Sazuna/UAT_keywords huggingface dataset:
Predicting Stellar Parameters of Massive Stars from Light Curves with Machine Learning. High-resolution spectroscopic measurements of OB stars are important for understanding processes like stellar evolution but require labor-intensive observations. In contrast, photometric missions like the Transiting Exoplanet Survey Satellite (TESS) can monitor hundreds of thousands of stars with a range of temporal resolutions but do not provide such detailed measurements. With surveys like the Legacy Survey of Space and Time promising unprecedented photometric coverage over the next 10 yr, it is increasingly important to develop methods that connect large-scale time-series photometry with the detailed stellar parameter measurements typically derived from spectroscopy. In this paper, we test whether machine learning can recover such parameters by combining TESS light curves with spectroscopic measurements from the IACOB project, using a sample of 285 light curves from 106 unique O stars. Using both multilayer perceptrons and convolutional neural networks, we demonstrate that (1) O star light curves contain sufficient information to meaningfully infer stellar parameters, and (2) periodograms derived from light curves capture substantially more information than previously identified correlation parameters. Our best model achieves moderate success in predicting both spectroscopic luminosity ( R2=0.641−0.167+0.107 ) and effective temperature ( R2=0.443−0.234+0.056 ), key stellar parameters for determining positions of stars on the spectroscopic Hertzsprung─Russell diagram, despite the small dataset size. Further progress will require expanded datasets of matched photometric and spectroscopic observations.

Keywords: Stellar astronomy, Massive stars, Astronomy data analysis
Magnetic Flux Cancellation in the Solar Atmosphere through 3D Realistic Numerical Modeling. We present a radiation-magnetohydrodynamics (RMHD) simulation of a magnetic cancellation event. The model is calculated with the Bifrost code and spans from the uppermost convection zone to the corona. The cancellation occurs between the positive polarity of an emerged magnetic bipole and a preexisting negative polarity. We try both to understand the RMHD aspects as well as to carry out comparison to observations, in part via spectral synthesis of optically thick photospheric and chromospheric lines using the RH1.5D code, and optically thin coronal ones. The reconnection between the opposite flux systems takes place at chromospheric heights without null points. Sharp V-shaped upward-moving field lines and highly warped downward-moving post-reconnection loops are created. The chromospheric reconnection is in full swing when the colliding magnetic patches are still separated by a granular cell at the photosphere. In a later phase, photospheric cancellation takes place with submergence of the closed magnetic loops linking the opposite polarities. We carry out comparisons with the observations of the photospheric magnetic flux loss rates, as well as of the horizontal magnetic field and vertical velocity at the polarity inversion line. The reconnection outflows cause intensity brightenings, jets, and different spectral features in the synthesized chromospheric spectral lines, strongly reminiscent of those found in recent observations. Coherent, twisted magnetic flux ropes are created by the flows associated with the process. Including coronal levels is crucial for proper modeling, even if no major ejection or brightening is produced in the corona in this event.

Keywords: Solar photosphere, Solar magnetic reconnection, Solar corona, Radiative transfer simulations, Solar chromosphere, Magnetohydrodynamical simulations
Magnetized Accretion Flows: The Key Roles of Viscosity and Black Hole Mass. In our previous work, we constructed a black hole accretion model incorporating magnetic fields and disk winds. However, this model was derived under conditions of a small viscosity parameter α (α &lt; αcrit, where αcrit is the critical viscosity parameter) and for accretion systems around stellar-mass black holes. In the present study, we extend this model to regimes with α &gt; αcrit and to supermassive black hole accretion systems. Our study reveals that under the condition of α &gt; αcrit, the topological structure of thermal equilibrium solutions in black hole accretion disks undergoes significant changes. In the saturated state, the region dominated by advective cooling is confined to the inner disk, yet it expands radially as α increases. This may provide a theoretical explanation for the strong advection-dominated accretion flow (ADAF) principle, specifically addressing the connection problem between the standard thin disk (SSD) and ADAF. Furthermore, we find that the properties of the accretion disk depend on the mass of the central black hole. For stellar-mass black hole accretion systems, the optically thick radiative cooling solutions (similar to the SSD) remain stable, whereas for black holes with M ≥ 105M⊙, the optically thick radiative cooling solutions exhibit unstable behavior. These differences may help explain the distinct variability behaviors observed between X-ray binaries and active galactic nuclei.

