Sazuna/UAT_keywords huggingface dataset:
Sulfur Enrichment in Close-in Exoplanet Atmospheres Induced by Pebble Drift across the Salt Line. Observations of JWST have revealed that several close-in exoplanets have sulfur-rich atmospheres through SO2 detections. Atmospheric sulfur is often thought to originate from solid accretion during planet formation, whereas recent simultaneous detections of SO2 and NH3 challenge this conventional scenario. In this study, we propose that ammonium salts, such as NH4SH, tentatively detected in comets and molecular clouds, play a significant role in producing sulfur-rich disk gases, which serve as the ingredients of giant planet atmospheres. We simulated the radial transport of dust containing volatile ices and ammonium salts, along with the dissociation, sublimation, and recondensation of these materials, thereby predicting the atmospheric chemical structures and transmission spectra of planets inheriting these compositions. Assuming that ammonium salts sequester 20% of the elemental nitrogen and sulfur budgets, our results reveal that they enhance sulfur and nitrogen abundances in disk gases to 2─10 times the solar values near the salt dissociation line. Photochemical simulations demonstrate that SO2, NS, H2S, NO, and NH3 become the dominant N and S chemical species in the atmospheres of planets that inherited the gas compositions inside the H2O snowline. SO2 features clearly appear in the infrared transmission spectra when the salt-bearing grains enhance the sulfur abundance of disk gas by pebble drift. Our model provides a novel scenario that explains the SO2 detected in some exoplanet atmospheres solely from disk gas accretion. Volatile-element ratios, particularly N/S and C/O, would provide a key to disentangle our scenario from the conventional solid-accretion scenario.

Keywords: Atmospheric composition, Planetary atmospheres, Protoplanetary disks, Planetary science
Evolution of Supermassive Black Hole Pairs on Inclined Orbits in Postmerger Galaxies. Theoretical models of the evolution of supermassive black hole (SMBH) pairs in postmerger remnant galaxies are necessary to motivate observational searches for dual active galactic nuclei (AGN) and gravitational-wave sources. Studies have explored the dynamical evolution of SMBH pairs under the influence of dynamical friction to calculate pairing times and predict the expected population of dual-AGNs at various redshifts. We formulate a 3D dynamical model of SMBH pairs in the innermost kiloparsec of a postmerger galaxy to investigate the impact of orbital inclination with respect to the galactic disk on pairing times. The SMBH pairs are evolved in 81 different galaxy configurations initialized using a Gauss─Seidel Poisson solver. The dynamics are calculated for 12 distinct initial inclinations ranging from 0° to 75° in each of the galaxies to gauge the impact of inclination on pairing time. Orbits characterized by initial inclinations greater than 20° frequently require longer pairing times when compared to uninclined orbits. Pairing times for orbits with inclinations ≳45° often exceed 14 Gyr. Galaxies with higher-mass SMBH pairs and faster rotating disks generally shorten pairing times relative to galaxies with less massive or slower rotating disks when the inclination is ≲45°. The model suggests that SMBH pairs that form from mergers at inclinations ≲20° are likely progenitors of dual-AGN and gravitational-wave sources.

Keywords: AGN host galaxies, Supermassive black holes, Galaxy dynamics, Dynamical friction
Inclination Bias in Techniques Used to Identify Be Star Candidates. Several methods for identifying Be star candidates are reviewed for observational bias with respect to system inclination, that is the angle between the stellar and disk rotation axis and the observer's line of sight, with focus on two photometric methods that leverage narrow-band filters centred on Hα and a spectroscopic method using an Hα peak-finding algorithm. Tests for bias were performed using a sample of 20,000 synthetic Be stars drawn from a Salpeter initial mass function and computed libraries of spectral energy distributions and Hα profiles. The spectroscopic method showed substantial bias against high inclinations (i &gt; 80°). Both photometric methods were biased against low inclinations, with one also biased against inclinations above 80°, resulting in a surplus in the Be star candidate detection rate for moderate inclinations (50° &lt; i &lt; 80°). Inclination probability distributions, including the random  sini  factor, are given for the three methods that can be applied to observational samples.

