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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Tuesday 1 September

Solar and Stellar Astrophysics

A wavelet-based model of magnetic turbulence over a Parker spiral field

Andrea Larosa, Francesco Pucci, Francesco Malara et al. (+7 more)

The propagation of Solar Energetic Particles (SEPs) through the heliosphere is strongly influenced by solar-wind magnetic turbulence, which governs particle scattering, field-line wandering, and cross-field transport. These processes shape SEP intensity profiles, anisotropies, and arrival times. Because heliospheric turbulence spans a vast range of scales, direct numerical simulations cannot capture its full spectrum. Synthetic turbulence models provide an efficient alternative by generating fields with prescribed statistical and spectral properties, enabling realistic studies of SEP transport. This work presents a numerical model able to generate synthetic magnetic turbulence in the heliosphere with the goal of studying field line and particle diffusion. The model is inspired by in situ solar wind observations, indicating that solar wind turbulence properties vary with the distance from the Sun. We extend the Cartesian wavelet-based Synthetic Turbulence Model (STM), presented in \cite{Malara2016PhRvE..94e3109M}, to the non-homogeneous expanding solar wind. This is achieved by finding a suitable change of coordinates that allows one to pass from a space in which the turbulence correlation length is homogeneous to one in which it is not. We present the analytical derivation, the numerical implementation, and testing. We obtain an improved and computationally efficient synthetic turbulence model characterized by a background Parker spiral, a broad inertial range and tunable radial scalings for both the correlation length and the magnetic-field fluctuation amplitude, as well as a controllable level of intermittency. The model capability of reproducing solar wind turbulence up to the particle Larmor scale and to take into account solar wind radial evolution makes it a powerful tool to study the propagation of SEPs throughout the heliosphere.
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All authors Andrea Larosa, Francesco Pucci, Francesco Malara, Oreste Pezzi, Silvia Perri, Gaetano Zimbardo, Giuseppe Nisticò, Federica Chiappetta, Massimo Chimenti, Luca Sorriso-Salvo

Solar and Stellar Astrophysics

Integrated Mass Loss for Very Metal-poor Stars: Asterosesimic Red Giant Masses of K2 Globular Cluster NGC 5897

Csilla Kalup, László Molnár, Madeline Howell et al. (+2 more)

Mass loss in low-mass stars during the red giant branch (RGB) and early asymptotic giant branch (EAGB) phases plays a key role in shaping stellar evolution, yet its dependence on stellar parameters such as metallicity remains poorly constrained, with observational studies yielding conflicting trends. We present the first asteroseismic analysis of RGB and EAGB stars in NGC 5897, the most distant and metal-poor globular cluster observed by the Kepler space telescope during the K2 mission. We detected solar-like oscillations and derived the frequency of maximum power excess, $\nu_{\rm max}$, for 20 RGB and 6 EAGB stars. Using asteroseismic scaling relations, we derived mean masses of $\overline{M}_{\rm RGB} = 0.74\pm0.01\,M_{\odot}$ and $\overline{M}_{\rm EAGB}=0.65\pm 0.03\,M_{\odot}$. The inferred integrated mass loss between the two phases is $\Delta M_{\rm RGB-EAGB}=0.08\pm 0.03 \,M_{\odot}$. We present an updated mass-loss–metallicity relation for Type I globular clusters, extending it to the very metal-poor regime and supporting decreasing integrated RGB mass loss with decreasing metallicity.
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All authors Csilla Kalup, László Molnár, Madeline Howell, Attila Bódi, András Pál

Solar and Stellar Astrophysics

Archival transients detected with the MeerLICHT telescope I: Supernovae

O.Mogawana, P.J. Groot, N. Blagorodnova et al. (+9 more)

