Sazuna/UAT_keywords huggingface dataset:
FAST Drift Scan Survey for H I Intensity Mapping: Simulation of Bayesian-stacking-based H I Mass Function Estimation. This study investigates the estimation of the neutral hydrogen (H I) mass function (HIMF) using a Bayesian stacking approach with simulated data for the Five-hundred-meter Aperture Spherical radio Telescope (FAST) H I intensity mapping (HIIM) drift-scan surveys. Using data from the IllustrisTNG simulation, we construct H I sky cubes at redshift z ∼ 0.1 and the corresponding optical galaxy catalogs, simulating FAST observations under various survey strategies, including pilot, deep-field, and ultradeep-field surveys. The HIMF is measured for distinct galaxy populations—classified by optical properties into red, blue, and bluer galaxies—and injected with systematic effects such as observational noise and flux confusion caused by the FAST beam. The results show that Bayesian stacking significantly enhances HIMF measurements. For red and blue galaxies, the HIMF can be well constrained with pilot surveys, while deeper surveys are required for the bluer galaxy population. Our analysis also reveals that sample variance dominates over observational noise, emphasizing the importance of wide-field surveys to improve constraints. Furthermore, flux confusion shifts the HIMF toward higher masses, which we address using a transfer function for correction. Finally, we explore the effects of intrinsic sample incompleteness and propose a framework to quantify its impact. This work lays the groundwork for future HIMF studies with FAST HIIM, addressing key challenges and enabling robust analyses of H I content across galaxy populations.

Keywords: Bayesian statistics, Large-scale structure of the universe, Surveys, Galaxy evolution, Extragalactic astronomy
Determining the Magnetic Field of Active Region Plages Using the Whole CLASP2/2.1 Spectral Window. The Chromospheric LAyer SpectroPolarimeter missions, CLASP2 and CLASP2.1, demonstrated that the near-UV spectral region between 279.30 and 280.68 nm is suitable for studying the magnetism of the solar chromosphere. In particular, the spectropolarimetric observations in the Mg II h and k resonant doublet, Mn I 279.91 and 280.19 nm resonant lines, and Fe II 279.79 and 280.66 nm lines acquired by these suborbital space experiments have been proven useful for inferring the magnetic field stratification in the solar chromosphere. However, several lines of the CLASP2/2.1 spectral region with significant circular polarization signals had remained unexplored. After identifying two Ni I (279.95 and 280.59 nm) lines, one Mn II (280.62 nm) line, and one Fe I (280.53 nm) line, here we apply the weak-field approximation to the spectropolarimetric observations of active region plages by CLASP2 and CLASP2.1. By comparing the results with previous studies, we are able to estimate the formation heights of these CLASP2/2.1 additional spectral lines and to demonstrate their suitability to determine the magnetic field stratification from the photosphere to the upper chromosphere.

Keywords: Spectropolarimetry, Solar photosphere, Solar active regions, Solar magnetic fields, Solar chromosphere, Active solar chromosphere
Spectroscopic Confirmation: Fast Rotators in the Young Clusters NGC 1856 and NGC 1953. We present the results of a spectroscopic investigation of two Large Magellanic Cloud globular clusters, NGC 1953 and NGC 1856. Both clusters have similar ages (250 and 300 Myr, respectively). Spectra were recorded with the Michigan/Magellan Fiber System located on the Magellan–Clay 6.5 m telescope. Spectra were visually inspected to assess the presence of stellar Hα emission lines attributed to B stars rotating close to breakup velocity (Be stars). High fractions of Be stars in the cluster typically indicate the presence of a large population of fast rotating stars, predicted by some models to explain the observed split and extended main sequence. There are numerous Be star candidates in NGC 1856, exhibiting weak but broad Hα emission. However, only one such target was detected in NGC 1953. This stark contrast between the observed populations for NGC 1856 and NGC 1953 may suggest that cluster density plays a key role in determining the fraction of Be stars. These results provide essential constraints for the different scenarios attempting to explain the bimodal distribution of rotational velocities and the multiple populations of stars observed in globular clusters. The impact of stellar radial velocity and nebular emission on photometric measures is assessed through simulations relying on the spectra. These simulations suggest that photometric studies can underestimate the fraction of Hα emitters in a cluster, in particular for stars with relatively weak emission features. The results also show that nebular emission has minimal impact on the photometric Hα excesses.