Keywords: Emission line stars, Fundamental parameters of stars, Early-type emission stars, Circumstellar matter, Circumstellar disks
Broadband Timing and Spectral Study of Accreting Millisecond X-Ray Pulsar SAX J1808.4─3658 during Its 2022 Outburst. We report on our investigation of the NuSTAR and AstroSat observations along with simultaneous NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4─3658, obtained during its tenth outburst from 2022. The NuSTAR observation captured the source near the outburst peak, while AstroSat observed it during the decay phase. Coherent pulsations at ∼401 Hz were detected throughout the outburst, with the fundamental amplitude in the 3─30 keV range increasing from ∼4% near the peak to ∼6% during the decay. The pulsations display strong energy dependence and negative time lags of ∼0.2─0.3 ms, with harder photons leading softer ones. The broadband spectra in both epochs are well described by a soft thermal component and Comptonized continuum, together with a prominent relativistic reflection component. As the outburst evolved, the continuum softened (Γ increasing from ∼1.88 to ∼1.99) and the coronal electron temperature decreased (kTe from ∼31 to ∼18 keV), consistent with enhanced Compton cooling at lower accretion rates. The ionization parameter declined ( logξ  from ∼3.4 to ∼1.8) while the reflection fraction increased, suggesting a changing accretion geometry with a more compact corona and a larger disk covering fraction during the decay phase. The X-ray luminosity decreased by a factor of ∼3 between the two epochs. Our results suggest the coupled evolution of the corona, disk, and magnetosphere as the mass accretion rate declines.

Keywords: Neutron stars, Accretion, Millisecond pulsars, Compact objects, Low-mass x-ray binary stars
Signatures of Large-scale Magnetic Field Disturbances and Switchbacks in Interplanetary Type III Radio Bursts. Type III solar radio bursts are driven by nonthermal electron beams travelling along heliospheric magnetic fields, with the radio emission frequency drift rate determined by the beam speed and the plasma density profile. Analyzing beam kinematics inferred from the drift rate reveals behavior inconsistent with the emitter moving radially through smooth, monotonically decreasing density. We examine whether these features are driven by disturbances in the guiding magnetic field direction, such as switchbacks, rather than plasma inhomogeneities along the beam path. Using simulations and remote observations of 24 interplanetary type III bursts observed by Parker Solar Probe, we relate measured drift rate variations to local field deflections. In 50% of events, we identify disturbances above a 2σ noise level that can be attributed to perpendicular deflections of the field between (0.7 and 1.7) R⊙, over scales (1.8─6.4) R⊙ at heliocentric distances (9─30) R⊙. The features correspond to either density changes of (10%─30%), or deflections of the field direction by (23°─88°). Further, beam transport simulations show field direction perturbations produce additional observational signatures in type III bursts: delayed emission, intensity breaks, and enhanced emission resembling stria fine structures. In addition, we identified four bursts where the observed variations are more plausibly explained by field deflections, possibly in the form of magnetic switchbacks than by unrealistically large density changes along the field line. The results show that variations in type III burst profiles can arise from magnetic as well as density fluctuations and demonstrate the value of type III bursts as remote probes of inner-heliospheric structure at kilometric wavelengths.

