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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Tuesday 25 August

Solar and Stellar Astrophysics

Black hole astrometric binaries in the Roman Galactic Bulge Time Domain Survey

Casey Y. Lam, Jessica R. Lu, Kareem El-Badry et al. (+6 more)

The Nancy Grace Roman Space Telescope (Roman), NASA's next flagship mission, is currently scheduled to launch in August 2026. As part of its mission, Roman will conduct the Galactic Bulge Time Domain Survey (GBTDS), which will generate $\sim$50,000 epochs of high-precision photometric and astrometric data for $\sim 10^8$ sources across 1.7 deg$^2$ in the Galactic Bulge. Roman GBTDS astrometry is comparable to Gaia Data Release 4 in terms of number of stars, astrometric precision, and time baseline, and is highly complementary in terms of wavelength and sky location. In this paper, we investigate a synthetic population of GBTDS sources to characterize the detectability of unresolved astrometric binaries, in particular those with compact object companions. Assuming the occurrence rate of black holes (BHs) and neutron stars (NSs) in AU-scale orbits around stars is $10^{-7}$ and $10^{-6}$, respectively, and that Roman achieves an astrometric precision of $1\%$ of a pixel, $\mathcal{O}(10)$ BH+star and $\mathcal{O}(10)$ NS+star detached binaries will be detectable. The BHs will have median mass measurement uncertainties of $\sim 25\%$, increasing the existing sample of detached astrometric BH binaries by a factor of three. Together with the $\mathcal{O}(10^2)$ isolated BHs expected to be discovered by microlensing in the Roman GBTDS and an additional $\mathcal{O}(10)$ detached BH binaries in Gaia DR4, this will provide a representative view of the quiescent Galactic stellar-mass BH population.
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All authors Casey Y. Lam, Jessica R. Lu, Kareem El-Badry, Anil Seth, Joshua D. Simon, Natasha S. Abrams, Andrea Bellini, Matthew W. Hosek Jr., Peter McGill

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

Connecting Granulation and Magnetic Activity in Radial Velocities: The Next Breakthrough for High-Precision Spectroscopy

Ancy Anna John, Khaled Al Moulla, Federica Rescigno et al. (+5 more)

Stellar variability has become the dominant limitation to achieving the radial velocity (RV) precision required for the detection and characterization of Earth-like exoplanets. While significant progress has been made in mitigating the effects of oscillations and magnetic activity, convective granulation and its interaction with stellar magnetic fields remain among the least understood sources of RV variability. To address these challenges, we organized the splinter session `Connecting Granulation and Magnetic Activity in Radial Velocities: The Next Breakthrough for High-Precision Spectroscopy' at Cool Stars 23. The session brought together researchers working on observations, numerical simulations, and data-driven techniques to discuss the current understanding of granulation-driven RV signals and identify the most promising directions for future progress. Through invited and contributed talks, followed by community discussions, participants emphasized the importance of combining physically motivated models with data-driven approaches, developing standardized benchmark datasets, and validating simulations against high-quality observations across a range of stellar types. The discussions also highlighted the need for coordinated observing strategies, improved characterization of individual spectral lines, and physically informed line-by-line analyses to disentangle convective and magnetic signals. This contribution summarises the scientific discussions and community perspectives that emerged during the session and outlines the key challenges that must be addressed to reach the sub-40 cm/s precision required for the next generation of RV planet searches.
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All authors Ancy Anna John, Khaled Al Moulla, Federica Rescigno, Carmen San Nicolas Martinez, Andrew Collier Cameron, Thomas G. Wilson, Nadège Meunier, Sophia Sulis

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

Flyby-induced high-eccentricity migration and the prevalence of hot Jupiters in M67

Mika V. Kontiainen, Cathie J. Clarke and Andrew J. Winter

Few planetary systems form in isolation. Rather, interactions in their birth environments may sculpt their architectures or drive them into unstable configurations. Here we study the role of environmental perturbations in triggering dynamical instabilities leading to hot Jupiter formation in dense clusters, focusing on whether the elevated occurrence rate of hot Jupiters in the open cluster M67 can be explained through flyby-induced high-eccentricity migration. We develop a hybrid method for modelling the secular and tidal evolution of planetary systems under external perturbations by passing stars using a combination of analytic and numerical approaches. We evolve 10,000 realizations each of systems with either a single planet, two planets, or a planet and a stellar companion for $\sim$4 Gyr in an M67-like cluster, comparing outcome statistics against a control sample without flybys. In single- and two-planet systems, the rate of flyby-induced hot Jupiter formation is negligible. However, in systems with an initially isotropically oriented stellar companion, the cluster environment boosts hot Jupiter formation by a factor of $\sim$2, accompanied by a factor of $\sim$3 increase in the rate of planets undergoing tidal disruption. Based on observationally motivated estimates of primordial populations, our hot Jupiter yields are consistent with both field and M67 occurrence rates, provided the primordial wide binary fraction among solar-type stars is close to $\sim$50 per cent, binary-driven high-eccentricity migration is the dominant formation pathway, and a substantial fraction of tidally disrupted systems survive as hot Jupiters through partial mass loss.
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Solar and Stellar Astrophysics

Calculation of Field Line Slippage Rates in Coronal Simulations

Valentin Aslanyan, David MacTaggart, Roger B. Scott et al. (+6 more)

We present the Universal Slippage calculator (USlip), an extension of the Universal Fieldline Tracer (UFiT), that computes magnetic field line slippage rates from an input magnetic field defined on a structured grid. The slippage rate provides a local, physically grounded diagnostic of non-ideal evolution, directly quantifying departures from ideal frozen-in motion. We outline the theoretical formulation and describe an efficient numerical implementation. The method is validated against analytical solutions and applied to simulations using three coronal codes treating varying spatial scales, all of which are standard inputs for USlip. In all the examples considered, the slippage rate not only identifies where magnetic connectivity changes occur, but also accurately reproduces the observed direction of field-line slippage. The consistency of the results across analytical tests and multiple simulation platforms demonstrates that USlip is a robust and versatile tool for diagnosing three-dimensional reconnection in dynamically evolving systems.
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All authors Valentin Aslanyan, David MacTaggart, Roger B. Scott, Chloe P. Wilkins, David I. Pontin, Anthony R. Yeates, Peter F. Wyper, Karen A. Meyer, Spiro K. Antiochos