Keywords: Globular star clusters, Be stars, Large Magellanic Cloud, Star clusters
Global Hot Gas Excess in (Ultra)Luminous Infrared Galaxies: Replicating Galactic Nuclei Scaling Relations between Diffuse X-Ray Emission and Star Formation on Galaxy-wide Scales. Hot ionized interstellar medium interlinks star formation and stellar feedback processes, redistributing energy, momentum, and material throughout galaxies. We use X-ray data from Chandra to extract the hot gas emission from 78 of the most luminous infrared-selected galaxies in the local Universe. In the extreme star-forming environments, the intrinsic thermal X-ray luminosity of hot gas ( L0.5−2keVgas ) shows a significant excess over the predictions of the standard linear LX−SFR relation for most objects with very high star formation rates (SFRs). The contribution of active galactic nuclei appears to have little impact on the global hot gas luminosity. For galaxies with SFR &gt; 50 M⊙ yr−1, the Bayesian analysis gives a superlinear relation of  log(L0.5−2keVgas/ergs−1)=1.34log(SFR/M⊙yr−1)+39.82 , similar to that found in the central regions of normal spiral galaxies. These results suggest a scenario in which the merger of galaxies delivers substantial amounts of gas, triggering intense star formation in both the nuclear region and the galactic disk, and ultimately enhancing the global thermal X-ray emission. The ratio of the apparent thermal luminosity in the 0.5−2 keV band ( L0.5−2keVappar ) to  L0.5−2keVgas  shows statistically significant negative correlations with the intrinsic column density (NH) and SFR. Moreover, in contrast to the luminosity ratio, SFR shows a moderate positive correlation with intrinsic NH. This suggests that the correlation between  L0.5−2keVappar / L0.5−2keVgas  and SFR may be driven by the underlying  L0.5−2keVappar / L0.5−2keVgas −NH and SFR−NH relations.

Keywords: X-ray astronomy, Scaling relations, X-ray active galactic nuclei, Star formation, Interstellar medium, Galaxy mergers, Ultraluminous infrared galaxies, Luminous infrared galaxies
Variabilities Driven by Satellite Black Hole Migration in Active Galactic Nucleus Disks. The physical origin of active galactic nucleus (AGN) variability remains unclear. Here we propose that the magnetic reconnection induced by the migration of satellite black holes (sBHs) in the AGN disk can be a new plausible mechanism for AGN short-term variability. During the sBH migration, the comoving plasmas surrounding the sBH could influence the large-scale magnetic field of the AGN disk and trigger the magnetic reconnections to contribute to AGN UV/optical variability. Meanwhile, high-magnetization plasmas are more likely to escape the disk and cause a secondary magnetic reconnection in the corona. For a ∼102–103 M⊙ sBH in the inner regions of the disk surrounding a supermassive black hole with ∼107 M⊙, the reconnection process that occurred in the space outside of the disk should produce X-ray emission, which can last ∼103–106 s with the luminosity ∼1038–1042 erg s‑1.

Keywords: Accretion, Active galactic nuclei, Black holes, Magnetic fields
Gravitational Influence from Planets on the Measured Rates of Period Change of Pulsating White Dwarfs. The measured rates of period change,  Ṗ , in the signals of pulsating white dwarf stars are often interpreted as direct detections of structural changes from secular cooling. Due to the intrinsic nature of this quantity,  Ṗ  analysis has been used to probe fundamental physics, such as constraining the mass of hypothetical axion particles. However, most white dwarfs are expected to host planets that could induce an external source of period change, caused by the light travel time variations from reflex motion about the system barycenter. Assuming a plausible distribution of planets that could orbit white dwarf stars, we quantify the amount of reflex motion expected from undiscovered planets as an important source of extrinsic error in  Ṗ  analyses. While the median error from reflex motion is ∼10‑15 s s‑1 (similar to the secular  Ṗ  rates expected for cool DAV pulsators), individual close-in planets could cause  Ṗ  errors as large as 10‑11 s s‑1.

