Sazuna/UAT_keywords huggingface dataset:
Monosilane Worlds: Sub-Neptunes with Atmospheres Shaped by Reduced Magma Oceans. High-precision infrared spectroscopic measurements now enable detailed characterization of sub-Neptune atmospheres, potentially providing constraints on their interiors. Motivated by this, atmospheric models have been developed to explore chemical interactions between hydrogen-dominated atmospheres and possibly underlying magma oceans with various redox states. Recent models have predicted monosilane (SiH4) as a potential atmospheric species derived from magma oceans in sub-Neptunes, but suggested that it is highly depleted in the observable atmospheric layers. Here, we propose that SiH4 can persist throughout the atmospheres of sub-Neptunes with FeO-free reduced magma oceans by considering the dissolution of H2O into the magma oceans, a factor not accounted for in previous models. We construct a one-dimensional atmospheric model to simulate the chemical equilibrium composition of hydrogen-dominated atmospheres overlying FeO-free magma oceans, incorporating H─O─Si chemistry. Our results show that the dissolution of H2O enhances the SiH4 molar fraction to levels of 0.1%─10%, preventing it from reverting to silicates in the upper atmospheric layers. We find that SiH4-rich atmospheres can exist across a broad parameter space with ground temperatures of 2000─6000 K and hydrogen pressures of 102─105 bar. We discuss that SiH4-rich atmospheres could contain the other silanes but lack C-/N-/O-bearing species. The detection of SiH4 in future observations of sub-Neptunes would provide compelling evidence for the presence of a rocky core with a reduced magma ocean. However, the accuracy of our model is limited by the lack of data on the nonideal behavior and radiative properties of SiH4, highlighting the need for further numerical and laboratory investigations.

Keywords: Exoplanet atmospheres, Planetary interior, Exoplanets
Seismic Constraints on the Spin Evolution of Slowly Rotating Young Intermediate-mass Stars. δ Scuti stars are hot, rapid rotators and a poorly understood class of pulsators. Asteroseismology provides the only means with which to probe their interior dynamics. However, their complex and unexplained oscillation patterns restrict analyses to only a small fraction with interpretable pulsations. Here, we identify 5381 δ Scuti stars from 63 sectors of TESS observations, of which 300 had interpretable oscillations, with 24 showing rotational splittings. We inferred compositions and ages (τ) for the 300 stars, finding them in near-zero-age-main-sequence (ZAMS) states, and measured the mean envelope rotation rates (&lt;frot&gt;) for 24 of them. Analyzing their age-dependent rotation, we found that these stars essentially exhibit weak to no spin-down while evolving past the ZAMS across a narrow time span during which they show regular pulsations. A quantitative fit to their spin evolution results in a trend frot(d‑1) ∝ (τ/Gyr)‑0.048 ± 0.016, much slower than the spin-down of cooler late-type stars due to magnetic braking (Skumanich's law: frot(d‑1) ∝ (τ/Gyr)‑0.5). Based on stellar evolution calculations, we show that this weak spin-down is consistent with the gradual increase in the moment of inertia.

Keywords: Delta Scuti variable stars
The Effects of Cuboid Particle Scattering on Reflected Light Phase Curves: Insights from Laboratory Data and Theory. Understanding the optical properties of exoplanet cloud particles is a top priority. Many cloud condensates form as nonspherical particles and their optical properties can be very different from those of spheres. In this study, we focus on KCl particles, which likely form as cuboids in warm (T = 500─1000 K) exoplanet atmospheres. We compare the phase functions (at 532 nm wavelength) of KCl particles computed with Mie theory, the two-term Henyey─Greenstein (TTHG) approximation, laboratory data, and the discrete dipole approximation (DDA). Mie theory assumes scattering from spheres, while TTHG functions are used to approximate cloud scattering in two-stream radiative transfer models like PICASO. Laboratory measurements and DDA allow for a robust understanding of scattering from cuboid and deformed cuboid particle shapes. We input these phase functions into PICASO using cloud distributions from the cloud model Virga, to determine how different phase functions can impact the reflected-light intensities of the benchmark sub-Neptune, GJ 1214b. Simulated reflected light phase curves of GJ 1214b produced using the TTHG, laboratory, and DDA phase curves differ by less than 3 ppm. Our findings suggest that TTHG phase functions may be useful for approximating the scattering intensity of certain cuboid and irregular particle shapes. Future work should expand upon the wavelengths and particles considered to better determine when scattering approximations, like TTHG, may be useful in lieu of more accurate, but time-consuming laboratory measurements and/or nonspherical scattering theory.