Keywords: Accretion, Magnetic fields, Black holes, High energy astrophysics
Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. IV. Broad Emission-line Evolution Sequence among Hα, Mg II, and Hβ. From a parent catalog of 561 changing-look active galactic nuclei (CL-AGNs) identified by W.-J. Guo et al., we investigate the evolutionary sequence of broad emission lines using a redshift-selected subset (0.35 &lt; z &lt; 0.45) of 54 CL-AGNs whose Dark Energy Spectroscopic Instrument (DESI) spectra simultaneously cover the Hα, Hβ, and Mg II emission lines. To provide a baseline for comparison, we construct a control sample of 19,897 normal Type 1 AGNs within the same redshift range from the DESI Year 1 data. Through stacked spectral analysis and line-continuum luminosity correlations, we identify a clear evolutionary sequence in all AGNs where broad Hβ fades first, followed by Mg II, and then Hα, as the AGN luminosity declines—consistent with expectations from reverberation mapping. This trend reflects a radially stratified broad-line region (BLR), where each line's responsivity depends on its ionization potential and radial distance from the central engine. In addition, we find that more massive supermassive black holes require lower Eddington ratios to fully suppress broad emission lines, suggesting that the critical accretion threshold for the changing-look phenomenon is mass-dependent. Our results present the first statistical confirmation of a stratified broad-line fading sequence in AGNs, reinforcing the central role of accretion state in shaping BLR structure and visibility.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei
A Detailed Chemical Analysis of the Red Giant Orbiting Gaia BH3: From Lithium to Thorium. Preliminary astrometric data from the fourth data release of the Gaia mission revealed a 33 M⊙ dark companion to a metal-poor red giant star, deemed Gaia BH3. This system hosts both the most massive known stellar-origin black hole and the lowest-metallicity star yet discovered in orbit around a black hole. The formation pathway for this peculiar stellar─black hole binary system has yet to be determined, with possible production mechanisms that include isolated binary evolution and dynamical capture. The chemical composition of the stellar companion in Gaia BH3 (hereafter BH3⋆) can help constrain the potential formation mechanisms of this system. Here, we conduct the most comprehensive chemical analysis of BH3⋆ to date using high resolution spectra obtained by the Tull Coudé Spectrograph on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory to constrain potential formation mechanisms. We derived 29 elemental abundances ranging from lithium to thorium and find that BH3⋆ is an α-enriched ([α/Fe] = 0.41), r-I neutron-capture star ([Eu/Fe] = 0.57). We conclude that BH3⋆ shows no chemical peculiarities (defined as deviations from the expected chemical pattern of an r-I halo red giant) in any elements, which is in alignment with both the dynamical capture and isolated binary evolution formation scenarios. With an upper limit detection on Th, we use the Th/Eu chronometer to place limits on the cosmochronometric age of this system. These observations lay the groundwork for heavy-element chemical analysis for subsequent black hole and low-metallicity stellar binaries that will likely be found in Gaia DR4. *This paper includes data taken with the Harlan J. Smith 2.7 m telescope at The McDonald Observatory of The University of Texas at Austin.

