Sazuna/UAT_keywords huggingface dataset:
Multifluid and Kinetic 2D and 3D Simulations of Thermal Farley─Buneman Instability Turbulence in the Solar Chromosphere. Models currently fail to reproduce observations of the coldest regions in the Sun's atmosphere, though recent work suggests the thermal Farley─Buneman instability (TFBI) may play a critical role. This meter-scale, electrostatic, multifluid plasma instability causes turbulence and heating in the coldest regions of the solar chromosphere. This paper describes how TFBI turbulence and heating varies across multifluid 2D, kinetic 2D, and kinetic 3D simulations. It also presents the first 3D simulations of the TFBI. We find that multifluid and kinetic 2D simulations produce similar results overall, despite using vastly different approaches. Additionally, our kinetic 3D simulations produce a similar or somewhat larger amount of heating compared to 2D, as contributions from the parallel electric field account for only (13 ± 2.5)% of the total turbulent heating in 3D.

Keywords: Solar chromospheric heating, Solar chromosphere, Astronomical simulations, Plasma physics
Galaxy Cluster Characterization with Machine Learning Techniques. We present an analysis of the X-ray properties of the galaxy cluster population in the z = 0 snapshot of the IllustrisTNG simulations, utilizing machine learning techniques to perform clustering and regression tasks. We examine five properties of the hot gas (the central cooling time, the central electron density, the central entropy excess, the concentration parameter, and the cuspiness) which are commonly used as classification metrics to identify cool core (CC), weak cool core (WCC) and non-cool core (NCC) clusters of galaxies. Using mock Chandra X-ray images as inputs, we first explore an unsupervised clustering scheme to see how the resulting groups correlate with the CC/WCC/NCC classification based on the different criteria. We observe that the groups replicate almost exactly the separation of the galaxy cluster images when classifying them based on the concentration parameter. We then move on to a regression task, utilizing a ResNet model to predict the value of all five properties. The network is able to achieve a mean percentage error of 1.8% for the central cooling time, and a balanced accuracy of 0.83 on the concentration parameter, making them the best-performing metrics. Finally, we use simulation-based inference to extract posterior distributions for the network predictions. Our neural network simultaneously predicts all five classification metrics using only mock Chandra X-ray images. This study demonstrates that machine learning is a viable approach for analyzing and classifying the large galaxy cluster data sets that will soon become available through current and upcoming X-ray surveys, such as the extended Roentgen Survey with an Imaging Telescope Array.

Keywords: Galaxy clusters, X-ray astronomy
A Low Metallicity Massive Contact Binary Star System Candidate in WLM Identified by Hubble and James Webb Space Telescope Imaging. We present archival Hubble Space Telescope (HST) and JWST ultraviolet through near-infrared time series photometric observations of a massive minimal-contact binary candidate in the metal-poor galaxy Wolf─Lundmark─Melotte (Z = 0.14Z⊙). This discovery marks the lowest metallicity contact binary candidate observed to date. We determine the nature of the two stars in the binary by using the eclipsing binary modeling software PHysics Of Eclipsing BinariEs (PHOEBE) to train a neural network to fit our observed panchromatic multiepoch photometry. The best-fit model consists of two hot main-sequence stars ( T1=29800−1700+2300  K,  M1=16−3+2  M⊙, and  T2=18000−5000+5000  K,  M2=7−3+5  M⊙). We discuss plausible evolutionary paths for the system, and suggest the system is likely to be currently in a contact phase. Future spectroscopy will help to further narrow down evolutionary pathways. This work showcases a novel use of data of JWST and HST imaging originally taken to characterize RR Lyrae. We expect time series imaging from LSST, BlackGEM, etc. to uncover similar types of objects in nearby galaxies.

