Sazuna/UAT_keywords huggingface dataset:
Engulfment of Eccentric Planets by Giant Stars: Hydrodynamics and Light Curves. Recent observations suggest that planetary engulfment by a giant star may produce radiation that resembles subluminous red novae. We present three-dimensional hydrodynamical simulations of the interaction between an eccentric 5 MJ giant planet and its 1 M⊙ red-giant host star. The planet's pericenter is initially 60% of the stellar radius and is fully engulfed after tens of orbits. Once inside the stellar envelope, the planet generates pressure disturbances that steepen into shocks, ejecting material from the envelope. We use post-processing to calculate the light curves produced by planetary engulfment. We find that the hot stellar ejecta enhance the stellar luminosity by several orders of magnitude. A prolonged hydrogen recombination plateau appears when the ejecta cool to about 104 K. The late-time rapid dimming of the light curve follows dust formation, which obscures the radiation. For planets with lower eccentricity, the orbital decay proceeds more slowly, although the observable properties remain similar.

Keywords: Star-planet interactions, Hydrodynamical simulations
RIOJA. A Clumpy Galaxy Assembly at Redshift 6.81 Revealed by JWST. Spatially resolved multiwavelength analysis is essential to study galaxy formation and evolution. A UV-bright galaxy COS-2987030247 at z = 6.81 is one of the Rosetta Stones in the epoch of reionization for which JWST NIRSpec Integral Field Spectroscopy, NIRCam imaging, and Atacama Large Millimeter/submillimeter Array data are available thanks to the RIOJA program. We identified the rest-frame optical emission lines from the ionized hydrogen, oxygen, and neon gas. The [O III] 5008 Å line emission and the NIRCam images show a complex kinematical and morphological structure where two bright main and three faint clumps are identified in a 10 kpc extent. The system is not classified as a purely rotation-dominated disk. The multiple clumps are instead consistent with a merger-related origin, including either distinct galaxies in interaction or star-forming clumps formed through tidal gas compression during a merger. The spatially resolved emission line fluxes show that dust attenuation, metal enrichment, and ionization parameter are preferentially enhanced in the star formation peaks. Our spectral energy distribution fitting suggests that the main clumps are in a moderately dust-attenuated star-forming phase (AV = 0.2─0.3 and SFR(Hα) ∼10 M⊙ yr−1) with almost zero escape fraction of ionizing photons. In contrast, the subclumps are dust-free and lying on or below the main sequence of star-forming galaxies. These subclumps may work as a perturber that triggers the clumpy starburst in the surrounding gas through the merger event.

Keywords: Galaxy formation, James Webb Space Telescope, Galaxy evolution, Galaxy mergers, High-redshift galaxies
Pair Instability Supernova Origin of the High-[Fe/Mg] and High-[Si/Mg] Nature of the Quasar ULAS J1342+0928 at Redshift z = 7.54. The discovery of ULAS J1342+0928, a metal-enriched quasar ([Fe/H]∼1) at redshift z = 7.54 with an extremely high iron-to-magnesium abundance ratio ([Fe/Mg]∼1), has sparked a new insight into the origin of heavy elements in the early Universe. An earlier study by Yoshii et al. has shown that standard chemical evolution models of the quasar host galaxy involving Type Ia supernovae (SNe Ia) and core-collapse supernovae cannot reproduce the high-[Fe/Mg] nature of the broad-line region (BLR) gas of this quasar. Rather, the [Fe/Mg] value estimated in their study would be the result of heavy-element enrichment from a Population III (Pop III) pair-instability supernova (PISN). To investigate their result, we have run a series of photoionization models of the BLR gas enriched by such a PISN and have developed a highly updated version of their original method to convert heavy-element emission-line intensities to their abundances in the BLR gas. Our analysis reveals, for the first time, that the observed equivalent widths of Mg II, Si IV, and Fe II emission lines in ULAS J1342+0928 indicate abundance trends of [Mg/H] = 0.10 ± 0.09 (random) ± 0.3 (systematic), [Si/Mg] = 0.93 ± 0.02 (random) ± 0.2 (systematic), and [Fe/Mg] = 0.87 ± 0.06 (random) ± 0.2 (systematic). Particularly, the values of [Si/Mg] and [Fe/Mg] are best explained by a Pop III PISN with a progenitor mass of 240─280 M⊙, in support of Yoshii et al.'s result. If future observations of ULAS J1342+0928 confirm the significant odd─even effect of [Al/Mg] ≲ −1, as predicted by nucleosynthesis calculations for Pop III PISN, this would provide unambiguous evidence for the existence of a Pop III PISN at z ≳ 7 and shed light on the first Pop III stars in the Universe.

