Sazuna/UAT_keywords huggingface dataset:
The Quasi-radial Field-line Tracing (QRaFT): An Adaptive Segmentation of the Open-flux Solar Corona. Optical observations of the solar corona provide key information on its magnetic geometry. The large-scale open field of the corona plays an important role in shaping the ambient solar wind and constraining the propagation dynamics of the embedded structures, such as interplanetary coronal mass ejections. Rigorous analysis of the open-flux coronal regions based on coronagraph images can be quite challenging because of the depleted plasma density, resulting in low signal-to-noise ratios. In this paper, we present an in-depth description of a new image segmentation methodology, the Quasi-Radial Field-line Tracing (QRaFT), enabling the detection of optical coronal features indicating the orientation of the steady-state open magnetic field. The methodology is tested using synthetic coronagraph images generated by a three-dimensional magnetohydrodynamic model. The results of the numerical tests indicate that the extracted optical features are aligned within ∼4°─7° with the local magnetic field in the underlying numerical solution. We also demonstrate the performance of the method on real-life coronal images obtained from a space-borne coronagraph and a ground-based camera. We argue that QRaFT outputs contain valuable empirical information about the global steady-state morphology of the corona, which could help improve the accuracy of coronal and solar wind models and space weather forecasts.

Keywords: Coronagraphic imaging, Space weather, Solar corona, Astronomy image processing
Quasiperiodic Polarized Emissions from Kink Structure in Magnetized Relativistic Jets. Recent polarimetric observations of blazars indicate the development of current-driven (CD) kink instability after passing the recollimation shocks in the relativistic jets and association with quasiperiodic oscillations (QPOs). To investigate multiwavelength polarized features of CD kink instability in jets, we develop RaptorP, a new special relativistic module of the polarized general relativistic radiative transfer code RAPTOR. Based on 3D SRMHD simulations of overpressured magnetized jets, we find that jet images vary at different frequencies. At low frequencies, the emission comes from the turbulent ambient medium surrounding the jet that obscures the inner jet structure. Electric Vector Position Angle (EVPA) patterns are perpendicular to the jet propagation direction, indicating a dominance of the poloidal magnetic field. At high frequencies, bright knots and twisted kink structures appear, and EVPA patterns are consistent with a toroidal magnetic field. We also find QPOs in light curves of intensity and linear polarization (degree and angle). The peak frequency in power spectral densities is well matched with the rotation period of the kink structure in relativistic jets. It shows an anticorrelation between total intensity and the degree of polarization at a lower inclination angle. Our findings, based on realistic polarized radiation calculations, will explain the observational signatures seen in blazars.

