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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Saturday 29 August

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

Dynamical Mass Demography of Single S-type Planets Shaped by Stellar Companions

Xiumin Huang and Jianghui Ji

More than 700 S-type planets have been identified from Gaia and TESS observations, including over 150 transiting targets, enabling the precise dynamical orbits and planetary mass characterization in binary environments. Here we present the first systematic N-body dynamical mass determination for 40 single S-type (Satellite-type orbit) planets in close binaries using an improved Markov Chain Monte Carlo (MCMC) framework with Gaussian priors to model stellar companion perturbations. {For binary systems with $a_\mathrm{B}<100$ au, companion-induced perturbations can bias the RV semi-amplitude and consequently the inferred planetary masses. The impact is strongest for short-period sub-Jovian planets, whose masses decrease by up to 20% when transitioning from Keplerian to N-body modeling, while massive Jovian planets with $M_{\mathrm{Jup}} < M_{\mathrm{p}} < 5$ $M_{\mathrm{Jup}}$ show only a 7.2% reduction.} Applying the NAFF stability criterion to TOI-4633, $i_{\mathrm{mut}} = 70^{\circ}$ is the upper limit for the fast rejection of unstable orbital solutions. Our results reveal that intermediate-mass planets exhibit both positive or negative biases in the inferred masses and influence the observed population of the sub-Jovian desert.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Can Little Red Dots Contribute To The Early Universe Cosmic Dust Budget?

Chris Ashall, Rohan P. Naidu, Alberto Torralba et al. (+11 more)

The origin of dust in the early Universe remains uncertain. We explore whether Little Red Dots (LRDs) could provide a high-redshift dust-production channel. Motivated by an analogy with Type IIn supernovae, we investigate whether LRDs may share the efficient dust-forming conditions. We consider dust formation in outer winds and later in a shielded cold dense shell after the central source fades. Such dust may avoid a global remnant-phase reverse shock, while longer LRD lifetimes may promote grain growth. We model the SEDs of two low-redshift LRD analogs as a thermal pseudo-photosphere plus optically thin dust components, obtaining dust reservoirs of order $10^{2}$-$10^{3}\,M_{\odot}$. Although photometry cannot exclude pre-existing dust, the narrow Balmer components of both analogs are close to the Case B ratio and their narrow-line environments are metal-poor, disfavoring a dominant diffuse host-ISM origin for the inferred reservoir. Formation within the LRD outflow is consistent with our optical-depth, sublimation, and energy-balance checks. In this scenario, the large dust masses do not produce a strong optical attenuation because a clumpy or asymmetric distribution can leave the dominant optical sightlines relatively unobscured. Our population calculation shows that the LRD contribution to early-Universe dust production can range from negligible to dominant. At higher efficiencies, LRDs can approach or exceed the lower CCSN contribution above $z\approx5$, whereas less favorable assumptions yield a minor contribution. We therefore propose that LRDs can act as early-Universe dust factories and, under some conditions, may dominate over CCSNe or provide seed grains for subsequent growth in the early ISM.
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All authors Chris Ashall, Rohan P. Naidu, Alberto Torralba, Irene Shivaei, John Chisholm, Hanpu Liu, Zhaoran Liu, Jorryt Matthee, Kyle Medler, Tyco Mera, Takashi J. Moriya, Devesh Nandal, Robert A. Simcoe, Wendy Q. Sun

Friday 28 August

Solar and Stellar Astrophysics

Statistical Energy Budget of the Solar Wind with Parker Solar Probe and Solar Orbiter : 1 - Unbalanced Total Energy Radial Evolution

Jean-Baptiste Dakeyo, Pascal Démoulin, Victor Réville et al. (+9 more)

The magneto-hydrodynamic (MHD) description of the solar wind has long been regarded as one of the most successful frameworks for investigating solar wind heating and acceleration. Under a set of simplifying assumptions, it provides a reduced large-scale description that is widely used to study the energetic role of electromagnetic fluctuations in the solar wind energy budget. In practice, applying simplification to MHD can result in the loss of some physics compared to an exact set of equations. However, an observational energy budget can help us to verify whether any energetic information has been lost in the process of simplification. To do so, we directly test the validity of the large-scale non-linear ideal MHD energy budget with solar wind observations from Parker Solar Probe (PSP) and Solar Orbiter (SO). After verifying the reliability of the measurements through comparison with previous studies of similar solar wind properties, we test the conservation of the total energy predicted by the MHD theory. We find that the average total energy increases with radial distance by $56\%$ ($\pm9\%$) between 14 and 203 solar radii. The increase in kinetic energy is not sufficiently compensated by the decrease of the thermal and electromagnetic contributions. We investigate the major sources of observational uncertainty and find that they cannot account for the observed energy increase. These results suggest that the large-scale theoretical description may neglect an energetically significant contribution to solar wind acceleration. Assuming that such a contribution exists, we predict that this extra energy would scale with radial distance as $r^{-0.54\pm0.38}$.
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All authors Jean-Baptiste Dakeyo, Pascal Démoulin, Victor Réville, Stuart Bale, Tamar Ervin, Milan Maksimovic, Olga Alexandrova, Mingzhe Liu, Roberto Livi, Nikos Sioulas, Orlando Romeo, Alexis Rouillard

Solar and Stellar Astrophysics

The Hot, Continuum-compact State of the Yellow Hypergiant V509 Cassiopeiae: CHARA Diameters, CO-band Angular-extension Constraints, and Companion Limits

Narsireddy Anugu, Gail H. Schaefer, Douglas R. Gies et al. (+4 more)

Yellow hypergiants are rare, evolved massive stars generally interpreted as post-red-supergiant objects evolving blueward through or near the dynamically unstable Yellow Evolutionary Void. V509~Cassiopeiae is a remarkable example: its spectroscopically inferred effective temperature increased from approximately 5000~K in the mid-1980s to about 7900~K by the late 1990s and has since remained near this value during its post-heating state. We use simultaneous six-telescope CHARA observations obtained in 2023 with MIRC-X in the $H$ band and MYSTIC in the $K$ band to measure its photospheric diameter, search for a luminous companion, and constrain any spatially extended CO atmosphere. Interferometric data fitting with fixed atmosphere-model center-to-limb variation profiles yield limb-darkened angular diameters of $1.1840$–$1.1950$~mas. Although nominally about 5% smaller than the previous Palomar Testbed Interferometer measurement, the difference is only $1.8\sigma$, indicating no significant secular change over 17–21~yr. The closure phases are consistent with a centrosymmetric brightness distribution, and no near-infrared-bright companion is detected over the sampled separations. The median $3\sigma$ limits are $\Delta H=5.28$~mag and $\Delta K=6.48$~mag. The B1~V companion proposed from ultraviolet spectroscopy is expected to lie below these limits and is not excluded. The CO first-overtone channels give a weighted mean CO-to-continuum diameter ratio of $1.011\pm0.004$, below the adopted $3\sigma$ detection criterion. We find no significant CO-band angular extension. V509~Cas is thus hot and molecularly compact despite retaining spectroscopically visible atomic circumstellar gas.
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All authors Narsireddy Anugu, Gail H. Schaefer, Douglas R. Gies, Anni Kasikov, John D. Monnier, Stefan Kraus, Karolina Kubiak

Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn

Internal heating in rapidly rotating convection is not a shortcut to geostrophic turbulence

Justin A. Nicoski, Tobias G. Oliver, Stefano Maffei et al. (+1 more)

Convective turbulence in planets and stars is often driven by internal heating. This forcing mechanism has also been proposed as a means of accessing the diffusion-free scalings of the geostrophic turbulence (GT) regime at modest forcing. We test this with the asymptotically reduced quasi-geostrophic model, which is formally valid in the limit of vanishing Ekman number, $Ek \rightarrow 0$, and retains the Prandtl number as an independent parameter. We find no such shortcut: the Nusselt and Reynolds numbers are no closer to their diffusion-free predictions than in the boundary-heated case, and at $Pr = 7$ they are further from them; the predicted $Pr^{-1/2}$ collapse fails; and the prefactor depends on the form of the heating. Our no-slip/stress-free cases track the radiatively driven simulations of Hadjerci et al. (2024) case by case, yet a $25\%$ variation in $Nu$ persists between sweeps that share the same reduced Rayleigh and Prandtl numbers but differ in Ekman number. Those data span only the narrow range of forcing over which the compensated Nusselt number is stationary; across the wider range accessible to the reduced model it rises to a maximum and then falls. We argue that bulk transport scalings are incomplete diagnostics of GT, whereas the saturation of the interior mean temperature gradient and of the vertical velocity kurtosis remain reliable indicators.
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All authors Justin A. Nicoski, Tobias G. Oliver, Stefano Maffei, Michael A. Calkins

Solar and Stellar Astrophysics

An All-Sky Catalog of 6.5 Million Primary Red Clump Stars from Gaia DR3 XP Spectra

Zheng Yu and Bingqiu Chen

Red clump (RC) stars are excellent standard candles for mapping the three-dimensional structure of the Milky Way. We construct an all-sky catalog of 6.5 million primary RC stars using spectroscopic estimates of asteroseismic parameters inferred from Gaia DR3 low-resolution XP spectra. We train a mixture density network (MDN) on a cross-matched sample. The network maps each 343-dimensional corrected XP spectrum to estimates of $\Delta\Pi_{1}$, the asymptotic period spacing of dipole gravity modes, and $\Delta\nu$, the large frequency separation. We select primary RC stars using these two estimates. We release two complementary catalogs defined by different parameter-space cuts and thresholds: a high-purity Tier 1 sample of 532,189 stars with 97% purity and a high-completeness Tier 2 sample of 6,534,931 stars with 86% completeness. Both catalogs cover the full celestial sphere. We provide distances and extinction values for all stars. We obtain a median photometric distance precision of 6% for Tier 1 RC stars. Using the resultant distances, we independently calibrate the Gaia DR3 parallax zero-point offset. The three-dimensional density distribution traced by the Tier 2 sample extends continuously to $R\approx25$ kpc. Both catalogs are publicly available. These catalogs provide a valuable resource for Galactic archaeology, delivering a homogeneous dataset to trace the chemo-dynamical evolution of the Milky Way and to calibrate models of stellar populations.
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Solar and Stellar Astrophysics

A high-frequency type II radio burst associated with an X2.3 class flare

Divya Paliwal, Anshu Kumari, Vishwa Vijay Singh et al. (+3 more)

Radio observations provide a powerful diagnostic of the solar corona, enabling investigations of dynamic phenomena associated with solar flares, coronal mass ejections (CMEs), and shock waves. We present a multiwavelength analysis of a rare high-frequency type II radio burst (starting frequency of $\sim$750 MHz and frequency drift rate of $\sim$0.5 MHz s$^{-1}$) associated with the X2.3-class solar flare that occurred on 6 November 2024. A propagating EUV disturbance was observed shortly after the flare onset in the SDO/AIA field of view, while radio spectrographs recorded the type II burst between 13:46 and 13:56 UT over a frequency range of $\sim$750 to 45 MHz. Radio imaging observations from the Nançay Radioheliograph (NRH) show that the radio sources propagate southward during the event. X-ray spectroscopy from HEL1OS onboard Aditya-L1 and imaging observations from STIX onboard Solar Orbiter reveal signatures of efficient non-thermal electron acceleration associated with the flare. An NLFFF extrapolation identifies a pre-eruptive magnetic flux rope in the source region, while white-light coronagraph observations obtained during the event show no detectable large-scale CME. The speed of the erupting flux rope, derived from stereoscopic EUV observations, is consistent, within measurement uncertainties, with the shock speed inferred from the radio dynamic spectrum. Together, these observations suggest that compact flux rope eruptions, even in the absence of a detectable white-light CME, can generate low-coronal shocks capable of producing high-frequency type II radio emission.
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All authors Divya Paliwal, Anshu Kumari, Vishwa Vijay Singh, Dinesh Mishra, Pritam Das, Nadiya K

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

Three-dimensional Core-Collapse Supernova Simulations: From shell burning to shock revival

Haakon Andresen, Evan P. O'Connor, C. E. Fields et al. (+1 more)