Wide-field optical transient surveys collectively discover $\sim$50 new transients per night, making rapid, multi-filter and/or spectroscopic follow-up of all but the most exceptional events unfeasible. Consequently, the (early) light-curve properties of most supernovae (SNe), particularly sub-luminous events, are often poorly characterised. Here, we showcase recovery of key parameters by combining publicly available data from multiple, contemporaneous surveys. We built a catalogue of $125$ SNe by cross-matching the MeerLICHT (ML) transient survey with the Transient Name Server list of spectroscopically classified SNe detected between August 2017 and October 2022. For a subset of $14$ SNe with good multi-survey photometric coverage, we combined ML-$q$, ZTF-$g,r$, and ATLAS-$c,o$ data to construct composite early-time light curves. We then applied an expanding fireball ($t^2$) model to constrain their explosion dates and rest-frame rise times. We find that this simple model provides a reliable description for the early emission of most SNe in our sample and successfully constrains their rise time, a key parameter for characterising SN categories and probing progenitor origins. This multi-survey approach, only using standard survey products, provides a powerful method to characterise large numbers of SNe that would otherwise be lost, a technique that will be essential for maximising the scientific return from current and future surveys such as GOTO, BlackGEM, the Vera C. Rubin Observatory's LSST, and Global Open Transient Telescope Array (GOTTA).
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All authors O.Mogawana, P.J. Groot, N. Blagorodnova, P.M. Vreeswijk, D.L.A. Pieterse, S. Bloemen, G. Leloudas, R.A.D. Wijnands, D. A. H. Buckley, P. A. Woudt, R. Fender, B. W. Stappers

Solar and Stellar Astrophysics

Fundamental effective temperature measurements for eclipsing binary stars - IX. Characterisation of 5 solar-type sclipsing binaries with M-dwarf companions

Axel Hahlin, Pierre F.L. Maxted, Ivanna Hernandez-Araya et al. (+2 more)

Large-scale spectroscopic surveys will need suitable benchmark stars that can be used to verify the performance of automatic pipelines. A promising type of object for this purpose is the detached eclipsing binary (DEB) containing an FG-star and a low temperature companion. For flux ratios $\lesssim1$~per~cent, the spectra obtained for the binary will be almost identical to a single star. As the methods for obtaining accurate parameters for binaries are well established, they would be excellent benchmark candidates. We analyse a group of DEBs with M-dwarf companions using TESS light curves and high resolution spectroscopy from NIRPS and HARPS on the ESO 3.6-m telescope. We obtain accurate fundamental parameters for the stellar components. The secondary component is visible with cross-correlation, allowing them to be characterised as well. With the stellar parameters obtained from the analysis, we can measure precise effective temperatures from Gaia parallaxes and archival magnitude data. Chemical compositions of the primary stars are also extracted from the stellar spectra. In this analysis, the secondary components have minimal impact on determined spectroscopic parameters. Our radii and masses are characterised to within sub per~cent precision as well as our primary effective temperatures. Beyond a new set of stellar benchmarks, the secondary components analysed in this work represent a well characterised sample of M-dwarf stars which will be useful to improve our understanding of low mass structure and evolution.
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All authors Axel Hahlin, Pierre F.L. Maxted, Ivanna Hernandez-Araya, Natasha Adshead, Claudia Aguilera-Gomez

