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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Tuesday 18 August

Solar and Stellar Astrophysics · Cross-listed from nucl-th

Confining density functional approach to the QCD phase diagram at low temperatures and thermal twin stars

David Blaschke and Oleksii Ivanytskyi

We present a density functional-based equation of state for warm, dense nuclear matter with a transition to deconfined quark matter for applications to simulations of supernova explosions and neutron star mergers, but also for the cosmological evolution of Q-balls. For the quark matter equation of state, we employ a recently developed confining density functional approach while nuclear matter is described within a relativistic density functional model of the DD2 class. The phase transition is obtained by a Maxwell construction at constant entropy per baryon. We discuss the solutions of TOV equations for isentropic hybrid stars for two hybrid equation of state models: DDf-SFM without and DD2-$\chi$CDF with color superconductivity. We find that at finite temperatures above a critical value of entropy per baryon sequences of disconnected third family branches ("thermal twin stars") may appear for the DDf-SFM model, while they are absent for the color superconducting model and at $T=0$. We discuss the relation of this critical entropy per baryon to the Seidov criterion of gravitational instability for $T=0$ and find that it is a good guide. We suggest that the presence of thermal twin stars may be regarded as an indicator for the core-collapse supernova explodability of massive blue supergiant stars with solar metallicity and thus serve as a new criterion for the reliability of hybrid equation of state models. By this argument, strong color superconductivity shall be excluded and it remains to be shown whether models with moderate diquark pairing could fulfill the thermal twin constraint. For the case of symmetric matter, we compare the resulting hybrid EOS with the flow constraint by Danielewicz et al. and find a a sensitivity of the onset density for deconfinement to the presence or absence of color superconductivity.
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Solar and Stellar Astrophysics

The instantaneous mass accretion rate of novae in quiescence: - an archival ultraviolet optical spectral analysis

Patrick Godon, Edward M. Sion, Tim Naylor et al. (+1 more)

Based on archival spectra, we derive the quiescent instantaneous mass transfer rates in novae using synthetic disk spectra generated with tlusty, Gaia parallax-derived distances, and updated color excess values. Our results for nine novae, based on ultraviolet spectra and on a number of optical spectra, yield mass accretion rates that are higher than those derived from simple integration of the UV and optical luminosity. HR Del, 20 years after its eruption, has a mass transfer rate of $4\times 10^{-7}M_\odot$/yr, and is likely burning the accreting H-rich material. V842 Cen, thought to be a low mass transfer system, has a comparable mass accretion rate. For both novae, the enhanced mass transfer must be self-sustained by a feedback loop. RR Pic, with $\dot{M}\approx 3\times 10^{-8}M_\odot$/yr, is better fitted with an accretion disk where the outer region is heated up to 12,000 K, in agreement with H and He emission lines coming from the outer disk and a large emission region on the leading side of the disk. Such a heated disk also gives a good fit to the spectra of CP Lac, and DI Lac with $\dot{M}\sim4.5$ and $9\times 10^{-9}M_\odot$/yr. V1974 Cyg and V533 Her, with an accretion rate of $\sim 3\times 10^{-9}M_\odot$/yr, have a rather flat spectrum. V446 Her and BK Lyn, caught in a state of low accretion, have the lowest mass accretion rates with $\dot{M} \sim 10^{-9}$ and $\sim 10^{-10}M_\odot$/yr respectively. The higher mass transfer rate systems, with $\dot{M}\approx \sim 10^{-7}M_\odot$/yr, agree with the standard disk model; the remaining systems are better fitted when the outer disk is heated to $\sim 12,000$~K. We suggest that irradiation from the heated WD, inner disk, together with tidal interaction, the bright spot, and material overflowing the disk edge, can increase the temperature of the outer disk.
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All authors Patrick Godon, Edward M. Sion, Tim Naylor, Frederick A. Ringwald

Solar and Stellar Astrophysics

Observations of Disrupted CME Material Falling Back Into the Low Corona

Brian E. Wood and Jason E. Kooi

We present an empirical study of a disrupted CME, parts of which fall back to the Sun, using observations from SOHO, STEREO-A, and SDO. At UT 18:00 on 2024 August 16, a slow CME is overtaken by a faster CME. A leg of the second CME carries part of the slower CME out with it, resulting in an unusually well-defined flux rope leg for this CME. This second CME is observed in radio by the VLA, with Faraday rotation measurements showing a clear magnetic flux rope signature. A strong response is also later seen when the radio-observed line of sight enters the CME leg enriched by material from the disrupted CME. Outside this leg, the rest of the disrupted CME simply disappears and is replaced by a large number of small jet-like downflows. We see clear evidence of this plasma falling back to the low corona in EUV images from SDO, roughly 6-17 hours after the CME is disrupted, with an inferred downward velocity of V=-30 km/s. There is a clear temperature dependence, with the downflows seen first in the 211 bandpass, followed successively by responses at 193, 171, and 304. The downflows are much slower than would be expected for a ballistic descent, so we model the downflows using a kinematic drag model. In the 304 bandpass, coronal rain activity is triggered by the downflowing CME material, suggesting that downflows from the upper corona could be contributing to coronal rain more generally.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM

Vera C. Rubin LSST Synthetic Magnitudes derived from Gaia XP Spectra

Oleksandra Razim, Krešimir Tisanič and Lovro Palaversa

Context. In the context of Milky Way studies, the Vera C. Rubin Observatory's Legacy Survey of Space and Time is often described as a deep extension of the Gaia survey. In the future, joint analysis of the Gaia and LSST data promises to bring new insights into our understanding of the Galaxy's structure and formation history. However, the relatively small overlap in the magnitude ranges of the two surveys raises the question of how to perform a joint calibration of these datasets. Aims. In this paper, we produce high-quality synthetic LSST photometry from Gaia XP low-resolution spectra, using SDSS and DES observed photometry to calibrate the spectra. Methods. We develop a method of empirical correction of Gaia XP spectra using SDSS Stripe 82 photometry. We project sources for which Gaia XP data are available onto a magnitude-magnitude grid and calculate residuals between uncorrected synthetic and observed SDSS magnitudes, which are then used to derive correction coefficients across spectral regions corresponding to each photometric band. Results. The correction significantly reduces systematic trends and scatter in the synthetic magnitudes: the median residuals decrease by an order of magnitude (e.g., for the u band the improvement is from 0.038 to 0.002 mag), and the standard deviation of residuals typically becomes up to factor of two smaller (e.g., for the u band from 0.2 to 0.07 mag). Conclusions. Our correction approach improves the reliability of synthetic photometry derived from Gaia XP spectra and enables joint analysis of Gaia and LSST data for studies of Galactic structure and stellar populations.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Hydrodynamics modeling of the water snow line in young protoplanetary disks with dust-size-dependent opacities

Eduard I. Vorobyov, Anastasiia Topchieva, Aleksandr Skliarevskii et al. (+2 more)

