Sazuna/UAT_keywords huggingface dataset:
Neutral Gas Phase Distribution from H I Morphology: Phase Separation with Scattering Spectra and Variational Autoencoders. Unraveling the multiphase structure of the diffuse interstellar medium as traced by neutral hydrogen (H I) is essential to understanding the lifecycle of the Milky Way. However, H I phase separation is a challenging and underconstrained problem. The neutral gas phase distribution is often inferred from the spectral line structure of H I emission. In this work, we develop a data-driven phase-separation method that extracts H I phase structure solely from the spatial morphology of H I emission intensity structures. We combine scattering spectra (SS) statistics with a Gaussian-mixture variational autoencoder model to (1) derive an interpretable statistical model of different H I phases from their multiscale morphological structures, and (2) we use this model to decompose the 2D channel maps of GALFA-H I emission in diffuse high-latitude (∣b∣ &gt; 30°) regions over narrow velocity channels (∆v = 3 km s−1) into cold neutral medium (CNM), warm neutral medium (WNM), and noise components. We integrate our CNM map over velocity channels to compare it to an existing map produced by a spectrum-based method. We find that the two maps are highly correlated, but ours recovers more spatially coherent structures at small scales. Our work illustrates and quantifies a clear physical connection between the H I morphology and H I phase structure, and it unlocks a new avenue for improving future phase-separation techniques by making use of both H I spectral and spatial information to decompose H I in 3D position─position─velocity space. These results are consistent with a physical picture where processes that drive H I phase transitions also shape the morphology of H I gas, imprinting a sparse, filamentary CNM that forms out of a diffuse, extended WNM.

Keywords: Neural networks, Astrostatistics, H I line emission, Cold neutral medium, Interstellar medium, Wavelet analysis, Warm neutral medium
The Variable Radio Emission of V830 Tau and Its Putative Planet. We report on the first moderate-length timescale observations of a young stellar object at microwave frequencies. V830 Tau was monitored over the course of 8 days with the Karl G. Jansky Very Large Array at a frequency range of 4─8 GHz. Previous brief radio observations of this purported planet-hosting star indicated a radio-bright source with sparse evidence of dramatic intensity changes. Our observations confirm variability larger than a factor of 5 over the 8 days, with closer-spaced data indicating a long-lived flare event spanning multiple days. We discuss a hypothesis that the large, long-duration radio flare may be produced as a result of magnetospheric interaction between the star and its purported planet, using multiyear monitoring of a few active binary systems with the Green Bank Interferometer to augment our discussion. Although we cannot disentangle the effect of the large stellar surface area from any effects of orbital separation, the disputed star─planet system would have a large amount of power generated from the stretching and breaking of magnetic fields. If this long-duration flare behavior repeats with additional data on timescales close to the planetary orbital period, microwave signatures of interacting magnetospheres could be a new observational tool to confirm the existence of planets around young, magnetically active stars.

Keywords: Discrete radio sources, T Tauri stars, Stellar flares
Effects of Dark Matter Self-interactions on Sagittarius and its Stream. This work explores how assumptions regarding the particle-physics nature of dark matter can alter the evolution of the Sagittarius (Sgr) dwarf spheroidal galaxy and its expansive stellar stream. We run a large suite of N-body simulations to model the infall of a spherically symmetric Sgr-like dwarf, exploring how the presence of dark matter self-interactions impacts its evolution. For a scattering cross section of σ/mχ = 30 cm2 g−1 (at orbital velocity scales), these interactions result in significantly less stellar mass and little to no dark matter bound to the progenitor at the present day. To isolate the cause of this mass loss, we introduce a novel technique for controlling which pairs of dark matter simulation particles can interact. This enables us to identify ram-pressure evaporation—the scattering of satellite and host dark matter particles—as the primary source of the enhanced mass loss. The rapid disintegration of the Sgr progenitor when self-interactions are allowed alters some key properties of the resulting stellar stream, most dramatically suppressing the presence of a "spur" on the apocenter of the trailing stream arm that correlates with the mass of the satellite at last pericenter. We demonstrate how the effects on the Sgr system scale with the particular choice of self-interaction cross section, which affects the degree of ram-pressure evaporation. These findings generalize beyond the Sgr system, underscoring that dwarf stellar streams and dwarf galaxies with close passages may serve as sensitive probes for dark matter self-interactions.

