Sazuna/UAT_keywords huggingface dataset:
Advancing Solar Flare Forecasting with a Deep Learning Approach Using Multimodal Inputs. Solar flares are among the most energetic phenomena in the solar system, and their forecasting remains a major challenge in space weather research. In this study, we present a deep learning framework that predicts the occurrence of ≥C5.0-class flares within a 2 hr forecast horizon by integrating multimodal, multiwavelength observations of solar active regions. The model combines sequences of Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms, continuum intensity images, and SDO/Atmospheric Imaging Assembly extreme-ultraviolet observations (193 and 304 Å) with physically derived Space-weather HMI Active Region Patch parameters—total unsigned magnetic flux and current helicity—within a unified end-to-end architecture. A convolutional encoder extracts spatial representations from images, which are fused with physical parameters and processed through a recurrent neural network to capture temporal evolution. Using time sequences spanning 36 minutes, our best-performing configuration achieves an accuracy of 92.7%, a recall of 97.6%, and a true skill statistic of 0.86 on an independent test set, significantly outperforming single-modality baselines. Our findings demonstrate that combining physically meaningful parameters with multiwavelength imaging substantially enhances model performance while maintaining good calibration. The proposed framework demonstrates the capability of deep learning to model the spatiotemporal and physical complexity of solar active regions, thereby enabling more accurate and physics-informed flare forecasting.

Keywords: Solar flares, Solar photosphere, Solar extreme ultraviolet emission, Neural networks, Classification, Space weather, Astronomy data analysis, Solar active regions, Solar magnetic fields, Solar chromosphere, Time series analysis
Merger of Noncompact Binaries: Triggering Mechanisms and Merger Timescales of W UMa Contact Binaries. The merger of noncompact binaries can produce a variety of significant celestial objects, including blue stragglers, luminous red novae, and others. However, several key details of the merger of noncompact binaries remain unclear. Using the MESA stellar evolution code, we investigate the triggering mechanisms and merger timescales of observed W UMa contact binaries (a type of noncompact binary that is closest to merging). Our results show that for the majority of observed W UMa contact binaries (89%), the merger-triggering mechanism is tidal instability, while thermal instability accounts for the remaining cases (11%). We suggest that tidal instability is the dominant mechanism for triggering the mergers of W UMa contact binaries. In addition, our results indicate that the distribution of merger timescales for observed W UMa contact binaries ranges from ∼2.5 Myr to ∼1.0 Gyr, peaking at 0.26 Gyr, with an average merger timescale of 0.36 Gyr. We suggest that the merger timescale of each W UMa contact binary may be a more comprehensive criterion for identifying potential merger candidates than the mass ratio or other individual parameters. Finally, we present some promising merger candidates of W UMa contact binaries (e.g., those with the shortest or undetermined merger timescales) for future studies on noncompact binary mergers.

Keywords: W Ursae Majoris variable stars, Contact binary stars, Stellar mergers
A Freefall-based Switching Criterion for P<SUP>3</SUP>T Hybrid N-body Methods in Collisional Stellar Systems. The P3T scheme is a hybrid method for simulating gravitational N-body systems. It combines a fast particle-tree (PT) algorithm for long-range forces with a high-accuracy particle─particle (PP; direct N-body) solver for short-range interactions. Preserving both PT efficiency and PP accuracy requires a robust PT─PP switching criterion. We introduce a simple freefall-based switching criterion for general stellar systems alongside the commonly used velocity-dispersion-based (σ-based) criterion. Using the PETAR code with the P3T scheme and slowdown algorithmic regularization for binaries and higher-order multiples, we perform extensive simulations of star clusters to evaluate how each criterion affects energy conservation and binary evolution. For systems in virial equilibrium, we find that the freefall-based criterion is generally more accurate for low-σ or loose clusters containing binaries, whereas the σ-based criterion is better suited for high-σ systems. Under subvirial or fractal initial conditions, both criteria struggle to maintain high energy conservation; however, the freefall-based criterion improves as the tree time step is reduced, whereas the σ-based criterion degrades due to its low-accuracy treatment of two-body encounters.