Solar and Stellar Astrophysics

Photospheric index of geomagnetic activity

Ismo Tähtinen, Timo Qvick, Timo Asikainen et al. (+1 more)

Geomagnetic indices quantify the disturbances of the Earth's magnetic field. They form an important space weather and space climate record that tracks solar-terrestrial effects on the Earth. Although geomagnetic activity has its origins in the photospheric magnetic fields, the two have so far not been directly related. We develop a photospheric index of geomagnetic activity (PIGA) that measures the geoeffectiveness of the Sun based on photospheric magnetic field as presented in synoptic magnetograms. We construct the PIGA from synoptic magnetograms of Wilcox Solar Observatory by relating the equatorial and axial dipole components of the photospheric magnetic field to the geomagnetic Kp index by means of linear regression. PIGA captures well the evolution of the geomagnetic activity over the past 50 years at the resolution of solar rotation, having linear correlation of 0.71 with the geomagnetic Kp index. PIGA makes it straightforward to measure the geoeffectiveness of the Sun using the dominant structure of the global solar magnetic field. PIGA can for example be used to study the geoeffectiveness of the Sun using historical simulations or the predicted solar magnetic field. PIGA also allows to use observed geomagnetic activity as an additional constraint for the early magnetic field reconstructions of the solar magnetic field.
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All authors Ismo Tähtinen, Timo Qvick, Timo Asikainen, Kalevi Mursula

Solar and Stellar Astrophysics

Improving the Physical Interpretability of Gaussian Processes in Stellar Activity Modeling: A Study Case on Photometric Variability Among Stellar Clusters

Leslie Moranta, Jonathan Gagné, Jacqueline K. Faherty et al. (+12 more)

Gaussian Processes (GPs) are widely used to model stellar variability in photometric surveys, but a statistically successful fit does not guarantee that the inferred hyperparameters correspond to physically meaningful stellar properties. This is especially important for young, active stars, whose TESS light curves contain evolving spots, harmonics, and non-sinusoidal variability. We use stellar rotation as a case study to examine when the period hyperparameter of a quasi-periodic GP can be interpreted as a physical rotation period. We introduce a regularized GP likelihood that reweights the covariance-complexity term in the marginal likelihood, reducing the tendency of unconstrained models to converge toward preferred but misleading solutions. We test this framework on 539 stars in IC2602, the Tucana-Horologium Association, Pisces-Eridanus, and GroupX, with independently reported and manually vetted rotation periods. This benchmark evaluates GP hyperparameter interpretability and automated period recovery with minimal human intervention. We compare regularized and unregularized models across several regularization strengths, {\lambda}, using literature agreement, sector-level diagnostics, and consistency across TESS sectors. Relative to the standard GP likelihood, regularization improves successful rotation-period recovery by an average of 7%. It also generally reduces the median absolute fractional deviation of periods across sectors, showing that the improvement is not limited to catastrophic failures but also mitigates smaller systematic errors. Regularization is particularly beneficial for non-sinusoidal or evolving modulation, where unconstrained GPs may recover harmonics or spurious timescales. These results show that likelihood regularization and cross-sector consistency are practical diagnostics for assessing when GP-based rotation periods are robust.
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All authors Leslie Moranta, Jonathan Gagné, Jacqueline K. Faherty, Mark Popinchalk, Jason Lee Curtis, Johanna M. Vos, Alexandrine L'Heureux, Andrew Ayala, Eleanor Johnson, Dawn McCullough, Nicole Munoz, Hannah Park, Xue Weng, Livia Poliquin, Ilhem Lazizi

Solar and Stellar Astrophysics

The Interplay of Magnetic Fields, Turbulence and Vorticity in Core-Collapse Supernovae

David Calvert, Michael Redle, Bibek Gautam et al. (+4 more)

The convective turbulent motion of the fluid below the shock in a core-collapse supernova stretches and amplifies the magnetic field of the progenitor star. The energy contained in the field is sourced from the work done by the fluid on the field which comes at the expense of the fluid's kinetic and internal energy. In addition to the energy exchange with the fluid, the magnetic field also has a back-reaction upon the fluid via a contribution to the baroclinic vector and thus affects the fluid vorticity. In this paper we explore the interaction of the magnetic field with the fluid in core-collapse supernovae using the ELEPHANT code with solar-metallicity stars of 15 and 20 \msun zero-age main sequence mass and purely toroidal initial magnetic fields of $B_0 = 0, 10^{10}, and 10^{12}$~G. We find that the magnetic field in the gain region does not become so large that it alters the global dynamics above the 10% level in the early post-bounce evolution. The turbulent kinetic energy of the fluid in the gain region is smaller in simulations with a strong initial magnetic field, but the exact amount of reduction is uncertain due to limitations of the methods for measuring turbulent kinetic energy. The structure of the field in the simulations quickly becomes a tangled mass of flux ropes as soon as convection begins, which leads to a large magnetic field contribution to the baroclinic vector that dominates over the hydrodynamic contribution. Although governed by very similar transport equations to the magnetic field, the fluid vorticity and magnetic field are always close to being randomly aligned at every stage of the evolution. The enstrophy, which is seen to be closely associated with the turbulent kinetic energy, is found to be reduced in simulations with a strong initial magnetic field supporting the inference that the magnetic field reduces the amount of turbulence in the fluid.
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All authors David Calvert, Michael Redle, Bibek Gautam, Carles J. Stapleford, Carla Frohlich, James P. Kneller, Matthias Liebendoerfer

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

Comprehensive solar eruption analyses enabled by the tools of the SOLER project

Nina Dresing, Jan Gieseler, Markus Baumgartner-Steinleitner et al. (+26 more)