Keywords: Milky Way dark matter halo, Stellar streams, Milky Way dynamics, Sagittarius dwarf spheroidal galaxy, Dark matter
Multispacecraft Observations of 2022 February 8 Prominence Cavity Eruption. Helmet streamers are common structures that shape the corona at the largest scales, as observed in eclipse and white-light images. Helmet streamers overlie one cavity embedding a prominence channel and are surrounded by an open field of opposite-polarity coronal holes. In this study, we present multispacecraft observations of a spectacular prominence-cavity eruption from the southeastern solar limb accompanied by a geoeffective coronal mass ejection (CME), observed by the Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, Solar Orbiter, Advanced Composition Explorer, and Wind. We produce 3D magnetic field configurations before and during the eruption using the flux-rope insertion method and magnetofrictional relaxation that are consistent with the observations. We also performed a differential emission measure analysis to study the thermal structure of the helmet streamer prominence-cavity region before and after the eruption. We note that because of the considerable length of the prominence, it was possible to capture the eruption using in situ measurements by multiple spacecraft. Moreover, our multispacecraft in situ analysis shows that the CME propagating in the precondition medium varies as a function of longitude in the heliosphere.

Keywords: Solar coronal streamers, Magnetic fields, Solar corona, Solar prominences
Tracing Planetary Accretion in a 3 Gyr old Hydrogen-rich White Dwarf: The Extremely Polluted Atmosphere of LSPM J0207+3331. We report the detection of 13 heavy elements (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Sr) in the photosphere of LSPM J0207+3331, a ∼3 Gyr old hydrogen-rich white dwarf with an effective temperature comparable to that of the Sun. Upper limits on carbon, obtained through the absence of molecular CH, suggest accretion from a carbon-volatile-depleted source. The accreted parent body exhibits slight deficits of Mg and Si relative to Fe but otherwise bulk Earth-like abundance patterns; a reasonable interpretation is that LSPM J0207+3331 is accreting a massive differentiated rocky body that had a core mass fraction higher than the Earth's. The high level of pollution indicates that substantial accretion events can still occur even after 3 Gyr of cooling. We also detect weak Ca II H &amp; K line core emission, making this only the second known isolated polluted white dwarf to exhibit this phenomenon and suggesting the presence of additional physical processes in or above the upper atmosphere. Our analysis also highlights the critical importance of including heavy elements in the model atmosphere structure calculations for highly polluted hydrogen-rich white dwarfs. Neglecting their contribution significantly impacts the inferred thermodynamic structure, leading to inaccuracies in derived stellar parameters. Finally, we show that the observed 11.6 μm infrared excess can be explained by a single silicate dust disk rather than a two-ring disk model.

Keywords: Stellar abundances, White dwarf stars, Exoplanet systems, Stellar atmospheres
Variations of the Vector Magnetic Structures in the Solar Polar Regions Observed by Hinode. Using the polar vector magnetic field data observed by Hinode from 2012 to 2021, we study the long-term variations of the magnetic flux, the flux proportion of different polarities, and the magnetic inclination with respect to the local normal in the solar polar regions above 70° latitude during solar cycle 24. In both polar regions, after the polarity reversal, the unsigned magnetic fluxes of the dominant polarity increased to a peak of about 1.3 × 1022 Mx during the solar minimum, while those of the nondominant polarity remained stable at approximately 0.5 × 1022 Mx. The proportions of the dominant polarity flux in the total flux in both polar regions increased to more than 70% at the solar minimum. These results reveal that the total magnetic flux and the number of open field lines in solar cycle 24 were larger than those in solar cycle 23, and also imply the existence of a local dynamo in polar regions. After the polarity reversal, the magnetic inclination of the dominant polarity fields decreased, indicating that the stronger the dominant polarity field, the more vertical the field lines. The inclination angle decreased with the increase of the threshold of radial magnetic flux density, revealing a fanning-out structure of the polar magnetic patches.