Keywords: Magnetohydrodynamics, Relativistic jets, Polarimetry, Radiative transfer
Simulation of the 2010 September 9 Solar Energetic Particle Event by Using a Data-constrained Transport Model. Solar energetic particles (SEPs) can cause damage to spacecraft systems and affect human activities in space. On 2010 September 9, a gradual SEP event was observed by spacecraft STEREO-A, Solar and Heliospheric Observatory (SOHO), and STEREO-B at widely separated longitudes. For investigating the differences in the observed time─intensity profiles among the three spacecraft, we take a physics-based model to simulate the energetic particles produced by a coronal mass ejection (CME) shock propagating in the interplanetary medium. Constrained by the observational data of spacecraft, we describe a fast CME/shock transport in a steady-state solar wind background. The distribution of SEPs at the CME-driven shock is defined by a form consistent with diffusive shock acceleration theory. By solving the focused transport equation, the temporal evolution of SEP intensity can be obtained at different locations. We find that the simulated results successfully reproduce the important observational features of the SEP event. The energetic particles remaining from prior shock acceleration constituted one of the significant sources of SEPs observed by STEREO-B and SOHO during the decay phase of the event. In contrast, STEREO-A maintained a direct magnetic connection with the shock front throughout the shock propagation, resulting in a slower decay of the SEP intensity.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Space weather
An Alternative Explanation for the Helium Star Pulsar Binary J1928+1815: The Most Heavyweight Black Widow System to Date. We present the results of deep near-infrared imaging of the recently discovered helium star pulsar binary J1928+1815 situated in the Galactic plane. Our observations did not achieve significant detections, providing limiting magnitudes of J = 23.7 and H = 22.2, which are both 2.4 mag deeper than the expected J and H magnitudes for a modeled stripped helium star with a mass of 1 M⊙ after extinction. Although we cannot completely rule out the possibility of more significant extinction and the exact evolutionary status of the supposed helium star is uncertain, by comparing J1928+1815 with other pulsar binaries, we propose a natural alternative solution: that J1928+1815 is a heavyweight black widow system with a massive ablated white dwarf. Due to the pulsar's relatively high spindown power and short orbital separation, the irradiation heating timescale is uniquely shorter than the cooling timescale for the WD companion. As a result, the WD effectively boils, with its outer layers expanding, overfilling the Roche lobe and producing low-density binary-scale haze opaque in the radio band. If this interpretation is correct, J1928+1815 would represent a new category distinct from canonical lightweight black widow systems. Radio eclipses can occur in pulsar binaries across a wider range of WD companion masses than previously thought. Therefore, they do not serve as a definitive indicator of a helium star without its direct detection. We contend that a spectroscopic identification remains the smoking gun for its existence. Given the crowding in this field, HST imaging in the near-infrared band would provide even better constraints.

Keywords: Compact binary stars, Binary pulsars, Millisecond pulsars
The SAGA Survey. VI. The Size─Mass Relation for Low-mass Galaxies Across Environments. We investigate how Milky Way (MW)─like environments influence the sizes and structural properties of low-mass galaxies by comparing satellites of MW analogs from the Satellites Around Galactic Analogs (SAGA) Survey with two control samples: an environmentally agnostic population from the SAGA background sample and isolated galaxies from the Sloan Digital Sky Survey NASA-Sloan Atlas. All sizes and structural parameters are measured uniformly using pysersic to ensure consistency across samples. We find the half-light sizes of SAGA satellites are systematically larger than those of isolated galaxies, with the magnitude of the offset ranging from 0.05 to 0.12 dex (10%─24%) depending on the comparison sample and completeness cuts. This corresponds to physical size differences between 85 and 200 pc at  log10(M⋆/M⊙)=7.5  and 220─960 pc at  log10(M⋆/M⊙)=10 . This offset persists among star-forming galaxies, suggesting that environment can influence the structure of low-mass galaxies even before it impacts quenching. The intrinsic scatter in the size─mass relation is lower for SAGA satellites than isolated galaxies, and the Sérsic index distributions of satellites and isolated galaxies are similar. In comparison to star-forming satellites, quenched SAGA satellites have a slightly shallower size─mass relation and rounder morphologies at low mass, suggesting that quenching is accompanied by structural transformation and that the processes responsible differ between low- and high-mass satellites. Our results show that environmental processes can imprint measurable structural differences on satellites in MW-mass halos.

Keywords: Galaxy environments, Galaxy structure, Dwarf galaxies, Galaxy evolution, Galaxy quenching
Searching for Stellar-feedback-driven Outflow Signatures: A Deep Dive into NGC 3741. Stellar feedback drives winds and outflows critical to the baryon cycles of low-mass galaxies whose shallow gravitational potential wells make them particularly susceptible to mass and metal loss through outflows. However, spatially resolved observations of stellar-feedback-driven outflows are limited due to their low surface brightness and transient nature. We present the pilot of a larger multiwavelength study searching for and quantifying stellar-feedback-driven winds and outflows on both spatially and globally resolved scales for a sample of 40 nearby low-mass galaxies. We search for outflow signatures in the star-forming dwarf galaxy NGC 3741 using new optical imaging and spectroscopy from the WIYN 3.5 m telescope in conjunction with Very Large Array 21 cm observations and local star formation histories derived from resolved Hubble Space Telescope photometry. With this extensive data set, we compare the neutral and ionized gas morphologies and kinematics, calculate mass-loading factors, and investigate spatial variations in the star formation history of NGC 3741. Though the galaxy is experiencing a burst in star formation, we find little evidence of strong outflows and calculate very low mass-loading factors. We suggest that, though star formation activity has increased dramatically in the central region of the galaxy over the last 40 Myr, the star formation rate is not high enough to produce a sufficient amount of high mass stars responsible for fueling outflows. Future analysis of the larger sample will allow us to explore how stellar feedback impacts mass loss on local scales, providing a deeper understanding of the interplay between stellar feedback and the interstellar medium in low-mass galaxies.