Keywords: Solar radio emission, Solar magnetic fields, Heliosphere
Unveiling the Hidden Radiation: The Persistent Emission of PSR B0823+26 in Its Quiescent State. In this study, we report on a detailed polarimetric single-pulse analysis of the radio emission from the pulsar B0823+26 (J0825+2637) during its quiescent state. Using the unprecedentedly high-sensitive observations carried out with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz, potentially interesting emission features are revealed, distinct from bright-state characteristics. The interpulse emission is completely absent, with only the main pulse and postcursor components detected. Notably, no bridging emission is observed between these two distinct emission components. Both the main pulse and postcursor exhibit continuous emission without any pulse nulling phenomenon throughout the observation period. During the nearly 3 hr continuous observation period, a total of 571 bright pulses with relative pulse energy larger than 10 are detected within the main pulse window. Their energy distribution follows a power-law distribution with an index of −2.39 ± 0.03. The interburst time distribution is consistent with a stationary Poisson process, yielding a burst rate of 158 ± 8 events per hour. Furthermore, the fluctuation spectral analysis of single pulse behavior reveals the existence of a periodic amplitude modulation of longitude-stationary subpulses with a periodicity of 20 ± 7 rotational periods across the main pulse window. Possible emission mechanisms are discussed.

Keywords: Radio pulsars, Rotation powered pulsars, Pulsars
Characterizing Density and Gravitational Potential Fluctuations of the Interstellar Medium. Substructure in the interstellar medium (ISM) is crucial for establishing the correlation between star formation and feedback and has the capacity to significantly perturb stellar orbits, thus playing a central role in galaxy dynamics and evolution. Contemporary surveys of gas and dust emission in nearby galaxies resolve structure down to ∼10 pc scales, demanding theoretical models of ISM substructure with matching fidelity. In this work, we address this need by quantitatively characterizing the gas density in state-of-the-art magnetohydrodynamic simulations of disk galaxies that resolve parsec to kiloparsec scales. The TIGRESS-NCR framework we employ includes sheared galactic rotation, self-consistent star formation and feedback, and nonequilibrium chemistry and cooling. We fit simple analytic models to the one-point spatial, two-point spatial, and two-point spatiotemporal statistics of the surface density fluctuation field. We find that for both solar neighborhood and inner-galaxy conditions, (i) the surface density fluctuations follow a log-normal distribution, (ii) the linear and logarithmic fluctuation power spectra are well approximated as power laws with indices of ≍−2.2 and ≍−2.8, respectively, and (iii) lifetimes of structures at different scales are set by a combination of feedback and effective pressure terms. Additionally, we find that the vertical structure of the gas is well modeled by a mixture of exponential and  sech2  profiles, allowing us to link the surface density statistics to those of the volume density and gravitational potential. We provide convenient parameterizations for incorporating realistic ISM effects into stellar-dynamical studies and for comparison with multiwavelength observations.

Keywords: Galaxy dynamics, Molecular clouds, Interstellar medium
When Magnetic Field Lines Stretch, Snap, and Expand: A New Look at Solar Flares with L-maps. Understanding the three-dimensional evolution of coronal magnetic fields during solar flares remains challenging due to the lack of direct coronal field measurements. Here, we combine data-driven MHD simulations of NOAA AR 11158 with flare-ribbon and coronal-dimming observations to investigate realistic coronal magnetic-field evolution during an X-class flare. We introduce L-maps—maps of natural logarithm of magnetic field-line lengths—as a diagnostic tool to track the dynamics of simulated coronal magnetic structures. Variations in L-maps identify flare ribbons through field-line shortening and coronal dimmings through field-line lengthening. Comparison with Solar Dynamics Observatory/Atmospheric Imaging Assembly observations demonstrates strong morphological and temporal agreement, validating the simulated field evolution. Applying K-means clustering to the L-map temporal profiles, we distinguish three stages of coronal evolution: (1) slow preflare rise phase, (2) flare reconnection accompanied by coronal mass ejection (CME) rise, and (3) post-reconnection CME expansion. We detect a slow preflare rise phase of magnetic field lines routed in ribbon footpoints and identify reconnection dimming—an area of rapid expansion of active-region core magnetic field lines during the flare impulsive phase due to reconnection. Our results show that L-maps provide a powerful and physically intuitive framework for bridging simulations and observations and for tracking the full three-dimensional evolution of coronal magnetic fields during flares.