Aims. We investigated the properties of the water snow line during the early stages of disk evolution, paying particular attention to the effects of gravitational instability and dust growth on the snow line's shape and position. Methods. We used the FEOSAD numerical hydrodynamics code to simulate the disk formation and evolution in the thin-disk limit. The simulations incorporate the coevolution of gas, dust, and volatiles, including dust growth, volatile phase transitions, and dust-size-dependent opacities. Results. The position of the water snow line is highly nonsteady during the considered disk evolution period, first moving outward during the disk build-up and then retreating back as the disk cools. Its form in the disk midplane deviates strongly from a circular shape in the early gravitationally unstable phase of disk evolution. An increase in the amounts of grown dust and water ice as well as in the maximum dust size just beyond the snow line, as is readily observed in one-dimensional viscous disk evolution models, in our hydrodynamic models occurs only after gravitational instability diminishes. Dust-growth-induced opacity changes have a profound effect on the position of the water snow line, shifting it closer to the star by almost a factor of two compared to models that do not take this effect into account. Conclusions. The shape, position, and properties of the water snow line in young, gravitationally unstable disks differ from those of older, axisymmetric disks. Our results highlight the importance of taking into account the dependence of opacity on dust size when studying disk evolution.
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All authors Eduard I. Vorobyov, Anastasiia Topchieva, Aleksandr Skliarevskii, Yaroslav Pavlyuchenkov, Konstanze Zwintz

Solar and Stellar Astrophysics

3D simulations of magnetospheric accretion in T Tauri stars: I. Disk truncation, stellar torques, and application to observations

George Pantolmos, Claudio Zanni and Jérôme Bouvier

Young stars accrete material from their circumstellar disk through their magnetosphere and undergo contraction; these two processes impact their rotational evolution. We investigate stable and unstable accretion regimes (due to the interchange instability) and examine the associated stellar torques to assess the spin evolution of young stars. We performed 3D MHD simulations of disk accretion onto an inclined stellar dipole. We ran 21 simulations with varying stellar rotation rates, dipole field strengths and obliquities, and mass accretion rates. We find that stars with a ratio of truncation to corotation radius $R_t/R_{co} \gtrsim 0.80-0.85$ accrete via a stable regime, while accretion becomes unstable otherwise. In addition, our $R_t/R_{\ast}$ parametrization weakly depends on the mass accretion rate and the dipolar intensity, while strongly depending on the stellar rotation rate. We derive torque formulae for each flow component affecting the stellar rotation, i.e., accretion, magnetospheric ejections and stellar winds. Finally, we apply our results to a sample of young stars with measured magnetic fields, mass accretion rates, and rotational periods and find that most of them should currently accrete in an unstable regime and undergo spin-up torques. Our study confirms and expands upon previous results. Unstable accretion should lead to a net spin-up torque on the central star, while stable accretion can lead to stellar spin-down. When applying our truncation radius and torque prescriptions to observational data, we find that most young stars in our sample should be in a spin-up state. Thus, the angular momentum problem for young stars remains.
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Solar and Stellar Astrophysics · Cross-listed from nucl-ex

Revised $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate and its impact on the production of $^{44}$Ti in core-collapse supernovae

R.S. Sidhu, Y. Luo, C. Sarma et al. (+2 more)

The thermonuclear $^{45}$V($p,\gamma$)$^{46}$Cr reaction is the primary leakage pathway from the $^{44}$Ti–$^{45}$V quasi-equilibrium cluster during $\alpha$-rich freeze-out in core-collapse supernovae (CCSN), governing the final abundance of the $\gamma$-ray-emitting isotope $^{44}$Ti. A recent high-resolution $\gamma$-ray study [C. Cousins et al., Phys. Rev. Lett. 136, 252701 (2026)] identified ten previously unknown low-spin proton-unbound states in $^{46}$Cr, enabling the first experimentally constrained $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate using the AME2020 mass excess, $\text{ME}(^{46}\text{Cr}) = -29472(11)$~keV. Here, we adopt the four-fold more precise CSRe mass excess $\text{ME}(^{46}\text{Cr}) = -29477.2(2.6)$~keV [M.~Wang et al., Phys. Rev. C 106, L051301 (2022)] to recalculate the reaction rate. Including proton capture on the ground and first two excited states of $^{45}$V alongside new shell-model proton spectroscopic factors, we reduce mass-related rate uncertainties to a subdominant level. The revised rate is up to 69% higher than that of Cousins et al. at $\alpha$-rich freeze-out temperatures ($T \simeq 1.5$–$2$~GK). CCSN nucleosynthesis calculations show this revised rate increases the ejected $^{44}$Ti yield by $\sim$26% in a $20\,M_\odot$ model compared to The et al. [ApJ 504, 500 (1998)], while causing negligible changes for the SN~1987A trajectory. We demonstrate that $^{44}$Ti production sensitivity is dictated by the ejecta electron fraction ($Y_e$): the reaction significantly affects proton-rich ejecta ($Y_e \approx 0.50$) but has little impact on neutron-rich ejecta ($Y_e \approx 0.496$), where lower free-proton abundances suppress reaction flow. This reconciles conflicting results from past sensitivity studies.
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All authors R.S. Sidhu, Y. Luo, C. Sarma, M. Wiescher, X. Xu

Solar and Stellar Astrophysics

A Catalog of Homogeneously Derived Stellar Parameters for Spectroscopic Survey Stars

Stefan Y. Stefanov, Evelina Zaharieva, Djemma Ruseva et al. (+9 more)

Uniformly derived stellar parameters are vital for exoplanet demographic studies because they directly influence the inferred planetary masses, radii, and bulk densities. This study presents a new homogeneous catalog of physical stellar parameters for 5533 single stars observed by the HARPS, HIRES, and CARMENES radial-velocity (RV) surveys. Stellar parameters are determined using a Bayesian framework with two independent sets of stellar evolutionary models: MIST and PARSEC, using published spectroscopic parameter estimates and catalog values as priors. The resulting stellar effective temperatures, masses, radii, and surface gravities are compared and evaluated for consistency with stellar parameters listed in major exoplanet catalogs. While our estimates show consistency with those listed in external catalogs, we identify method-dependent differences in stellar masses for low-mass and pre-main-sequence stars, as well as G and K giants, where isochrone-based solutions may be affected by age-mass degeneracies. For low-mass stars such as M-dwarfs, the catalog provides masses derived from established mass-luminosity empirical relations, which tend to be more reliable. This catalog provides the largest uniformly derived stellar reference sample for Doppler survey targets and also illustrates the applicability and limitations of stellar-parameter homogenisation methods for future RV exoplanet demographics studies.
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All authors Stefan Y. Stefanov, Evelina Zaharieva, Djemma Ruseva, Milen Minev, Denitza Stoeva, Volker Perdelwitz, Lev Tal-Or, Jerusalem T. Teklu, Elena Vchkova Bebekovska, Desislava Antonova, Vladimir Bozhilov, Trifon Trifonov