Keywords: Stellar feedback, Dwarf galaxies, Galaxy winds, Galaxy evolution, Galaxies
Environmental Regulation of Dust and Star Formation Unveiled by Subaru Dual Narrowband Imaging: Degree-scale Balmer Decrement Mapping Across a z = 0.9 Supercluster. We present results from a dual narrowband imaging survey targeting the CL1604 supercluster at z = 0.9 using the Subaru Telescope. By combining the NB921 filter on Hyper Suprime-Cam and the NB1244 filter on SWIMS, we can detect redshifted Hα and Hβ emission lines from the supercluster. This unique technique allows us to measure both star formation rates and dust extinction for a sample of 94 emission-line galaxies across the supercluster. We find that dust extinction, estimated from the Balmer decrement (Hα/Hβ ratio), increases with stellar mass in star-forming galaxies, whereas relatively quiescent systems exhibit comparatively low extinction. Among galaxies with intermediate masses (108.5 &lt; M* &lt; 1010.5 M⊙), the dust-corrected Hα-based star formation rates align with the main sequence at this epoch. More massive galaxies, however, deviate from this relation, exhibit redder colors, and reside predominantly in higher-density environments. Although stellar mass, star formation rate, and galaxy color are clearly influenced by environment, we detect no strong, systematic environmental dependence of dust extinction for the whole sample. However, a trend of increasing dust extinction toward denser regions becomes evident only after excluding quiescent galaxies, as the massive quiescent populations in cluster cores contain little dust and thereby mask this relationship.

Keywords: Interstellar dust extinction, Galaxy evolution, Emission line galaxies, High-redshift galaxy clusters
Hunting for Hidden Axion Signals in Pulsar Dispersion Measurements with Machine Learning. In axion models, interactions between axions and electromagnetic waves induce frequency-dependent time delays determined by the axion mass and decay constant. These small delays are difficult to detect, limiting the effectiveness of traditional methods. We compute such delays under realistic radio telescope conditions and identify a prominent dispersive feature near half the axion mass, which appears nondivergent within the limits of observational resolution. Based on this, we develop a machine learning method that achieves 90% classification accuracy and demonstrates performance well in low signal-to-noise regimes. The method's robustness is confirmed against false positives using both simulated noisy data and real-world, known-null observations. Future improvements in optical clock precision and telescope bandwidth, particularly with instruments such as the Qitai Radio Telescope, may enhance constraints on the axion decay constant by up to 4 orders of magnitude in the 10−6 ∼ 10−4 eV mass range.