Keywords: Algorithms, N-body simulations, Star clusters
Extending the Micro-hertz Detection Horizons via Orbital Resonance Effect for Geocentric Gravitational Wave Antennas. The μHz gravitational wave (GW) band holds crucial insights into coalescing supermassive black hole binaries (SMBHBs) and stochastic backgrounds but remains inaccessible due to technical challenges. We demonstrate that geocentric space-based GW detectors (e.g., TianQin, gLISA, GADFLI) can bridge this gap by considering orbital resonance effects, circumventing the need for prohibitively long baselines. When GW frequencies match with integer multiples of a satellite's orbital frequency, sustained tidal forces induce cumulative orbital deviations through resonant effects, which, combined with orbital modulation, improve detector sensitivity by 1─2 orders of magnitude in the μHz band. Consequently, geocentric missions can detect SMBHBs across significantly expanded mass─redshift parameter space. Crucially, such observations could synergize with pulsar timing array data of the same binaries at earlier inspiral stages, enabling unprecedented joint tests of strong-field gravity and binary evolution. Our findings establish geocentric antennas as a cost-effective, near-term precursor for unlocking the μHz GW astronomy.

Keywords: Gravitational wave astronomy, Supermassive black holes, Gravitational wave detectors, Orbital resonances
Spectral Connection between Far UV and Soft X-Ray Emission from Active Galactic Nuclei Using AstroSat. We present the UV/X-ray joint spectral analyses of four Seyfert 1 galaxies (PG 0804+761, NGC 7469, SWIFT J1921.1-5842, and SWIFT J1835.0+3240) using the data acquired with the Ultraviolet Imaging Telescope and Soft X-ray Telescope on board AstroSat. We model the intrinsic UV/X-ray continuum with the accretion disk and warm and hot Comptonization using the OPTXAGNF and FAGNSED models, where the disk seed photons are Comptonized in the warm and hot corona. The Eddington ratio of the four Seyferts ranges from 0.01 to 1. In the case of SWIFT J1835.0+3240, we infer a compact warm corona (Rwarm − Rhot ≲ 18rg), while PG 0804+761, NGC 7469, and SWIFT J1921.1-5842 may exhibit a larger warm Comptonizing region (≳32rg). We could constrain the spin parameter in PG 0804+761,  a⋆=0.76−0.20+0.08  (1σ error), with the FAGNSED model. In SWIFT J1835.0+3240 and SWIFT J1921.1-5842, the UV/X-ray spectral variability may be driven by the thermal Comptonization of the disk seed photons in the hot corona. Furthermore, the observed spectral hardening with the decrease in disk temperature and accretion rate compared to earlier observations may indicate a state transition in SWIFT J1835.0+3240 from a high/soft to a low/hard state.

Keywords: Accretion, Seyfert galaxies, Ultraviolet spectroscopy
Novel Physics of Escaping Secondary Atmospheres May Shape the Cosmic Shoreline. Recent James Webb Space Telescope observations of cool, rocky exoplanets reveal a probable lack of thick atmospheres, suggesting the prevalent escape of the "secondary" atmospheres formed after losing primordial hydrogen. Yet, simulations indicate that the hydrodynamic escape of secondary atmospheres, composed of nitrogen and carbon dioxide, requires intense fluxes of ionizing radiation (X-ray and extreme ultraviolet (XUV)) to overcome the effects of high molecular weight and efficient line cooling. This transonic outflow of hot, ionized metals (not hydrogen) presents a novel astrophysical regime ripe for exploration. We introduce an analytic framework to determine which planets retain or lose their atmospheres, positioning them on either side of the cosmic shoreline. We model the radial structure of escaping atmospheres as polytropic expansions—power-law relationships between density and temperature driven by local XUV heating. Our approach diagnoses line cooling with a three-level atom model and incorporates how ion─electron interactions reduce the mean molecular weight. Crucially, hydrodynamic escape onsets for a threshold XUV flux depend upon the atmosphere's gravitational binding. The ensuing escape rates either scale linearly with XUV flux when weakly ionized (energy limited) or are controlled by a collisional─radiative thermostat when strongly ionized. Thus, airlessness is determined by whether the XUV flux surpasses the critical threshold during the star's active periods, accounting for expendable primordial hydrogen and revival by volcanism. We explore atmospheric escape from the young Sun Mars and Earth, LHS 1140 b and c, and TRAPPIST-1 b. Our modeling characterizes the bottleneck of atmospheric loss on the occurrence of observable Earth-like habitats and offers analytic tools for future studies.