Solar and Stellar Astrophysics

Complex morphology and kinematics at the heart of the very low luminosity object IRAM 04191+1522

N. Otten, I. de Gregorio-Monsalvo, N. Huélamo et al. (+3 more)

The formation of the majority of brown dwarfs (BDs) remains uncertain. They may form in molecular cloud cores in a process akin to low mass star formation, or via fragmentation in circumstellar discs. Studying the youngest, most embedded sources is crucial for distinguishing these scenarios. We investigate molecular gas morphology and kinematics around one young & embedded very low luminosity object (VeLLO), IRAM 04191+1522, utilising archival ALMA observations of 13CO, C18O, and SO. We trace gas on scales of a few 10s to 100s of au around the source to search for outflowing and/or infalling structures. The red and blueshifted 13CO (3-2) emission show distinct morphologies and kinematics. The blueshifted emission to the north-west may trace shocked material oriented differently from the previously reported approx. 0.1 pc CO outflow. Redshifted emission mainly to the south-east and south-west may trace the base of an outflow cavity. The position angle of this cavity suggests the presence of a second outflow, which supports the possible binary nature of this VeLLO. The C18O (2-1) emission is highly complex, comprising structures at different spatial scales and distances from the source. These may trace a mix of molecular outflow, outflow cavity, and disc emission. SO 65-54 reveals evidence for anticlockwise rotation around the central source, together with a northern structure of uncertain origin. We have identified a complex set of 13CO (3-2) and C18O (2-1) structures alongside evidence of a new outflow cavity at a distinct position angle from previously detected outflows. This supports the scenario that IRAM 04191+1522 is a binary system. The northern SO gas structure remains unexplained. Higher spectral resolution observations at intermediate scales are needed to characterise these substructures, their connection to larger scale structures, and to determine this system's final fate.
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All authors N. Otten, I. de Gregorio-Monsalvo, N. Huélamo, E. Artur de la Villarmois, G. Blazquez Calero, E. Whelan

Solar and Stellar Astrophysics

Modelling s-process chemical clocks: insights from high-precision Kepler data

G. Casali and M. Molero

We present Galactic chemical evolution (GCE) models for the chemical clocks [Zr/Ti] and [Ce/Ti], tracing first- and second-peak s-process nucleosynthesis, and compare them with a high-precision sample of 68 Kepler red giant stars with asteroseismic ages from individual-mode frequencies and high-resolution spectroscopy. Using a multi-zone GCE framework, we explore variations in metallicity-dependent asymptotic giant branch (AGB) nucleosynthetic yields, including proposed enhancements to high-metallicity Ce production. Our baseline model reproduces [Zr/Ti] and the high-$\alpha$ sequence in both age and metallicity space, but systematically underestimates [Ce/Ti] at young ages and intermediate metallicities, indicating a persistent deficit in second-peak s-process enrichment over the last $\sim6$ Gyr of Galactic disc evolution. Increasing second-peak yields from high-metallicity AGB stars only partially reduces this discrepancy, suggesting that simple yield rescaling is insufficient and more fundamental revisions to s-process nucleosynthesis at high metallicity, alongside a self-consistent treatment of stellar dynamics, may be required. In fact, models reproduce abundance trends more tightly in metallicity than in age space, with additional age scatter partly attributed to radial migration. This Letter highlights the diagnostic power of precise asteroseismic ages for GCE studies and the limitations of current models in capturing the complex interplay between s-process nucleosynthesis and stellar dynamics.
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Solar and Stellar Astrophysics

Ejecta clumps revealed by study of reverse-shocked ejecta through MUSE integral field spectroscopy of SNR 0509-67.5

Priyam Das, Ivo Seitenzahl, J. Martin Laming et al. (+3 more)

We report the discovery of a spatially resolved clumpy ejecta structure in the reverse-shocked ejecta of SNR 0509-67.5, revealed through multiple faint and broad forbidden coronal emission lines in deep MUSE observations. We also identify two new broad coronal emission lines not reported before in this remnant, [Fe xi] 7894 A and [Fe x] 6374.5 A , which extend the set of previously reported [Fe xv] 7059.59 A, [Fe xiv] 5302.86 A , [Fe ix] 8236.55 A , [Ca xv] 5695 A, and [S xii] 7611.0 A. Near-continuous ionisation states of Fe allow us to follow the ionisation progression behind the reverse shock. We use a 1D analytical model to evolve Fe charge states following reverse shock interaction to compare with observations, indicating the need for preshock clumping or over-density in order to reproduce the observed surface brightness of the [Fe xiv] line. Additionally, we report the spatially resolved distribution of ejecta clumps and show that reverse-shock interaction drives their compression and fragmentation. We also find a clear trend of decreasing velocity width with increasing Fe ionisation state, from the broadest [Fe ix] emission to the narrowest [Fe xv], with intermediate-ionisation species ([Fe x], [Fe xi], [Fe xiv]) showing intermediate widths. Finally, we compare our observations to a dynamically driven double-degenerate double detonation (D6) 3D remnant model at similar Fe and S ionisation states and conclude that the observed clumps are predominantly due to Rayleigh-Taylor instabilities.
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All authors Priyam Das, Ivo Seitenzahl, J. Martin Laming, Gilles Ferrand, Simon J. Murphy, Ashley Ruiter

Solar and Stellar Astrophysics

Formation of heavy double neutron stars II: the role of heavy first-born neutron stars and low metallicity

Ashwathi Nair and Simon Stevenson

The high total mass of GW190425 challenges our understanding of double neutron star (DNS) formation, as no such heavy ($\ge 3$\, M$_\odot$) DNS system has been observed in the Milky Way disk. Numerous formation scenarios have been proposed to explain its formation. We test these within a self-consistent binary evolution framework calibrated to the Galactic DNS population. In Paper~I of this series, we studied the evolution of a $1.4$\,M$_\odot$ neutron star (NS) in a binary with a $2.5$–$10$\,M$_\odot$ helium star at solar metallicity ($Z = Z_\odot$), assuming Eddington-limited accretion onto the NS using MESA. In this paper, we consider the evolution of NS-He star binaries with a broad range of NS masses from $1.1$–$1.9$\,M$_\odot$ at $Z=Z_\odot$, 0.1\,$Z_\odot$ and 0.01\,$Z_\odot$. We find that the formation of heavy DNSs is rare, accounting for only $\sim 0.5$ per cent of DNSs. The majority of these are formed through the `standard formation' channel, widely believed to form GW170817 and observed Galactic DNSs. We find no contribution through the `fast-merger' channel at solar metallicity, but systems at low metallicity predominantly form through unstable mass transfer. Furthermore, we find no significant dependence of the heavy DNS formation fraction on metallicity over the range considered here. We conclude that heavy DNSs do not form a separate subpopulation and merely represent the high-mass tail of the standard DNS population.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Candidates for the most [$O_{III}$] $\lambda5007$-luminous planetary nebula in the Milky Way. I. Integrated light properties of NGC 6572, NGC 6884, and M 1-71