Keywords: Mini Neptunes, Interdisciplinary astronomy, Atmospheric clouds, Exoplanet atmospheres
The Moon as a Cosmic-Ray Spectrometer: Prospects for MeV Gamma-Ray Observations. The Moon is the closest celestial gamma-ray emitting object. Its gamma-ray emission arises from interactions between Galactic cosmic rays (CRs) and the lunar surface. While the lunar GeV gamma-ray spectrum is dominated by a continuum from hadronic decay processes, the MeV emission exhibits both continuum and distinctive spectral lines from nuclear de-excitation and radioactive decay processes. Using Geant4 Monte Carlo particle simulations, we model the lunar gamma-ray spectrum. Our results demonstrate its consistency with Fermi-Large Area Telescope observations, and predict that next-generation MeV gamma-ray instruments will detect both the lunar MeV continuum and several key spectral line features, notably the 1.779 MeV line from 28Si de-excitation enhanced by the lunar surface composition, the e+e‑annihilation line, and radioactive decay lines from 22Na (τ ≈ 3.75 yr) and long-lived 26Al (τ ≈ 1 Myr). These gamma-ray lines are sensitive to CRs with energies ≲1 GeV nuc‑1, offering unique temporal probes of CR activity over different timescales. Observations of the lunar MeV gamma-ray spectrum will therefore open a new window to study the current irradiation of the solar-terrestrial environment by low-energy CRs and its long-term temporal evolution.

Keywords: Gamma-ray lines, Cosmic rays, Monte Carlo methods, The Moon, Gamma-ray astronomy, Nuclear physics
The Nonthermal Emission Following GW170817 is Consistent with a Conical Radially Stratified Outflow with Initial Lorentz Factor ≲10. We show that the nonthermal radio to X-ray emission following the neutron star merger GW170817 is consistent with synchrotron emission from a collisionless shock driven into the interstellar medium (ISM) by a conical radially stratified outflow observed ≈0.25 rad off-axis, with a power-law mass dependence on momentum, M(&gt;γβ) ∝ (γβ)‑4, maximum Lorenz factor γ = 10, opening (half-)angle ≈0.15 rad, and total energy of ≈5 × 1050 erg. The temporal dependence of the flux during its rising phase is determined by the radial stratification structure, which determines the rate at which outflow energy is deposited in the ISM. This is in contrast with highly relativistic, γ ≈ 100, structured jet models, where the angular jet structure determines the time dependence through the gradual "unveiling" by deceleration of larger angular sections of the jet (which are initially "hidden" by relativistic beaming), typically leading to a predicted flux decline after the peak that is faster than observed. Our model predicts a dependence on the observing angle, which is different than that predicted by highly relativistic jet models. Particularly, similar merger events observed closer to the symmetry axis are predicted to show a similarly extended duration of flux increase with time. Our analysis demonstrates that the data do not require a highly relativistic γ ≈ 100 component, but the presence of such a component with opening angle ≪0.15 rad and energy ≪5 × 1050 erg cannot be excluded.

Keywords: Neutron stars, Relativistic jets, Gravitational wave sources, X-ray transient sources, Non-thermal radiation sources, Radio transient sources
Comparison of Empirical and Deep Learning Models for Solar Wind Speed Prediction. In this study, we compare representative empirical models with a deep learning model for predicting solar wind speed at 1 au. The empirical models are the Wang–Sheeley–Arge–ENLIL model, which combines empirical methods with a magnetohydrodynamic model, and the empirical solar wind forecast model, which uses the relationship between the fractional coronal hole area and solar wind speed. Our deep learning model predicts solar wind speed over 3 days ahead using extreme-ultraviolet images and up to 5 days of solar wind speed before the prediction date. We evaluate the models over the test period (October–December in each year from 2012 to 2020) in view of solar activity phases and the entire period. To validate the model's performance, we use two evaluation methods: a statistical approach and an event-based approach. For statistical verification during the entire period, our model outperforms the other empirical models, with a much lower mean absolute error of 51.4 km s‑1 and rms error of 68.6 km s‑1, along with a much higher correlation coefficient of 0.69. For the event-based verification for high-speed solar wind streams, our model has superior performance in most of the six metrics evaluated within a ±1 day time window. In particular, it achieves a high success ratio of 0.82, emphasizing the model's stable performance and ability to minimize false alarms. These results show that our deep learning model has strong potential for practical application as a reliable tool for fast solar wind forecasting with its high accuracy and stability.

