ALT Stars form within circumstellar disks, and some binary stars develop circumbinary disks surrounding the pair. Observations suggest that disks that form around binary star systems are less common than those around single stars. One possible explanation is that binary stars may disrupt or shorten the lifespan of their surrounding disks relative to those around single stars. To investigate this, we used the DISCO hydrodynamics code to compute the lifetimes of circumstellar disks with and without a binary. Our results indicate that binary systems can reduce the lifetime of a circumbinary disk by a modest factor of two to three compared to disks around single stars. This effect is present when the binary separation is at least one-tenth of the disk radius. While our findings show that binaries can shorten circumbinary disk lifetimes, this alone might not be enough to fully account for the scarcity of these disks.

ALT Homologous coronal mass ejections (CMEs) are sequential eruptions from the same active region. They are of particular space weather interest because they can interact and coalesce into compound ejecta, potentially amplifying their geomagnetic impact. Yet the full chain from recurrent initiation to magnetic merging has not been captured self-consistently in a single global simulation. We present a three-dimensional magnetohydrodynamic model that generates three homologous CMEs from a bipolar active region by recurrent photospheric shearing. All three eruptions follow the same initiation mechanism by tether-cutting reconnection within a recurrently formed sigmoid, while the later CMEs propagate significantly faster than the first. We demonstrate that this speed hierarchy arises from progressive coronal preconditioning; preceding eruptions evacuate the overlying corona, reducing both mass loading and ambient drag. The faster later CMEs catch up with their predecessors, and the compression

ALT The magnetic field is the most fundamental observable in solar physics, while solar flares are the most violent, rapid magnetic energy-release events in the solar atmosphere. Decades of observations and theory have sketched the framework of flare evolution and magnetic-field-related physical process, yet the actual magnetic field variations during flares remained poorly understood. The main obstacle is that magnetic-diagnostic spectral lines are distorted by transient flare activity, making traditional spectro-polarimetry inversions complicated. Using a mid-infrared solar telescope, we investigate spectroscopic evolution of the Mg 12.32 microns line during an X1.5-class flare. Owing to the exceptionally large Zeeman sensitivity of this line, magnetic field strength can be directly determined from the measured line separation. Our analysis reveals apparent magnetic field weakening beneath flare ribbons in the impulsive phase. Radiative-hydrodynamic simulations and atmospheric inversions

ALT We propose fast-spinning, magnetic white dwarfs in binary systems as promising sources of continuous gravitational waves for future space-based detectors. The aim of this work is to determine the maximum ellipticities and gravitational wave amplitudes achievable by magnetically confined mountains accreted on the star's magnetic poles, and to assess their detectability against predicted sensitivity curves. Self-consistent magnetohydrodynamic equilibrium simulations are used to characterize the structure of the accreted mountain. A parametric search is then performed on these simulations to determine the maximum mass values that can be confined by the star's magnetic field. The stellar ellipticity ε grows nearly linearly with accreted mass Mₐ up to a maximum, and was found to scale as εₘₐₓ ≃ 1.6×10⁻²T₅⁻² B,₈², while the maximum gravitational wave amplitude as h₀,ₘₐₓ ≃ 1.2×10⁻²³T₅⁻² B,₈², where T₅ represents the temperature of the mountain in units of 10⁵ K and B*,₈ represents the star's

ALT V5668 Sgr is an Fe II classical nova (CN) that exploded on 15 March 2015. We present near-infrared (NIR) spectroscopy of the ejecta from the Mt. Abu observatory which exhibits emission lines of species H, He, N, S, Ti, and Si. We also present SOFIA (+FORCAST) spectroscopy which shows two forbidden emission lines, [Ne II] at 12.8 μm and [O IV] at 25.9 μm, as well as two emission features attributed to polycyclic aromatic hydrocarbons (PAH) at 6.2 μm and 11.3 μm. 1D Cloudy photoionization simulations require two components to model the system, which suggests a multifaceted, morphologically complex ejecta. The 1D simulations also reveal He, N, Ne, S, Ti, Si, and O chemical abundances elevated above fiducial solar levels. 3D pyCloudy photoionization emission profiles visualize the ejecta and elucidate the system's complex composition.