Keywords: Population III stars, Quasars, Chemical abundances, Active galactic nuclei, Stellar nucleosynthesis, Supernovae
The Cosmic Star Formation History: Insights from Kilonova-associated Gamma-Ray Bursts. The origin of the Universe and its material content remains one of the most fundamental questions in science. Gamma-ray bursts (GRBs), with their extreme luminosities and detectability at high redshifts, provide a unique window into the history of cosmic formation and chemical evolution. Consequently, the GRB formation rate (FR) has been employed to trace the star formation rate (SFR) across cosmic time. GRBs are conventionally classified into long and short categories (lGRBs and sGRBs) based on their T90 duration. sGRBs are widely employed as tracers of the delayed SFR, owing to their origin linked to the inspiral timescales of compact binary systems. However, some studies suggest that the detection of supernova-associated sGRBs may indicate potential contamination by core-collapse events. In this work, we move beyond the T90 classification and focus exclusively on GRBs with confirmed kilonova signatures, which provide unambiguous evidence of binary compact star mergers, to reassess their connection with the delayed SFR. Through analysis of a sample of kilonova-associated GRBs (KN/GRBs), we find that even within this robust subset, the KN/GRB FR displays a trend contrary to that of the delayed SFR at low redshifts (z &lt; 1). This result challenges the conventional theory by indicating that low-redshift KN/GRBs may not accurately trace the delayed SFR, independent of core-collapse contamination, while further validation with larger KN/GRB samples is essential to determine the reliability of compact binary mergers as probes of delayed SFR.

Keywords: Luminosity function, Gamma-ray bursts, Compact binary stars, Star formation, Compact objects
Possible Dynamical Pathways to the Misalignment of the VHS 1256─1257 System. Circumbinary planets (CBPs) provide a unique window into planet formation and dynamical evolution in complex gravitational environments. Their orbits are shaped not only by the protoplanetary disk but also by the perturbations from two stellar hosts, making them sensitive probes of both early- and late-stage dynamical processes. In this work, we investigate the unusual architecture of the VHS J125601.92−125723.9 system, where a retrograde, nearly polar tertiary orbits an extremely low-mass substellar binary in a hierarchical triple configuration. We find that triple-body dynamics can naturally reproduce the observed high eccentricity of the inner binary and the tertiary's near-polar obliquity. However, this configuration alone cannot account for the observed mutual inclination, which is both near-polar and retrograde. This tension suggests two possible formation pathways: either the planet formed in an aligned, protoplanetary disklike configuration and was later tilted by an additional, undetected fourth companion (below current Gaia limits), or the system formed close to its current state. Stellar flybys, in contrast, are unlikely due to their long timescales. Our results highlight both the explanatory power and the limitations of triple dynamics, and the potential role of hidden companions in shaping extreme planetary architectures.

Keywords: Orbits, Binary stars, Dynamical evolution
SN 2022acko and the Properties of Its Red Supergiant Progenitor: Direct Detection, Light Curves, and Nebular Spectroscopy. We present ultraviolet, optical, and infrared observations of the Type II-P supernova SN 2022acko in NGC 1300, located at a distance of 19.0 ± 2.9 Mpc. Our dataset spans 1─350 day postexplosion in photometry, complemented by late-time optical spectroscopy covering 200─600 days, and includes deep preexplosion imaging. We use this extensive multiwavelength dataset for both direct and indirect constraints on the progenitor system. Using the early time photometry and shock cooling models, we infer that SN 2022acko likely originated from a red supergiant with a radius of R ∼ 580 R⊙ and an initial mass of M ∼ 9─10 M⊙. From the radioactive decay tail, we infer a synthesized 56Ni mass of 0.014 ± 0.004 M⊙. We further model nebular-phase spectra using radiative transfer models and nucleosynthesis yields for core-collapse supernovae, which suggest a progenitor initial mass in the range of 10─15 M⊙. Meanwhile, a blackbody fitting of the detected preexplosion counterpart in the F814W and F160W bands indicates a red supergiant with a lower initial mass of approximately 7.5 M⊙. The light curve exhibits a 116 day plateau, indicative of a massive hydrogen-rich envelope, inconsistent with the preexplosion analysis. We investigated the discrepancy between direct and indirect progenitor mass estimates, focusing on the roles of binary interaction, early time modeling limitations, and systematic uncertainties in spectral calibration. Our results indicate that there may be tension among mass estimates, potentially arising from modeling limitations and flux calibration uncertainties rather than from insufficient data and highlighting the need for more physically realistic models and a deeper understanding of systematic effects.