Keywords: Space weather, Solar wind, Neural networks
NuSTAR Observations of GS 1826-238 in the Extended Soft State. We report on the first focused NuSTAR observations of the neutron star low mass X-ray binary GS 1826-238, the "Clocked Burster," since the extended soft state began in 2014. Throughout this day-long observation, we see spectral variability that is consistent with the "banana" branch of atoll LMXBs. The NuSTAR hard X-ray spectrum is consistent with that seen during the initial soft-state excursion in 2014 and is modeled as a double Comptonized plasma: one with low temperature and high optical depth, the other with high temperature and low optical depth. The spectral variations that we see in this source are mostly consistent with variations in the optical depth of the hot component, though the total flux from the source remains nearly constant. A single Type I X-ray burst is seen during this observation, which has a short main peak (timescales of seconds) followed by an extended tail of emission. The shape of this burst is not consistent with a PRE and provide diagnostic information on the regions of the NS surface supplying the fuel for the thermonuclear reaction.

Keywords: X-ray bursts
Modeling Asteroseismic Yields for the Roman Galactic Bulge Time-domain Survey. The Galactic Bulge Time-Domain Survey (GBTDS) of the Roman Space Telescope will take high-cadence data of the Galactic bulge. We investigate the asteroseismic potential of this survey for red giants. We simulate the detectability of global asteroseismic frequencies,  νmax  and ∆ν, by modifying Kepler data to match nominal GBTDS observing strategies, considering different noise models, observing cadences, and detection algorithms. Our baseline case, using conservative assumptions, consistently leads to asteroseismic  νmax  detection probabilities above 80% for red clump and red giant branch (RGB) stars brighter than the 16th magnitude in Roman's F146 filter. We then inject these detection probabilities into a Galaxia model of the bulge to estimate asteroseismic yields. For our nominal case, we detect 290,000 stars in total, with 185,000 detections in the bulge. Different assumptions give bulge yields from 135,000 to 349,000 stars. For stars with measured  νmax , we find that we can recover ∆ν in 21%─42% of red clump stars, and 69%─92% of RGB stars. The expected yield and stellar parameter precision we predict for Roman asteroseismology promise to characterize planet-hosting stellar populations and to resolve questions regarding the formation history of the bulge.

Keywords: Stellar ages, Asteroseismology, Galactic bulge
The Impact of Physical Processes on the Radial Evolution of the Distant Pickup Ion Mediated Solar Wind. H+ pickup ions (PUIs), formed through charge exchange between solar wind (SW) protons and interstellar neutral hydrogen (ISN H) atoms or by the photoionization of ISN H atoms, play a key role in governing SW dynamics. These PUIs induce MHD waves by generating instabilities, driving turbulence in the outer heliosphere. The ionization cavity size is the distance at which the ISN H density becomes e‑1, which is smaller in the upwind direction than in the downwind direction. Consequently, the turbulent shear source affects the SW over a larger distance in the downwind direction than in the upwind direction. Here, we integrate the continuity, momentum, and pressure equations for ISN H with the three fluid (protons, electrons, and H+ PUIs) equations and the turbulence transport equations. We numerically solve the coupled four-fluid and turbulence transport equations between 10 and 68 au, and 10 and 115 au, before the heliospheric termination shock in the New Horizons (NH) and Pioneer 10 (P10) directions, respectively. We present the comparison of the theoretical results with the SW proton and PUI data of NH and the SW proton data of P10. We present the theoretical results of the low-frequency MHD turbulence and the cosmic-ray mean free paths along these directions. Finally, we derive the equation for the scattering angle of radio waves by assuming isotropic and Gaussian density turbulence and calculate the scattering angle in the NH and P10 directions.