Keywords: White dwarf stars, Pulsation frequency method, Star-planet interactions, Asteroseismology, Variable star period change
Pioneering High-speed Pulsar Parameter Estimation Using Convolutional Neural Networks. Accurate thermal emission models of neutron stars are essential for constraining the dense matter equation of state. However, incorporating realistic magnetic field structures is computationally prohibitive, severely constraining feasible parameter space exploration. In this work, we develop a neural network (NN) emulator to generate model thermal bolometric X-ray light curves of millisecond pulsars with multipolar magnetic fields. We assess the NN's predictive and computational performance across a broad parameter space. We find that for a static vacuum field model, the NN provides a &gt;400 times speedup. We integrate this NN emulator into a Monte Carlo Markov Chain (MCMC) framework to replace the computationally expensive physical model during parameter exploration. Applied to PSR J0030+0451, this approach allows the MCMC to reach equilibrium in ∼1 day on 4000 cores, where with the original physical model alone it would have taken more than a year on the same hardware. We compare posterior distributions by running equivalent MCMC iterations with both the NN and the physical model, evaluate differences in distributions when continuing the physical model MCMC from the NN MCMC equilibrium state, and assess variations in posterior distributions resulting from NNs trained on data sets of different sizes. Our NN architecture is agnostic to the underlying physics of the physical model and can be trained for any other physical model, opening many previously intractable avenues of analysis. The NN speed remains the same regardless of the complexity of the physical model it was trained to emulate, allowing greater speedups for more complex physical models.

Keywords: Neural networks, Posterior distribution, Millisecond pulsars, Convolutional neural networks, Pulsars
Tracing the Origins of Hot Halo Gas in Milky Way─type Galaxies with SMUGGLE. Current galaxy formation models predict the existence of X-ray-emitting gaseous halos around Milky Way (MW)─type galaxies. To investigate properties of this coronal gas in MW-like galaxies, we analyze a suite of high-resolution simulations based on the SMUGGLE framework and compare the results with X-ray observations of both the MW and external galaxies. We find that for subgrid models incorporating any form of stellar feedback, e.g., early feedback (including stellar winds and radiation) and/or supernova (SN) explosions, the total 0.5─2 keV luminosity is consistent within uncertainties with X-ray observations of the MW and with scaling relations derived for external disk galaxies. However, all models exhibit an X-ray surface brightness profile that declines too steeply beyond ∼5 kpc, underpredicting the extended emission seen in recent eROSITA stacking results. Across all subgrid prescriptions, the simulated surface brightness and emission measure fall below MW observations by at least 1─2 orders of magnitude, with the most severe discrepancy occurring in the no-feedback model. Our results suggest that (i) stellar feedback primarily shapes the innermost hot atmosphere (central ∼5 kpc), with comparable contributions from early feedback and SNe to the resulting X-ray luminosity; (ii) additional mechanisms such as gravitational heating, active galactic nuclei feedback, and/or Compton effects of GeV cosmic ray are necessary to generate the extended, volume-filling hot gaseous halo of MW-mass galaxies; (iii) the origins of hot corona in MW-like galaxies are partially distinct from those of the warm (∼105 K) gas, by combining our previous finding that the SMUGGLE model successfully reproduces the kinematics and spatial distribution of MW O VI absorbers.

Keywords: Stellar feedback, Diffuse radiation, Hot ionized medium, Interstellar medium, Circumgalactic medium
Abundance Diagnostics from a Slitless Imaging Spectrometer: A Proof-of-concept for MaGIXS-2. Elemental abundance diagnostics in the solar corona are crucial for understanding energy transport, plasma heating, and magnetic activity. Most earlier imaging-spectroscopic studies have relied on slit-based spectrometers, which offer high spectral resolution but are limited in spatiotemporal coverage and temperature diagnostics. In contrast, slitless spectrographs like the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) produce overlapping spatial-spectral data (overlappograms) to enable wide-field imaging spectroscopy with broader temperature coverage. However, extracting elemental abundances from overlappogram data remains inherently challenging due to spatial and spectral confusion. In this work, we present a proof-of-concept technique for elemental abundance diagnostics from overlappograms, demonstrating its feasibility with simulated MaGIXS-2 observations.