ALT Proxima Centauri is the nearest known exoplanet-hosting star and a benchmark for low-mass stellar models. Published diameters differ by several percent, affecting its inferred radius and temperature. Model-dependent near-infrared limb darkening introduces an additional 2-5% correction to the inferred radius. We re-reduced two previously published VLTI/PIONIER interferometric epochs from 2014 and combined them with three previously unpublished archival epochs from 2017 and 2019. We fit all five data sets jointly with uniform-disk and atmosphere-grid-based center-to-limb models. The joint fit gives a uniform-disk angular diameter, θ_UD=1.117±0.024 mas. Using the PHOENIX model and adopted bolometric flux, we obtain a PHOENIX limb-darkened angular diameter, θLD,PHX=1.154±0.026 mas, a stellar radius, R⋆=0.162±0.004 R⊙, and a Stefan–Boltzmann effective temperature, Teff,SB=2833±49 K. No significant close companion is detected across the five epochs over the searched separation and contrast r

ALT We present phase-resolved photometry, spectroscopy, photopolarimetry, and circular spectropolarimetry of the polar QS Telescopii, obtained between 2017 and 2025 using the South African Astronomical Observatory (SAAO) 1.0-m and 1.9-m telescopes, the Transiting Exoplanet Survey Satellite (TESS), Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Southern African Large Telescope (SALT). From ground-based photometry, we report the first detection of quasi-periodic oscillations (QPOs) in QS Tel, with timescales ranging between 2 and 11 minutes. This makes QS Tel one of only seven polars to show QPOs. The average spectra of QS Tel show broad and strong Balmer (Hδ, Hγ, Hβ and Hα) and Hetextscii 4686 Å emission lines, along with weaker emission from Hetextsci at (6678 Å, 5017 Å, 4921 Å, 4712 Å, 4471 Å, and 4387 Å) and the Bowen fluorescence complex Ctextsciii/Ntextsciii at 4650 Å. For the first time detailed Doppler tomography of the Hα and Hetextscii 4686 Å lines are presented whic

ALT The conditions governing the existence and evolution of trapped sausage waves in photospheric magnetic pores are investigated, with particular emphasis on the limitations of analytical cut-off criteria and the role of viscous dissipation. A pore is modelled as a cylindrical magnetic flux tube with smoothly varying radial profiles of magnetic field and density, subject to the constraint that its temperature is lower than that of the surrounding atmosphere. For finite plasma-β, the linearised equations governing sausage-mode perturbations are derived, and an initial-value problem is solved numerically to obtain the full spatio-temporal evolution of the waves. The applicability of the analytical cut-off relation derived for a flux tube with step-function equilibrium profiles is examined, revealing that its predictions depend on the equilibrium parameters. The simulations reveal distinct wave behaviours across different parameter regimes, including the simultaneous excitation of trapped fa

ALT The metallicity dependence of Wolf-Rayet (WR) mass-loss rates is a critical input for massive star evolutionary models, chemical yield predictions, and ionizing radiation budgets of young stellar populations. The Triangulum Galaxy (M33), with 213 spectroscopically confirmed WR stars spanning a ∼0.5 dex radial metallicity gradient, is the premier laboratory for this calibration. However, the ground-based fiber spectra on which the current census rests blend each target with neighboring OB stars, diluting diagnostic emission-line equivalent widths and biasing spectral classifications, inferred mass-loss rates, and surface hydrogen abundances. Using 0farcs1-resolution HST/PHATTER survey imaging, we quantify this contamination for 123 WR stars within the survey footprint, finding that ∼27% suffer moderate-to-severe dilution from unresolved neighbors with WR continuum flux contributions F_WR < 0.85. We provide crowding classifications, F_WR fractions, and six-band photometry in the F275W, F

ALT The light curves of nascent eclipsing binaries (EBs) feature sinusoidal reflection effects as a hot B-type main-sequence (MS) primary irradiates the near side of a cool, low-mass, pre-MS companion. We obtained multi-epoch echelle spectra with the MIKE spectrograph on the 6.5m Magellan-Clay Telescope of three nascent EBs embedded in H II regions within the LMC. By fitting atmospheric models to the spectra, the primaries are found to be mid-B dwarfs (Tₑff,1 = 18,600-22,800 K; M₁ = 6.8-8.5 Msun). The dynamical masses of the secondaries are only M₂ = 0.38-0.95 Msun, yielding extremely small mass ratios q = M₂/M₁ = 0.05-0.11. Unlike solar-type primaries, which exhibit a dearth of close companions with q < 0.1 known as the brown dwarf desert, massive stars can readily form with very close companions below q < 0.1. By fitting PHOEBE models to the OGLE-III light curves, we measure the secondary radii R₂ = 2.0-2.8 Rsun and temperatures Tₑff,2 = 4,000 K. The pre-MS companions are located high on