The outcome of core-collapse supernova simulations depends sensitively on the multi-dimensional structure of the progenitor star at the onset of collapse. We perform three-dimensional simulations of the final ~10-15 minutes of stellar evolution for five non-rotating solar-metallicity progenitors with zero-age main-sequence masses of 20, 21.5, 24.5, 26, and 29 solar masses, mapped from one-dimensional MESA models into the FLASH hydrodynamics code. Convection develops in the oxygen-rich layers of all five models, with convective velocities reaching several hundred km/s, and in some models strong convection also develops in the inner silicon- and oxygen-burning shells. For the 24.5 solar mass progenitor, we carry out three core-collapse simulations: one initialised from the fully three-dimensional model, one from its angle-averaged counterpart, and one from the original one-dimensional MESA progenitor. We find that the multi-dimensional progenitor leads to 35 to 50% higher non-radial kinetic energy in the post-shock region and an average shock radius 5 to 10% larger than in the angle-averaged model, and shows the earliest shock revival of the three. The gravitational-wave emission is similar in all three models and strengthens after shock revival, driven by a change in the downflows reaching the protoneutron star rather than by progenitor asymmetries.
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All authors Haakon Andresen, Evan P. O'Connor, C. E. Fields, Sean M. Couch

Solar and Stellar Astrophysics

On the Origin of a Dusty Circumstellar Medium around Red Supergiants

Das Sujit, Arkaprabha Sarangi and Sutirtha Sengupta

Red supergiant (RSG) stars are widely recognized as significant sources of dust, enriching the interstellar medium. However, the physical conditions that regulate dust nucleation in their winds remain poorly constrained. We investigate the formation of molecules and dust in RSG and explore how enhanced mass loss can produce a dense, dust-rich circumstellar medium (CSM) before core collapse. We couple time-dependent mass loss with non-equilibrium chemistry to model the formation of molecules and dust precursors using mass loss rates ranging from 10$^{-6}$ to 10$^{-2}$ \Mdot\ and both constant and accelerating wind profiles. Molecules such as CO, H$_2$O, SiO, HCN, CS, SO, NH$_3$, H$_2$, and O$_2$ form efficiently in the CSM, with masses varying between 10$^{-15}$–10$^{-2}$ \Ms. O-rich dust, namely silicates and alumina, dominates the dust composition. The total dust mass ranges between 10$^{-8}$ and 3$\times$10$^{-3}$ \Ms. Accelerated winds produce more dust and allow dust formation closer to the stellar surface. The resulting fluxes exhibit strong mid-infrared excesses. The 9.7 and 18 \mic\ silicate features appear in either emission or absorption depending on the optical depth of the circumstellar medium. The time-dependent mass-loss history of our SN~2023ixf progenitor models results in a gradual increase in CSM dust mass toward explosion. A clumpy CSM provides a substantially better match to the observed optical and infrared fluxes, demonstrating the importance of time-dependent mass loss, CSM structure, and wind acceleration in shaping the observable properties of red supergiant progenitors.
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Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

Solar Magnetic Configuration Control over Radiation Belt Electrons

Ahmad Lalti, Jonathan Rae, Clare Watt et al. (+2 more)

Earth is surrounded by two highly dynamic concentric belts of particle radiation. The outer radiation belt exhibits coherent variability at solar-cycle, seasonal, and 27-day (Carrington) timescales. While the solar-cycle and Carrington variations have been attributed to the recurrence of coronal hole solar wind, the seasonal variation has long been explained by local geometric effects that modulate the solar wind-magnetosphere coupling. Here, we challenge this paradigm by showing that the periodic recurrence of coronal hole solar wind likewise drives the seasonal variation. We further demonstrate that the Alfvénic nature of this solar wind is responsible for the observed electron flux enhancement in the outer radiation belt. These findings provide a unifying framework linking solar magnetic topology, solar wind properties, and magnetospheric dynamics across multiple timescales at Earth and beyond.
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All authors Ahmad Lalti, Jonathan Rae, Clare Watt, Stephanie Yardley, Savvas Raptis

Solar and Stellar Astrophysics

Probing magnetic fields in stars: A 2D oscillation framework including rotation and magnetism

Antoine Fort, Rhita-Maria Ouazzani, Lucas Barrault et al. (+2 more)

Understanding the role of internal magnetic fields in stars remains a major challenge for the description of angular momentum transport and stellar evolution. It is therefore essential to probe these magnetic fields within the star, and asteroseismology provides a powerful means to do so. In this work, we present a new implementation of the 2D oscillation code ( ), which incorporates the effects of both stellar rotation and magnetic fields. Adaptive Code of Oscillations towards Realistic modeling The code has been rendered modular, making it possible to specify the set of equations to solve and the assumptions through a symbolic calculus approach. The full set of adiabatic, non-radial pulsation equations is solved using a spectral approach for the angular part of the modes and high-order finite differences for the radial part. As a first step, we focus on a magnetic field that is purely toroidal and axisymmetric about the star's rotation axis. The numerical results are compared against first-order perturbative predictions in the weak-field regime and with the traditional approximation of rotation and magnetism (TARM) in the case of stronger magnetic fields. We validate this new implementation of against perturbative and TARM approaches, showing good agreement and demonstrating the robustness of the code. The breakdown of these methods provides general validity limits. We show that internal magnetic fields leave signatures in the period spacing of g modes. These features provide a promising seismic diagnostic to probe deep stellar magnetism in {\gamma} Dor stars. Future work will aim to extend this framework to more realistic magnetic field topologies and a broader range of pulsating stars, including red giants.
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All authors Antoine Fort, Rhita-Maria Ouazzani, Lucas Barrault, Louis Manchon, Ludovic Petitdemange

Solar and Stellar Astrophysics

Search for magnetic fields in seven slowly rotating A stars

Pablo de Frutos Rull, Coralie Neiner, Jonathan Labadie-Bartz et al. (+3 more)

A small fraction of A-type stars host strong fossil magnetic fields. Identifying them relies on indirect indicators such as chemical peculiarities, slow rotation, and rotational modulation, which are also shared by non-magnetic stars. Assessing their reliability is essential for future surveys. We magnetically characterise seven slowly rotating, chemically peculiar A-type stars selected through two complementary strategies. Three were selected from abundance analysis combined with potential intrinsically slow rotation, and four from a spectral depression at 5200 Angstrom combined with rotational modulation in TESS photometry. We obtained high-resolution spectropolarimetry, applied least squares deconvolution, and measured longitudinal field strengths for detections. For non-detections, we derived upper limits on polar field strength and evaluated the critical fields of Zahn and Spruit. We detect magnetic fields in all four stars selected via the spectral depression and photometric criterion, with longitudinal field strengths of approximately 145-2900 G, while none of the three stars selected via abundance and slow rotation shows a Zeeman signature. Combined upper limits for two non-detections lie below or near the magnetic desert boundary, but only one is also below the critical fields required for rigid rotation. The non-detections are most naturally interpreted as Am stars. Among the detections, HD 63843 stands out as a magnetic $\delta$ Scuti pulsator, promising for magneto-asteroseismology. In conclusion, slow rotation combined with chemical peculiarity alone does not reliably trace large scale magnetic fields, whereas adding the 5200 Angstrom depression and stable rotational modulation in space photometry appears to select magnetic A-type stars with high efficiency, providing a practical guideline for future spectropolarimetric surveys.
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All authors Pablo de Frutos Rull, Coralie Neiner, Jonathan Labadie-Bartz, Frédéric Royer, Richard Monier, Keegan Thomson-Paressant