Keywords: Solar abundances, Solar flare spectra, Solar x-ray flares
Stellar Obliquity Excitation via Disk-dispersal-driven Resonances in Binaries. The stellar obliquity of a planetary system is often used to help constrain the system's formation and evolution. One of the mechanisms to reorient the stellar spin involves a secular resonance crossing due to the dissipation of the protoplanetary disk when the system also has an inclined, distant (∼300 au) binary companion. This mechanism is likely to operate broadly due to the ∼50% binary fraction of FGK dwarfs and can play an important role in setting the initial stellar obliquities prior to any dynamical evolution. In this work, we revisit this mechanism analytically for idealized, homologously evolving disk models and show that the resulting stellar obliquities are broadly distributed between 60° and 180° for most warm and cold planets. We further show that nonhomologous disk dissipation, such as the development of a photoevaporatively opened gap at ∼2 au, can help maintain the orbital alignment of warm planets, in agreement with observations. Our results represent the proper primordial obliquities for planetary systems with distant binary companions. They also represent the obliquities of stars with no present-day binary companions if these companions are dynamically unbound during the birth cluster phase of evolution, a process that occurs on a comparable timescale as the disk-driven obliquity excitation.

Keywords: Protoplanetary disks, Exoplanet systems
A Spectroscopic Hunt for Post─Red Supergiants in the Large Magellanic Cloud. II. Turbulent Line Broadening in the Spectra of LMC Yellow Supergiants. Massive stars in the Hertzsprung gap are a mixed population of objects in short-lived evolutionary phases: yellow supergiants (YSGs) evolving toward the red supergiant (RSG) phase, partially stripped post-RSGs, and other, rarer outcomes of stellar evolution. Studies of sufficiently large samples of these objects can constrain massive star structure and evolution during these poorly understood phases. As part of our ongoing program searching for post-RSGs, we characterized the spectral line profiles of 32 YSGs in the Large Magellanic Cloud using high-resolution spectra obtained with the Magellan Inamori Kyocera Echelle spectrograph on the Magellan 2/Clay telescope at Las Campanas Observatory. We find that the line profiles are strongly broadened by turbulent photospheric motion. After fitting the profiles to measure microturbulent and macroturbulent velocities, we identify two groups within our sample that are separated by the ratio of the two velocity scales. In both groups, the macroturbulent velocity ζRT scales with stellar properties such as effective temperature. Additionally, we find statistically significant correlations between the macroturbulent velocity and other possible probes of large-scale photospheric motions: line profile asymmetry, as well as the amplitude and quality factor of the stochastic low frequency variability measured from Transiting Exoplanet Survey Satellite lightcurves. These correlations differ between the two groups of YSGs. Finally, we construct 1D evolutionary models of YSGs in both pre- and post-RSG phases, and find reasonable agreement between the convective velocities in these models and our measured microturbulent velocities. However, the macroturbulent velocities are much higher than the convective velocities in the models.

Keywords: High resolution spectroscopy, Observational astronomy, Stellar structures, Evolved stars, Hertzsprung gap, Massive stars, Yellow hypergiant stars, Large Magellanic Cloud, Stellar mass loss, Late-type supergiant stars, Stellar evolution
Challenging Classical Paradigms: Recurrent Nova M31N 2017-01e, a BeWD System in M31?. M31N 2017-01e is the second-fastest recurrent nova known, with a recurrence period of 2.5 yr in the Andromeda galaxy (M31). This system exhibits a unique combination of properties: a low outburst amplitude (∼3 mag), starkly contrasting with known recurrent novae (typically ≥6 mag), and a very fast evolution (t2 ∼ 5 days). Its position coincides with a bright variable source (MV ∼ −4.2, B − V = 0.042) displaying a 14.3 day photometric modulation, which has been suggested as the likely progenitor. We present a multiwavelength analysis of optical and UV data spanning quiescence and the 2019 and 2024 outbursts. Archival high-resolution imaging reveals two nearby faint sources within 5″ of the proposed nova system, which we identified as unrelated field stars. Color analysis and spectral energy distribution fitting suggest the progenitor is likely an early-type star. Combined with archival spectra consistent with a B-type star with Hα in emission, this points to the quiescent counterpart being a Be star with a circumstellar disk. We propose that M31N 2017-01e arises from a rare BeWD binary, where the white dwarf (WD) accretes from the decretion disk of its companion, explaining its rapid recurrence, low-amplitude outbursts, and unusual quiescent luminosity and color. This analysis highlights M31N 2017-01e as a compelling outlier among recurrent novae, suggesting a distinct accretion mechanism and evolutionary path that challenges the prevailing paradigm.