Keywords: Interplanetary turbulence, The Sun, Solar wind, Pickup ions, Cosmic rays
The Coronal Plasma Density Structure over a Solar Cycle: A Comparison of Tomography and Magnetohydrodynamic Simulations. The large-scale plasma density structure of the extended solar corona is a tracer of the underlying magnetic field configuration and dictates the structure of the solar wind in interplanetary space. Accurate density maps are therefore important to probe the physics of the solar corona and the solar wind, and to improve space-weather forecasting. Density can be estimated from coronagraph observations using solar rotational tomography and is independently provided by global magnetohydrodynamic models. This study compares densities from tomography with the Magnetohydrodynamic Algorithm outside a Sphere (MAS) model across the whole corona over a solar cycle from 2007 to late 2023. The dependence of electron densities on latitude and heliocentric height is compared, with densities in better agreement at equatorial regions and lower heights. The streamer and nonstreamer regions are compared separately, as well as the average width of the streamer belt over the duration of solar cycle 24. The MAS model densities contain more fine-scale detail than those of the tomography, but there is a very good overall agreement in the structure and location of high-density features. In polar regions, where the photospheric magnetic field measurements that drive the MAS simulations present very large uncertainties, the tomographic densities are more accurate. Investigating the accuracy and reliability of these models, and understanding their limitations is crucial. Comparisons with observations highlight their advantages and disadvantages while stressing the importance of observational techniques to help constrain current and future models.

Keywords: Solar cycle, Magnetohydrodynamics, Solar corona, Solar coronal streamers, Magnetohydrodynamical simulations
Population Models for Star Formation Timescales in Early Galaxies: The First Step toward Solving Outshining in Star Formation History Inference. James Webb Space Telescope (JWST) has revealed temporarily quenched and ultraviolet-luminous galaxies in the early Universe, suggesting enhanced star formation stochasticity. Verifying this hypothesis is critical yet challenging. Outshining, wherein light from young stars dominates the spectral energy distribution, represents perhaps the greatest challenge in inferring the formation histories of unresolved galaxies. In this paper, we take a simple model of burstiness and show that state-of-the-art inference methods with flexible star formation histories (SFHs) and neutral priors, while recovering average star formation rates (SFRs; ∼0.1 dex median offset), fail to recover the complexities of fluctuations on tens of Myr timescales, and typically underestimate masses in bursty systems (∼0.15 dex). Surprisingly, detailed SFH recovery is still sensitive to priors even when data quality is optimal, e.g., including high signal-to-noise (20 pixel‑1) spectroscopy with wide coverage (rest-frame 0.12–1.06 μm). Crucially, however, refitting the same data with a prior correctly encoding the bursty expectation eliminates these biases: median offsets in mass and SFRs decrease to ∼0.04 dex and ∼0.05 dex, respectively. Under the assumption that current population burstiness predicts past SFH, the solution to outshining in modeling statistical samples is empirically measuring recent galaxy SFHs with population modeling. A prototype is Hα/UV: while helpful, it is insufficient to constrain the expected complex burstiness. To this end, we introduce a more complete, quantitative population-level approach and demonstrate that it promises to recover the typical amplitude, timescale, and slope of the recent SFH to high accuracy. This approach thus has the strong potential to solve outshining using observations from JWST.

Keywords: Starburst galaxies, Galaxy formation, Star formation, Spectral energy distribution, Galaxy evolution, Post-starburst galaxies
How do Massive Primordial Black Holes Impact the Formation of the First Stars and Galaxies?. We investigate the impact of massive primordial black holes (PBHs; mBH ∼ 106 M⊙) on the star formation and first galaxy assembly process using high-resolution hydrodynamical simulations from z = 1100 to z ∼ 9. We find that PBH accretion is self-regulated by feedback, suppressing mass growth unless feedback is weak. PBHs accelerate structure formation by seeding dark matter (DM) halos and gravitationally attracting gas, but strong feedback can delay cooling and suppress star formation. In addition, the presence of baryon-DM streaming creates an offset between the PBH location and the peaks induced in gas density, promoting earlier and more efficient star formation compared to standard ΛCDM. By z ∼ 10, PBH-seeded galaxies form dense star clusters, with PBH-to-stellar mass ratios comparable to observed high-z active galactic nuclei like UHZ-1. Our results support PBHs as viable supermassive black hole (SMBH) seeds but do not exclude alternative scenarios. We emphasize that PBH-seeding provides a natural explanation for some of the newly discovered overmassive SMBHs at high redshift, in particular those with extreme ratios of BH-to-dynamical (virial) mass that challenge standard formation channels. Future studies with ultra-deep JWST surveys, the Roman Space Telescope, and radio surveys with facilities such as the Square Kilometre Array and Hydrogen Epoch of Reionization Array will be critical in distinguishing PBH-driven SMBH growth from other pathways.