Solar eruptions comprise of a multitude of phenomena such as flares, coronal mass ejections (CMEs), large-scale coronal waves, radio bursts, and energetic particles traveling through interplanetary space. These phenomena are observed with a variety of instrumentation, including remote sensing and in-situ detectors. Obtaining a global understanding of a solar eruption often requires the analysis of various of these different datasets, including a multitude of analysis and modeling tools and a wide range of expertise. Usually, such a comprehensive analysis can only be achieved by a skilled and broad team. The Energetic Solar Eruptions: Data and Analysis Tools (SOLER) project aims at creating a comprehensive analysis platform for the study of solar eruptions that allows a single user to easily apply analysis methods addressing various counterparts of the solar event. Therefore, each partner of the project developed Python-based software, including interfaces in the form of Jupyter Notebooks, which provides application examples and concise step-to-step documentation. In this paper we introduce the comprehensive solar-eruption-analysis infrastructure developed within the SOLER project. We explain where to find the software, how to use it, and give dedicated use-case examples of how to employ selected tools in a combined manner.
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All authors Nina Dresing, Jan Gieseler, Markus Baumgartner-Steinleitner, Carine Briand, Karin Dissauer, Annamaria Fedeli, Robert Jarolim, Jaclyn T. Lang, Diana E. Morosan, Jake A. J Mitchell, Christian Palmroos, Jens Pomoell, Jinge Zhang, Otso Santala, Astrid M. Veronig, Laura Vuorinen, Alexander Warmuth, Oliver Flor, Myrthe Flossie, Emilia K. J. Kilpua, Werner Pötzi, Daniel J. Price, Antonio Gomes, Emil J. Hotti, Ruth A. Hyndman, M. Liebel, Amaia Razquin, Song Tan, Ramio Vainio

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

Fingerprints of thermal Comptonization in accreting neutron stars. Plasma-vacuum interplay in cyclotron lines and polarisation

E. Sokolova-Lapa, D. K. Maniadakis, J. J. R. Stierhof et al. (+11 more)

X-ray emission from accreting, strongly magnetised neutron stars and its pulse-phase variability probe their magnetic-field geometry, spin orientation, and emission processes. Whether the radiation emerges mainly from a hot spot or column, and whether its properties are shaped by bulk or thermal Comptonization, remain debated across luminosity regimes. We aim to disentangle intrinsic emission from visibility effects and identify observables characteristic of thermal Comptonization in hot spots and columns. We therefore derived energy-dependent beam patterns and observable signatures without assigning the model to a luminosity regime, focusing on cyclotron-resonance and polarisation effects as tracers of anisotropy. To do so, we computed angle-dependent polarised broadband spectra, including the fundamental cyclotron line, for a homogeneous, self-emitting, magnetised Comptonizing plasma over a broad parameter range. Accounting for light bending and projection, we obtained phase-dependent fluxes for different geometries and, for hot spots, observed linear polarisation. The beam patterns evolve with energy, driving pulse-profile changes. Near the cyclotron resonance, plasma-vacuum interplay produces a narrow central beam and side petals. Their visibility creates geometry-dependent dips, bumps, and M- and W-shaped structures in hot-spot pulsed fraction spectra, but only dips and bumps for columns. Thermally Comptonized cyclotron lines do not reliably trace plasma temperature; plasma-induced ellipticity and band averaging reduce observed soft-X-ray linear polarisation to 0-30%. Under typical X-ray pulsar accretion-channel conditions, thermal Comptonization leaves robust energy-dependent anisotropic signatures. Energy-resolved pulse profiles, pulsed fraction spectra, and polarisation thus provide complementary diagnostics of neutron star geometry, emission-region shape, and spectral formation.
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All authors E. Sokolova-Lapa, D. K. Maniadakis, J. J. R. Stierhof, E. Ambrosi, A. D'Aì, C. Ferrigno, N. Schettino, M. Middleton, A. Gúrpide, V. Grinberg, G. Lipunova, I. El Mellah, P. Kretschmar, J. Wilms

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

Sub-diffraction-limited coronagraphic imaging with nano-printed PIAACMC phase masks

Elena Tonucci, Sebastiaan Y. Haffert, Warren B. Foster et al. (+22 more)

Imaging Earth-like exoplanets in the habitable zone of their host star is among the main science objectives of future ground-based and space-based observatories. However, the extreme contrast and small separations needed to image such planets cannot be reached with current technology. The Phase-Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is a promising coronagraph to reach this goal. The PIAACMC uses a set of aspheric lenses to apodize the entrance pupil without throughput losses and a phase-shifting focal plane mask for starlight suppression. These allow us to maintain high throughput and achieve a small inner-working angle (IWA), unlocking the capability to observe exoplanets at the diffraction limit. The masks are manufactured in-house at Leiden University with Nanoscribe, a micro-3D-printer that uses two-photon polymerization to achieve sub-micron precision in height. We present the first scientific results with a focal plane mask for the PIAACMC on the Magellan Adaptive Optics eXtreme (MagAO-X) instrument for the 6.5-meter Magellan Clay telescope at Las Campanas Observatory, Chile. We show laboratory and on-sky contrast curves with a broadband z' filter centered at 908 nm with a 14% bandwidth. We use the PIAACMC to detect binary companions at separations ~0.8-5 lambda/D (~23-144 mas). This demonstrates the PIAACMC's capability to observe at the diffraction limit and below, with a sub-lambda/D IWA. Future work includes exploring new mask designs to improve the contrast in broadband light and performing active focal plane wavefront sensing and control.
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All authors Elena Tonucci, Sebastiaan Y. Haffert, Warren B. Foster, Jared R. Males, Olivier Guyon, Laird M. Close, Kyle van Gorkom, Alexander D. Hedglen, Parker T. Johnson, Maggie Y. Kautz, Jay K. Kueny, Rico Landman, Jialin Li, Joshua Liberman, Joseph D. Long, Miles Lucas, Jennifer Lumbres, Matthijs Mars, Eden A. McEwen, Avalon McLeod, Tiffany Nguyen, Logan A. Pearce, María Eugenia Redondo González, Lauren Schatz, Katie Twitchell

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

Anomalous Electric Fields in Earth's Turbulent Magnetosheath: Insights From 3D Hybrid Simulations

Jeffersson A. Agudelo Rueda, Julia E. Stawarz, Luca Franci et al. (+3 more)