Solar and Stellar Astrophysics

On the theoretical instability strips of {\gamma}-Doradus stars including the effect of the metallicity and rotation

L. Fellay and M.-A. Dupret

Recent space missions such as Kepler have provided large-scale observations of the {\gamma}-Doradus instability strips (IS), which can be used to constrain models and explore their limitations. One persistent limitation is the prediction of the blue edge of the {\gamma}- Doradus IS, where a significant number of {\gamma}-Doradus stars are observed. Despite these observational advances, no systematic study has been undertaken to explore the effects of different physical processes on the {\gamma}-Doradus. Our aim is to systematically explore the theoretical {\gamma}-Doradus IS with modern tools, accounting for the effects of rotation and metallicity, providing a large grid of models and their oscillation parameters for the scientific community. We investigated the non-adiabatic pulsation properties of stars in a grid of stellar models with masses between 1.35 M{_\odot} and 2.5 M{_\odot}, metallicities between Z= 0.01 and Z= 0.025, and solid-body rotation rates ranging from {\Omega} = 0 to 0.5 {\Omega_{crit}}, where {\Omega_{crit}} denotes the critical rotation rate. We find that, across all computations, the theoretical {\gamma}-Doradus IS agrees well with the observed IS, except in the extended blue region. In terms of radial orders, our models consistently reproduce the excited modes in broad agreement with observations for l= 1, l= 2, and Rossby modes. We also show that the range of excited radial orders is strongly dependent on the effective temperature. The range of excited radial orders can be used to constrain the position of a star within the {\gamma}-Doradus IS and may provide insights into the physical mechanisms responsible for the discrepancies observed in the blue region. All computed grids are made available and include mode damping and growth rates for {\gamma}-Doradus stars, obtained with a time-dependent treatment of the convection-oscillation interaction.
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Solar and Stellar Astrophysics

Extremely Low Mass Ratio Contact Binaries. III. Photometric and Spectroscopic Investigations of Eleven Systems

Youmo Lai, Kai Li, Raul Michel Murillo et al. (+6 more)

We present photometric and spectroscopic investigations of 11 totally eclipsing contact binaries with mass ratios below 0.15, classifying them as extremely low mass ratio contact binaries. The ground-based multiband light curves were modeled with PHysics Of Eclipsing BinariEs to derive the photometric parameters of these systems. The TESS light curves of J011323 and J002747 show pronounced asymmetries and continuous variations. Markov Chain Monte Carlo modeling suggests that these variations are related to longitudinal migration of spots on the primary components. Spectral subtraction of the LAMOST spectra reveals excess chromospheric emission in six systems, while no detectable excess emission is found in the other five. The O$-$C analysis indicates secular period increases in six systems and secular decreases in five systems. We estimated their orbital angular momenta and performed a dynamical analysis. {Within our adopted semi-analytical framework without energy transfer, the formation of these observed systems requires additional angular momentum loss beyond saturated magnetic braking and gravitational radiation, but this requirement could be modified by different assumptions on mass transfer or radius evolution.
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All authors Youmo Lai, Kai Li, Raul Michel Murillo, Difu Guo, Liheng Wang, Xiang Gao, Han-ning Zhang, Xing Gao, Guo-You Sun

Solar and Stellar Astrophysics

CoBiToM project. III. Physical characterisation of the potential merger candidates AL Lep, ASAS J082243+1927.0, and ZZ PsA

Sofia Palafouta, Kosmas D. Gazeas, Pasi Hakala et al. (+3 more)

Contact binaries (CBs) are key systems for investigating the late evolutionary stages that may lead to stellar coalescence. Systems with an extremely low mass ratio and high fill-out factor are of particular interest as potential merger candidates and possible progenitors of luminous red novae. A combined photometric and spectroscopic study of the CB systems AL Lep, ASAS J082243+1927.0, and ZZ PsA is presented. The aim is to derive self-consistent orbital and physical parameters, assess their evolutionary state, and examine whether they have reached the terminal and unstable phase of their evolution. High-resolution VLT/UVES spectra were analysed to derive radial velocity values, spectroscopic mass ratio, and metallicity. The results were combined with multi-band light-curve modelling within a Monte Carlo framework to determine the system geometries and absolute parameters. Orbital period variations were investigated through O-C analysis, while the evolutionary status of the systems was assessed using the Darwin instability criterion, critical mass ratio estimates, fill-out factor, and orbital period variation. Mass ratio values of q = 0.1332, 0.1041, and 0.0789 were derived for AL Lep, ASAS J082243+1927.0, and ZZ PsA, respectively. The corresponding primary mass values are M1 = 1.656 +/- 0.081 Msun, 1.275 +/- 0.078 Msun, and 1.795 +/- 0.111 Msun. The locations of their components show significant deviations from single-star ZAMS and TAMS reference curves, indicating strong binary interaction and energy redistribution through the common envelope. The spin-to-orbital angular momentum ratio for AL Lep and ASAS J082243+1927.0 remains below the standard Darwin instability threshold, while ZZ PsA lies close to the instability regime and may be consistent with an unstable configuration within the derived uncertainties.
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All authors Sofia Palafouta, Kosmas D. Gazeas, Pasi Hakala, Stanislaw Zola, Athanasios Kafkas, Maria Garro

Solar and Stellar Astrophysics

A decade of radial-velocity monitoring of rho Leo: moment analysis and periodic variability

V.A. Checha, A. Aret, I. Kolka et al. (+6 more)