Azlizan A. Soemitro, Martin M. Roth, Jeremy R. Walsh et al. (+3 more)

The bright-end cutoff of the planetary nebula luminosity function (PNLF) serves as an extragalactic standard candle. However, the physical properties of planetary nebulae (PNe) at the PNLF cutoff have been studied only in nearby galaxies, where the PNe appear mostly as point sources. Galactic PNLF is further poorly constrained, primarily due to uncertainties in Galactic PN distances. Following a recent Galactic PNLF survey based on Gaia distances, we aim to characterise PN candidates at the Galactic PNLF cutoff. We observed three PN candidates at the Galactic PNLF cutoff using the Potsdam Multi-Aperture Spectrophotometer (PMAS). We determined their chemical abundances and constructed photoionisation models to derive the central star luminosity (L) and effective temperature (Teff). We constrained the central star masses and most likely distances consistent with the prediction of stellar evolution models. Using these distances, we determined the absolute magnitude M5007. PNe of our sample are located within the top 1 mag of the Galactic PNLF (-4.20 < M5007 <-3.60), with similar nebular properties and a narrow progenitor mass range (1.30-1.75 Msolar). The measured extinction is mostly dominated by the foreground Galactic extinction. The trend between the circum-nebular extinction and central star mass of our PNe is in agreement with those derived in the Large Magellanic Cloud (LMC) and M31. All PNe in our sample exhibit weak-emission line star (wels) features in their spectra, but we confirmed that some of these lines originate from the nebula. The PNe are similar in terms of their nebular properties and evolutionary stage. Their characteristics are also consistent with the most [OIII]5007-luminous PNe in the LMC and M31. We demonstrate the importance of circum-nebular extinction and the initial-final mass relation (IFMR) to understand the universality of PNLF as a standard candle.
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All authors Azlizan A. Soemitro, Martin M. Roth, Jeremy R. Walsh, Ana Monreal-Ibero, Brigitte G. A. Pruijt, Nicholas Chornay

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

The FLARE Facility

Hantao Ji, Jongsoo Yoo, Peiyun Shi et al. (+53 more)

The Facility for Laboratory Reconnection Experiments (FLARE) has been constructed to study magnetic reconnection in multiple X-line regimes relevant to space, astrophysical, and fusion plasmas. Building upon the successful design of the Magnetic Reconnection Experiment (MRX), FLARE features a larger physical volume, stronger magnetic fields, and an independent ohmic heating drive to significantly extend the accessible parameter space, targeting Lundquist numbers up to S ~ 10^5 and normalized system sizes up to \lambda ~ 10^3. This paper details the facility's core engineering components, including the primary vacuum vessel, internal flux cores, highly segmented external coil systems, modular capacitor banks, and the safety interlock and control architecture. An initial diagnostic suite is presented, comprising high-resolution 2D magnetic probe arrays, triple Langmuir probes, a fully fiber-coupled interferometer, ion Doppler spectroscopy, and fast camera imaging. Initial operations demonstrate the device's experimental flexibility and reliability, successfully executing symmetric push-pull reconnection, spheromak merging, and asymmetric downstream configurations. Currently operating within "Stage 2.5" with S ~ 2,500 and \lambda ~ 60 for anti-parallel reconnection, FLARE provides immediate access to the multiple X-line regimes. Planned hardware upgrades, advanced diagnostic additions, and integration with fully kinetic simulations will further expand its capabilities as it transitions into a collaborative user facility for the broader plasma science community.
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All authors Hantao Ji, Jongsoo Yoo, Peiyun Shi, Euichan Jung, Kush Maheshwari, Adam Robbins, Sunghyun Son, Adam Stanier, Yang Ren, Sayak Bose, Dylan Corl, Keith Corrigan, Robert Cutler, William Daughton, Robert Ellis, Geoffrey Gettelfinger, Ronald Hatcher, Philip Heitzenroeder, Frank Hoffmann, Jonathan Jara-Almonte, Michael Kalish, Thomas Kozub, Enrique Merino, Weiguo Que, Benjamin Smith, John Wallace, Xin Zhao, Sofia Avrutsky, Neal Crocker, Seth Dorfman, Yuka Doke, Corina Dunn, William Fox, Boting Li, Xiaocan Li, Clayton Myers, Shohgo Okazaki, Joshua Pawlak, Tongnyeol Rhee, Byonghoon Seo, Taiju Suzuki, Yang Zhang, Stuart Bale, Amitava Bhattacharjee, Troy Carter, Chuanfei Dong, James Drake, Jan Egedal, Erik Gilson, Michiaki Inomoto, Jonathan Menard, Yasushi Ono, Stewart Prager, John Sarff, Hiroshi Tanabe, Masaaki Yamada

Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

JWST-MIRI's multi-dimensional view of mass loss in the irradiated disks of NGC 1977

Alice S. Booth, Qijia Zhou, Jinyoung Serena Kim et al. (+10 more)

The evolution of protoplanetary disks, and consequently the outcomes of planet formation, are thought to be significantly altered in regions containing massive stars. Extreme cases in the Orion Nebula Cluster (ONC) demonstrate the impact of external irradiation (FUV$\gtrsim10^{4}$ G$_{0}$) on disk evolution, but intermediate environments remain less observationally constrained. We present JWST/MIRI Medium Resolution Spectroscopy (MRS) observations of seven proplyds in NGC 1977 exposed to an external FUV field of $10^{3}-10^{5}$ G$_{0}$ from the B1V star 42 Orionis (42 Ori). We characterize emission from molecular (H$_{2}$) and atomic (e.g., [Ne II], [Ar II], HI) species, and in some cases, MIRI reveals extended emission tracing the proplyd ionization front and wind. The closest disk to 42 Ori, KCFF#1, is undergoing extreme mass loss, traced by a 1000s-of-au-long dusty tail, and lacks clear H$_{2}$ or HI emission, indicating an advanced stage of dispersal. The remaining six disks exhibit two-temperature components of H$_{2}$ emission (500–700 K and 1000–1500 K), likely tracing the disk molecular layer and a photoevaporative wind, alongside HI lines which are used to estimate mass accretion rates. When comparing KCFF#2 and #6, which have similar host stars, KCFF#2 (closer to 42 Ori) is dominated by externally driven mass loss, with extended molecular and atomic emission, whereas KCFF#6 only shows extended H$_{2}$ emission, with roughly equal contributions from accretion and external mass loss. While the sample is small, this work demonstrates how JWST/MIRI can assess environmental impacts on disk evolution, with NGC 1977 bridging strongly irradiated disks in the ONC and the more local population.
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All authors Alice S. Booth, Qijia Zhou, Jinyoung Serena Kim, Karin Öberg, Jenny Calahan, Klaus Pontoppidan, Thomas J. Haworth, Ilaria Pascucci, Ryan Boyden, Mayank Narang, Karina Maucó, Aditya M. Arabhavi, Nicholas Ballering