In both collisional and collisionless plasmas the presence of a broad range of electromagnetic and plasma fluctuations provides anomalous electric fields that can be important for the dynamical evolution of the system as it is the case of magnetic reconnection, plasma turbulence and dynamo theory. In the context of plasma turbulence at scales larger than the ion's inertial length, the plasma satisfies the frozen-in condition, and the anomalous electric fields are produced by correlations between turbulent velocity and magnetic fields. Conversely, for collisionless plasmas and at kinetic scales, the total electric field has additional contributions that arise from kinetic phenomena, namely, charge separation, ambipolar electric fields and electron inertia, and each of these terms presents an anomalous counterpart. In this work we characterize the anomalous electric fields. We present a framework that can explain partial balance between the anomalous resistivity and anomalous transport, and we use it to study anomalous electric fields at kinetic scales. We establish how the different contributions to the anomalous electric field couple to the large-scale electric fields and show that the anomalous terms act back-reacting on magnetic-field organization and they may contribute to effective turbulent magnetic diffusion or shielding. Finally, we test two Sub-Grid-Scale models including anisotropic transport coefficients and show that although these models partially recover the spectral information, the phase coherence is not entirely recovered by these models suggesting a more complex non-linear contribution of the anomalous terms to the resolved scales.
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All authors Jeffersson A. Agudelo Rueda, Julia E. Stawarz, Luca Franci, Nobumitsu Yokoi, Camille Granier, Silvio S. Cerri

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

Self-Consistent Determination of the Transition Temperature Between the $^{14}\mathrm{C}(n,\gamma)^{15}\mathrm{C}$ and $^{14}\mathrm{C}(p,\gamma)^{15}\mathrm{N}$ Reactions

R. Ya. Kezerashvili, N. A. Burkova, A. S. Tkachenko et al. (+1 more)

We present the first self-consistent theoretical study of the competing $^{14}\mathrm{C}(n,\gamma)^{15}\mathrm{C}$ and $^{14}\mathrm{C}(p,\gamma)^{15}\mathrm{N}$ reactions within the same modified potential cluster model (MPCM). For the $^{14}$C$(p,\gamma_{0})^{15}$N reaction, total cross sections, astrophysical $S$ factors, and reaction rates are calculated using interaction potentials constrained by the available scattering and bound-state data. The astrophysical $S$-factor is estimated as $S(0)=4.5(1)$~keV$\cdot \text{b}$. Combining these results with our recent MPCM calculations for $^{14}\mathrm{C}(n,\gamma)^{15}\mathrm{C}$, we determine the transition temperature at which proton capture overtakes neutron capture in the production of $^{15}\mathrm{N}$. The self-consistent comparison predicts a transition temperature $T_9^{\rm c.p.}=2.5$ under Maxwell–Boltzmann statistics, significantly higher than previous estimates. The analysis is extended to Tsallis statistics, demonstrating that deviations from thermal equilibrium produce substantial shifts of the transition temperature. These results provide improved nuclear-physics input for astrophysical nucleosynthesis calculations.
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All authors R. Ya. Kezerashvili, N. A. Burkova, A. S. Tkachenko, S. B. Dubovichenko

Solar and Stellar Astrophysics

Flare waiting time as a novel proxy of stellar magnetic activity

Henggeng Han, Song Wang, Chuanjie Zheng et al. (+3 more)

Stellar flares have long served as stellar magnetic activity tracers. The flare waiting time, defined as the interval between two consecutive flares, provides a valuable diagnostic for probing underlying mechanisms of energy storage and release in stellar atmospheres. In this work, utilizing flaring M dwarfs observed by the Kepler satellite, we establish a simple yet effective activity proxy, i.e., median flare waiting time ($t_{\rm{w, med}}$). Our results show that the $t_{\rm{w, med}}$ can trace long-term activity levels similar to the flare rate. However, $t_{\rm{w, med}}$ corresponding to different waiting time percentiles may encode richer physical insights than flare rate. In addition, for the first time we construct a clear relation between $t_{\rm{w, med}}$ and stellar rotation period, which is quite similar to the canonical activity–rotation relation. More intriguingly, this relation exhibits a more notable supersaturation effect (i.e., below a critical rotation period, $t_{\rm{w, med}}$ begins to increase instead of keeping constant) compared to other activity proxies. The filling factor–rotation period relation favors poleward migration of active regions as the explanation for supersaturation, rather than coronal stripping. With the dramatic increase in stellar flares detected by missions like TESS and the upcoming Earth 2.0 satellite, $t_{\rm{w, med}}$ will become a powerful diagnostic for probing stellar magnetic activity and underlying physics.
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All authors Henggeng Han, Song Wang, Chuanjie Zheng, Cunshi Wang, Xue Li, Jifeng Liu

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

Linking high-mass X-ray binaries to binary compact object mergers in Milky Way-like galaxies

Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti et al. (+5 more)

High-mass X-ray binaries (HMXBs) constitute a potential intermediate phase connecting massive stellar binaries to the formation of coalescing binary compact objects (BCOs). Yet, the specific circumstances that allow HMXBs to later develop into merging BCOs are still under debate. In this study, we focus on wind-fed HMXBs and investigate this link by generating synthetic catalogs with the population-synthesis code SEVN and assigning them to a sample of 66 Milky Way-like galaxies. Using stellar particles drawn from the TNG50 cosmological simulation, we assign HMXBs according to particle mass, age, and metallicity, and follow their subsequent evolution to BCOs. In this way, our approach provides a realistic framework for modelling HMXBs in the Milky Way by explicitly accounting for the varied metallicities and spatial distributions of binary systems. Our method recovers the spatial distribution inferred from the observed properties of Galactic HMXBs: their positions follow the spiral arms and agree with the measured radial profile. The age distribution aligns well with observations and shows that BH-HMXBs tend to be younger than NS-HMXBs. We find that the fraction of HMXBs that evolve into merging BCOs within a Hubble time for BH-HMXBs is ~0.2-3.2% (or ~0.3-5.4% when restricting to 10^35 <= L_X <= 10^40 erg s^-1), while for NS-HMXBs is ~3.6-23.4% (or ~3.5-26.0% with the same luminosity cut). We show that common envelope (CE) episodes and natal-kick magnitudes are the primary processes determining the number of merging systems. Successful BCO mergers are typically produced by systems that experienced significant orbital hardening (early CE), whereas stable mass transfer often yields wide, non-merging binaries unless extreme eccentricities are induced by kicks. Metallicity plays a secondary but important role by modulating compact-remnant masses and wind-driven orbital widening.
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All authors Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti, Gaston Escobar, Giuliano Iorio, Ankit Kumar, Boyuan Liu, Michela Mapelli