We investigate the origin of long-term spectroscopic and photometric variability in the blue supergiant rho Leo, with particular emphasis on distinguishing between intrinsic pulsations and variability induced by a possible companion. Our analysis is based on an 11.5-year spectroscopic time series obtained at Tartu Observatory, complemented by high-cadence, high-resolution spectroscopy from the Hertzsprung SONG telescope and space-based photometry from TESS. We studied line-profile variability using normalised moments of the HeI 6678, HeI 5875, and SiIII 4552 lines. Periodic signals were identified using the generalised Lomb-Scargle periodogram with iterative pre-whitening, and their temporal stability was examined with the weighted wavelet Z-transform. We detect a persistent periodic signal at P = 16.46 d in the first and third moments, present throughout the full observing interval, with a radial-velocity amplitude of 3.9 km/s. This signal is also present in the SONG data and is visible in multiple spectral lines, indicating a global origin. Photometric observations reveal a dominant variability timescale near 33 d, approximately twice the spectroscopic period. The stable 16.46-day period, present throughout the entire observing interval, most likely results from non-radial pulsations of the supergiant. A binary origin of the signal is not excluded, but distinguishing between these scenarios is complicated by the supergiant's complex variability pattern.
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All authors V.A. Checha, A. Aret, I. Kolka, T. Liimets, V. Mitrokhina, A. Kasikov, T. Eenmäe, S. P. D. Borthakur, H. Ramler

Solar and Stellar Astrophysics

Dynamically driven collapse of a thermally stable accretion disk in a nova-like system

Wentao Li, Jie Lin, Tinggui Wang et al. (+8 more)

While standard disk instability theory predicts thermal-steady, outburst-free disks in nova-like variables due to their high mass transfer rates, mass transfer variations are prevailingly invoked to explain the occasional flaring/fading phenomena observed in these systems. Here we report the observational evidence for a dynamical collapse of a thermally stable accretion disk, captured serendipitously by TESS during a fading episode of the VY Scl-type nova-like system MASTER OT J072703.91-631952.8, and traced by the emergence of an unusual negative superhump that evolves toward its orbital frequency. Simultaneously, the system underwent an anomalous eruptive event featuring a remarkably symmetric 45-day light-curve profile, indicative of a mild energy-release mechanism fundamentally distinct from documented eruptive events in cataclysmic variables. Notably, the concurrence of the eruption and the disk collapse is difficult to reconcile with the paradigm of mass transfer variations: the eruption implies enhanced mass transfer, whereas the disk collapse indicates a decline. The morphological disk evolution over $\sim 700$ days, characterized by both negative and positive superhumps, indicates a transition from a circular disk to an eccentric disk, followed by a tilted state and ultimately a minimal disk configuration. This evolutionary sequence provides evidence for a previously unrecognized dynamics-driven cycle operating in the thermally stable accretion disk of a VY Scl-type nova-like star.
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All authors Wentao Li, Jie Lin, Tinggui Wang, Yongkang Sun, Chengyuan Wu, Heran Xiong, Krystian Iłkiewicz, Luca Casagrande, Michael Bessell, Ning Jiang, Chengyi Wang

Solar and Stellar Astrophysics

Quiescent and Interacting Compact Remnant Binary Populations in the Space Telescope Era

Erin Eastep, Jan J. Eldridge and J. C. Bray

Since the discovery of Gaia BH1, interest in quiescent binary systems has grown. Two additional black-hole binaries have since been discovered alongside several candidate neutron-star binaries, yet the formation pathways of these systems remain poorly understood. Theoretical studies of these systems, together with the populations into which they evolve, such as X-ray binaries (XRBs), can help constrain their formation channels. We present predictions for the Galactic population of quiescent binary systems and their later evolutionary phases, including XRBs and post-interaction quiescent binaries. We combine stellar models from the Binary Population and Spectral Synthesis code (BPASS) with a synthetic Milky Way generated using Feedback In Realistic Environments (FIRE) simulations. We compare our results with existing observations to assess how well the synthetic population reproduces the observations. We find generally good agreement, with observed donor masses, compact-object masses, and orbital periods largely reproduced, except for the Gaia BH systems. Our results also suggest that some accreting compact remnants with low-mass donors and wide orbital periods may not be X-ray bright. Remaining discrepancies indicate that the BPASS initial parameter space should be expanded, the common-envelope evolution prescription revised, and magnetic braking included in low-mass donor models. We also predict the number of systems detectable in future Gaia data releases and by the Nancy Grace Roman Space Telescope (hereafter referred to as Roman). In particular, the Galactic Bulge Time Domain Survey is expected to yield a significant population of quiescent black-hole binaries. We predict that ~200-600 candidate quiescent binary systems will be detected in the Galactic Bulge Time Domain Survey, while ~2500-4000 candidate systems will be identified in Gaia DR5.
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Thursday 27 August

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

High Dispersion Measure Fast Radio Bursts from Young, Dust-Poor H II Regions

Eliza C. Diggins, Calvin Leung and Wenbin Lu

Several repeating fast radio burst (FRB) sources exhibit host-frame dispersion measure (DM) excesses far exceeding those expected from the interstellar medium in their host galaxies, implying a substantial contribution from the sub-kiloparsec-scale local environment. These excesses are often attributed to an expanding supernova remnant; however, this canonical interpretation does not explain their apparent preference for low-metallicity dwarf galaxy hosts, suggesting that the mechanism producing the local DM is coupled to the properties of the host galaxy. In this work, we investigate whether the H II regions generated by young, massive stellar associations can simultaneously explain these DM excesses and their preferential association with low-metallicity dwarf galaxies. We develop a semi-analytic model for FRB-emitting neutron stars in cluster-forming molecular clouds and perform idealized one-dimensional radiation-hydrodynamic simulations using time-dependent ionizing luminosities from pySTARBURST99. Our findings indicate that high-mass $(M_\star \sim 10^5-10^6\;M_\odot)$, young ($\lesssim 10\;{\rm Myr}$) stellar associations in low-metallicity environments (LMC-like or lower) can produce ${\rm DM}_{\rm HII} \gtrsim 10^3\;{\rm pc\;cm^{-3}}$ for FRBs that form early ($\lesssim 5$ Myr) and remain embedded in the ionized gas. The low-mass/metallicity preference arises from dust: absorption of the Lyman continuum suppresses the ionized column at higher metallicity, making extreme local DMs preferentially generated in dust-poor, low-metallicity environments. At cosmological distances, selection of a metal-rich, massive, and quiescent host galaxy sample where such extreme local contributions are likely to be suppressed may yield a cleaner FRB sample for using extragalactic DMs as tracers of the intervening intergalactic and circumgalactic media.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Magnetospheric birefringence breaks the rotating-vector model and depolarises X-ray pulsars