Keywords: Eclipsing binary stars, Massive stars, Contact binary stars
Multicomponent Ionized Gas Outflows in the Hot Dust-obscured Galaxy W2026+0716 with Keck/OSIRIS. We present narrowband-filtered integral field unit observations of the hot dust-obscured galaxy (Hot DOG) WISE J202615.27+071624.0 (hereafter W2026+0716) at redshift z = 2.570 using Keck/OSIRIS. Our analysis reveals a multicomponent ionized gas outflow structure in this heavily obscured active galactic nucleus (AGN) host galaxy. Multicomponent Gaussian decomposition of the [O III] and Hα emission lines uncovers extremely broad and asymmetric profiles, characteristic of AGN-driven outflows. Kinematic mapping shows spatially distinct structures: the [O III]- and Hα-dominated components (with radii of 1.20 ± 0.56 kpc) are separated by a projected offset of ∼1.1 kpc and exhibit divergent velocity regimes. The [O III] outflow reaches a velocity of 3210 ± 50 km s−1, while the Hα outflow component attains 2310±840 km s−1. Dynamical modeling supports a biconical outflow structure, with [O III] and Hα emissions dominating separate cones and significant dust obscuration of the redshifted outflow. Their comparable momentum outflow rates and energy outflow rates suggest a potential physical connection in their driving mechanisms. Spectral energy distribution analysis reveals anomalous optical/UV excess, attributed to AGN photon scattering by dust or outflowing material, classifying W2026+0716 as a "Blue Hot DOG". The derived outflow timescale (∼105 yr) aligns with the evolutionary phase of Blue Hot DOGs, suggesting AGN feedback operates persistently during this transitional stage.

Keywords: Active galaxies, High-redshift galaxies, Infrared galaxies
Evidence for a Catastrophically Disrupted Open Cluster. Of the many discoveries uncovered by the Gaia astrometric mission, some of the most exciting are related to nearby dispersed stellar structures. We analyze one such structure in the Milky Way disk, OCSN-49, a coeval stellar stream with 257 identified members spanning approximately 30° across the sky. We obtained high-resolution spectroscopic data for four members that span the stream's extent, finding these four stars to have solar metallicities and remarkably homogeneous chemistry. Through a combination of isochrone fitting, lithium abundance analysis, and gyrochronology, we find a consistent stellar age of 400─600 Myr. Integrating stellar orbits backwards reveals that OCSN-49 converged to a single point at a much younger age. By integrating unbound model stars forward and comparing them to the current phase-space distribution of OCSN-49, we derive a dynamical age of 83 ± 1 Myr, inconsistent with the age of the stellar population. The discrepancy between the kinematic and stellar age indicators is naturally explained by a disruptive event that unbound OCSN-49 roughly 500 Myr into its lifetime. Based on rate estimates, disruption due to a passing giant molecular cloud (GMC) is the most likely culprit. Assuming a single encounter, we find that a nearly head-on collision with a fairly massive GMC (∼105 M⊙) was necessary to unbind the cluster, although encounters with multiple GMCs may be responsible. To our knowledge, OCSN-49 serves as the first known remnant of a catastrophically disrupted open cluster, and therefore serves as a benchmark for further investigating cluster disruption in the Milky Way.

Keywords: Galaxy tides, Stellar dynamics, Chemical abundances, Gravitational disruption, Astrometry, Star clusters
Event Rate Density and Luminosity Function of Newborn-magnetar-driven X-Ray Transients from Neutron Star Binary Mergers. X-ray transients (XTs) driven by newborn magnetars from mergers of neutron star binaries (NSBs) have occasionally been detected in the narrow-field Chandra Deep Field-South (CDF-S) survey and the Swift/X-Ray Telescope observations of short gamma-ray bursts. Quantifying their event rate density (ERD) and luminosity function (LF) is critical for understanding NSB coalescence and magnetar formation. Utilizing population synthesis calculations incorporating various equations of state (EoSs), we derive a local ERD of ∼300 Gpc‑3 yr‑1 and a redshift-dependent ERD profile peaking at z = 1.81 followed by a rapid decline beyond z ∼ 4. Constructing an XT sample based on CDF-S and Swift observations, we characterize the LF by a single power-law function at L ≤ 4.75 × 1046 erg s‑1 with a slope of ‑1.03, followed by a broken power-law function in which the break luminosity is Lb = 4.38 × 1047 erg s‑1 and the slopes are ‑0.28 and ‑1.66. Based on the ERD and the LF, we estimate that the Einstein Probe (EP) detection rate is ∼31 yr‑1, adopting a conservative threshold flux of 10‑9 erg s‑1, a luminosity range of L ∈ [2 × 1044, 2 × 1049] erg s‑1, and a correction for the jet opening angle of ∼16∘. This detection rate is consistent with the EP observations during its first year of operation. It is important to note that our estimation is subject to uncertainties arising from the LF derivation. Future EP observations of these XT events will be crucial in reducing these uncertainties.

