feet protrude laterally from the filament spine. When observed at the limb of the Sun, they reach into the chromosphere or even further down. For a long time, the magnetic field orientation of barbs has remained a mystery due to the paradox that the barbs possess vertical fine structures and flows but are likely to be supported in a horizontal magnetic field. Here we present unambiguous observations of a magnetic dip in a quiescent prominence foot with an upward-curved field. That is indicated by the horizontal bidirectional outflows probably produced by magnetic reconnection between the fields of a tiny erupting filament and those in a prominence foot. The altitude at the bottom of the dip is ∼30 Mm. At the edge of the prominence foot, the angle between the dip field and the local horizontal is ∼4°. Additionally, the curvature radius of the dip bottom is estimated to be around 73 Mm. We also conduct magnetofrictional simulation to self-consistently form a large-scale magnetic flux rope with magnetic dips resembling the spine and feet of the quiescent prominence. The observations shed light on the field structure of prominences, which is crucial for the instability that accounts for the eruption of prominences and coronal mass ejections.

Keywords: Solar prominences, Solar magnetic reconnection, Quiet sun, Solar filaments, Solar activity
The Gradient of Mean Molecular Weight across the Radius Valley. Photoevaporation shapes the observed radii of small exoplanets and constrains the underlying distributions of atmospheric and core masses. However, the diversity of atmospheric chemistries corresponding to these distributions remains unelucidated. We develop a first-principles carbon─hydrogen─oxygen─sulfur─silicon (CHOSSi) outgassing model that accounts for nonideal gas behavior (via fugacities) at high pressures, as well as the tendency for water and hydrogen to dissolve in melt (via solubility laws). We use data-driven radius valley constraints to establish the relationship between the atmospheric surface pressures and melt temperatures of sub-Neptunes. Sub-Neptunes with less massive rocky cores retain less of their primordial hydrogen envelopes, which leads to less heat retention and diminished melt temperatures at the surfaces of these cores. Lower melt temperatures lead thermodynamically to the dominance of carbon-, oxygen-, sulfur-, and silicon-bearing molecules over molecular hydrogen, which naturally produce a diversity of mean molecular weights. Our geochemical outgassing calculations robustly predict a gradient of mean molecular weight across the radius valley, where the strength of this gradient is primarily driven by the oxygen fugacity of the molten cores and not by the carbon enrichment (or "metallicity") of the atmosphere. Smaller sub-Neptunes are predicted to have less hydrogen-dominated atmospheres. Establishing the precise relationship between the observed and outgassed chemistries requires an understanding of how convection near the core interacts with large-scale atmospheric circulation (driven by stellar heating) near the photosphere, as well as the influence of photochemistry.

Keywords: Exoplanets
Simulations of Multiple Dust Ring Formation in a Subsolar-metallicity Protoplanetary Disk. Super-Earths exist around subsolar-metallicity host stars with a frequency comparable to that around solar-metallicity stars, suggesting efficient assembly of dust grains even in metal-deficient environments. In this study, we propose a pathway for the formation of multiple dust rings that will promote planetesimal formation in a subsolar-metallicity disk. We investigate the long-term evolution of a circumstellar disk with 0.1 Z⊙ over 750 kyr from its formation stage using two-dimensional thin-disk hydrodynamic simulations. The motion of dust grains is solved separately from the gas, incorporating dust growth and self-consistent radial drift. The disk is initially gravitationally unstable and undergoes intense fragmentation. By 300 kyr, it tends toward a stable state, leaving a single gravitationally bound clump. This clump generates tightly wound spiral arms through its orbital motion. After the clump dissipates at ∼410 kyr, the spiral arms transition into axisymmetric substructures under the influence of viscosity. These axisymmetric substructures create local gas pressure bumps that halt the inward radial drift of dust grains, resulting in the formation of multiple ring-shaped dust distributions. We observe several rings within ≃200 au of the central star, with separations between them of the order of ∼10 au, and dust surface density contrasts with inter-ring gaps by factors of ∼10─100. We also demonstrate that turbulent viscosities at observationally suggested levels are essential for converting spiral arms into axisymmetric substructures. We speculate that the physical conditions in the dust rings may be conducive to the development of streaming instability and planetesimal formation.