Keywords: Aurorae, Analytical mathematics, Star-planet interactions, Astrophysical fluid dynamics, Habitable planets, Exoplanet atmospheric evolution
Subtracting and Monitoring Tilt-to-length Noise under High Differential Wavefront Sensing Noise Using Convolutional Neural Networks and Time Delay Interferometry. Gravitational waves (GWs) provide a powerful tool to probe energetic astrophysical events and test fundamental physics, with space-based detectors enabling access to low-frequency signals from massive black hole mergers, extreme mass-ratio inspirals, and other sources. However, the sensitivity of space-based interferometers can be severely compromised by tilt-to-length (TTL) coupling noise, which contaminates phase measurements by converting angular jitter into apparent path length fluctuations. This problem is exacerbated when differential wave front sensing (DWS) systems suffer from high readout noise due to optical misalignments and wave front aberrations. In this work, we introduce a novel framework that integrates convolutional neural networks (CNNs) with time delay interferometry (TDI) to improve the robustness of TTL coupling coefficient estimation under high-noise conditions. The CNN is trained to identify and exclude DWS angular measurements corrupted by noise, while the TDI module adaptively selects optimal combinations that minimize TTL-induced contamination. In addition, an analytical error-based monitoring algorithm is incorporated to track the stability of TTL coefficients. When coefficients remain within their nominal range, the predicted uncertainty band covers the true values, while abrupt excursions beyond the monitoring threshold can be reliably detected. Simulations demonstrate that our method maintains TTL coefficient errors below 0.1 mm rad−1 for the coefficients associated with the selected TDI combination even under degraded DWS readout conditions, while simultaneously providing monitoring bands that capture excursions up to tens of millimeters per radian in agreement with analytical predictions. Our approach ensures that space-based detectors remain effective in resolving weak astrophysical signals despite actual measurement imperfections.

Keywords: Gravitational wave detectors, Gravitational wave sources
On the Significance of Covariance for Constraining Theoretical Models from Galaxy Observables. In this study, we investigate the impact of covariance within uncertainties on the inference of cosmological and astrophysical parameters, specifically focusing on galaxy stellar mass functions derived from the CAMELS simulation suite. Utilizing both Fisher analysis and implicit likelihood inference, we explore how different covariance structures, including simple toy models and physics-motivated uncertainties, affect posterior distributions and parameter variances. Our methodology utilizes forward modeling via emulators that are trained on CAMELS simulations to produce stellar mass functions based on input parameters, subsequently incorporating Gaussian noise as defined by covariance matrices. We examine both toy model covariance matrices and physically motivated covariance matrices derived from observational factors like the stellar initial mass function and photometric aperture size. Our results demonstrate that covariance terms significantly influence parameter inference, often leading to tighter constraints or revealing complex, multimodal posterior distributions. These findings underscore the necessity of accounting for covariance when interpreting astrophysical observations, especially in fields where accurate parameter estimation is critical for model validation and hypothesis testing.