Monday 17 August

Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM

The Roman Coronagraph Community Participation Program: pre-launch reference star list and impact of reference star properties on post-processing performance

Justin Hom, Schuyler G. Wolff, Jessica Gersh-Range et al. (+51 more)

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star for both wavefront calibration and reference differential imaging post-processing. Reference star criteria for the most demanding coronagraph mode are restrictive, limiting the sample to only 40 candidates for which thorough observational vetting is needed to assess their suitability. Reference star properties such as resolved diameters, presence of circumstellar dust, and close point sources may also have more subtle impacts on post-processing efficacy that may inhibit final contrast performance. In this work, we describe the current progress of the CoronaGraph Instrument Reference stars for Exoplanets (CorGI-REx) observing campaign, a 300+-hour observing campaign that utilizes instruments from around the world to vet reference stars for high-order wavefront control suitability. We will present the pre-launch list of reference star candidates being utilized for the Roman Coronagraph Observation Phase constructed from a thorough analysis of high contrast and interferometric observations. We will also present the results of simulations investigating the impact of reference star resolved diameters and companions on post-processing performance. We conclude by discussing the importance of reference star selection for scheduling observations and optimizing contrast performance for the Roman Coronagraph along with implications for HWO coronagraph operations.
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All authors Justin Hom, Schuyler G. Wolff, Jessica Gersh-Range, Ramya M. Anche, Vanessa P. Bailey, Jean-Philippe Berger, Beth A. Biller, Wolfgang Brandner, Marah Brinjikji, Gaël Chauvin, David R. Ciardi, Catherine A. Clark, Laird M. Close, Robert J. De Rosa, Sarah Deveny, Warren B. Foster, Julien H. Girard, Alexandra Z. Greenbaum, Olivier Guyon, Sebastiaan Y. Haffert, Alexander D. Hedglen, Steve B. Howell, Parker T. Johnson, Maggie Y. Kautz, Jay K. Kueny, Masayuki Kuzuhara, Manon Lallement, Rico Landman, Colin Littlefield, Jean-Baptiste Le Bouquin, Jialin Li, Joshua Liberman, Joseph D. Long, Miles Lucas, Jennifer Lumbres, Bruce Macintosh, Jared R. Males, Eric Mamajek, Matthijs Mars, Eden A. McEwen, Avalon L. McLeod, Maxwell A. Millar-Blanchaer, Toshiyuki Mizuki, Sophie Noiret, Tiffany Nguyen, Lauren Schatz, Nicholas T. Schragal, Adam K. Taras, Elena Tonucci, Katie Twitchell, Kyle Van Gorkom, Macarena C. Vega-Pallauta, Jason J. Wang, Jingwen Zhang

Solar and Stellar Astrophysics

Tracking nonlinear solar-wind dynamics over three solar cycles using Wind observations

Dario Javier Zamora and Facundo Maximo Abaca

The solar wind is a turbulent, weakly collisional plasma characterized by non-Gaussian fluctuations, long-range correlations, and multifractal dynamics. We investigate the long-term evolution of these properties using hourly proton density measurements obtained directly by the Wind spacecraft over 1995–2025. The use of a single-spacecraft dataset provides an independent test of previous results derived from the multi-spacecraft OMNI database. The three components of the nonextensive $q$-triplet are estimated within one-year sliding windows shifted monthly: $q_{stat}$ from the distribution of density increments, $q_{rel}$ from the decay of the autocorrelation function, and $q_{sens}$ from the multifractal spectrum. Their mean values, $q_{stat}=1.71\pm0.07$, $q_{rel}=4.62\pm0.52$, and $q_{sens}=-0.45\pm0.27$, confirm the persistent presence of heavy-tailed statistics, slow relaxation, and weakly chaotic multifractal dynamics. The parameters nevertheless exhibit distinct temporal variability and relationships with solar activity. The Fourier spectrum of $q_{stat}$ contains a dominant period of approximately $10.1$ years, while its correlation with the sunspot number is positive and moderate ($r=0.611$). Correlation and mutual-information analyses show that $q_{stat}$ is primarily associated with solar proxies, whereas $q_{sens}$ displays stronger relationships with geomagnetic indices and $q_{rel}$ exhibits weaker dependencies. An anomalous enhancement of $q_{stat}$ around 2004 coincides with a sequence of intense interplanetary disturbances, although possible effects related to Wind's orbital transition must also be considered. These findings demonstrate the robustness of the nonextensive description and show that the statistical and dynamical properties of solar wind proton density show evidence of modulation by solar activity.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Understanding the Energy Input Required for Methane Emission on CWISEP J193518.59-154620.3: A Comprehensive Analysis

Kayla J. Smith, Mark S. Marley, Tommi T. Koskinen et al. (+1 more)

The Y dwarf WISE 1935 exhibits a thermal inversion in its radiative atmosphere, producing methane emission features in its JWST spectrum, but the physical mechanism responsible for this inversion remains unknown. Using the open-source radiative–convective equilibrium code PICASO, we model atmospheric heating with Chapman energy deposition profiles to reproduce the observed thermal inversion and methane emission feature. Our models require heating rates of approximately 10^5-10^6 erg cm^-2 s^-1. We show that the atmospheric response depends primarily on the integrated heating deposited in the observable atmosphere, revealing a degeneracy between heating magnitude, vertical extent, and emitting surface fraction. Disequilibrium chemistry lowers the required energy input by lowering CH$_4$ opacity and strengthening the inversion. Comparison with recent electron-beam heating models indicates that reproducing the thermal inversion in W1935 requires substantially greater energy deposition than currently predicted for brown dwarf auroral heating, while the observed methane emission favors energy deposition near 10^-3-10^-2 bar. Our models also predict a prominent methane emission feature near 7.8 microns, along with energy-sensitive ammonia features near 6 microns, implying a bolometric luminosity greater than that yet measured. Finally, we investigate potential sources of the inferred upper-atmospheric heating. We find that Joule heating would require a strong magnetic field and large electron densities, the latter supported by external ionization from an unidentified source. We also consider cometary impacts as a possible source of atmospheric heating.
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All authors Kayla J. Smith, Mark S. Marley, Tommi T. Koskinen, James Mang

Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

SCExAO/CHARIS High-Contrast Pre-Launch Vetting of Roman Coronagraph Technology Demonstration PSF Reference Stars

Thayne Currie, Jie Li, Mona El Morsy et al. (+9 more)