Keywords: White dwarf stars, Cataclysmic variable stars, Recurrent novae, Be stars, Andromeda Galaxy
The Arizona Molecular ISM Survey with the SMT: The Diverse Carbon Monoxide Line Ratios and Spectral Line Energy Distributions of Star-forming Galaxies. The carbon monoxide (CO) spectral line energy distributions (SLEDs) of galaxies contain a wealth of information about conditions in their cold interstellar gas. Here, we use galaxy-scale observations of the three lowest energy CO lines to determine SLEDs and line ratios in a sample of 47 nearby, predominantly star-forming galaxies. We find a systematic trend of higher gas excitation with increasing star formation rate (SFR) and SFR surface density (ΣSFR), with the range of variations being even larger than predicted by simulations. Power-law fits of the CO line ratios as a function of SFR and ΣSFR provide a good description of the trends seen in our sample and also accurately predict values for a wide range of galaxy types compiled from the literature. Based on these fits, we provide prescriptions for estimating CO(1–0) luminosities and molecular gas masses using CO(3–2) or CO(2–1) in cases where CO(1–0) is not observed directly. We compare our observed SLEDs with molecular cloud models in order to examine how the physical properties of cold gas vary across the galaxy population. We find that gas conditions in star-forming and starburst galaxies lie on a continuum with increasing gas density in more actively star-forming systems.

Keywords: Molecular gas, Starburst galaxies, Millimeter astronomy, Star formation, Galaxy evolution, Interstellar medium, Galaxies
Radiative Transfer Modeling of a Shadowed Protoplanetary Disk Assisted by a Neural Network. We present observations and detailed modeling of a protoplanetary disk around the T Tauri star V1098 Sco. Millimeter-wavelength data from the Atacama Large Millimeter/submillimeter Array (ALMA) show a ring of large dust grains with a central cavity that is filled with molecular gas. Near-infrared data from the Very Large Telescope (VLT) detect the scattered starlight from the disk surface and reveal a large shadow that extends over its entire southern half. We model the ALMA continuum and line data to determine the outer-disk geometry and the central stellar mass. Using radiative transfer models, we demonstrate that a misaligned inner disk, tilted in both inclination and position angle with respect to the outer disk, can reproduce the salient scattered-light features seen with VLT. Applying an image threshold algorithm to compare disk morphologies and training a neural network on a set of high-signal-to-noise-ratio models, we forward model the data and determine the inner-disk geometry. We find that the rotation axes of the inner and outer disks are misaligned by 38° and constrain the mass and location of a perturbing planetary or substellar companion. The technique of simulation-based inference that is illustrated here is broadly applicable for radiative transfer modeling of other objects.

Keywords: Protoplanetary disks, Radiative transfer, Neural networks
Illuminating Hidden Pulsars: Scintillation-enhanced Discovery of Two Binary Millisecond Pulsars in M13 with FAST. We conducted a sensitive acceleration search using fast Fourier transform techniques on full-length and segmented data from 84 observations of the globular cluster M13 with the Five-hundred-meter Aperture Spherical radio Telescope. Employing a low detection threshold (2σ) to maximize sensitivity to faint pulsars, here we report the discovery of two binary millisecond pulsars: J1641+3627G (M13G) and J1641+3627H (M13H). Both pulsars were detected during scintillation-brightened states, revealing systems that would otherwise remain undetected. For M13G, we obtained a phase-connected timing solution spanning 6.4 yr, identifying it as a black widow system with an orbital period of 0.12 days hosting an extremely low-mass companion (∼9.9 × 10−3 M ⊙), though no eclipses were observed. M13H, however, shows significant apparent acceleration but was detected in only 2 of 84 observations; its extremely low detection rate currently prevents constraints on orbital parameters or classification.

Keywords: Globular star clusters, Radio telescopes, Millisecond pulsars