Monday 24 August

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

The Role of the Core in Setting Massive Neutron-Star Radii

R.V. Lobato, J.E. Horvath and M. Malheiro

Recent observations by the Neutron Star Interior Composition Explorer (NICER) indicate that the massive pulsar PSR J0740+6620 ($2.08\,M_{\odot}$) has a radius comparable to those inferred for stars near $1.4\,M_{\odot}$, as shown by PSR J0030+0451 and updated analyses. Such near-vertical mass-radius behavior is difficult to obtain unless the high-density equation of state (EOS) stiffens strongly. We show that, for massive pulsars, the leading radial scale can be set by a relativistic, high-sound-velocity core beginning near twice the nuclear saturation scale, while the outer low-density layer, comprising the true crust and outer core, supplies only a subdominant correction. The key evidence comes from radius decomposition: replacing the low-density branch below the matching point with unified EOS models spanning a factor of two in transition pressure changes the $2.08\,M_{\odot}$ core radius by only $\sim160$ m, about half the variation of the total radius. This convergence is genuinely a high-mass phenomenon: at $1.4\,M_{\odot}$ the core radius remains more branch-sensitive, varying by about $0.5$ km. Fixed-fraction comparisons confirm that core dominance emerges systematically as the star grows more massive, where the traditional separation between “radius physics” and “maximum-mass physics” breaks down. We establish this picture by combining analytical Tolman VII profiles and thin-crust matching, numerical Tolman-Oppenheimer-Volkoff integration with a piecewise EOS, and direct-grid Bayesian inference using NICER and GW170817 constraints under causal and mass-support filters. Data modestly constrain the transition stiffness but leave the quadratic stiffening governed mainly by causality. A comparison with a constant-sound-speed core remains inconclusive: both descriptions produce comparable core-dominated radii, leaving a degeneracy that sub-kilometre radius measurements can break.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

An Evolving Cosmic Shoreline and Sandbar Bounding the Rocky Airless Valley

Barron K. Nguyen, Laura K. Schaefer, Xuan Ji et al. (+7 more)

Recent JWST observations challenge the traditional 'cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial planets around M dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated 'cosmic sandbar' and a cooler, escape-regulated 'cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by tidal heating from secular eccentricity excitation in multi-planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M stellar types as a function of volatile inventory, planetary mass, age, and tidal heating. Lava worlds with thick atmospheres are unlikely around stars cooler than K-type unless sustained by extreme tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.
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All authors Barron K. Nguyen, Laura K. Schaefer, Xuan Ji, Christopher A. Theissen, Fei Dai, Bo Peng, Yao Tang, Andrea Zorzi, Michelle Hill, Megan Weiner Mansfield

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

An analysis of the Herbig star population and their protoplanetary disks within 1 kpc

L. M. Stapper, M. Vioque, A. J. Winter et al. (+6 more)

Herbig stars are intermediate mass pre-main sequence stars of 1.5 to $\sim15$~M$_\odot$ and are in between low and high-mass star formation. This work provides a catalog of all 243 known bona-fide Herbig stars with clear infrared excess and in many cases accretion signatures within 1~kpc. It contains archival, recalibrated, and newly derived stellar parameters, accretion rate properties, and disk dust mass measurements. We derive the latter by using newly obtained millimeter photometry and literature values. We find that 50% of Herbig dust disks are more massive than 10~M$_\oplus$, while this is only true for 20% and 5% of the T~Tauri disks in Lupus and Upper~Scorpius respectively. Furthermore, the Herbig disk dust mass distribution is bimodal, it consists of a high and low disk mass population with a mean dust mass of 21~M$_\oplus$ and 0.45~M$_\oplus$ respectively. We find that the catalog is near complete for within 300~pc, however, this decreases to 24% out to 1~kpc. We observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10~M$_\oplus$) disks to occur at $\sim$1-2~M$_\odot$ stars, coinciding with the peak in occurrence rate of giant exoplanets. The small number of Herbig stars with low accretion rates ($<10^{-8}$~M$_\odot$~yr$^{-1}$) or low disk dust masses ($\lesssim1$~M$_\oplus$), combined with the lack of an age dependence in the disk dust mass distribution, suggests that the observed Herbig star population represents the surviving disk-hosting phase in the optically visible late stages of intermediate-mass star formation. We argue that this is either due to the formation of deep dust traps in these disks or replenishment by late-infall, or a combination of the two.
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All authors L. M. Stapper, M. Vioque, A. J. Winter, D. J. Wilner, J. P. Williams, M. Benisty, A. S. Booth, S. L. Grant, M. R. Hogerheijde

Solar and Stellar Astrophysics

Periodic activity on the (sub)mm surface of the AGB star Mira A

M. Andriantsaralaza, B. Bojnordi Arbab, W. Vlemmings et al. (+7 more)

Evolved stars on the asymptotic giant branch (AGB) lose mass through stellar winds launched from their dynamic extended atmospheres. Recent high-angular-resolution observations of the archetypal AGB star Mira A (o Ceti) have revealed compact hotspots on its submillimetre (submm) surface, whose origin remains unclear. We aim to characterise the submm photosphere of Mira A and investigate the properties and temporal behaviour of the compact hotspots detected on its surface. We analysed 19 epochs of high-angular-resolution observations obtained with the Atacama Large Millimetre/submillimetre Array in Bands 4, 6, 7, and 9, ranging from 134.34 to 669.25 GHz. The complex visibilities were fitted with parametric models to derive the flux density, size, morphology, and brightness temperature of the stellar disc and an additional more compact component across multiple pulsation phases and observing frequencies.Our results show that the flux density of the stellar disc increases with frequency while its apparent size decreases, in agreement with the expected stratified radio photosphere. In Band 6, both the flux density and the size of the stellar disc vary with pulsation phase, reaching maximum values close to optical maximum light and decreasing toward minimum light. Compact hotspots are detected in Bands~6 and 7 near maximum light, with their brightness temperatures exceeding those of the stellar disc by several thousand kelvins, reaching T>8600 K in Band 6. They are highly energetic and persist on timescales of weeks but evolve over longer timescales, showing changes in both position and intensity. Hotspot activity appears to occur repeatedly across multiple pulsation cycles and may be linked to strong shocks, magnetic activity, and/or episodic mass ejections, and could therefore play an important role in the mass-loss process in AGB stars.
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All authors M. Andriantsaralaza, B. Bojnordi Arbab, W. Vlemmings, T. Khouri, L. Planquart, J. Alcolea, E. Humphreys, S. del Palacio, M. Wittkowski, K. T. Wong

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

Sub-Millisecond Pulsars: Missing or Impossible?