Keywords: Solar cycle, Solar photosphere, Solar magnetic fields
Assessing the Geoeffectiveness of Stream Interaction Regions through Physically Interpretable Machine Learning. Stream interaction regions (SIRs) are common solar wind structures that mainly drive moderate geomagnetic storms, especially during the declining and minimum phases of the solar cycle. Despite substantial progress in identifying their solar wind drivers, predicting SIR geoeffectiveness remains challenging due to the nonlinear and multivariate nature of solar wind─magnetosphere coupling. In this study, we apply an interpretable machine learning framework based on a Support Vector Machine (SVM) classifier to evaluate the geoeffectiveness of 879 SIR events from 1995 to 2019. A comprehensive feature set is constructed using OMNI solar wind data, incorporating interplanetary magnetic field (IMF) components, plasma parameters, and event-level statistical descriptors, including pre- and post-event conditions. A two-step feature reduction strategy, combining Fisher score ranking with grid search optimization, is used to identify an optimal subset of input variables. The SVM model achieves a True Skill Statistic of 0.80 and an F1-score of 0.81 on the geoeffective class (Dst &lt; ─50 nT), demonstrating strong performance in identifying moderate and stronger geomagnetic storms. SHapley Additive exPlanations values and Uniform Manifold Approximation and Projection visualization are employed to interpret and validate the model's behavior. The analysis reveals that features related to the duration of southward IMF, the solar wind electric field, and IMF Bz components play dominant roles in the model's decision-making, consistent with known reconnection-driven energy transfer processes. These results highlight the capability of classical machine learning models, coupled with physically meaningful feature engineering and interpretability methods, to support space weather research and improve understanding of SIR-driven geomagnetic activity.

Keywords: Solar-terrestrial interactions, Geomagnetic fields, Corotating streams, Support vector machine
A Stellar Dynamical Mass for the Central Black Hole in MCG─06-30-15. We present the stellar dynamical (SD) mass of the central black hole in the nearby Seyfert galaxy MCG─06-30-15 using the Schwarzschild orbit-superposition method implemented in the open-source code FORSTAND. We obtained spatially resolved K-band nuclear stellar spectra for this galaxy with SINFONI on the Very Large Telescope. We extracted the bulk stellar kinematics using Gauss─Hermite (GH) parameterization of the line-of-sight velocity distributions. A multicomponent surface-brightness profile of the galaxy was determined from a Hubble Space Telescope medium-band V image. Our best-fit models indicate a black hole mass of MBH = (4.4 ± 1.4) × 107M⊙ and a stellar mass-to-light ratio of M/L = (3.0 ± 0.3)M⊙/L⊙, within 1σ confidence intervals. Our constraint on MBH agrees with an upper limit on the mass from stellar dynamics based on the Jeans anisotropic modeling method, but is ∼10 times larger than the reported mass from reverberation mapping (RM). However, our best-fit MBH may be systematically biased high due to the counterrotating disk in the nucleus of MCG─06-30-15 and the inability of the GH parameterization to fully describe such a complicated set of stellar kinematics. In addition, a dynamical MBH value depends heavily on the assumed source distance, which is not yet accurately constrained for this galaxy. MCG─06-30-15 is only the fourth galaxy in which we can compare MBH from SD modeling with that from RM. A direct comparison of MBH allows us to identify and investigate the possible sources of bias associated with different mass measurement techniques, which may influence our understanding of black hole and galaxy coevolution across cosmological timescales.

Keywords: AGN host galaxies, Supermassive black holes, Seyfert galaxies, Stellar dynamics
Bridging Unstratified and Stratified Simulations of the Streaming Instability for τ<SUB>s</SUB> = 0.1 Grains. The streaming instability (SI), driven by aerodynamic coupling between solids and gas under a global radial pressure gradient, concentrates solids and facilitates planetesimal formation. Unstratified simulations are commonly used to study the SI, based on the assumption that they approximate conditions near the disk midplane. However, it remains unclear how accurately these unstratified simulations capture the midplane dust─gas dynamics in stratified disks. To address this, we examine the saturated state of the SI in stratified simulations and compare the dust─gas dynamics to those in unstratified simulations across various radial pressure gradients. To this end, we consider a dimensionless dust stopping time (τs) of 0.1 and perform 2D axisymmetric, stratified simulations. We find that the formation of dust filaments during dust settling exhibits morphological similarities to those in unstratified simulations. Vertical gravity acts to redistribute momentum vertically in response to momentum flux, resulting in midplane velocities in the center-of-mass frame that are consistent with those from unstratified models at any given pressure gradient. Furthermore, the velocity dispersions and density distributions of the gas and dust near the midplane of our stratified simulations closely match those in unstratified simulations. While further exploration across the parameter space is needed, our results suggest that, for τs = 0.1, unstratified simulations represent well the midplane dust─gas dynamics in stratified disks before any strong clumping occurs. Consequently, our results confirm that in the saturated state, the streaming turbulence in stratified simulations behaves similarly to that in unstratified simulations for the parameter values explored here.