Keywords: Stellar abundances, Galactic archaeology, Black holes, R-process
Bayesian and Deterministic Neural Network Approaches to Faraday Cup Calibration and Plasma Parameter Estimation. We describe a novel scheme for analyzing particle detector measurements when a well-calibrated, similarly instrumented spacecraft is present in a similar orbit. To prepare ground truth from measurements provided by a reference spacecraft, the method uses dynamic time warping—a technique often used for pattern matching in time series data. An artificial neural network (ANN) is created and trained to reproduce this ground truth from measurements at the target spacecraft. Unlike previous approaches, this procedure is insensitive to calibration errors in the target data stream, as the neural network may be trained from poorly calibrated particle spectra or even directly from low-level data in engineering units. We demonstrate a proof of concept by training an ANN to estimate solar wind proton densities, temperatures, and speeds from the DSCOVR PlasMag Faraday Cup, using the Wind Solar Wind Experiment as a reference. We present both deterministic and Bayesian neural network approaches. Applications for Parker Solar Probe, HelioSwarm, and other missions are discussed.

Keywords: Heliopause, Slow solar wind, Observational astronomy, Astrostatistics tools, Fast solar wind, Neural networks, Convolutional neural networks, Astronomy data analysis, Solar physics, Stellar winds, Bayesian information criterion, Interplanetary physics
Observation and Modeling of Shear Evolution of Post-reconnection Flare Loops. A solar flare releases magnetic energy by reconnecting field lines across a current sheet, thereby allowing their relaxation to a lower-energy state. The maximum possible energy is released if all field lines relax to a current-free (potential) state. The progress of a flare's reconnection is often measured as the angle-complement between the observed post-reconnection flare loops and the polarity inversion line of the photospheric magnetic field: shear angle. Many observations have shown strong-to-weak shear evolution over the course of a flare. A field line's shear angle is, however, an imperfect measure of its relaxation. We develop a new technique for observationally inferring the 3D structure of post-reconnection field lines, including their local twist, α, which will vanish for potential fields. Our method fits loops in extreme-ultraviolet (EUV) images to extrapolations subject to constraints such as matching the feet of model field lines to observed flare ribbons. We apply the new method to an eruptive two-ribbon flare (SOL2014-12-18T22), which exhibits strong-to-weak shear-angle evolution. We find that, as the flare progresses, α decreases in post reconnection loops anchored to newly brightened ribbons. Our study demonstrates that post-reconnection magnetic field is neither potential nor linear force-free. The method quantifies, for the first time, the time-history of a flare's energetic relaxation. It also quantifies the increasing height of the subsequently reconnected field, and the time delay between reconnection forming a flare loop and its appearance in EUV passbands. These results promise to enable improvements in both magnetic modeling and hydrodynamic modeling of flares.

Keywords: Solar magnetic fields, Solar flares, Solar magnetic reconnection, Solar extreme ultraviolet emission
The 2025 Failed Outburst of IGR J17091−3624: Spectral Evolution and the Role of Ionized Absorbers. IGR J17091−3624 is the only black hole X-ray binary candidate—aside from the well-studied black hole system GRS 1915+105—observed to exhibit a wide range of structured variability patterns in its light curves. In 2025, the source underwent a "failed" outburst: it brightened in the hard state but did not transition to the soft state before returning to quiescence within a few weeks. During this period, IGR J17091−3624 was observed by multiple ground- and space-based facilities. Here, we present results from six pointed NuSTAR observations obtained during the outburst. None of the NuSTAR light curves showed the exotic variability classes typical of the soft state in this source; however, we detected, for the first time, strong dips in the count rate during one epoch, with a total duration of ∼4 ks as seen by NuSTAR. Through spectral and timing analysis of all six epochs, we investigate the hard-state spectral evolution and the nature of the dips. A clear evolution of the coronal properties with luminosity is observed over all six epochs, with clear signatures of relativistic disk reflection that remain largely unchanged across the first five epochs. The first five epochs also show a strong and stable quasiperiodic oscillation feature in the power spectra. The dips observed in Epoch 5 are consistent with partial obscuration by ionized material with a column density NH ≍ 2.0 × 1023 cm−2. We discuss possible origins for this material and place constraints on the orbital parameters and distance of the system.