We present deep, SCExAO/CHARIS high-contrast integral field spectroscopy and archival imaging of four candidate Roman Coronagraph PSF reference stars within/near the Roman Continuous Viewing Zone and potentially suitable for the Coronagraph's key technology demonstration targets HIP 71618 and HIP 54515. For CHARIS data, we achieve 5-$\sigma$ contrasts down to $\sim$1.4$\times$10$^{-5}$, $\sim$6$\times$10$^{-6}$, and 10$^{-6}$ to 4$\times$10$^{-7}$ at 0\farcs{}16, 0\farcs{}25, and 0\farcs{}5 to 1\arcsec{}. Companion mass limits rule out brown dwarfs at $\rho$ $\sim$ 0\farcs{}15–0\farcs{}25 and massive planets at wider separations around all targets. More critically, for three of the four references our analysis disfavors companions with $V$ band contrasts brighter than 10$^{-8}$, 10$^{-9}$, and $10^{-10}$ at 0\farcs{}15, 0\farcs{}3, and 1$\arcsec{}$. Unless these targets have faint substellar companions within $\rho$ $\sim$ 0\farcs{}15, they likely lack background stars or companions that could corrupt the Roman Coronagraph's dark hole digging to preclude detecting reflected-light planets. For $\alpha$ Cep, our limits are a factor of $\sim$10 worse but still meet the TTR5 limit of 10$^{-7}$ beyond $\rho$ $\sim$ 0\farcs{}25: beyond 0\farcs{}4, they exclude a Jupiter-twin reflected-light companion (10$^{-9}$). Archival Keck/NIRC2 data likewise find no substellar companions with $\Delta$V $>$ 10$^{-8}$ at wider separations. Finally, we assess the observability of HIP 71618 and HIP 54515 – updated for Roman's launch date of August 30, 2026. Adding $\gamma$ Boo – not currently in the Roman CPP team reference-star list – would improve schedulability for the tech demo's key targets.
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All authors Thayne Currie, Jie Li, Mona El Morsy, Olivier Guyon, Julien Lozi, Erica Dykes, Danielle Bovie, Sebastien Vievard, Garima Singh, Kyohoon Ahn, Vincent Deo, Yoshito Ono

Solar and Stellar Astrophysics

Sr and Ba yields of the First Generation(s) of stars: Constraints from metal-poor stars

Sarah Hughes, Anna Frebel, Xiaowei Ou et al. (+6 more)

We present our chemical abundance analysis of ten new extremely metal-poor stars with $-4.05\leq\mbox{[Fe/H]}\leq-2.33$, based on high-resolution (R $\sim28,000$) Magellan/MIKE spectra. Eight of our stars have low heavy-element abundances of $\mbox{[Sr/H]}<-4.5$ and $\mbox{[Ba/H]}<-4.0$, making them Small Accreted Stellar System (SASS) stars. Four are hyper neutron-capture-element poor with $\mbox{[Sr/H]}<-5.0$, including Gaia DR3 5729400267359655680, which sets a new record for the lowest detected Sr abundance of $\mbox{[Sr/H]} =-6.4$. We identify four distinct [Sr/Ba] groups within the wider SASS star population which span a large range from $\mbox{[Sr/Ba]} =-2.0$ to +1.6, pointing to multiple types of progenitor events and different nucleosynthesis processes/sites. To explore the origins of this large [Sr/Ba] range, we adopt site-agnostic Sr yields of $\mbox{[Sr/H]}=-6$, $-5.75$, $-5.42$, and $-4.93$ for the four groups. Applying those yields suggests that the majority of SASS stars formed from gas enriched by $\sim$1-10 progenitor events, consistent with expectations from their extremely metal-poor nature. We thus attribute the [Sr/H] abundance scatter to intrinsic variations in the Sr yield per nucleosynthesis site/event. Our proposed Sr yields for each [Sr/Ba] group and associated nucleosynthesis origin are a reasonable and representative approximation, good to within a factor of a few, and can constrain future theoretical heavy element nucleosynthesis calculations in early core-collapse supernovae.
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All authors Sarah Hughes, Anna Frebel, Xiaowei Ou, Alexander Yelland, Felicia Xiao, Jorian Benke, Kali Kraus, Reidyn Wingate, Mohammad Mardini

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

A comprehensive cluster census of Orion. An application of the Significance Mode Analysis (SigMA) algorithm

Alena Rottensteiner, Sebastian Ratzenböck, João Alves et al. (+2 more)

Precise astrometric surveys and modern clustering algorithms are working in step to transform our view of star-forming regions. By revealing a much richer substructure than previously accessible, they pave the way for reconstructing star formation histories by accurately resolving and age-dating individual sub-populations. The Orion star-forming complex is the best-studied stellar nursery in the solar neighborhood and the nearest one currently forming massive stars. Even so, a comprehensive characterization of its substructure, including a homogeneous age mapping and extinction analysis, is still incomplete. Here, we present the most complete census of stellar populations across the Orion complex from the newest version of the SigMA algorithm and outline our additions and improvements to the algorithm that have extended its usage to distant (>300 pc) regions. We separate the Orion complex into 47 co-spatial and co-moving stellar groups comprising 11,996 reliable members, with ages ranging from 1.5 to 25 Myr. To evaluate the statistical robustness of each group, we derive cluster persistence values and individual membership probabilities for each source from 10 independent clustering repetitions. Our group memberships agree well with the literature, but SigMA consistently finds a factor of ~2-3 more members. In particular, it resolves more very young populations, such as NGC 2024, RV Orionis, B30, NGC 1977, NGC 2068, and NGC 2071, than previous algorithms. In addition to recovering 28 known clusters and three groups previously classified as substructures, we present 16 new co-eval substructure candidates of the Orion star-forming complex. This work builds up a new high-resolution time-resolved picture of Orion. This spatio-temporal map allows us to relate its stellar content to the surrounding ISM and paves the way for a detailed analysis of its star formation history in the future.
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All authors Alena Rottensteiner, Sebastian Ratzenböck, João Alves, Stefan Meingast, Sebastian Hutschenreuter

Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM

TomoSphero: Fast Differentiable Projector for Planetary and Solar Tomography on Spherical Grids

Evan Widloski and Lara Waldrop

Computational tomography is a tool for determining the internal structure of objects from a set of projections, typically taken along some regular path. In recent years, methods and GPU-accelerated libraries have emerged that allow for fast reconstruction from projections along more complicated paths. Most of these libraries rely on a Cartesian discretization of the object, which is not appropriate for all scenarios. We present TomoSphero, a differentiable tomographic projector over spherical grids which are often used in planetary and solar tomography. TomoSphero is designed to be used as a building block in reconstruction algorithms and includes common projection types such as cone-beam and parallel-beam, but is flexible enough to accommodate arbitrary projections. TomoSphero is implemented in PyTorch which allows for fast projection computation on GPUs, easy access to modern machine learning optimizers, and automatic differentiation for rapid prototyping of parametric models.
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Solar and Stellar Astrophysics