Keywords: Hydrodynamics, Protoplanetary disks, Planetesimals, Astrophysical fluid dynamics, Planet formation
FEAST: JWST Uncovers the Emerging Timescales of Young Star Clusters in M83. We present JWST NIRCam observations of the emerging young star clusters (eYSCs) detected in the nearby spiral galaxy M83. The NIRcam mosaic encompasses the nuclear starburst, the bar, and the inner spiral arms. The eYSCs, detected in Paα and Brα maps, have been largely missed in previous optical campaigns of young star clusters (YSCs). We distinguish between eYSCI, if they also have compact 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission associated with them, and eYSCII, if they only appear as compact Paα emitters. We find that the variations in the 3.3 μm PAH feature are consistent with an evolutionary sequence where eYSCI evolve into eYSCII and then optical YSCs. This sequence is clear in the F300M−F335M (tracing the excess in the 3.3 μm PAH feature) and the F115W−F187N (tracing the excess in Paα) colors, which become increasingly bluer as clusters emerge. The central starburst stands out as the region where the most massive eYSCs are currently forming in the galaxy. We estimate that only about 20% of eYSCs will remain detectable as compact YSCs. Combining eYSCs and YSCs (≤10 Myr), we recover an average clearing timescale of 6 Myr in which clusters transition from embedded to fully exposed. We see evidence of shorter emergence timescales (∼5 Myr) for more massive (&gt;5 × 103 M⊙) clusters, while star clusters of ∼103 M⊙ about 7 Myr. We estimate that eYSCs remain associated with the 3.3 μm PAH emission for 3─4 Myr. Larger samples of eYSC and YSC populations will provide stronger statistics to further test environmental and cluster mass dependencies on the emergence timescale.

Keywords: Polycyclic aromatic hydrocarbons, Star forming regions, Young star clusters
Late-time Evolution of Magnetized Disks in Tidal Disruption Events. In classic time-dependent 1D accretion-disk models, the inner radiation-pressure-dominated regime is viscously unstable. However, late-time observations of accretion disks formed in tidal disruption events (TDEs) do not exhibit evidence of such instabilities. The common theoretical response is to modify the viscosity parameterization, but the typically used viscosity parameterizations are generally ad hoc. In this study, we take a different approach and investigate a time-dependent 1D α-disk model, in which the pressure is dominated by magnetic fields rather than photons. We compare the time evolution of thermally stable, strongly magnetized TDE disks to the simpler linear viscosity model. We find that the light curves of magnetized disks evolve as LUV ∝ t−5/6 for decades to centuries and that this same evolution can be reproduced by the linear viscosity model for specific parameter choices. Additionally, we show that TDEs remain ultraviolet-bright for many years, suggesting we could possibly find fossil TDEs decades after their bursts. We estimate that ULTRASAT could detect hundreds of such events, providing an opportunity to study late-stage TDE physics and supermassive black hole properties. Finally, we explore the connection between TDE disks and quasiperiodic eruptions (QPEs) suggested by recent observations. One theoretical explanation involves TDE disks expanding to interact with extreme-mass-ratio inspirals (EMRIs), which produce X-ray flares as the EMRI passes through the disk. Our estimates indicate that magnetized TDE disks should exhibit QPEs earlier than those observed in AT2019qiz, suggesting that the QPEs may have begun before their first detection.