Keywords: Dark matter, Pulsars, Neural networks
High-Resolution Modeling of Coronae and Winds in Solar-Type Stars with Varying Rotation Rates. I. X-Ray Coronae. Stellar coronae are believed to be the main birthplace of various stellar magnetic activities. However, the structures and properties of stellar coronae remain poorly understood. Using the Space Weather Modeling Framework with the Alfvén Wave Solar Model (SWMF-AWSoM) and dynamo-generated surface magnetic maps, here we model the coronae of four solar-type stars. By incorporating the Sun, our work covers a range of stars with the rotation varying from 1.0 to 23.3Ω⊙ (periods of 25─1 days). Guided by observations, we scale the magnetic field strength with increasing rotation, covering a range between 6.0 G and 1200 G approximately. In our models, energy release associated with small-scale magnetic flux is a key source of coronal heating and is essential for reproducing realistic coronal structures. Our models capture dense (1─2 orders of magnitude higher than solar values) and ultra-hot (∼10 MK) coronae dominated by closed field structures. Using the CHIANTI atomic database, we also compute synthetic X-ray spectra and derive the corresponding X-ray luminosities (LX), which follow a scaling law to magnetic field LX ∝ &lt;∣B∣&gt;1.75. Furthermore, the coronal X-ray emission is found to be rotationally modulated by the alternating presence of bright active regions and dark coronal holes. These results provide new insights into the extremely high-energy coronae of rapidly rotating solar-type stars, which differ markedly from the Sun.

Keywords: Stellar coronae, Solar analogs, Stellar magnetic fields
Flow Regimes in Hot Jupiter Atmospheres: Insights from Anelastic Models. Hot Jupiters are Jupiter-sized exoplanets with close-in orbits, characterized by extreme day─night temperature contrasts due to synchronous rotation. These planets offer unique observational opportunities through transit photometry, transmission spectroscopy, and infrared (IR) phase curve analysis, which reveal information about heat redistribution and atmospheric dynamics. Complementary to common generalized circulation models (GCMs), we introduce a more comprehensive approach using the anelastic fluid equations that fully capture the 3D nature of the emerging nonlinear flows. We identify various nonlinear flow regimes and analyze the heat distribution when irradiation and thermal advection reach equilibrium. Eastward zonal winds can reach velocities comparable to the planetary rotation (up to several kilometers per second), while slower radial flows, though less prominent, contribute significantly to heat advection and can cause both eastward and westward hotspot shifts. The efficiency of day-to-night heat redistribution and the positioning of brightness maxima are shown to depend strongly on pressure and the interplay of advective and radiative processes. These findings improve our understanding of the diversity observed in the IR phase curves and suggest a nonmagnetic mechanism for retrograde hotspot shifts. By extending the scope of traditional GCM models, our work demonstrates the usefulness of anelastic models in capturing the complex, multidimensional dynamics of irradiated exoplanetary atmospheres.

Keywords: Exoplanet atmospheric dynamics
The Role of the Secondary White Dwarf in a Double-degenerate Double-detonation Explosion, in the Supernova Remnant Phase. Type Ia supernovae (SNe) are believed to be thermonuclear explosions of white dwarf (WD) stars, but their progenitor systems and explosion mechanisms are still unclear. Here, we focus on double-degenerate systems, where two WDs are interacting, and on the double detonation mechanism, where a detonation of a helium shell triggers a detonation of the carbon─oxygen core of the primary WD. We take the results from 3D SN simulations of R. Pakmor et al. and carry them into the supernova remnant (SNR) phase, until 1500 yr after the explosion. We reveal signatures of the SN imprinted in the SNR morphology. We confirm the impact of a companion on the SNR: Its presence induces a conical shadow in the ejecta, which is long-lived. Its intersection with the shocked shell is visible in projection as a ring, an ellipse, or a bar, depending on the orientation. Next, we test the case of a nested explosion model, in which the explosion of the primary induces the secondary to also explode. As the explosion of the secondary WD is weaker, only the primary outer ejecta interact with the ambient medium and form the main SNR shell. The secondary inner ejecta collide with the reverse shock, which enhances the density and thus the X-ray emissivity. The composition at the points of impact is peculiar, since what is revealed are the outer layers from the inner ejecta. This effect can be probed with spatially resolved X-ray spectroscopy of young SNRs.