Keywords: Observational astronomy, Galaxy mass distribution, Astronomical simulations, Cosmological parameters
JADES: Rest-frame UV-to-NIR Size Evolution of Massive Quiescent Galaxies from Redshift z = 5 to z = 0.5. We present the UV-to-near-IR (NIR) size evolution of a sample of 161 quiescent galaxies with M* &gt; 1010 M⊙over 0.5 &lt; z &lt; 5. With deep multiband NIRCam images in GOODS-South from JADES, we measure the effective radii (Re) of the galaxies at rest-frame 0.3, 0.5, and 1 μm. On average, we find that quiescent galaxies are 45% (15%) more compact at rest-frame 1 μm than they are at 0.3 μm (0.5 μm). Regardless of wavelengths, the Re of quiescent galaxies strongly evolves with redshift, and this evolution depends on stellar mass. For lower-mass quiescent galaxies with M* = 1010─1010.6 M⊙, the evolution follows Re ∝ (1 + z)−1.1, whereas it becomes steeper, following Re ∝ (1 + z)−1.7, for higher-mass quiescent galaxies with M* &gt; 1010.6 M⊙. To constrain the physical mechanisms driving the apparent size evolution, we study the relationship between Re and the formation redshift (zform) of quiescent galaxies. For lower-mass quiescent galaxies, this relationship is broadly consistent with  Re∝(1+zform)−1 , in line with the expectation of the progenitor effect. For higher-mass quiescent galaxies, the relationship between Re and zform depends on stellar age. Older quiescent galaxies have a steeper relationship between Re and zform than that expected from the progenitor effect alone, suggesting that mergers and/or post-quenching continuous gas accretion drive additional size growth in very massive systems. We find that the z &gt; 3 quiescent galaxies in our sample are very compact, with mass surface densities Σe ≳ 1010 M⊙ kpc−2, and their Re are possibly even smaller than anticipated from the size evolution measured for lower-redshift quiescent galaxies. Finally, we take a close look at the structure of GS-9209, one of the earliest confirmed massive quiescent galaxies at zspec ∼ 4.7. From UV to NIR, GS-9209 becomes increasingly compact, and its light profile becomes more spheroidal, showing that the color gradient is already present in this earliest massive quiescent galaxy.

Keywords: Galaxy formation, Galaxy structure, High-redshift galaxies, Galaxy evolution
The Remarkable Late-time Flux Excess in Hubble Space Telescope Observations of the Type Iax Supernova 2012Z. Type Iax supernovae (SNe Iax) are thermonuclear explosions of white dwarfs (WDs), peculiar and underluminous compared to the normal Type Ia supernovae (SNe). Observations of SNe Iax provide insight into the physics of WD explosions and suggest that some may not be terminal events. Late-time photometry (∼1400 days postpeak) of the SN Iax SN 2012Z, the only WD SN with a preexplosion detection of a progenitor system, revealed a flux excess that may be explained by a gravitationally bound remnant driving a radioactively powered wind. We present further late-time Hubble Space Telescope photometry of SN 2012Z, ∼2500 days after the explosion, and find that the SN is still brighter than, but trending toward, the preexplosion flux. Additionally, we observe that the excess F555W flux seen in previous data has grown more pronounced. The color of the excess flux disfavors a light echo or interaction with the circumstellar material. The decline rate of the excess flux is consistent with energy deposition from 55Fe, but the luminosity is higher than expected from models of the ejecta, further suggesting evidence for a bound remnant. Combining our data with future observations should allow for the detection of emission from the ejecta shock-heating of the companion He star seen in the progenitor system.

Keywords: White dwarf stars, Type Ia supernovae, Supernovae
A Modified 3D Biconical Outflow Model: Spatial Constraints on Active Galactic Nuclei─Driven Outflows. We present a modified outflow model and its application to constrain ionized outflow properties of active galactic nuclei (AGNs). By adding a rotating disk component to the biconical outflow model of H.-J. Bae &amp; J.-H. Woo, we find that models with a rotating disk require faster launching velocities (≲1500 km s−1) than outflow-only models to be consistent with the observed gas kinematics of local type 2 AGNs. We perform Monte Carlo simulations to reproduce the observed distribution of gas kinematics of a large sample (∼39,000), constraining the launching velocity and opening angle. While the launching velocity is moderate for the majority of the local AGNs, the notable cases of 2%─5% show strong outflows with Vmax ∼ 1000─1500 km s−1. By examining the seeing effect based on the mock integral field unit data, we find that the outflow sizes measured based on velocity widths tend to be overestimated when the angular size of the outflow is comparable to or smaller than the seeing. This result highlights the need for more careful treatments of the seeing effect in the outflow size measurement, yet it still supports the lack of global feedback by gas outflows for local AGNs.