Keywords: Protoplanetary disks, Planet formation, Circumstellar disks
CIBER Fourth-flight Fluctuation Analysis: Measurements of Near-infrared Auto and Cross Power Spectra on Arcminute to Subdegree Scales. We present new anisotropy measurements in the near-infrared for angular multipoles 300 &lt; ℓ &lt; 105 using imaging data at 1.1 and 1.8 μm from the fourth flight of the Cosmic Infrared Background Experiment (CIBER). Using improved analysis methods and higher-quality fourth-flight data, we detect surface brightness fluctuations on scales ℓ &lt; 2000 with CIBER auto power spectra at ∼14σ and 18σ for 1.1 and 1.8 μm, respectively, and with cross power spectra at ∼10σ. The CIBER measurements pass internal consistency tests and represent a 5─10× improvement in power spectrum sensitivity on several-arcminute scales relative to that of existing studies. Through cross correlations with tracers of diffuse galactic light (DGL), we determine that scattered DGL contributes &lt;10% to the observed fluctuation power at high confidence. On scales ℓ &lt; 2000 ( θ&gt;5' ), the CIBER auto and cross power spectra exceed predictions for integrated galactic light (IGL) and integrated stellar light (ISL) by over an order of magnitude, and are inconsistent with our baseline IGL+ISL+DGL model at high significance. We cross-correlate two of the CIBER fields with 3.6 and 4.5 μm mosaics from the Spitzer Deep Wide-field Survey and find similar evidence for departures from Poisson noise in Spitzer-internal power spectra and CIBER × Spitzer cross power spectra. A multiband analysis indicates that the wavelength dependence of low-ℓ auto power fluctuations is bluer than the Poisson noise from IGL and ISL; however, the cross correlation coefficient rℓ of nearly all band combinations decreases with decreasing ℓ, disfavoring astrophysical explanations that invoke a single correlated sky component.

Keywords: Large-scale structure of the universe, Diffuse radiation, Galaxy evolution, Cosmic background radiation, Near infrared astronomy
UHECRs Propagation and Their Multimessengers: Upper Limits and the Impact of the Extragalactic Magnetic Field. The detection of high-energy astrophysical multimessengers establishes a connection between ultra-high-energy cosmic rays (UHECRs) and powerful cosmic accelerators. Interactions of UHECRs with radiation fields and interstellar matter generate very-high-energy (VHE) gamma rays and neutrinos, making them key components in the multimessenger framework. This study examines the cosmogenic gamma-ray and neutrino fluxes resulting from UHECR propagation in starburst galaxies with supernova remnants, with a particular focus on NGC 1068, a well-established high-energy neutrino source. Using extragalactic simulations, we calculate the upper limit on cosmic-ray luminosity, applying upper limits on gamma-ray fluxes derived from observations by H.E.S.S. and MAGIC observatories. Our analysis incorporates the effects of both extragalactic and galactic magnetic fields on particle propagation, constraining the maximum extragalactic magnetic field (EGMF) intensity to 10−14 G to ensure that at least 90% of injected UHECRs successfully reach Earth. The results provide upper limits on gamma-ray and neutrino fluxes, estimates of UHECR luminosity for individual sources, and predictions for the detection capabilities of the Cherenkov Telescope Array Observatory regarding gamma-ray emission from NGC 1068. Combining gamma-ray, neutrino, and UHECR observations reinforces the importance of multimessenger approaches in understanding the nature of high-energy astrophysical sources and their role in cosmic-ray acceleration.

Keywords: Gamma-ray observatories, Neutrino astronomy, Gamma-rays, Cosmic rays
Bursty or Heavy? The Surprise of Bright Population III Systems in the Reionization Era. The nature of the first, so-called Population III (Pop III hereafter) stars has long remained largely unconstrained. However, the James Webb Space Telescope (JWST) finally opened new concrete prospects for their detection during the Epoch of Reionization, notably providing promising observational constraints on the Pop III ultraviolet luminosity function at z ≍ 5.6─6.6. These preliminary data hint toward an unexpected population of UV-bright Pop III sources, which challenges the prevailing view that Pop III star formation is confined to molecular-cooling mini-halos. Here we show that there are two families of models that can explain these surprising observations, either by allowing for late-time Pop III formation within massive, atomic-cooling halos (with halo masses up to  MupIII≳1010M⊙ ) or by invoking a highly bursty Pop III star formation activity (with a stochasticity parameter  σUVIII≳1.5 ). In these scenarios, Pop III systems would have to be either heavier or burstier than usually assumed, underscoring the need to reconsider common assumptions about Pop III star formation sites, and the potential implications of JWST candidates for current and future observations.

Keywords: Luminosity function, Early universe, Population III stars, Theoretical models, James Webb Space Telescope, Reionization, High-redshift galaxies