Keywords: Accretion, Black hole physics, High energy astrophysics, Atomic physics, X-ray transient sources, Radiative processes
Testing the Origin of Hot Jupiters with Atmospheric Surveys. In spite of their long detection history, the origin of hot Jupiters remains to be resolved. While dynamical evidence suggests high-eccentricity migration is most likely, conflicts remain when considering hot Jupiters as a population in the context of warm and cold Jupiters. Here, we turn to atmospheric signatures as an alternative means to test the origin theory of hot Jupiters, focusing on population level trends that arise from post-formation pollution, motivated by the upcoming Ariel space mission whose goal is to deliver a uniform sample of exoplanet atmospheric constraints. We experiment with post-formation pollution by planetesimal accretion, pebble accretion, and disk-induced migration and find that an observable signature of post-formation pollution is only possible under pebble accretion in metal-heavy disks. If most hot Jupiters arrive at their present orbit by high-eccentricity migration while warm Jupiters emerge largely in situ, we expect the atmospheric water abundance of hot Jupiters to be significantly elevated compared to warm Jupiters. We report on the detectability of such signatures and further provide suggestions for future comparative atmospheric characterization between hot Jupiters and wide-orbit directly imaged planets to elucidate the properties of the dust substructures in protoplanetary disks.

Keywords: Exoplanet atmospheric composition , Exoplanet formation, Exoplanet migration, Exoplanet atmospheres
Curious Case of CGRaBS J0211+1051: Observational Evidence of the Lepto-hadronic Origin of High-energy Emission?. We present an extensive analysis of the multiwavelength data of the low-synchrotron-peaked BL Lac object CGRaBS J0211+1051 that have been gathered over more than 10 yr with many observatories. Two major γ-ray flares have been observed during the Fermi era: one in 2011 January and the other in 2019 June. During these events, CGRaBS J0211+1051 was also bright in other energy bands. On the other hand, there are also examples of optical activity that do not exhibit any comparable γ-ray variability. Here, we study the temporal and spectral characteristics of the object in an attempt to understand the emission mechanisms operating in this source. A peculiar feature in its spectrum is the X-ray domain, which is unusually soft considering its object class. Interestingly, the relatively soft UV and optical spectrum does not extrapolate well to X-rays. To mimic the observed spectral energy distributions (SEDs) during quiescent and flaring periods, we use both a purely leptonic and a hadro-leptonic modeling approach to reproduce four broadband SEDs from various epochs. When taking into account the steep optical─UV spectrum, we find that the hadro-leptonic scenario better explains the SEDs compared to the purely leptonic model. The hadro-leptonic interpretation of the two γ-ray flares suggests that CGRaBS J0211+1051 could be both a potential neutrino emitter and TeV-bright (E &gt; 10 TeV). Thus, it may offer a unique test bed to check for hadro-leptonic contributions to the multimessenger emission in blazar jets.

Keywords: BL Lacertae objects, Jets, High energy astrophysics, Blazars, Light curves, Neutrino astronomy, Active galactic nuclei, Spectral energy distribution
Spectropolarimetric Inversion in Four Dimensions with Deep Learning (SPIn4D). II. A Physics-informed Machine Learning Method for 3D Solar Photosphere Reconstruction. Inferring the three-dimensional (3D) solar atmospheric structures from observations is a critical task for advancing our understanding of the magnetic-fields and electric currents that drive solar activity. In this work, we introduce a novel, physics-informed machine learning method to reconstruct the 3D structure of the lower solar atmosphere based on the output of optical-depth-sampled spectropolarimetric inversions, wherein both the fully disambiguated vector magnetic fields and the geometric height associated with each optical depth are returned simultaneously. Traditional techniques typically resolve the 180° azimuthal ambiguity assuming a single layer, either ignoring the intrinsic nonplanar physical geometry of constant optical-depth surfaces (e.g., the Wilson depression in sunspots) or correcting the effect as a postprocessing step. In contrast, our approach simultaneously maps the optical depths to physical heights, and enforces the divergence-free condition for magnetic fields fully in 3D. Tests on magnetohydrodynamic simulations of quiet Sun, plage, and a sunspot demonstrate that our method reliably recovers the horizontal magnetic-field orientation in locations with appreciable magnetic field strength. By coupling the resolutions of the azimuthal ambiguity and the geometric height problems, we achieve a self-consistent reconstruction of the 3D vector magnetic fields and, by extension, the electric current density and Lorentz force. This physics-constrained, label-free training paradigm is a generalizable, physics-anchored framework that extends across solar magnetic environments while improving the understanding of various solar puzzles.