Keywords: Active galactic nuclei, Galaxy winds, Galaxy kinematics
Escaping Ionizing Photons from Massive Spiral Galaxies at z ∼ 1. We report the detection of Lyman continuum (LyC) photons from three massive (M* &gt; 1010 M⊙) spiral galaxies at a redshift of nearly 1 in the AstroSat UV Deep Field South. Notably, all three systems are viewed at low inclination (i.e., nearly face-on), prompting an investigation into the role of galaxy orientation in the detectability of LyC emission from disk systems. Two of the three galaxies, however, host active galactic nuclei, adding complexity to the interpretation of the LyC signal. We present a detailed analysis of the likely star-forming case and report tentative evidence that a face-on viewing angle may enhance the likelihood of LyC detection in disk galaxies. This represents the first detection of LyC emission from well-characterized spiral galaxies at high redshift, offering a new window into LyC escape mechanisms in such systems. Our findings highlight the need to consider geometric factors and anisotropic escape pathways facilitated by feedback processes alongside more traditional density-bounded scenarios that imply isotropic escape.

Keywords: Ultraviolet astronomy, Reionization
Shocks, Winds, and a Torus: the Large Binocular Telescope Interferometer (LBTI) Resolves the Active Nucleus of NGC 4151. We present mid-infrared (MIR) observations of the Seyfert 1 galaxy NGC 4151 using the Large Binocular Telescope Interferometer (LBTI). We took open-loop Fizeau images with 66─104 mas (5.8─9.1 pc) resolution in the N-band (at 8.7 and 10.5 μm), using the full resolution of the LBTI—equivalent to that of a 28.8 m telescope. These images were complemented by adaptive optics imaging in the LM-bands (3.7 and 4.8 μm), with 50─62 mas (4.4─5.4 pc) resolution. These images bridge the scales between previous Very Large Telescope Interferometer (VLTI)/MIDI and VLT/VISIR data, delivering Extremely Large Telescope (ELT)─like imaging resolution in the N-band. We resolve a dusty torus (with a diameter of 32 pc and position angle of 125°), and detect dusty clouds within the narrow-line region. Matching the resolution across four bands, we measured spatially resolved SEDs of the central ∼100 pc. Modified blackbody fitting revealed dust temperature and extinction profiles, indicating both heating from the accretion disk and additional shock heating due to the radio jet. The spatial coincidence of ionized emission (e.g., [Fe II] and [O III]), extended MIR structures, and radio features further supports the interpretation of shock heating. Comparison with NGC 1068 tests the Unified Model of Active Galactic Nuclei: structures are similar, despite differences in orientation and Eddington ratio. NGC 4151's torus is smaller than NGC 1068's following a r ∝ L0.5 scaling. These ELT-like observations of NGC 4151 and NGC 1068 highlight the need to revise MIR radiative transfer models of AGN to account for jet-related heating.

Keywords: Radio active galactic nuclei, Active galactic nuclei, Interferometry
Gravitational Wave Phase Shifts of Black Hole Mergers in AGN Disks. Ground-based gravitational wave (GW) detectors have discovered about 200 compact object mergers. The astrophysical origins of these events are highly debated, and it is possible that at least a fraction of them originate from dynamical environments. Among these, the disks of active galactic nuclei (AGN) are particularly interesting as promising environments, as some observed properties may be more readily produced there. When compact objects merge in these environments, acceleration from the central supermassive black hole or nearby companions is inevitable. Such acceleration induces a phase shift in the observed GW waveforms, which can serve as a useful tool to distinguish the underlying merging environments for each GW event. In this paper, we investigate the expected distribution of such acceleration-induced GW phase shifts, using a semianalytical model combined with a 1D AGN population synthesis code. We find significant contributions from three-body interactions involving a nearby third object. Our results indicate that the GW phase shift is likely to be larger compared to other channels, making it distinguishable by future GW facilities such as TianQin, DECIGO, Taiji, Einstein Telescope, and Cosmic Explorer. Interestingly, a notable fraction of mergers in fact exhibit a significant GW phase shift (≳1 rad) at frequencies above 10 Hz, which could even be detectable by current GW detectors such as LIGO/Virgo/KAGRA. Additionally, if gas-hardening during three-body interactions is taken into account, the GW frequency can be boosted to ≳10 Hz, potentially further aiding in the detection of the phase shift.

Keywords: Black holes, Stellar dynamics, Gravitational wave sources, Active galactic nuclei, Stellar accretion disks