Alexander A. Mushtukov, Sergey S. Tsygankov, Silvia Zane et al. (+4 more)

Accreting X-ray pulsars have long been expected to show large linear polarisation below the cyclotron resonance. In the standard picture, this follows from two facts: radiative opacities in the strongly magnetised neutron star environment depend strongly on polarisation mode, and the emission comes from compact polar regions. The emerging radiation should therefore be locally polarised and add almost coherently, with a polarisation angle tracing the projected magnetic field as in the rotating-vector model. Recent X-ray polarimetric observations, instead, show modest polarisation fractions and position angle swings that often depart from this simple picture. Here we show that propagation through the magnetosphere of an accreting neutron star can naturally produce both effects. Using general-relativistic ray tracing and Stokes-parameter transport, we find that photons emitted from compact polar regions acquire ray-dependent polarisation angle offsets in two ways. First, nearly field-aligned trajectories can cross local non-adiabatic pockets inside the QED birefringent region. Second, photons that intersect the plasma-loaded accretion flow accumulate additional phase shifts between plasma normal modes. Both effects broaden the distribution of polarisation angles across the ray bundle and reduce the hotspot-integrated linear polarisation, while also producing systematic deviations from rotating-vector-model expectations. Magnetospheric propagation should therefore be treated as part of the polarimetric transfer problem in accreting X-ray pulsars, and may help explain the observed low polarisation fractions and anomalous angle swings.
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All authors Alexander A. Mushtukov, Sergey S. Tsygankov, Silvia Zane, Nabil Brice, Ruth M. E. Kelly, Roberto Taverna, Roberto Turolla

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

Spin-disc misalignment drives periodic accretion and pulse profile asymmetry in X-ray pulsars

A. A. Mushtukov, V. Ganesh, S. S. Tsygankov et al. (+2 more)

We investigate magnetospheric accretion in disc-fed X-ray pulsars assuming that the neutron star spin axis is not perpendicular to the disc plane. We focus on X-ray pulsars, where a geometrically thin disc is truncated far from the stellar surface the channelled part of the accretion flow is expected to be guided by the large-scale dipolar magnetic field after coupling to it near the disc-magnetosphere boundary. Using numerical simulations of plasma motion from the inner disc edge to the neutron star surface, we show that a finite inclination between the disc normal and the stellar spin axis leads to periodic modulation of the mass accretion rate onto the magnetic poles even for a steady mass supply through the disc. This purely geometrical effect arises because stellar rotation changes the orientation of the magnetosphere relative to the disc, producing phase-dependent mass loading of magnetic field lines. The amplitude and shape of the modulation are determined by the system geometry and by the ratio of the stellar spin period to the flow time through the magnetosphere. The resulting variability affects the structure and luminosity of emitting regions near the neutron star surface and leads to asymmetric X-ray pulse profiles. Even without intrinsic asymmetries of the emission regions, this mechanism breaks the time-reversal symmetry expected for stationary accretion and naturally contributes to the observed asymmetry of pulse profiles and phase-resolved spectral features. The effect may also be relevant for ULX pulsars, where intrinsic accretion rate modulation can help preserve strong pulsations in the presence of geometric beaming.
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All authors A. A. Mushtukov, V. Ganesh, S. S. Tsygankov, S. Portegies Zwart, A. Palyam

Solar and Stellar Astrophysics

A 500 pc volume-limited sample of hot subluminous stars III. The short-period binary population

H. Dawson, M. Dorsch, J. Munday et al. (+16 more)

Hot subdwarf stars of spectral types O and B (sdO/B) in binaries form as products of substantial mass loss near the tip of the red giant branch and offer powerful constraints on binary-star evolutionary models. However, details of some formation channels remain missing. We present a comprehensive analysis of the short-period binary population in the 500 pc volume-limited sample of hot subdwarfs, enabled by precise Gaia DR3 parallaxes. Besides 45 known binaries within 500 pc, this work identifies 50 new single-lined radial-velocity variable systems, 34 with orbital solutions with periods between 0.07 and 22 days. We derive an overall short-period binary fraction of 34.7 (+2.8/-2.9)% for the full sample of 301 hot subdwarfs within 500 pc, corrected for orbital inclination and detection efficiency. The newly solved binaries predominantly occupy the 1-20 day range, a parameter space previously under-represented in the literature. We identify five new reflection-effect systems, three ellipsoidal modulation systems, a newly solved HW Vir system, and a new triple candidate. The sdB and sdO binary fractions are similar, while the sdOB class shows a fraction roughly half that of sdB/sdO stars, with periods over one day, suggesting a different evolutionary pathway. Underluminous hot subdwarfs below the canonical extreme horizontal branch show a binary fraction comparable to other sdB/sdO stars but host only white dwarf companions, which are more massive and mainly found at periods under one day. We provide the first volume-complete birthrate estimates for sub-populations, determining a Galactic merger rate of 2.5+-1.5x10^-5 yr^-1 for sdO/B binaries, explaining no more than ~12% of the eHe-sdO population. We also derive birthrates for two SN Ia progenitor channels, finding hot subdwarf binaries could account for up to 2.5 (+0.7/-0.5)% of the observed Galactic SN Ia rate.
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All authors H. Dawson, M. Dorsch, J. Munday, S. Geier, F. Mattig, M. Pritzkuleit, D. Benitez-Palacios, M. Vučković, K. Deshmukh, A. Bhat, U. Heber, I. Pelisoli, R. Raddi, P. Fernandez-Schlosser, A. Durán-Reyes, E. Arancibia-Rojas, A. Bobrick, V. Schaffenroth, G. T. Jones

Solar and Stellar Astrophysics

Spectral Synthesis for Classical Ae Stars: H${\alpha}$ and CaII

R. Anusha and T. A. A. Sigut

Classical Ae stars (CAe) are main sequence, A-type stars with H${\alpha}$ emission but no signature of dust; they are thought to be the cool extension of the classical Be (CBe) stars to lower stellar masses. We investigate the use of H${\alpha}$ and the CaII IR triplet observed at low spectroscopic resolution ($R=1800$) as diagnostics for the circumstellar disks of the CAe stars. Using a sample of 159 CAe stars from the LAMOST survey (DR5), we find that circumstellar disk masses and star/disk viewing inclination angles can be reliably determined from low resolution H${\alpha}$ profiles. The CAe disk mass distribution agrees well with the previous range found for late-type CBe stars, although there is an apparent increase in disk mass for the latest CAe spectral sub-types (A3 and A4) which we attribute to selection effects. Over the spectral range A2 through B6, the average disk-to-star mass ratio for the CAe and CBe stars is consistent with $\log_{10}(M_{\rm disk}/M_*)=-9.1$. A minority of the CAe sample ($\sim$16%) also show emission in the CaII IR triplet. The observed emission is well within the range predicted by the disk models, and there is statistical evidence that the CaII emitters have systematically larger H${\alpha}$ disk masses.
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Solar and Stellar Astrophysics