Keywords: Magnetars, Gamma-ray bursts, Stellar mergers
Dynamically Driven Evolution of Molecular Gas in the Barred Spiral Galaxy M83 Traced by CO J = 2–1/1–0 Line Ratio Variations. We show the variations of the CO J = 2–1/1–0 line ratio (R21/10) across the barred spiral galaxy M83, using the 46 pc resolution data from the Atacama Large Millimeter/submillimeter Array. The R21/10 map clearly evidences the systematic large-scale variations as a function of galactic structures. Azimuthally, it starts from low R21/10 ≲ 0.7 in the interarm regions and becomes high ≳0.7 in the bar and spiral arms, suggesting that the density and/or kinetic temperature of molecular gas increase by about a factor of 2–3. This evolution is seen even in the parts of spiral arms without star formation, and R21/10 is often elevated even higher to ∼0.8–1.0 when H II regions exist in the vicinity. Radially, R21/10 starts very high ≳1.0 at the galactic center, remains low ≲0.7 in the bar region, increases to ≳0.7 around the bar end, and again decreases to ≲0.7 in the rest of disk where the spiral arms dominate. The evolutionary sequence is synchronized with galactic rotation, and therefore, it is determined largely by the galactic structures and dynamics and is governed by the galactic rotation timescales. The R21/10 map also shows that the influence of stellar feedback is localized and limited. Massive, large, and non-star-forming molecular structures have low R21/10, which also suggests that the bulk molecular gas in the disk is not regulated by stellar feedback, but more likely by galactic structures and dynamics. These results are consistent with suggestions by the earlier studies of the Milky Way and other barred spiral galaxies, and thus, are likely general among barred spiral galaxies in the local Universe.

Keywords: Molecular gas, Galaxy dynamics, Galaxy structure, Molecular clouds, Star formation, Interstellar medium, Barred spiral galaxies
Binding Energies of Small Interstellar Molecules on Neutral and Charged Amorphous Solid Water Surfaces. The interstellar medium (ISM) is all but empty. To date, more than 300 molecules have already been discovered. Because of the extremely low temperature, the gas-phase chemistry is dominated by barrierless exothermic reactions of radicals and ions. However, several abundant molecules and organic molecules cannot be produced efficiently by gas-phase reactions. To explain the existence of such molecules in the ISM, gas-surface interactions between small molecules and dust particles covered with amorphous solid water (ASW) mantles must be considered. In general, surface processes such as adsorption, diffusion, desorption, and chemical reactions can be linked to the binding energy of molecules to the surface. Hence, a lot of studies have been performed to identify the binding energies of interstellar molecules on ASW surfaces. Cosmic radiation and free electrons may induce a negative charge on the dust particles, and the binding energies may be affected by this charge. In this study, we calculate the binding energies of CO, CH4, and NH3 on neutral and charged ASW surfaces using density functional theory calculations. Our results indicate that CO can interact with the surface charge, increasing its binding energy. In contrast, the binding energy of CH4 remains unchanged in the presence of surface charge, and that of NH3 typically decreases.

Keywords: Interstellar dust, Molecular clouds, Computational methods, Quantum-chemical calculations, Interstellar medium
Clumpy Starburst in a Local Dwarf Galaxy, NGC 1522. To investigate the star-forming process in nearby dwarf galaxies, we present integral field unit observations of the star-forming dwarf galaxy NGC 1522 with the Very Large Telescope/Multi Unit Spectroscopic Explorer as a part of the Dwarf Galaxy Integral Survey. Our observations reveal the presence of a star-forming clumpy ring in its central region. We identify nine distinct star-forming clumps based on an extinction-corrected Hα emission line map, with a total star formation rate of about 0.1 M⊙ yr−1. The nine clumps are considered to be starbursts, which represent an extreme case in the local Universe, without invoking major merging. We investigate the properties of ionized gas using the strong emission lines and "BPT" diagrams, in conjunction with velocity mapping. Our analysis unveils intriguing patterns, including a positive metallicity gradient and low N/O abundance ratio. This peculiar distribution of metallicity may signify external gas accretion. Our results suggest that the ongoing star formation in NGC 1522 might be triggered and sustained by the inflow of external metal-poor gas.