ALT Molecular clouds exhibit complex, multi-scale dynamics driven by the interplay of turbulence, self-gravity, and gas pressure. Modelling these systems with conventional grid-based methods becomes increasingly expensive as spatial resolution and dimensionality increase. Physics-Informed Neural Networks (PINNs) offer a mesh-free alternative by incorporating the governing equations directly into the training objective, but their ability to model realistic turbulent self-gravitating flows remains largely unexplored. We apply PINNs to isothermal molecular clouds initialized with astrophysically motivated turbulent velocity fields, considering subsonic and supersonic evolution in two and three dimensions. We benchmark the predicted density and velocity fields against the finite-volume code Athena++. PINNs accurately recover the global evolution of the flow over multiple free-fall times across turbulent realizations, Mach numbers, and dimensionalities. Their training cost also exhibits weak de

ALT Predicting solar flares is a challenging space-weather forecasting problem with potentially significant impacts on Earth's upper atmosphere, including disruptions to radio communications. We propose Active Region attENtion Aggregation (ARENA), a neural network architecture that predicts solar flares from a variable number of active-region cutouts while learning to identify the region most relevant to the prediction. ARENA is trained using multiple-instance learning under weak supervision, requiring only a flare/no-flare label for the observation and no labels specifying the flare origin. The learned attention mechanism therefore provides a means of localizing the active region driving the prediction without explicit origin annotations. ARENA achieves a heidke skill score of 0.45 which is comparable to other flare prediction approaches. These results demonstrate that active-region-based aggregation can provide an efficient and interpretable approach to solar flare prediction. The code i

ALT The chromospheric and coronal heating problem is among the major open questions in solar physics. Some of the possible mechanisms that can explain the rise in temperature that is needed to reproduce the observations require the estimation of electric currents. Since these depend on the spatial derivatives of the magnetic field components, it is necessary to obtain the full magnetic field vector from observational data in a 3D geometrical grid. We developed a new method to obtain the 3D geometrical configuration of the atmosphere using the approximation of hydrostatic equilibrium in three dimensions to determine the gas pressure and density as a function of optical depth, column mass, or geometrical distance. This development has been designed as an extension for any inversion code that outputs a stratification of temperature and gas pressure or density to enable the estimation of electric current densities from observations. We investigated our approach using a snapshot from a sunspot

ALT Context. Since 2019, HD 99458 has been known as a unique example of a δ Sct variable with chemical peculiarities of Ap type in an eclipsing binary. Aims. We aim to review the peculiar status of the star with new observational materials. Methods. The current study is the result of meticulous analysis of space-based photometry from Kepler K2 and TESS, multi-site spectroscopic and spectropolarimetric observations, as well as speckle-interferometric data. Asteroseismic modelling of stellar pulsation is an essential part of the research. Results. We find HD 99458 to be an eclipsing Algol-type system with active mass transfer from the cool companion filling its Roche lobe to the pulsating primary. We identified signatures of a disc and accretion with varying rates in spectra and light curves. The system's orbital period increases with the rate Ṗₒrb of 5.045 s yr⁻¹, indicating potential multiplicity. We failed to detect traces of the primary's magnetic field or excessive abundances, both of w

ALT Building on Paper I, which constrained core overshooting to fₒᵥ < 0.01 for M < 1.4 M⊙ and found αₘₗₜ ≃ 2.0 for metal-rich red giants, we extend this analysis to four lower-mass Kepler red giants spanning a broad metallicity range: KIC 6117517, KIC 9475697, KIC 10123207, and KIC 10200377. Two complementary model grids are constructed: Grid A fixes αₘₗₜ = 2.0 while varying metallicity; Grid B adopts spectroscopic metallicities with αₘₗₜ as a free parameter. Grid A successfully reproduces both asteroseismic and spectroscopic constraints for the metal-rich targets (KIC 6117517 and KIC 9475697), confirming αₘₗₜ = 2.0 for metal-rich red giants. For the metal-poor targets (KIC 10123207 and KIC 10200377), Grid B yields larger mixing-length parameters of αₘₗₜ ≈ 2.16–2.18. Although only four stars are analyzed with unequal sensitivity to αₘₗₜ, these results suggest a tentative increase in convective efficiency toward lower metallicity, consistent with 3D hydrodynamical simulations but opposite t