Keywords: Magnetohydrodynamics, Solar flares, Stellar astronomy, Solar physics, Stellar physics, Solar coronal mass ejections, Stellar flares, Stellar coronal mass ejections
Empirical Modeling of the Fast Solar Wind. In this work we derive empirical models of the fast solar wind by applying a Monte Carlo Markov Chain technique to in situ measurements of the wind charge state distributions to determine the wind's electron temperature, electron density, and bulk speed from the source region to the freeze-in point. We utilize 6 month averages of ACE/SWICS measurements carried out at seven different times along the solar cycle, to monitor whether the solar cycle causes any changes in the results. We use the results to estimate several wind plasma properties as well as the wave pressure and energy needed to power the solar wind in the 1-temperature wind model by S. R. Cranmer et al. We find that the bulk of the momentum and energy is injected between 1.5 and 3.0 solar radii and that the solar cycle does not qualitatively affect the results. However, the plasma acceleration predicted by our empirical model occurs much closer to the Sun than indicated by SoHO/UVCS measurements: we discuss this discrepancy as well as other approximations and limitations of the present work.

Keywords: Solar wind, Fast solar wind
The SPHEREx Satellite Mission. Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), a NASA Explorer satellite launched on 2025 March 11, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 μm with a resolving power ranging from λ/∆λ = 35─130 in 6 .″ 2 pixels. The observatory obtains a 5σ depth of 19.5─19.9 AB mag for 0.75 &lt; λ &lt; 3.8 μm with λ/∆λ ∼ 40 and 17.8─18.8 AB mag for 3.8 &lt; λ &lt; 5.0 μm with λ/∆λ ∼ 120 after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that use intensity mapping to probe the evolution of galaxies over cosmic history. By mapping the depth of infrared absorption features over the Galactic plane, SPHEREx will comprehensively survey the abundance and composition of water and other biogenic ice species in the interstellar medium. The project will release initial data rapidly in the form of spectral images, and specialized data products over the life of the mission as the surveys proceed. The science team will also produce spectral catalogs of planet-bearing and low-mass stars, solar system objects, and galaxy clusters three years after launch. We describe the design of the instrument and spacecraft, which flow from the core science requirements. Finally, we present an initial evaluation of the satellite's in-flight performance and key characteristics.

Keywords: Cosmology, Space vehicle instruments, Infrared spectroscopy, Interstellar abundances, Galaxy evolution
The Keck/DEIMOS Stellar Archive. I. Uniform Velocities and Metallicities for 78 Milky Way Dwarf Galaxies and Globular Clusters. We present a homogeneous spectroscopic dataset of 22,339 stars in 78 Milky Way dwarf galaxy satellites and globular clusters. All data were taken with the Keck II telescope and Deep Extragalactic Imaging Multiobject Spectrograph (DEIMOS) using the 1200G grating (spectral resolution R ≃ 6000). Based on a uniform data reduction of 411 DEIMOS masks, we present a catalog of individual stellar radial velocities, equivalent-width-based [Fe/H] metallicities, and membership estimates. The Milky Way satellites range from MV = 2 to −14 (M⋆ = 101.5─107.5 M⊙); the majority of individual stars presented in these systems have magnitudes between 17 &gt; r &gt; 22. We additionally present redshifts for 2097 compact background galaxies and QSOs in the same magnitude range. The data were reduced to 1D spectra using PypeIt, which provides near Poisson-statistics-level sky subtraction. Radial velocities were determined via dmost, a forward modeling method first presented here, which combines both synthetic telluric and stellar templates to determine stellar radial velocities. We assess the accuracy and precision our method via comparison to thousands of repeat measurements and literature values. We determine a velocity error floor of 1.1 km s−1 and a Ca II-triplet-based metallicity error floor of 0.1 dex. We calculate internal velocity dispersions and compare to literature values, demonstrating 20%─50% improved precision over the literature in most cases. In a companion paper, we use our homogeneous catalogs to explore properties of these Milky Way satellites, including previously unpublished measurements in several systems including Boötes II and Draco II. We provide full access to the data catalogs to enable further studies.