Keywords: Solar atmosphere, Solar photosphere, Convolutional neural networks, Computational methods, Solar magnetic fields
Particle Loads for Cosmological Simulations with Equal-mass Dark Matter and Baryonic Particles. Traditional cosmological hydrodynamical simulations usually assume equal-numbered but unequal-mass dark matter and baryonic particles, which can lead to spurious collisional heating due to energy equipartition. To avoid such a numerical heating effect, a simulation setup with equal-mass dark matter and baryonic particles, which corresponds to a particle number ratio of NDM:Ngas = Ωcdm/Ωb, is preferred. However, previous studies have typically used grid-based particle loads to prepare such initial conditions, which can only reach specific values for NDM:Ngas due to symmetry requirements. In this study, we propose a method based on the glass approach that can generate two-component particle loads with more general NDM:Ngas ratios. The method simultaneously relaxes two Poisson particle distributions by introducing an additional repulsive force between particles of the same component. We show that the final particle load closely follows the expected minimal power spectrum, P(k) ∝ k4, exhibits good homogeneity and isotropy properties, and remains sufficiently stable under gravitational interactions. Both the dark matter and gas components individually also exhibit uniform and isotropic distributions. We apply our method to two-component cosmological simulations and demonstrate that an equal-mass particle setup effectively mitigates the spurious collisional heating that arises in unequal-mass simulations. Our method can be extended to generate multicomponent uniform and isotropic distributions. Our code based on GADGET-2 is available at https://github.com/liaoshong/gadget-2glass.

Keywords: Galaxy formation, Dark matter, N-body simulations, Large-scale structure of the universe
Black-hole Shadows and Null Geodesics in Hamaus─Sutter─Wandelt Void Spacetimes with a Quintessential Field: Observational Signatures from EHT Data of M87<SUP>∗</SUP> and Sgr A<SUP>∗</SUP>. We study horizon-scale lensing and shadow formation for a static, spherically symmetric black hole embedded in a cosmic void modeled by the Hamaus─Sutter─Wandelt (HSW) density profile and immersed in a quintessential field. Starting from the enclosed mass implied by the HSW profile, we derive a metric function f(r) that augments the Schwarzschild term by void-dependent contributions and a quintessence term. We obtain analytic small and large r expansions and a global interpolant for f(r), then analyze null geodesics to determine the photon sphere and the shadow radius  Rs=rp/f(rp) . The photon-sphere condition does not admit a closed form and is solved numerically. We confront the predicted shadows with Event Horizon Telescope (EHT) measurements of M87* and Sgr A*, translating angular diameters, distances, and masses into dimensionless shadow sizes. The comparison yields quantitative bounds on the void and quintessence parameters: δc ∈ [−0.55, 0] and ρs ∈ [0.003, 0.012], with γ ∈ [0.005, 0.12] (Sgr A*, 1σ), and correspondingly broader intervals for M87* that accommodate slightly larger values. Across the explored space, increasing δc (toward zero), or increasing γ and ρs, reduces Rs, reflecting a softer effective curvature near the photon sphere. A dynamical-systems analysis of the radial motion shows that circular null orbits remain unstable saddles, with their location shifting monotonically with δc, γ, and ρs. Finally, using the limiting absorption cross section  σlim≃πRs2 , we show that the Hawking energy-emission rate is enhanced by decreasing γ and ρs and suppressed as these increase, while larger underdensities (more negative δc) favor higher emission. Our results establish EHT-level, data-driven constraints on HSW quintessence environments and quantify their imprint on black-hole shadows and thermodynamics.

Keywords: Black hole physics, Theoretical models, Quintessence, Compact objects, Astrophysical black holes, Dark energy