BSN-VIII: Detailed Photometric Modeling of Ten W UMa Contact Binaries and a Revised Empirical Period-Mass Relationship

Atila Poro, S. Javad Jafarzadeh, Kai Li et al. (+15 more)

This study continues our ongoing research on contact binary systems by presenting a detailed analysis of 10 targets. Ground-based observations from six different observatories were conducted and used together with TESS data for the analysis process. Photometric data from our observations were reduced with the recently developed AutoWISP pipeline, yielding high-quality light curves with reliable precision for analysis. An investigation of orbital period variations identifies long-term trends in six of the ten analyzed binaries, including three that also display cyclic variations. Four targets show essentially constant orbital periods. The secular trends are attributed to mass transfer. The cyclic modulations in three systems are caused by either magnetic activity cycles or the Light-Travel Time Effect (LTTE) of a third body, while that in the remaining system is solely due to the LTTE. The BSN application was used to model the photometric light curves of the 10 target binaries. Iterative fitting and MCMC refinement provided robust estimates of the system parameters, while starspot modeling was applied for systems showing O'Connell-effect asymmetries. We refine the empirical orbital period-mass relationship for short-period contact binaries by analyzing a homogeneous dataset of systems and deriving an updated primary-mass calibration based on the spectroscopic subset. Using this calibrated relation, the fundamental parameters of the studied systems were subsequently estimated.
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All authors Atila Poro, S. Javad Jafarzadeh, Kai Li, Jean-François Coliac, Sabrina Baudart, Meng Guo, Patrick Wullaert, David Valls-Gabaud, Anis Ben Lassoued, Daniel Verilhac, Laurent Corp, Emmanuel Foguenne, Hervé Lerat, Jean-Baptiste Marquette, Serge Vasseur, Anica Lekic, Fahri Alicavus, Neslihan Alan

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

Formation of black hole stars via star–black hole collisions

Yanlong Shi, Qingru Hu, Zhenghao Xu et al. (+2 more)

In dense stellar environments such as globular clusters and active galactic nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar evolution calculations, focusing on collisions between sBHs and a $100\,M_\odot$ main-sequence star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\sim2\sqrt{G(M_\star+M_\bullet)/R_\star}$. The post-collision outcome depends primarily on the BH-to-star mass ratio. For $M_\bullet\gtrsim30\,M_\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\bullet\lesssim10\,M_\odot$, the collision forms a “black hole star” (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\bullet\lesssim0.2\,M_\star$. Follow-up MESA calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated star–sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-redshift nuclear star clusters and may be relevant to the origin of the “little red dots” discovered by JWST.
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All authors Yanlong Shi, Qingru Hu, Zhenghao Xu, Douglas N. C. Lin, Norman Murray

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

Dynamical formation of high-eccentricity compact binaries through BH–BH*/TZO collisions

Qingru Hu, Yanlong Shi, Douglas N. C. Lin et al. (+1 more)

The rapidly accumulating discoveries of binary stellar-mass black-hole (sBH) coalescences, detected by LIGO, have opened a new window into the formation and evolution of compact binaries. In particular, residual orbital eccentricity may provide a distinctive signature of their formation channels. Here, we investigate a scenario in which high-eccentricity compact binaries form through the sequential capture of multiple sBHs by massive main-sequence stars, using a combination of hydrodynamical and semianalytic few-body simulations. We find that sBHs with $M_\bullet\lesssim 0.2\,M_{\star}$ can be captured by massive stars and settle into a quasi-hydrostatic black-hole star (BH*) through gas dynamical friction. A subsequent encounter with a second sBH can then produce a compact binary embedded within the stellar envelope. Our hydrodynamical simulations show that through captures with small impact parameter, some binaries are born with high eccentricity ($e\gtrsim 0.5$), with its orbital frequency already entering the LISA band. Our semianalytic models further demonstrate that gas dynamical friction can pump the eccentricity to $e_{\rm 10\,Hz}>0.9$ before gravitational-wave emission eventually circularizes the binary during the final stage of coalescence. Once formed, the binary can merge quickly in $\sim 10$ hours. This channel may operate in dense stellar environments, such as star clusters and active galactic nucleus (AGN) disks. The same mechanism can also be applied to Thorne-Żytkow objects. A high-eccentricity binary in the LIGO band could therefore provide a distinctive signature of this formation scenario.
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All authors Qingru Hu, Yanlong Shi, Douglas N. C. Lin, Norman Murray

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

Stellar Flares Rather than High $T_{int}$ As Possible Cause for the Missing Methane in Young Exoplanets: The Case Study of V1298~Tau\,b

Danica Adams, Pierre-Alexis Roy, Hilke Schlichting et al. (+1 more)

Recent observations of V1298~Tau\,b, a warm sub-Neptune (R$=9.85 \pm 0.3\,R_\oplus$, M$=13.1 \pm 5.3, M_\oplus$, T$_\mathrm{eq} = 670\,$K) orbiting a young (10-30\,Myr) K star, show depleted methane and surprising abundances of CO$_2$ in its atmosphere. This makes the planet an interesting target to study the "missing methane problem", where HST, Spitzer, and JWST have revealed many sub-Jovian planets with effective temperatures cooler than 800\,K to be depleted in methane compared to equilibrium chemistry predictions. On V1298~Tau\,b, an intrinsic temperature (T$_\mathrm{int}$) of 500\,K is required to explain the methane depletion if strong mixing from a warm interior is the reason for the missing methane, but this T$_\mathrm{int}$ is too large for a planet of its age and size according to standard interior structure evolution theories. Here, we show that stellar flares can result in methane depletion in a warm planet's atmosphere with nominal T$_\mathrm{int} \sim 100$\,K. During a stellar flare, fast methane photolysis rates cannot be balanced by diffusion from below into the upper atmospheric layers probed by observations. Young active stars flare frequently, and we show that the timescale of diffusion for the methane to recover from a flare-induced depletion can be slow compared to the flare frequency. Over time, the atmosphere reaches a new steady state set by the average flare frequency and energy. This new steady state shows depleted methane in the 2\,mbar region, and abundant CO, CO${_2}$, and HCN, which results in synthetic transmission spectra that reproduce the main features of the recent JWST observations of V1298~Tau\,b.
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All authors Danica Adams, Pierre-Alexis Roy, Hilke Schlichting, Björn Benneke