Keywords: Accretion, Supermassive black holes, Black hole physics, High energy astrophysics, Tidal disruption, Transient sources, Newtonian gravitation
Detecting Electromagnetic Counterparts to LIGO/Virgo/KAGRA Gravitational-wave Events with DECam: Neutron Star Mergers. With GW170817 being the only multimessenger gravitational-wave (GW) event with an associated kilonova detected so far, there exists a pressing need for realistic estimation of the GW localization uncertainties and rates, as well as optimization of available telescope time to enable the detection of new kilonovae. We simulate GW events assuming a data-driven distribution of binary parameters for the LIGO/Virgo/KAGRA fourth and fifth observing runs (O4 and O5). We map the binary neutron star (BNS) and neutron star─black hole (NSBH) properties to the kilonova optical light curves. We use the simulated population of kilonovae to generate follow-up observing plans, with the primary goal of optimizing detection with the Gravitational Wave Multi-Messenger Astronomy DECam Survey. We explore the dependence of kilonova detectability on the mass, distance, inclination, and spin of the binaries. Assuming that no BNS was detected during O4 until the end of 2024, we present updated GW BNS (NSBH) merger detection rates. We expect to detect BNS (NSBH) kilonovae with DECam at a per-year rate of 0─2.0 (0) in O4 and 2.0─19 (0─1.0) in O5. We expect the majority of BNS detections and also those accompanied by a detectable kilonova to produce a hypermassive NS remnant, with a significant fraction of the remaining BNSs promptly collapsing to a BH. We release GW simulations and depths required to detect kilonovae based on our predictions to support the astronomical community in their multimessenger follow-up campaigns and analyses.

Keywords: Observational astronomy, Transient detection, Gravitational waves, High energy astrophysics
Asymptotic Giant Branch Mass-loss Rates and Metal Yields from Scaled Mixing-length and Mass-loss Parameters. Stars on the asymptotic giant branch (AGB) enrich the interstellar medium with carbon, nitrogen, and dust, which in turn boost cooling and promote future generations of planet and star formation. They are poorly constrained observationally because they remain in this phase briefly and modeling them is also challenging due to complex convective mixing and nucleosynthesis. By incorporating updated opacity tables and instability management techniques into MESA, we compute a new grid of AGB models that densely samples a wide range of initial masses (0.8 ≤ M/M⊙ ≤ 7) and metal mass fractions (0.0001 ≤ Z ≤ 0.03), and generate updated AGB mass-loss rates and metal yields up to 28Si for evolution models and cosmological simulations. We develop scaling formulas for varying the convective mixing-length and Blöcker mass-loss parameters, enabling calibration against recent carbon star luminosity observations and hydrodynamic simulation results. Our results are consistent with white dwarf initial─final mass observations, typical AGB mass-loss rates of ∼10−7─10−5 M⊙ yr−1, and average luminosities of carbon stars in AGB populations of ∼8200 L⊙. We compare yields to previous models, finding similar C, N, O, F, and Ne but significantly enhanced Mg. The surface C/O ratios match other models at high metallicity but tend to be higher at Z ≤ 0.005. Predicted surface metallicities match previous simulation assumptions, but significantly higher AGB outflow rates suggest large systematic uncertainties in the theoretically expected cosmological carbon yield.

Keywords: Asymptotic giant branch stars, Stellar evolutionary models
The Effects of Linear Matter Power Spectrum Enhancement on Dark Matter Substructure. We present cosmological dark matter (DM)─only zoom-in simulations of a Milky Way analog originating from enhanced linear matter power spectra P(k) relative to the standard cold, collisionless DM (CDM) cosmology. We consider a Gaussian power excess in P(k) followed by a cutoff in select cases; this behavior could arise from early-Universe physics that alters the primordial matter power spectrum or DM physics in the radiation-dominated epoch. We find that enhanced initial conditions (ICs) lead to qualitative differences in substructure relative to CDM. In particular, the subhalo mass function (SHMF) resulting from ICs with both an enhancement and a cutoff is amplified at high masses and suppressed at low masses, indicating that DM substructure is sensitive to features in P(k). Critically, the amplitude and shape of the SHMF enhancement depend on the wavenumber of the P(k) excess and the presence or absence of a cutoff on smaller scales. These alterations to the SHMF are mainly imprinted at infall rather than during tidal evolution. Additionally, subhalos are found systematically closer to the host center, and their concentrations are increased in scenarios with P(k) enhancement. Our work thus reveals effects that must be captured to enable P(k) reconstruction using DM substructure.

Keywords: Galaxy dark matter halos, Dark matter, N-body simulations