Keywords: Astronomy data modeling, Red supergiant stars, Type II supernovae, Light curves, Spectroscopy
Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots. The James Webb Space Telescope (JWST) has unveiled a population of enigmatic, compact sources at high redshift known as "little red dots" (LRDs), whose physical nature remains a subject of intense debate. Concurrently, the rapid assembly of the first supermassive black holes (SMBHs) requires the formation of heavy seeds, for which supermassive stars (SMSs) are leading theoretical progenitors. In this work, we perform the first quantitative test of the hypothesis that LRDs are the direct observational manifestation of these primordial SMSs. We present a novel, first-principles pipeline generating synthetic spectra for a nonrotating, metal-free SMS up to 106 M⊙. We establish that its luminosity (Lλ ≍ 1.7 × 1044 erg s−1 μm−1 at 4050 Å) provides a decisive constraint, matching prominent LRDs. Our model self-consistently reproduces their defining spectral features: the V-shaped Balmer break morphology is shown to be an intrinsic photospheric effect, while the complex line phenomenology, strong Hβ in emission with other Balmer lines in absorption arises from non-LTE effects in a single stellar atmosphere. With wind and macroturbulent broadening, we match LRD spectra at z = 7.76 and z = 3.55, including the Hβ width of MoM-BH*-1 to within 4%. We predict a luminosity-dependent observability window, ∼104 yr for the most luminous systems and 105─106 yr if Lλ(4050 Å) is lower by 1─2 dex. These results provide a self-consistent alternative to multicomponent obscured active galactic nucleus scenarios and suggest JWST may be witnessing luminous stages of SMBH progenitors before collapse.

Keywords: Supermassive black holes, Early universe, Stellar properties, Massive stars, Stellar evolutionary models, Stellar accretion
The Shape of FIREbox Galaxies and a Potential Tension with Low-mass Disks. We study the intrinsic and observable shapes of approximately 700 star-forming galaxies with stellar masses of 108─1011M⊙ from the FIREbox simulation at z = 0. We calculate intrinsic axis ratios using inertia tensors weighted by three morphology types: "All Stars," "Young Stars," and "Luminosity-weighted Stars." Young Stars shows mass-dependent 3D configurations, with spheroidal, elongated, and disky shapes dominant at stellar masses of 108.5, 109.5, and 1010.5 M⊙, respectively. Using the radiative transfer code SKIRT, we construct mock images for each galaxy and show that projected short-to-long axis ratios, q, inferred from 2D Sérsic fits are most closely related to Luminosity-weighted Stars tensor shapes and least resemble the All Stars' shapes. This suggests observed 2D shape distributions should not be compared to predictions based on 3D stellar mass shapes. Next, we construct a sample of mock images projected in random orientations and compare them to observed axis ratio distributions from the GAMA survey. At stellar masses below 1010 M⊙, we produce too few galaxies with observed q &lt; 0.4 and none with q &lt; 0.2, suggesting that FIREbox does not produce enough low-mass disk galaxies. At higher masses, 1010─1011 M⊙, we find that the predicted q distribution is sensitive to the dust-to-metal ratio; using our fiducial model, the distribution of q values is formally consistent with observations, but there is tension with our ability to produce enough very thin systems with q &lt; 0.2. Future observational and theoretical programs aimed at understanding disk and thin-disk fractions will provide crucial tests of galaxy formation models.