Solar and Stellar Astrophysics

CHARA Array Observations of the Evolved Components in Symbiotic Star Systems

Thomas Martin Gaudin, Ryan Norris, Magdalena Otulakowska-Hypka et al. (+30 more)

The nature of the mechanisms that drive mass transfer in symbiotic stars remains an area of active research in stellar astronomy. Constraining the role that both stellar winds and Roche-lobe overflow play in this process is crucial to improving our understanding of these binaries and connecting them to important transient events such as recurrent novae and Type Ia supernovae. The high-resolution capabilities of an optical interferometer can resolve the geometric structure of the red giant in symbiotic stars and help answer this question. This work presents the results of an optical interferometric study using the Center for High Angular Resolution Astronomy (CHARA) Array for the purpose of measuring the angular diameter of and imaging the cool giant in four symbiotic and related systems. Here we report H band observations collected with MIRC-X. Model fitting and image reconstruction are used to test for Roche-lobe-filling geometries. Near-simultaneous infrared spectroscopy taken using the NASA InfraRed Telescope Facility (IRTF) is used to determine the fundamental stellar parameters of the cool giant in each system. The parametric fits reported here favor circularly symmetric disk models over elongated geometries, while imaging suggests the presence of surface features on three of these stars. We find that the three systems with constrained orbits have inferred time-averaged filling factors below unity.
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All authors Thomas Martin Gaudin, Ryan Norris, Magdalena Otulakowska-Hypka, Rachael M. Roettenbacher, Nirupam Roy, Yesenia Beltran, Cameron Caruso, Cody Gustafson, Mason Earick, Andrew Kotowski, Rebecca Proni, Jacob Sandusky, Fabien Baron, Michelle J. Creech-Eakman, John D. Monnier, Stefan Kraus, Narsireddy Anugu, Jean-Baptiste Le Bouquin, Sorabh Chhabra, Isabelle Codron, Calire Davies, Jacob Ennis, Tyler Gardner, Mayra Gutierrez, Noura Ibrahim, Cyprien Lanthermann, Benjamin R. Setterholm, Christopher D. Farrington, Olli Majoinen, Norm Vargas, Douglas R Gies, Theo ten Brummelaar, Gail H. Schaefer

Solar and Stellar Astrophysics

The JWST/NIRCam Scattered Light Disks GTO 2780 program: panchromatic coronagraphic imaging of the HD 10647, HD 32297, HD 61005, HD 107146, and HD 181327 debris disk systems

András Gáspár, Jarron M. Leisenring, Schuyler Grace Wolff et al. (+13 more)

Debris disks, composed of rocks, boulders, planetesimals, and the dust produced in their collisions, present the most readily observable components of mature planetary systems. They also serve as valuable diagnostic tools, enabling studies of planetary dynamical interactions and mineral compositions. Observed from optical to radio wavelengths, each band reveals unique information about the dust populations. Optical and near-infrared observations are specifically sensitive to light scattered off the surfaces of the micron-sized particles. Here, we present results from the JWST/NIRCam GTO program 2780, designed to observe five disk systems previously identified to be exceptionally bright at optical wavelengths (HD 10647, HD 32297, HD 61005, HD 107146, and HD 181327) with six filters using the NIRCam coronagraphs. The NIRCam data complement previous shorter-wavelength images of these same systems. They reveal scattered light from the disks and from the extended halos of tiny grains under the influence of radiative forces, at high resolution and signal to noise. All the systems show evidence for water ice, although it can have differing radial distributions and tends to show stronger signatures in the halos. In the two cases we could analyze, the scattering phase function in the disks resembles the behavior of dust in the Solar System with evidence for enhanced forward scattering in the halos, consistent with the latter being composed of tiny grains. MIRI images for two systems are more centrally concentrated than the shorter wavelength ones, suggesting a role for dragged-in larger grains.
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All authors András Gáspár, Jarron M. Leisenring, Schuyler Grace Wolff, Kellen Lawson, George H. Rieke, Dingshan Deng, Marcia J. Rieke, Antranik A. Sefilian, Charles Beichman, Joshua B. Lovell, John Krist, Marie Ygouf, Jorge Llop-Sayson, Geoffrey Bryden, Christopher C. Stark, Christine H. Chen

Solar and Stellar Astrophysics

Panchromatic Spectra of Nearby Low-mass and Sun-like Stars with Directly Imageable Habitable Zones

Sarah Peacock, Breanna A. Binder, Edward W. Schwieterman et al. (+4 more)

Characterizing the high-energy radiation environments of stars plays a critical role in determining which systems' planets are capable of retaining atmospheres and sustaining habitable conditions. X-ray through ultraviolet (UV) radiation drives atmospheric photochemistry, heating, and escape, making accurate characterization of stellar high-energy emission essential for both interpreting future exoplanet observations and identifying the most promising targets for life detection. We construct panchromatic spectral energy distributions (SEDs) spanning the X-ray through radio for 12 nearby low-mass and Sun-like stars with directly imageable habitable zones that are prioritized targets for the Habitable Worlds Observatory (HWO) and Extremely Large Telescopes (ELTs). These SEDs are generated using forward stellar atmosphere models guided and constrained by available archival X-ray and UV observations. We find that many stars in this sample exhibit elevated high-energy radiation environments relative to the modern Sun, with habitable zone X-ray and extreme UV (XUV) fluxes frequently exceeding solar values by 1-2 orders of magnitude. The elevated emission likely reflects a combination of sample selection effects, differences in stellar age and rotation, and intrinsic magnetic variability, with multi-epoch observations demonstrating that variability alone can significantly alter inferred radiation environments. These results highlight high-energy radiation as an important discriminator in identifying the most promising habitable planet hosts and demonstrate the need for expanded X-ray and UV observations to complete the stellar characterization necessary for HWO target prioritization.
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All authors Sarah Peacock, Breanna A. Binder, Edward W. Schwieterman, Margaret C. Turnbull, Stephen R. Kane, Katherine Garcia-Sage, Alison Farrish