T.M. Tauris, V. Venkatraman Krishnan, R. Senzel et al. (+7 more)

The minimum spin period attainable by a neutron star has been debated since the discovery of the first millisecond pulsar in 1982. A neutron star rotating faster than 1 ms would have far-reaching implications for the dense-matter equation of state, gravitational-wave emission, and the physics of accretion and spin-up. Yet despite the discovery of over 700 millisecond pulsars with spin periods between 1.4 and 10 ms, no sub-millisecond pulsar has been identified. Here we review the physical and observational constraints governing the formation, survival, and detectability of ultra-fast neutron stars. We discuss physical constraints imposed by the neutron star equation of state and their implications for the minimum attainable spin period, and we summarise gravitational-wave emission from both accreting and rotation-powered millisecond pulsars. We argue that sub-millisecond spins are not primarily excluded by equilibrium spin limits, magnetospheric physics, or selection effects, but instead by a combination of inefficient recycling, short mass-transfer lifetimes in the most favourable binaries, and rapid post-formation spin-down unless magnetic fields are exceptionally weak. Together, these effects make sub-millisecond pulsars intrinsically rare. If they exist at all, they are most likely to be detected transiently during accretion, rather than as long-lived radio pulsars. Finally, we show that stellar-mass black holes can attain sub-millisecond horizon spin periods, reflecting fundamentally different spin constraints.
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All authors T.M. Tauris, V. Venkatraman Krishnan, R. Senzel, P.C.C. Freire, S.M. Ransom, A. Papitto, C.A.N. Biscio, N. Langer, E.P.J. van den Heuvel, M. Kramer

Solar and Stellar Astrophysics

A giant magnetic eruption from the asymptotic giant branch star Mira A

W. Vlemmings, M. Andriantsaralaza, B. Bojnordi Arbab et al. (+14 more)

Mass loss during the advanced evolutionary stages of low- and intermediate-mass stars is traditionally attributed to dust-driven winds, whereas the influence of magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB) star Mira~A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO $v=1$, $J=5\rightarrow4$ maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that magnetic eruptions can dominate mass loss from evolved stars and imply that magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.
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All authors W. Vlemmings, M. Andriantsaralaza, B. Bojnordi Arbab, T. Khouri, B. Lankhaar, L. Planquart, E. De Beck, S. Del Palacio, E. Humphreys, D. Jadlovsky, M. Maercker, H. Olofsson, M. Saberi, M. Siebert, R. Unnikrishnan, S. Wedemeyer, M. Wittkowski

Solar and Stellar Astrophysics

Agentic Active Learning Meets Visual Embeddings: Finding Anomalies among 370 000 Variable Stars from ASAS-SN

Milan Pesta and Yuan-Sen Ting

Unusual light-curve morphologies can point to rare physical configurations or new phenomena, but automatic searches for anomalies are often dominated by artifacts. Separating genuine anomalies from false positives has traditionally required manual vetting, which does not scale to modern surveys. We present an active learning framework for detecting anomalies in samples of periodic variable stars, with the vetting delegated to multimodal large language model agents. The initial ranking comes from isolation forests trained on DINOv2 ViT-g/14 embeddings of phase-folded light curves. The agents iteratively review the light-curve images of the top-ranked candidates and assign relevance scores, which are propagated through the embedding space to prioritize the next targets. A logistic regression step then extends the search beyond label propagation, and a multi-agent consensus review filters false positives. Using Gemini~3 Flash agents, we applied the pipeline to $373\,646$ periodic variables from ASAS-SN Sky Patrol V2.0. Across $51$ iterations, the agents labeled ${\sim}1\%$ of the sample in roughly $3$ hours at a cost of ${\approx}$ $$40$, yielding our final catalog of $24$ anomalies ($18$ newly reported) and $153$ potentially interesting objects. The anomalies include eclipsing binaries with extremely deep primary eclipses, high-amplitude contact binaries and pulsators, and a symbiotic nova in outburst for over two decades. At the same labeling budget, the initial ranking would have recovered only $30%$ of our catalog, while reaching its lowest-ranked anomaly would have required ${\sim}70$ times the budget. These results demonstrate the feasibility of agentic active learning for anomaly detection in existing and upcoming photometric surveys.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Signatures of Compact Object Mergers Inside Stars in AGN Disks

Matteo Cantiello, Alexander J. Dittmann, Saavik Ford et al. (+4 more)

Disks of gas accreting onto supermassive black holes, powering active galactic nuclei (AGN), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. The dense, hot disk environment can drive rapid accretion onto embedded stars, dramatically altering their evolution. Models predict that, for sufficiently rapid accretion, fresh gas replenishes hydrogen in stellar cores as quickly as it is burned, and the stars reach a quasi-steady state. Here we study encounters of such massive, long-lived (”immortal”) stars with compact objects in AGN disks. We estimate the encounter rate and the timescale for a single compact remnant to spiral into an AGN star; depending on how strongly feedback regulates the ensuing accretion, the star is either consumed in a collapsar-like, engine-driven transient or converted into a long-lived, quasi-star-like object hosting a central black hole. We then study the merger of a binary black hole (BBH) inside the AGN star, and show that gas drag hardens the binary to merger far faster than gravitational-wave emission alone. The resulting merger is a loud LIGO-Virgo-KAGRA (LVK) source, but the characteristic imprint of the dense environment -a strong suppression and dephasing of the inspiral relative to vacuum- falls in the deci-Hz band rather than the milli-Hz LISA band, and is best resolved by next-generation detectors such as DECIGO. We estimate that this channel could contribute a BBH merger rate of up to $\sim8\,{\rm Gpc^{-3}\,yr^{-1}}$ in favorable scenarios, and discuss the model uncertainties and directions for future work.
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All authors Matteo Cantiello, Alexander J. Dittmann, Saavik Ford, Barry McKernan, Carlos Palenzuela, Rosalba Perna, Taeho Ryu