Keywords: Supernova remnants, Hydrodynamical simulations, Type Ia supernovae, Supernovae
The Two-zone Temperature Distribution Model: Inferences on the Structure and Composition of Dusty Protoplanetary Disks. In order to understand the mineralogy and structure of protoplanetary disks, it is important to analyze them from both an empirical spectrum-based perspective and a radiative transfer image-based perspective. In a prior paper, we set forth an empirical mineralogy mid-infrared spectral model that conveyed spatial information and worked in tandem with a radiative transfer model, which formed the Empirical and Radiative Transfer Hybrid (or EaRTH) Disk Model. In this article, we take the empirical portion of that model, the two-zone temperature distribution model, and refine it with a newly derived protoplanetary disk thermal emission formulation which uses a temperature distribution without requiring discrete integration. This simplified model uses an empirical relation between spatial distribution variables, which permits radiative transfer models to directly fit these spatial distribution variables more freely within the provided empirical constraints. We test this model against several Spitzer Space Telescope Infra-Red Spectrograph spectra, primarily transition disks, and discuss the mineralogical and structural implications of the fits, including the implications for grain growth and processing within the atmospheric zones of the disks.

Keywords: Circumstellar dust, Dust composition, Astronomy data modeling, Protoplanetary disks
"X-Raying" a Be Star Disk: Fundamental Parameters of the Eclipsing Binary Be Star V658 Car. With its two stellar eclipses and two disk attenuations per binary orbit, V658 Carinae stands out as the first clear eclipsing Be + sdOB system. This rare alignment offers a unique opportunity to probe the structure and dynamics of a Be star disk with unprecedented detail. In this study, we present the most comprehensive observational data set and modeling effort for this system to date, including optical, near-infrared, and ultraviolet spectroscopy, space-based photometry, and optical polarization. Using a new ray-tracing code, we apply a three-component model, consisting of an oblate, rapidly rotating Be star, a symmetric circumstellar disk, and a compact stripped companion, to reproduce the system's light curve, polarization, and spectral features. Our analysis yields precise constraints on the stellar and disk parameters, determining its status as the second-known late-type Be + stripped star, and also provides strong spectroscopic evidence for a tenuous circumsecondary envelope. Despite the model's overall success, several key observables, such as the Hα equivalent width and the secondary attenuation, remain poorly reproduced, pointing to the need for more sophisticated modeling. In particular, future improvements should incorporate the companion's radiative feedback on the disk and account for asymmetric disk structures expected by the gravitational interaction with the companion. Owing to its unique geometry and rich diagnostics, V658 Car establishes itself as a benchmark system for Be stars (and rapid rotators in general), stripped stars, post-RLOF massive binaries, and circumstellar disk structures.

Keywords: Binary stars, B subdwarf stars, Radiative transfer, Eclipsing binary stars, Be stars
Power Transmission of Whistlers in the Lunar Ionosphere. This study investigates the power transmission ratio of lunar whistlers below 10 Hz for the first time by solving full wave equations that incorporate collisional effects for waves propagating upward from the surface to 100 km high in an ionosphere with four dominant ion species at temperatures of 150 K and 400 K in the lunar crustal field environment. The results indicate that increasing wave frequencies lead to decreasing power transmission ratios. This trend is consistent with the satellite observations near the Moon, which predominantly detect peak wave intensities at lower frequencies. Stronger magnetic field intensities and larger angles between the field and the surface led to an increase in power transmission ratios. This finding is consistent with the increased detection of waves in regions with higher field intensities and the more frequent occurrence rate of broadband whistlers linked to larger angles. As the temperature increases, the power transmission ratio increases, consistent with the higher occurrence rates of broadband whistlers at regions with smaller solar zenith angles. Incorporating the Doppler shift effect from solar wind on the observed wave frequency, the selenographic distribution of power transmission ratios exceeding −3 dB within the instrumentally detectable frequency range shows a heightened northern─southern asymmetry, aligning with the established patterns of wave intensities and occurrence rates. The preference to measure harmonic whistlers at lower altitudes can be attributed to the attenuation of the higher-frequency component at higher altitudes. The fact that the intensities of left-hand polarized components are more pronounced can also be interpreted.

Keywords: The Moon, Space plasmas, Solar wind, Lunar science