Eta Carinae's historical light curve: evidence for cyclic Roche lobe overflow from the primary star

Augusto Damineli, Leonardo A. Almeida, Francisco J. Jablonski et al. (+5 more)

The large amount of ground-based photometric measurements of $\eta$ Carinae obtained since 1940 have remained problematic for quantitative modeling due to the blending of flux from the stellar core and the surrounding circumstellar nebula. In the era of the Hubble Space Telescope, spatially resolved imaging & spectrophotometry have enabled disentanglement of these components, allowing recovery of the stellar core $V$-band brightness from ground-based observations. We isolate the $V$-band fluxes of the stellar core and nebula using 1999–2020 HST (ACS and STIS) observations, and use these to calibrate coeval ground-based photometry. The main finding is an orbital light curve with an amplitude $\Delta m \approx \pm 0.2\,$mag, many times higher than that modeled by ellipsoidal deformation of the primary. The observations suggest that Roche lobe overflow starts at $- 75$ days before periastron in coincidence with the start of rising in the orbital light curve, and remains for 150 days. An expanding (and afterwards dissipating) gas cloud reflecting the light from the primary would explain the observed large amplitude of the orbital light curve. A sharp periodic photometric peak occurs at $\sim -18$ days from the periastron. It is followed by a broad minimum around the superior conjunction of the secondary (T$_0+5.2$ days), which we interpret as a partial eclipse of the ejected material, in coincidence with the shallow minimum in X-rays, which also has been attributed to an eclipse.
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All authors Augusto Damineli, Leonardo A. Almeida, Francisco J. Jablonski, Eduardo Fernández-Lajús, Felipe Navarete, Eder Martioli, Gerd Weigelt, Rodrigo Capobiango

Solar and Stellar Astrophysics · Cross-listed from nucl-th

Nuclear Drip Line and the Composition of Supernova Matter

S. Maity and S. Mallik

The nuclear drip line plays a crucial role in determining the composition of matter under extreme astrophysical conditions. In core-collapse supernovae and neutron-star crusts, matter is driven far from saturation density and nuclear stability; nuclei coexist with a sea of free neutrons, an effect that is present even at zero temperature in neutron-star crusts and becomes more pronounced in the hotter, neutron-rich supernova environment. This makes a careful treatment of drip-line physics essential for a realistic description of the equation of state and composition. In this work, the influence of the nuclear drip line on the baryonic composition of supernova matter is investigated within the framework of nuclear statistical equilibrium (NSE). The composition is evaluated in terms of free nucleons, light clusters, and heavy nuclei at finite temperature and global sub-saturation densities. The results indicate that, at low proton fractions and higher densities, the inclusion of nuclei beyond the drip line enhances the formation of extremely neutron-rich light clusters, leading to a significant reduction in the free-neutron density and the charge fraction of heavy nuclei. These findings demonstrate that drip-line physics has a significant impact on the composition of supernova matter and should be carefully incorporated in supernova modeling and nucleosynthesis studies.
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Solar and Stellar Astrophysics

CO rotational line emission in very red carbon stars in the Magellanic Clouds

M.A.T. Groenewegen, A. Nanni, M.L. Boyer et al. (+11 more)

Stars of low and intermediate initial mass lose most of their stellar mass at the end of their lives during the asymptotic giant branch (AGB) phase. Determining their gas and dust mass-loss rates (MLRs) is crucial for quantifying the contribution of evolved stars to the life cycle of dust and gas in the Universe. The Atacama Large Millimeter/submillimeter Array was used to observe 38 carbon stars (C stars) in the large Magellanic cloud (LMC) and three C stars in the small Magellanic cloud (SMC) in the CO J= 2-1 line. Line profiles were fitted to derive stellar velocities and wind-expansion velocities (Vexp). CO emission is detected in two C stars in the SMC and 33 C stars in the LMC. This is the first detection of carbon monoxide around an AGB star in the SMC. One object in the LMC shows emission in $^{13}$CO. The wind-expansion velocity ranges from \sim7.5 to \sim30 km/s. Archival data were used to determine the pulsation periods as well as construct and model the spectral energy distributions using two dust radiative transfer codes. Mass-loss rates were independently derived from these two codes as well as from the intensity of the CO line, using a simple formula. On average, the dust-based MLRs higher than the MLRs based on the CO line by a factor of 1.6. Additional CO data in other transitions, combined with proper modelling, is required to further investigate this possible discrepancy. Mass-loss rates, pulsation periods, and expansion velocities were compared to a sample of Galactic C stars. There is a strong bias, as the Magellanic Cloud targets sample the highest MLRs and luminosities, yet they represent only a minority of stars in a Galactic sample. Comparing this sample with a similarly extreme set of Galactic stars with periods longer than 500 days, we identify no correlation between metallicity and either the MLR or Vexp.
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All authors M.A.T. Groenewegen, A. Nanni, M.L. Boyer, L. Decin, S.R. Goldman, K. Justtanont, F. Kerschbaum, I. McDonald, H. Olofsson, R. Sahai, G. C. Sloan, J. Th. van Loon, W.H.T. Vlemmings, A.A. Zijlstra

Solar and Stellar Astrophysics

Detection and Characterization of Microlensing Events due to Isolated Black Holes towards the Magellanic Clouds in the Rubin Observations

Sedighe Sajadian and Martin Makler

Gravitational microlensing surveys potentially discover isolated black holes (IBHs) at large distances through their gravitational effects on apparent brightness and motion of collinear stars. Here, we study detecting and characterizing IBHs within the mass range $[3,~5000]M_{\odot}$ with either stellar or dark matter origins in the upcoming observations by Vera~C.~Rubin Observatory towards the Large and Small Magellanic Clouds (LMC and SMC). We consider four lens mass functions (MFs:~$dN/dM\propto M^{-\beta}$ for $\beta=0,~0.5,~1,~2$), and generate long-duration microlensing events due to IBHs detectable by Rubin. By assuming the fraction of IBHs's mass in total Galactic mass as $\mathcal{F}$, Rubin potentially detects $\sim0.3,~\rm{and}~2$ microlensing events towards SMC and LMC due to IBHs if $\beta=1,~\rm{and}~\mathcal{F}=5\times10^{-3}$. These IBHs are inside our galaxy with the probability $\gtrsim70\%$. These events have on average $\theta_{\rm{E}}\sim30-50~\rm{mas}$, so that the probabilities of resolving their lensing-induced images through the Rubin astrometric observations are $\sim1.4,~\rm{and}~16.3\%$ towards LMC and SMC. In $\sim1,~5.2\%$ of these events their astrometric deflections are realizable. The probabilities of discerning their parallax are $\sim40,~25\%$. We evaluate relative errors with simulating synthetic data points and by assuming the true models as the best-fitted ones. We conclude for a log-uniform MF for $\lesssim0.1,~\rm{and}~0.3\%$ of photometrically detectable microlensing events towards in LMC and SMC the relative errors in the lens mass, distance and velocity are $\lesssim3\%$. We calculate the number of detectable IBHs versus by assuming their complete contribution of compact objects in halos' darkmatter, and conclude Rubin specifies $95\%$~C.L. upper-limit on IBHs exclusion by masses $\lesssim208,~8M_{\odot}$ for $\mathcal{F}\simeq4\times10^{-3}$.
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Solar and Stellar Astrophysics