Keywords: Galaxy evolution
Ion Acoustic Wave Observations Near Low-Mach Reverse Shocks. Interactions between particles and ion acoustic waves (IAWs) are considered a potential energy dissipation mechanism in low-Mach number shocks, particularly in forward shocks. However, their role in reverse shocks remains unclear. Compared with forward shocks, IAW occurrence in 88 reverse shocks (63 reliable shocks) observed by Wind at 1 au (2008─2020) is extremely low; none are detected within the shock ramp, and only 75 IAWs appear in upstream or downstream regions (only one with amplitude &gt;5 mV m−1). This scarcity should be attributed to enhanced Landau damping under high-speed solar wind and low electron-to-ion temperature ratios (Te/Ti &lt; 1). The detected IAWs could be excited by a compression-driven fluid instability associated with the shock's spatial density gradient or the electron heat flux. To quantify the ability of IAWs to contribute to shock dissipation, we found that the anomalous resistivity from IAWs (ηIA ~ 9.5 × 10−3─46 Ω m) is 1─2 orders of magnitude smaller than that reported for forward shocks. Corresponding dissipation ratios (RΨ and YΨ) remain well below 1 for all events, indicating that IAW dissipation falls far short of the macroscopic entropy-related energy dissipation requirement. However, nonlinear wave─particle interactions can enhance ηIA by 2─3 orders of magnitude, suggesting that IAWs may contribute intermittently but cannot dominate the dissipation in low-Mach number reverse shocks. These results imply that reverse shocks rely on a dissipation pathway fundamentally different from that of forward shocks, one not primarily mediated by IAWs. *Released on 2025 March 1.

Keywords: Solar wind, Interplanetary shocks
The Role of Plasma Lensing in Fast Radio Bursts. Growing evidence indicates that some fast radio bursts (FRBs) reside in dense, magnetoionic environments where extrinsic propagation effects can substantially reshape the observed signal. Within a 1D Gaussian plasma-lens framework, we show that small, monotonic variations in the incidence angle of the FRB wavefront naturally generate both downward and upward sub-burst frequency drifts. We further demonstrate that distinct lensed paths that probe different rotation measures (RMs) can produce orthogonal polarization-angle (PA) jumps at gigahertz frequencies. In this picture, a ∼90° PA transition requires only a modest RM contrast of order a few ×10 rad m−2 between the multiple images. The chromatic activity of FRB 20180916B—earlier and narrower activity windows at higher frequencies—can be explained as preferential magnification near the outer caustic. Finally, the intrinsic resolution of a plasma lens provides an upper limit on the transverse emission size: lenses located close to the source yield magnetospheric-scale constraints and offer a practical means of discriminating between inner- and outer-magnetospheric emission scenarios. These results suggest that plasma lensing could account for multiple complex observational features of FRBs and may play a nonnegligible role in modulating their observable properties.

Keywords: Radio bursts, Gravitational lensing, Radio transient sources
Presupernova Eruptions Triggered by Sudden Energy Deposition in Low-mass Core-collapse Supernova Progenitors. In low-mass core-collapse supernova (SN) progenitors, nuclear burning beyond oxygen can become explosive under degenerate conditions, triggering eruptive mass loss before the final explosion. We investigate such pre-SN eruptions using SNEC hydrodynamic simulations and realistic stellar models, parameterizing the nuclear energy deposition as a fraction of the binding energy of the combined He layer and H-rich envelope. For the lowest-mass model (9M⊙), the ejecta mass (Mej) scales with the energy gained by the H-rich envelope via a power law (index ∼ 3.5). Across 9─10M⊙, this relation shows limited scatter within a factor of ∼2.6, enabling an estimation of the gained energy from Mej. The shock passage also flattens the bound envelope, which can affect the SN light-curve morphology and provide another diagnostic for the eruption. Then, we compute the associated precursor light curves for the 9M⊙model with the multigroup radiative-transfer code STELLA. These signals are typically faint, with bolometric luminosities of ∼1039 erg lasting hundreds of days. Their cool blackbody spectra make them brighter in the infrared yet several magnitudes fainter than observed pre-SN precursors at the threshold for full envelope ejection. To aid future studies, we make our posteruption stellar profiles and precursor light curves publicly available.