ALT Modelling data from modern spectroscopic surveys and time-resolved spectropolarimetric observations requires stellar synthetic spectra to be computed rapidly over wide wavelength ranges from line lists that increasingly reach hundreds of millions of transitions. Spectropolarimetric analyses of magnetically active stars additionally demand a solution of the polarised radiative transfer problem. We present FastSpec, a new LTE spectrum synthesis code designed around two goals: increased raw computational speed and broad astrophysical applicability, including the calculation of the full Stokes vector in the presence of a magnetic field. FastSpec computes emergent intensity and flux spectra from plane-parallel and spherical model atmospheres. Chemical and ionisation equilibrium is obtained from the updated SME equation-of-state package, continuum opacities follow the ATLAS family of routines, hydrogen bound-bound and bound-free absorption uses the occupation-probability formalism, and line

ALT Recent evidence suggests that Betelgeuse may host a stellar companion whose orbit will decay through tidal interactions, ultimately leading to engulfment and merger within the next several thousand years. If confirmed, this system could represent the nearest and best-characterized progenitor of a future luminous red nova (LRN). We investigate whether the shock-breakout and cooling emission preceding the LRN can be used to constrain the properties of the companion and its disruption within the stellar envelope. Using binary stellar evolution calculations, we evolve Betelgeuse with companions of 0.7, 1.0, and 2.0 M⊙ to the onset of common envelope evolution (CEE). We then perform one-dimensional radiation-hydrodynamic simulations that follow companion disruption, energy deposition, and shock propagation through the envelope. We find that the peak luminosity increases systematically with companion mass, from 2.44×10⁴¹ to 6.17×10⁴¹ erg s⁻¹ across the 0.7-2.0 M⊙ models, while the duration i

ALT We present a systematic investigation of the connection between magnetic activity and the low-surface-gravity-like near-infrared spectral morphology of late-M dwarfs. Our sample includes TRAPPIST-1 observed with JWST NIRISS/SOSS and 22 late-M dwarfs observed with IRTF/SpeX, together with flare observations from K2, TESS, JWST NIRISS/SOSS, and literature-reported X-ray luminosities. Using one-component PHOENIX/NewEra spectral modeling, we find that all targets are better reproduced by lower-surface-gravity model spectra than by models with the expected high gravities of field late-M dwarfs. The retrieved surface gravities moderately correlate with independently measured gravity-sensitive spectral indices, with the strongest trends seen for FeHz at 0.998 μm and FeH_J at 1.2 μm, both showing statistically significant Pearson and Spearman correlations with p<0.005. They also show strong anti-correlations with flare luminosity and X-ray luminosity: for both relations, Pearson and Spearman c

ALT Granulation,caused by convection in low-mass stars like the Sun, introduces small amplitude variations in the stellar brightness on timescales of minutes to hours. Often referred to as flicker or microvariability this signal can impede detecting Earth-sized planets around Sun-like stars via stellar transits. Stellar flicker can also introduce uncertainties in determining stellar fundamental parameters and cause errors of up to 10% in the radius determination of transiting exoplanets. Both sources of uncertainties will propagate into planetary transmission spectra and resulting atmospheric retrievals. We present a method for modelling stellar flicker that enables scaling the flicker of Sun-like stars between different wavelengths and passbands to facilitate better solar-stellar comparisons. We use the 3D radiative magnetohydrodynamic code MURaM to simulate the granulation pattern on a Sun-like star and employ the radiative transfer code MPS-ATLAS for the spectral synthesis of the MURaM

ALT The scarcity of optically visible O stars near the theoretical zero-age main sequence (ZAMS) has puzzled astronomers for over four decades. We argue that it reflects prolonged accretion. If massive stars assemble over Myr timescales, as the inertial-inflow model predicts, core-hydrogen burning begins before accretion ends, and the stars become optically visible at the end of accretion on a birthline displaced from the standard ZAMS. We test this interpretation by comparing the hot-side envelope of Galactic O stars in the Kiel diagram with accreting stellar-evolution models, adopting a growth law t_form=τ₀(mf/60 M⊙)ᵅ with formation time t_form and final mass mf. The resulting birthlines reproduce both the displacement and the high-mass turnover of the observed envelope, with best-fitting parameters (α,τ₀)=(0.52,4.3 Myr), consistent with independent constraints from the luminosity functions of compact H II regions and OB stars. The two constraints have orthogonal degeneracy directions, s