Solar and Stellar Astrophysics

Solar-Cycle Variation of Newly Emerging Coronal Holes during Solar Cycle 24

Akash Vinod Shirke and Khagendra Katuwal

Coronal holes (CHs) are regions of predominantly open magnetic field and important sources of high-speed solar wind streams. We present a manually compiled catalogue of newly emerging CHs during Solar Cycle 24 (2010-2019), identified from daily CHIMERA maps provided by SolarMonitor. Unlike existing area-based catalogues, our dataset tracks the daily emergence of new CHs in northern, southern, and equatorial latitude zones. The emergence rate of equatorial CHs is anti-correlated with the International Sunspot Number (Pearson r = -0.523, p = 6.2 x 10^-9), indicating reduced formation of low-latitude CHs near solar maximum. The hemispheric asymmetry of CH emergence is also anti-correlated with the hemispheric asymmetry of sunspot activity (r = -0.461, p = 5.2 x 10^-7), suggesting that new CHs preferentially emerge in the hemisphere with lower sunspot activity. The total CH emergence rate is lowest near solar maximum and highest during the declining phase. These results provide new observational constraints on the evolution of open magnetic flux over the solar cycle.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Preparing for the Early eVolution Explorer: The Impact of Flare Temperature on Ozone Column Depth in Earth-Like Atmospheres

Jaime S. Crouse, Nicholas F. Wogan, Ward S. Howard et al. (+4 more)

Atmospheric photochemical models incorporating the impacts of stellar flares often assume a $\sim$9,000 K spectrum at ultraviolet-optical wavelengths. Recent multiwavelength observations, however, reveal a more complex picture with temperature measurements spanning 4,000-40,000 K, although the occurrence rates for flares with different temperatures remain unknown. Here, we model the evolution of a Proterozoic Earth-like world with 0.01 bar of O$_2$ under repeated flaring to identify the impact of flare effective temperatures. We explore four scenarios - two host star types (K2V and M2.5V) and two flare temperatures (9,000 K and 19,000 K) - selected to bound the potential parameter space. The hotter flares have a larger impact on O$_3$ photochemistry for both stellar types. M-star planetary atmospheres are more volatile and exhibit rapid changes in their O$_3$ production and destruction rates. Meanwhile, K-star planetary atmospheres are more stable and are only impacted by the hottest flares, proving advantageous for biosignature searches. We simulate 0.2-1.0 $\mu$m reflected light spectra for all four scenarios, and find that 19,000 K flares can result in either production or destruction of O$_3$ depending on the host star spectral type increasing the 0.2 $\mu$m feature by $\sim$2$\times$ for the K2V star but decreasing it by 50% for the M2.5V star. Future missions such as the EVE SMEX mission concept will provide robust flare temperature constraints for young FGKM stars, which will serve as inputs to improve photochemical models to inform future HWO observations.
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All authors Jaime S. Crouse, Nicholas F. Wogan, Ward S. Howard, Meredith A. MacGregor, Guadalupe Tovar Mendoza, Jacob Lustig-Yaeger, Evgenya L. Shkolnik

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

The ALMA EGO-10 Survey of Massive Protoclusters: Correlation of 1.3 mm Continuum Source Clustering with Evolutionary State

Michael C. Logue, Claudia J. Cyganowski, Crystal L. Brogan et al. (+4 more)

Massive stars characteristically form in clustered environments. Characterising young massive 'protoclusters' is therefore crucial to constraining the mechanism(s) of massive star formation, and of the assembly of stellar clusters. We present 1.3 mm continuum results from the ALMA EGO-10 imaging survey, targeting ten Spitzer GLIMPSE Extended Green Objects (EGOs) - massive protostars with active outflows traced by extended 4.5 $\mu$m emission. Our sensitive 1'.6$\times$1'.6 mosaics reveal rich protoclusters associated with all targets. With a mean spatial resolution 2200$\times$1600 AU, we identify 570 cores - between 13 and 135 per field. We quantify protocluster structure with the $Q$-parameter, finding structural diversity with 0.5 $\lesssim Q \lesssim$ 0.9. The sample is notable for the wealth of complementary high-resolution multiwavelength data available. Correlating our cores with these observations, we find only 2%, 5% and 4% of cores host 6.7 GHz CH$_3$OH masers, 22 GHz H$_2$O masers and cm-$\lambda$ continuum sources, respectively. The massive protostars traced by 6.7 GHz masers typically reside near protocluster centres (median offset 0.045 pc), and all at $d<$ 3 kpc are found in clustered locales, with $>$10 cores within 10,000 AU. Using VLA cm-$\lambda$ continuum observations, we construct a new evolutionary indicator: the ratio of protocluster cm-$\lambda$ continuum luminosity to the mass of the associated ATLASGAL clump ($L_\text{cm}/M_\text{AGAL}$). This ratio correlates positively with $Q$, with the correlation driven primarily by the cm-$\lambda$ continuum emission from MYSOs. This suggests dynamic protocluster structure, evolving from subclustered to centrally condensed, consistent with the global collapse in hierarchical, clump-fed models of massive star formation.
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All authors Michael C. Logue, Claudia J. Cyganowski, Crystal L. Brogan, Todd R. Hunter, Alessio Traficante, Allison P. M. Towner, Stella S. R. Offner

Solar and Stellar Astrophysics

BLG723.31.34651 as an eclipsing Roche lobe-filling sdOB+WD binary

Alekzander Kosakowski, Charles E. Derbyshire, Sydney Jetton et al. (+1 more)

We present a detailed observational analysis of BLG723.31.34651, the fourth reported eclipsing member of the class of Roche lobe-filling hot subdwarfs, using time series spectroscopy and multi-band photometric observations from the Goodman High Throughput Spectrograph on the 4.1-m SOAR telescope. Our light curves show periodic photometric variability at $P=64~{\rm min}$ from the tidally-deformed hot subdwarf donor and deep eclipses of the donor by an opaque accretion disc. We report two light curve model solutions that agree with each other to within $2\sigma$, both suggesting that BLG723.31.34651 contains a typical hot subdwarf donor, a white dwarf accretor, and an irradiated opaque accretion disc. Our spectroscopic analysis identifies statistically significant phase-dependent variations in the effective temperature and surface gravity coinciding with the phase-dependent variations seen in our observed light curves. We attribute these variations to a combination of intrinsic variations in local atmospheric parameters due to tidal deformation of the donor and unmodeled spectroscopic flux contributions from an accretion disc.
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All authors Alekzander Kosakowski, Charles E. Derbyshire, Sydney Jetton, Brad N. Barlow