Keywords: Late stellar evolution, Circumstellar matter, Transient sources, Core-collapse supernovae
Novel Polarimetric Analysis of Near-horizon Flaring Episodes in M87* in Millimeter Wavelength. Recent multiwavelength observations of M87* revealed a high-energy γ-ray flare without a millimeter counterpart. We present a theoretical study of potential millimeter flares in M87*, using general relativistic magnetohydrodynamical simulations with varying black hole (BH) spins and magnetic field configurations. The emergence of a millimeter flare is strongly influenced by both spin and magnetic structure, with limited sensitivity to the electron distribution. We model the intensity light curve with a damped random walk and compare the characteristic timescale (τ) with recent Submillimeter Array observations, finding that simulated τ exceeds observed values by over an order of magnitude. For BH spin a = +0.5, we identify a distinct flare followed by an order-of-magnitude flux drop. All Stokes parameters vary near the flare, including a sign reversal in the electric vector position angle. Most βm modes remain stable, but the EB-correlation phase is sensitive to both the flare peak and decay. We examine polarimetric signatures in photon subrings, focusing on modes ns = (0, 1). The ns = 0 signal closely matches the full image, while ns = 1 exhibits distinct behavior, highlighting the potential of space very long baseline interferometry to isolate subring features. Magnetic reconnection near the disk plane triggers a flux eruption that injects magnetized plasma into the jet funnel, enhancing outflow speeds and temporarily disrupting jet collimation before gradual recollimation. These results suggest transient variability near flares encodes key information about BH spin and magnetic structure, offering new probes of active galactic nuclei.

Keywords: Polarimetry, Astrophysical black holes
Excitation of Inertial Modes in 3D Simulations of Rotating Convection in Planets and Stars. Thermal convection in rotating stars and planets drives anisotropic turbulence and differential rotation, both capable of feeding energy into global oscillations. Using 3D simulations of rotating convection in spherical shells, we show that inertial modes—oscillations restored by the Coriolis force—emerge naturally in rotationally constrained turbulence, without imposing any external forcing other than thermal/buoyancy driving. By varying the rotation rate at fixed Rayleigh number, we find that coherent modes appear only when the convective Rossby number, the ratio of the rotation period to the convective turnover time, falls below about one-half, where rotation dominates the dynamics. These modes are mostly retrograde in the rotating frame, equatorially symmetric, and confined to mid and high latitudes, with discrete frequencies well below twice the background rotation rate. At lower viscosities, or a smaller Prandtl number, mode excitation becomes more efficient and a broader spectrum of inertial modes emerges. While the precise excitation mechanism remains uncertain, our results suggest that the modes are driven by instabilities due to differential rotation rather than stochastic forcing by convection. We conclude that similar inertial modes are likely to exist in the interiors of giant planets and stars, though their low frequencies will make them difficult to detect.

Keywords: Stellar oscillations, Internal waves, Astrophysical fluid dynamics
The Milky Way Project: Bridging Intermediate- and High-mass Star Formation with the MIRION Catalog of Yellowballs. We describe the construction and use of the Mid-InfraRed Interstellar Objects and Nebulae (MIRION) catalog, which was compiled from 6176 objects identified as "yellowballs" (YBs) by participants in the Milky Way Project. The majority of YBs are compact photodissociation regions generated by intermediate- and high-mass young stellar objects that are embedded in star-forming clumps ranging in mass from 10 to 106 M⊙ and luminosity from 10 to 104 L⊙. The MIRION catalog increases the number of candidate intermediate-mass star-forming regions (SFRs) by nearly 2 orders of magnitude, providing an extensive database with which to explore the transition from isolated low-mass to clustered high-mass star formation. The catalog comprises five tables that include mid- and far-infrared photometry, velocities of source-associated molecular clouds, distances to these molecular clouds, physical properties of source-associated star-forming clumps, and source crossmatches with other catalogs. The structure of the catalog enables users to easily sort objects for further study based on distance or environmental properties. Our preliminary analysis extends our earlier findings that indicate a relationship between infrared (IR) colors and the physical properties and evolutionary stages of SFRs. Photometry will be periodically updated online to incorporate measurements from volunteers participating in a classroom activity known as the People Enabling Research: a Yellowball Survey of the Colors Of Protostellar Environments (or PERYSCOPE) project. These updates will continue to refine the IR flux measurements and reduce photometric errors. A follow-up paper will present a detailed analysis of how IR colors can be used to predict the properties of star-forming environments.

Keywords: Surveys, Star forming regions, Star formation, Infrared sources