Keywords: Globular star clusters, Dwarf galaxies, Spectroscopy, Radial velocity, Metallicity
Eccentricity Evolution of Warm Jupiters: The Role of Distant Perturbers and nearby Companions. Warm Jupiters (WJs)—giant exoplanets with orbital periods between 10 and 200 days—exhibit a broad range of eccentricities and are often accompanied by nearby low-mass planets. Understanding the origins of their orbital architectures requires examining both their migration histories and subsequent dynamical interactions. In this study, we perform extensive N-body simulations to explore how distant giant planet perturbers affect the eccentricity evolution of WJs and the role of nearby super-Earth (SE) companions in mediating these interactions. We find that while distant perturbers can induce large-amplitude eccentricity oscillations in WJs via the von Zeipel─Lidov─Kozai mechanism, the presence of nearby SE companions often suppresses these variations via strong dynamical coupling. This mechanism naturally leads to a bimodal eccentricity distribution: WJs with nearby companions tend to maintain low eccentricities, whereas those without exhibit significantly broader eccentricity distributions. We show that reproducing the observed eccentricity distribution of WJs lacking nearby companions is most naturally explained if a substantial fraction of distant perturbers occupy dynamically extreme orbits, either with large mutual inclinations or high orbital eccentricities. These results support a scenario in which WJs experience substantial postdisk dynamical evolution, shaped jointly by distant perturbers and nearby companions.

Keywords: Exoplanet dynamics, Exoplanet systems, Exoplanets
Disentangling the Spectroscopic Signatures of Clumping and Corotating Interaction Regions in the Wolf─Rayet Star WR 6. Wolf─Rayet (WR) winds exhibit variability driven by small-scale clumping and large-scale corotating interaction regions (CIRs), but their interplay remains uncertain. Archival high-resolution ESPaDOnS spectra of WR 6 were analyzed using wavelet decomposition to isolate variability on different scales. Time variance spectrum diagnostics confirm that clumping contributes 1% variability relative to line intensity, consistent with empirical trends for WR stars. Correlation analysis reveals strong coherence among He II lines, while the N V λ4945 and He I λ5876 lines display weaker or shifted correlations, reflecting differences in their line-formation regions relative to He II. Models in which CIRs locally suppress clumping demonstrate that if such interactions occur, spectroscopic diagnostics remain inconclusive. These results provide direct evidence that CIRs and clumping can coexist in WR winds.

Keywords: Wolf-Rayet stars, Stellar winds, Massive stars
2D Kelvin─Helmholtz Instability with Anisotropic Pressure. The Kelvin─Helmholtz (KH) instability occurs in multiple heliospheric (solar-wind stream interfaces, planetary magnetospheres, cometary tails, heliopause flanks) and interstellar (protoplanetary disks, relativistic jets, neutron star accretion disks) environments. While the KH instability has been well studied in the magnetohydrodynamic (MHD) limit, only limited studies were performed in the collisionless regime, which is conducive to the development of anisotropic pressures. Collisionless plasmas are often described using the Chew, Goldberger, and Low (CGL) equations, which feature an anisotropic pressure tensor. This paper presents a comprehensive analysis of the CGL version of the KH instability using linearized and numerical techniques. We find that the largest growth rates and the greatest incidence of magnetic effects occur in the MHD limit. In the large relaxation time CGL limit, part of the energy goes into the formation of pressure anisotropies, resulting in smaller amounts of energy being available for bending the field lines. Consequently, when we cross-compare CGL and MHD simulations that are otherwise identical, the current densities are largest in the MHD limit, and the largest magnetic islands also form in that limit. Early time and late-time formations of pressure anisotropies have also been studied. We also find that the strongest trend for forming intermittencies in the flow also occurs in the MHD limit. The paper also discusses possible consequences of our results for turbulence and reconnection in the heliosheath (the layer between the solar wind termination shock and the heliopause).

Keywords: Magnetic fields, Astrophysical fluid dynamics, Heliosphere, Magnetohydrodynamical simulations