Machine Learning in Application to Automatic Noise Processing of Solar Spectrograms

I. I. Yakovkin, A. O. Bartenev and N. V. Petrova

In this paper, a machine learning approach for processing solar spectral data were developed. Its performance was demonstrated using the example of the limb solar flare on July 17th, 1981. The results indicated that machine learning can be effectively utilized to transform between differently digitized spectra, fill gaps in unique experimental data, and undertake spectrum cleaning. Specifically, convolutional neural networks were devised to transform between reflective and transmissive scans of a solar flare spectrogram. This can be a convenient technique for treating the spectrograms of unique solar events, most notably increasing the proportion of observational spectra that can be further analyzed. Namely, in subsequent research, we will be able to confidently incorporate data such as that captured on the edges of spectrograms, which was previously deemed insufficiently reliable due to limitations of available processing techniques. This will consequently increase the number of spectral lines studied for certain observed events, which is paramount for constructing physical models, as the spectral peculiarities are expected to manifest consistently across different spectral lines. The developed approach also notably facilitates the detection and removal of impurities in the spectrograms. Previously, each distinct feature in the spectra was manually scrutinized to check its integrity in order to be excluded if identified as an impurity, such as a scratch or a dust particle. By employing the suggested protocol for treating the spectrogram, which includes scanning the spectrogram using multiple distinct techniques and then leveraging machine learning for comparison, the process of excluding impurities can now be automated. Furthermore, the spectrum areas affected by such exclusions can be restored, enabling further analysis.
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Solar and Stellar Astrophysics

Characterizing Stellar Flares in Ariel Targets: Activity Analysis and Transit Contamination

G. Galletta, S. Colombo and G. Micela

Stellar flares are sudden releases of magnetic energy that can distort exoplanet transit photometry and transmission spectroscopy, biasing planet radius estimates, transit timings, and atmospheric characterization. Understanding flare activity in Ariel targets is therefore essential to identify stars where flares may compromise observations and to characterize the radiation environment affecting atmospheric escape and photochemistry. We analyzed 290 Ariel target stars using TESS light curves. Flares were identified via iterative Gaussian process detrending, and their energy distributions were modeled with two-segment power laws. We performed injection-recovery tests by adding synthetic flares to detrended light curves and running the full pipeline to quantify completeness and detection biases. We detected 15,857 flares across 1,638 TESS sectors, with 2-86 events per sector. We defined a normalized flare index GF.01 to compare activity across stellar luminosities. Near 3% of the sample exhibits enhanced flare activity (GF.01 > 1). AU Mic and HD 28109 show a high likelihood of flare contamination during transit observations. GF.01 correlates negatively with stellar bolometric luminosity, indicating higher relative flare output in lower-luminosity stars. AU Mic is an extreme case: four of five observed transits of AU Mic b are affected by flares, consistent with statistical expectations. We validate the framework by comparing predicted flare-contamination probabilities with observed flare occurrences in a representative subset of transits, finding agreement within uncertainties. These results confirm that energetic flares can significantly impact transit observations and provide quantitative guidance for Ariel target selection and analysis strategies.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Catalytic formation of H_2 on carbonaceous dust grains - implications for interstellar observations

Aryav Das, Julia Gao, Daniel Vrinceanu et al. (+1 more)

We use kinetic Monte Carlo (KMC) simulations to study molecular hydrogen formation on carbonaceous dust grain surfaces, validated against recent laboratory measurements of H$_2$ formation on coronene films at temperatures from 10 to 250 K. The model uses a three-dimensional amorphous carbon lattice with heterogeneous physisorption ($45 \pm 5$ meV) and chemisorption ($1.75 \pm 0.25$ eV) sites, and tracks both Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) formation channels within a stochastic Gillespie event-driven framework. The model reproduces the measured efficiency curve within the experimental uncertainties, including the isothermal (constant surface temperature) measurements at 100 - 250 K. The simulations correctly describe the phase boundary between the LH and ER driven processes as functions of grain temperature and the observed crossover. Under interstellar medium conditions, 10 - 250 K and n = 10 - 10$^4$ cm$^3$, the model predicts three distinct regimes for the formation efficiency $\epsilon$, the fraction of impinging H atoms released as H$_2$. At 10 K diffusion is slow and $\epsilon \approx 0.06$. Between 20 K and 80 K, LH dominates and $\epsilon \approx 0.28$. Above 150 K, an ER plateau at $\epsilon = 0.19$ is sustained by chemisorption-trapped H atoms. The LH-to-ER crossover occurs between 100 and 120 K. At 100 K we observe a 16% density-dependent stochastic enhancement, which rate-equation models cannot capture. At T$_{dust}$ = 60 K, n = 10$^3$ cm$^3$ we find the ratio of H$_2$ formation to free-fall time $t_{{\rm H}_2}/t_{\rm ff} \approx 0.93$, so dust-catalysed H$_2$ chemistry can keep pace with gravitational collapse in high-redshift star-forming environments.
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All authors Aryav Das, Julia Gao, Daniel Vrinceanu, H. R. Sadeghpour

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Gaia DR3 Limits on Stellar Engine Technosignatures in Nearby Stars

Bo-Lun Huang, Zhen-Zhao Tao, Tong-Jie Zhang et al. (+1 more)

An operating stellar engine that transfers momentum to its host star could produce an approximately persistent transverse acceleration during the Gaia Data Release 3 (DR3) observing epoch. We search for such accelerations among 406,984 quality-selected Gaia DR3 stars with nominal distances below 200 pc (about 650 light-years), using 8,890 published Acceleration7 solutions. Because long-period binaries and astrometric systematics can produce similar sky-plane curvature, we model these conventional explanations together with a broad component that can absorb any remaining persistent acceleration or model mismatch. At $a_0 = 2.60 \times 10^{-4}$ m s$^{-2}$, where essentially the entire parent sample is searchable, mapping the residual weights evaluated at the one-sided 95% profile-limit point gives a parent-population fraction limit of $1.21 \times 10^{-5}$. Multiplying this fraction by the parent-sample size gives a summed upper-limit weight of about five star-equivalents above the threshold. Toward the lowest acceleration thresholds, the searchable fraction declines rapidly, so the corresponding bounds primarily describe the reach of the search. No individual source is interpreted as a technological signal.
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All authors Bo-Lun Huang, Zhen-Zhao Tao, Tong-Jie Zhang, Zhi-E Liu