Keywords: Early universe, Galaxy formation, Supermassive black holes, Population III stars, Dark matter
Medium-band Astrophysics with the Grism of NIRCam In Frontier Fields (MAGNIF): Spectroscopic Census of Hα Luminosity Functions and Cosmic Star Formation at z ∼ 4.5 and 6.3. We measure Hα luminosity functions (LFs) at redshifts z ∼ 4.5 and 6.3 using the JWST Medium-band Astrophysics with the Grism of NIRCam In Frontier fields (MAGNIF) survey. MAGNIF obtained NIRCam grism spectra with the F360M and F480M filters in four Frontier Fields. We identify 248 Hα emitters based on the grism spectra and photometric redshifts from combined Hubble Space Telescope and JWST imaging data. The numbers of the Hα emitters show a large field-to-field variation, highlighting the necessity of multiple fields to mitigate cosmic variance. We calculate observed and dust-corrected Hα LFs at the two redshifts. Thanks to the gravitational lensing, the measured Hα LFs span three orders of magnitude in luminosity, and the faint-end luminosity reaches LHα ∼ 1040.3 erg s−1 at z ∼ 4.5 and 1041.5 erg s−1 at z ∼ 6.3. They correspond to star formation rates of ∼0.1 and 1.7 M⊙ yr−1, respectively. We conclude no or weak redshift evolution of the faint-end slope of Hα LF across z ≃ 0.4─6.3, and the comparison with the faint-end slopes of UV LF indicates stochastic star formation history among low-mass Hα emitters. The derived cosmic star formation rate densities are  0.058−0.006+0.008M⊙yr−1Mpc−3  at z ∼ 4.5 and  0.025−0.007+0.009M⊙yr−1Mpc−3  at z ∼ 6.3. These are approximately 2.2 times higher than previous estimates based on dust-corrected UV LFs, but consistent with recent measurements from infrared surveys. We discuss uncertainties in the Hα LF measurements, including those propagated from the lens models, cosmic variance, and active galactic nucleus contribution, and we find that they have a negligible impact on the above results.

Keywords: Luminosity function, Strong gravitational lensing, James Webb Space Telescope, Star formation, High-redshift galaxies
Thermophysical Properties of Lunar Regolith Revealed by Thermal-infrared Observations of the Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer. The thermophysical properties of lunar regolith are crucial for lunar sciences and engineering. Here, we evaluate the thermophysical properties of lunar regolith between 75°N and 75°S from Diviner data by treating the radius of lunar regolith grains as a proxy. By the ground-truth median/average grain radius and Diviner data at several lunar landing sites, we recalibrate the reference rolling force for a grain radius of 0.475 μm as 0.9 ± 0.1 × 10‑7 N. On a global scale, the estimated grain radius values focus mostly between 40 and 60 μm and show an average value of ∼55.3 μm. Some regions of Oceanus Procellarum, Mare Imbrium, and Mare Frigoris show abnormally large grain radius 80–100 μm, which are associated with the late high-Ti volcanism during 2.3–1.2 Ga within Procellarum KREEP Terrane. Mare Humorum is dated to be as old as 3.9 Ga, but still shows large grain radius values of ∼100 μm that are far greater than those in other contemporaneous mares. Such an anomaly may indicate a distinguished evolution for the local lunar regolith. For the surficial lunar regolith on the global scale, the contact component of thermal conductivity normalized to a temperature of 250 K varies mostly within 0.0008–0.0014 W (m K)‑1, whereas the radiative component normalized to 250 K varies mostly within 0.002–0.004 W (m K)‑1. The thickness of the topmost loosely packed layer is estimated as 0.02–0.07 m and tends to increase with the evolution of lunar regolith, which relates to the modification of packing style with the decrease of grain radius.

Keywords: The Moon