Keywords: Dwarf galaxies, Star formation, Interstellar medium
Polarization Evolution of Gamma-Ray Burst Prompt Emission with Bulk Acceleration. During the prompt phase, Poynting-flux-dominated jets undergo acceleration accompanied by magnetic dissipation. By using an outward-propagating thin-shell model, where bulk Lorentz factors Γ increase with radius and the magnetic field strength decay is related to the acceleration and the energy conversion rate, this process can be investigated through time-resolved polarization analysis. Faster acceleration produces a greater flux, steeper light-curve growth followed by a sharper decline, and polarization degree decreases sharply. With a fixed acceleration index, lower energy conversion rates are associated with lower flux, shallower rises and declines in light curves, lower polarization degree, smoother decline for on-beam (q = θv/θj &lt; 1) emission, and sharper decline for off-beam (q &gt; 1) emission in polarization curves. Both jet acceleration and magnetic dissipation enhance the likelihood of polarization angle flips in observations with small viewing angles, while also leading to higher polarization degrees after the flip in observations with larger viewing angles. The joint analysis of light curves and polarization provides valuable insights into gamma-ray burst motion and energy conversion processes. Rapid decline in the light curve indicates fast acceleration and high energy conversion rates, while gradual light-curve decline coupled with polarization angle flips (for small viewing angles) or the higher polarization degree after flipping (for large viewing angles) suggests acceleration accompanied by magnetic dissipation. Otherwise, the jet is coasting or slowly accelerating at this time.

Keywords: Gamma-ray bursts, Magnetic fields
Stability and Dynamics of Three-mode Coupling in δ Scuti Stars. Recent observations of δ Scuti stars find evidence of nonlinear three-mode coupling in their oscillation spectra. There are two types of three-mode coupling likely to be important in δ Scuti stars: (i) direct coupling, in which two linearly unstable modes (driven by the κ-mechanism) excite a linearly stable mode, and (ii) parametric coupling, in which one linearly unstable mode excites two linearly stable modes. M. Breger &amp; M. H. Montgomery find especially strong evidence of direct coupling in the δ Scuti star KIC 8054146. However, direct coupling is inherently unstable and cannot be the mechanism by which the modes saturate and achieve nonlinear equilibrium. By integrating the amplitude equations of small mode networks, we show that the modes can achieve equilibrium if parametric coupling operates in tandem with direct coupling. Using mode parameters calculated from a δ Scuti model, we also find that parametric and direct coupling are likely to be simultaneously active. Importantly, parametric coupling does not necessarily disrupt the correlations found in KIC 8054146 between the amplitudes and phases of the directly coupled modes. We conclude that δ Scuti stars are likely impacted by both parametric and direct coupling, and that accounting for both in future large-mode-network calculations may help explain the complicated mode dynamics observed in many δ Scuti stars.

Keywords: Internal waves, Delta Scuti variable stars, Stellar oscillations, Asteroseismology, Astrophysical fluid dynamics
A Sample of Extreme Eclipsing Binaries with Accretion Disks from LAMOST and ZTF. Extreme eclipsing binaries may harbor peculiar physical properties. In this work, we aim to identify a sample of such systems by selecting binaries with pronounced eclipsing light curves, characterized by large variability (Δmag &gt; 0.3 in the g band of the Zwicky Transient Facility, ZTF) and significant differences between primary and secondary eclipses (eclipse depth ratio &gt;20 in the ZTF g band). We identified 23 candidates by combining the photometric data and the LAMOST spectroscopic survey. Spectroscopic analysis revealed that all of these systems are dominated by A-type stars in the optical band. Further investigation confirmed that all 23 candidates are Algol-type binaries, with 22 of them being newly discovered. Their orbital periods range from 2.57 to 19.21 days. These systems consist of low-luminosity, highly stripped subgiant donors and accreting A-type stars. The donor stars, with radii of 2.5–8.9 R⊙ and effective temperatures around 4000 K, have typical masses of M2 ∼ 0.3 M⊙, indicating substantial mass loss through Roche-lobe overflow. The presence of ellipsoidal variability and Hα emission provides strong evidence for ongoing mass transfer. By fitting the spectral energy distributions, spectra, and light curves, we found that most of the accretors have luminosities lower than expected from the mass–luminosity relation, aligning with the predicted faint phase for mass-gaining stars. Three objects of our sample exhibit pulsations with periods from 18 minutes to 8 hr, providing opportunities for asteroseismic studies. The low mass transfer rates and stability make the sample excellent systems for studying mass accretion, advancing our understanding of the evolution of Algol-type binaries.