Solar and Stellar Astrophysics

Breakout/Interchange Reconnection as a driver of Jets, Fast CME, and Solar Energetic Particles

Pankaj Kumar, Judith T. Karpen, David Lario et al. (+4 more)

Understanding how energetic particles are accelerated and released from the low corona into the interplanetary medium during solar eruptions is crucial for space weather research. Here, we present multiwavelength observations of a solar eruption that are consistent with breakout reconnection playing an important role in driving a fast coronal mass ejection (CME) and the associated solar energetic particle (SEP) event. Extreme-ultraviolet and radio observations reveal evidence of breakout reconnection within a fan-spine topology. The filament eruption begins after the pre-eruption opening, accompanied by quasiperiodic jets and associated downflows near the null point, as well as recurrent faint Type III radio bursts during the ongoing slow breakout reconnection. Furthermore, the observations also reveal the formation of pre-eruption coronal rain via slow interchange reconnection near the null point. A large-scale circular ribbon, along with simultaneous four hard X-ray footpoint sources and intense Type III radio bursts, was observed during the explosive breakout reconnection that enabled opening of field lines and allowed energetic particles to escape into interplanetary space. In situ measurements by PSP and Wind confirm the prompt injection of electron beams consistent with the timing of the explosive breakout reconnection. A fast shock associated with the erupting flux rope during interchange reconnection played a major role in producing the gradual SEP event. These observations highlight the key role of breakout reconnection in producing a fast CME/shock with the SEP release and acceleration process. These results have broader implications for particle acceleration and release processes in multiscale null-point topologies, which produce a continuum of eruptions ranging from small-scale jets to large-scale CMEs.
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All authors Pankaj Kumar, Judith T. Karpen, David Lario, Benjamin J. Lynch, Peter F. Wyper, Spiro K. Antiochos, P. K. Manoharan

Solar and Stellar Astrophysics

Preparing for the Early eVolution Explorer: Photometric Diagnostics of Magnetospheric Accretion Geometry in Young Stellar Objects

Laura Venuti, Connor E. Robinson, Ann Marie Cody et al. (+13 more)

The inner disk truncation radius, $R_T$, plays a crucial role in the regulation of star-disk interaction and the early evolution of star-disk-planet systems; however, measuring this parameter is observationally challenging. We present a new method for determining $R_T$ in young accreting systems that hinges on the color dependence of the accretion shock emission in multi-band time-domain surveys. Based on the accretion simulations of Robinson et al. (2017, 2021), we produce synthetic color-magnitude diagrams at near-UV and optical wavelengths that predict the loci of accreting stars as a function of $R_T$. We test these model predictions on young stars with interferometric $R_T$ estimates, finding very good agreement in our results. We apply this novel technique to a pilot survey of 26 classical T Tauri stars in Taurus and Upper Scorpius. We find a predominance of sources with small truncation radii, $R_T < 4\ R_\star$, and an overall distribution of $R_T$ that is statistically similar to that inferred from interferometric studies, while differing from those inferred from emission line modeling. Finally, we discuss the application of this technique to NASA's mission concept EVE, with the goal to provide simultaneous measurements of inner disk truncation radii, corotation radii and mass accretion rates for hundreds of young stars across the Galaxy. The unprecedented survey of inner disk properties that the mission would produce would enable the first stringent test of angular momentum evolution theories in young stars and reveal the impact of the inner disk conditions on early planet architectures.
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All authors Laura Venuti, Connor E. Robinson, Ann Marie Cody, Eric Gaidos, Meredith A. MacGregor, Neal J. Turner, Mark R. Swain, George Zhou, Sydney Vach, Lukas Gehrig, Christopher M. Johns-Krull, Zhaohuan Zhu, Jennifer A. Burt, Ward S. Howard, Damon Landau, Evgenya Shkolnik

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

Potential sublimating exocomets around the young star PDS 70

Aline Novais, H. Jens Hoeijmakers, Alexandra Stockwell Murphy et al. (+4 more)

Recent observations by the James Webb Space Telescope (JWST) have indicated the presence of water in the inner regions of the disc around the young protostar PDS 70, but the origin of this water remains unclear. Here we report the discovery of variable absorption lines of neutral sodium in archival High Accuracy Radial velocity Planet Searcher (HARPS) spectra of PDS 70. These lines vary strongly and stochastically on a daily basis, in amplitude, number, and radial velocity. Our measurements indicate that this gas tends to be optically thick, and partially cover the stellar disc, meaning this fast-moving gas is often spatially confined. We explore several hypotheses for the origin of these lines, and conclude that a likely source of the observed sodium is sublimation of planetesimals that transit the star on highly elliptical orbits, reminiscent of the exocomet phenomenon seen in other seen in other extrasolar systems. These sublimating exocomets could play a role in sourcing the previously observed water in the inner, terrestrial-planet forming region of the PDS 70 system.
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All authors Aline Novais, H. Jens Hoeijmakers, Alexandra Stockwell Murphy, Bibiana Prinoth, Anders Johansen, Klaudia Jaworska, Luan Ghezzi

Solar and Stellar Astrophysics

Solar chemical composition

A. M. Amarsi and N. Grevesse

The Sun is one of the fundamental benchmarks in astronomy, and there is ever growing interest in precise and accurate determinations of its chemical composition. We present the current state-of-the-art in spectroscopic determinations of the solar elemental abundances, that now routinely employ three-dimensional (3D) radiative-hydrodynamic simulations of the solar photosphere and post-processing in non-local thermodynamic equilibrium (non-LTE). We critically review the recent literature and present recommended present-day and protosolar abundances of the 83 long-lived elements, and discuss their implications vis-à-vis primitive meteorites, helioseismology, neutrino fluxes, and the Solar Modelling Problem.
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