Keywords: Eclipsing binary stars, Algol variable stars, Light curves, Stellar accretion
Nonstandard Thermal History and Formation of Primordial Black Holes and SIGWs in Einstein–Gauss–Bonnet Gravity. In this article, we examine the formation of primordial black holes (PBHs) in the mutated hilltop inflation model coupled with the Einstein–Gauss–Bonnet term. A suitable choice of the coupling function can produce the ultra-slow-roll (USR) regime during the inflationary phase, which lasts for some number of e-folds leading to a significant enhancement to the curvature power spectrum for small scales so that it grows up to the order of  O(10‑2) ; a crucial feature for producing PBH and scalar-induced gravitational waves (SIGWs). We investigate the formation of PBHs for different sets of parameters. The presented model is capable of producing PBH in a wide range of mass, from  O(10‑14)M⊙  to  O(10)M⊙ . PBHs with mass  O(10‑5)M⊙  can account for the microlensing event in Optical Gravitational Lensing Experiment as well as the asteroid masses  O(10‑15)M⊙‑O(10‑12)M⊙ ; PBH can be attributed to 100% of the dark matter present in the Universe. Whereas PBHs in the mass range  O(10)M⊙  are compatible with LIGO-Virgo data. Our investigation is generalized to include the effect of nonstandard thermal history with an equation of state 1/3 &lt; ω ≤ 1 on PBHs, and it is shown that this possibility can severely impact the formation and abundance of PBHs. The enhancement of the scalar power spectrum also leads to the SIGWs. It is realized that, by increasing ω, there is a slight enhancement of the SIGWs. Moreover, produced SIGWs are well within the detectable frequency ranges of current and future detectors.

Keywords: Cosmic inflation, Gravitational waves, Primordial black holes
HOLESOM: Constraining the Properties of Slowly Accreting Massive Black Holes with Self-organizing Maps. Accreting massive black holes (MBHs, with M• &gt; 103 M⊙) are known for their panchromatic emission, spanning from radio to gamma rays. While MBHs accreting at significant fractions of their Eddington rate are readily detectable, those accreting at much lower rates in radiatively inefficient modes often go unnoticed, blending in with other astrophysical sources. This challenge is particularly relevant for gas-starved MBHs in external galaxies and those possibly wandering in the Milky Way. We present HOLESOM (HOLESOM is publicly available at: https://github.com/valentinalatorre/holesom), a machine learning-powered tool based on the self-organizing maps (SOMs) algorithm, specifically designed to identify slowly accreting MBHs using sparse photometric data. Trained on a comprehensive set of ∼20,000 spectral energy distributions, HOLESOM can (i) determine if the photometry of a source is consistent with slowly accreting MBHs and (ii) estimate its black hole mass and Eddington ratio, including uncertainties. We validate HOLESOM through extensive tests on synthetic data and real-world cases, including Sagittarius A⋆ (Sgr A⋆), demonstrating its effectiveness in identifying slowly accreting MBHs. Additionally, we derive analytical relations between radio and X-ray luminosities to further constrain physical parameters. The primary strength of HOLESOM lies in its ability to accurately identify MBH candidates, which can then be targeted for follow-up photometric and spectroscopic observations. Fast and scalable, HOLESOM offers a robust framework for automatically scanning large multiwavelength data sets, making it a valuable tool for unveiling hidden MBH populations in the local Universe.

Keywords: Accretion, Intermediate-mass black holes, Supermassive black holes, Neural networks, Surveys
Initiation Route of Coronal Mass Ejections. II. The Role of Filament Mass. A thorough understanding of the initiation of coronal mass ejections (CMEs), which is manifested as a slow rise of pre-eruptive structures before the impulsive ejection in kinematics, is key for forecasting solar eruptions. In our previous work, we showed that the slow rise of a hot flux rope with coronal mass density is caused by the moderate magnetic reconnection occurring in the hyperbolic flux tube (HFT) combined with the torus instability. However, it remains unclear how the initiation process varies when a filament is present in the pre-eruptive flux rope. In this work, we reveal the complete initiation route of a CME containing filament mass with a state-of-the-art full-magnetohydrodynamics simulation. The comprehensive analyses show that the filament mass has an important impact on the CME initiation through triggering and driving the slow rise of flux rope with its drainage, besides the contributions of HFT reconnection and torus instability. Finally, in combination with our previous work, we propose that the enhanced drainage of filament mass and various features related to the HFT reconnection, such as the split of pre-eruptive structure and the preflare loops and X-ray emissions, can serve as precursors of CME initiation in observations.

Keywords: Solar flares, Solar coronal mass ejections, Solar filaments, Solar corona