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

Superfluidity and Vortex Dynamics in Neutron Stars

Bennett Link and Armen Sedrakian

Neutron stars contain several forms of quantum condensed matter whose microscopic properties control macroscopic rotational dynamics and magnetic behavior of these fascinating objects. This review surveys superfluidity and superconductivity in compact stars, with emphasis on phenomena associated with quantized vorticity and magnetic-flux structures, and the possible connections to observed phenomena. We first summarize the microphysics of nucleonic pairing, including spin-singlet $^1S_0$ neutron pairing in the inner crust, proton superconductivity in the outer core, and spin-triplet $^3P_2$–$^3F_2$ neutron pairing at higher densities, together with the principal many-body uncertainties affecting the corresponding pairing gaps. We then discuss the dynamics of neutron vortices, including pinning, vortex creep, and dissipative motion, and the role of vortex dynamics in angular-momentum exchange between the superfluid and the observable crustal component. We give special attention to proton flux tubes in type-II superconducting cores, the possible realization of type-I superconductivity, and vortex–flux-tube interactions. We also review collective rotational phenomena, including Tkachenko oscillations of the vortex lattice and free precession, and their possible relation to long-term variability in pulsar timing. Finally, we discuss the possible deconfinement of hadronic matter into quark matter, the formation of color-superconducting phases, and the topological defects associated with these phases, together with their possible observational consequences. Throughout the review, we identify key open questions connecting microscopic pairing, mesoscopic defect dynamics, and observable neutron-star phenomena.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Exoplanets in star clusters

T. Broza and E. Paunzen

The field of exoplanetary research is rapidly evolving, thanks to TESS and Kepler/K2. With the latest data release, Gaia DR3, Gaia has transformed the study of star clusters. By combining the known properties of exoplanets and those of star clusters, in which they are found, it is possible to study the planets in greater detail and test theories of planetary evolution. We aim to create a catalogue of Gaia IDs for known exoplanets and use it to link the planets to a catalogue of star clusters. We utilised the NASA Exoplanet Archive and the Extrasolar Planets Encyclopaedia to compile a catalogue of known exoplanets. We then cross-matched the data with Gaia DR3 sources to obtain the Gaia IDs of the exoplanets. Using this information, we inferred the potential association of these exoplanets with star clusters. We described the statistical properties of these exoplanets. We compiled a catalogue of Gaia IDs for known exoplanets and identified those associated with star clusters. This resource facilitates detailed studies of exoplanet properties and their evolutionary contexts within stellar clusters.
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Solar and Stellar Astrophysics

Revisiting candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud

W. Narloch, C. Galan, G. Pietrzynski et al. (+5 more)

We analyzed photometric and spectroscopic data for 11 candidates for non-pulsating stars located in the Cepheid instability strip (IS) of the Large Magellanic Cloud (LMC) in order to investigate the reasons for the lack of pulsations. We used available temperature calibrations based on photometric colors to estimate the effective temperatures of the candidates, which served as initial parameters for the spectroscopic analysis. We also applied surface brightness-color relations calibrated for Cepheid variables, giants, and supergiants to estimate stellar radii. The spectral analysis was performed using the spectral synthesis method to determine the atmospheric parameters; namely, the effective temperature, metallicity, surface gravity, microturbulent velocity, projected rotational velocity, and chemical abundances for up to ~30 elements. For most objects, only a single spectrum was available. However, no significant variations in radial velocities were detected among the stars with repeat observations; therefore, all stars were treated as single object in the analysis. Two stars exhibit broad spectral lines, which may indicate high rotational velocities or possible binarity; however, additional spectra are required to confirm this interpretation. One of these objects also shows asymmetric line profiles, which might be related to the presence of non-radial pulsation modes causing line-shape variations. A common feature among all analyzed candidates is an enhancement of barium-peak s-process elements compared to solar values. This may indicate past mass transfer from a companion during its post-asymptotic giant branch phase. This study provides an insight into the physical parameters of candidates for non-pulsating stars residing within the Cepheid IS in the LMC, although the lack of pulsations remains a mystery and challenges pulsation theory.
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All authors W. Narloch, C. Galan, G. Pietrzynski, B. Pilecki, W. Gieren, R. Smolec, H. Netzel, P. Wielgorski

Solar and Stellar Astrophysics

X-shooter survey Across Regions and Ages to probe Disk Evolution (ARADE): Accretion properties in Orion A and their relation with disk masses

Lara Piscarreta, Giacomo Beccari, Carlo Manara et al. (+10 more)

We present a homogeneous VLT/X-Shooter study of accretion in young stellar objects spanning the entire Orion A complex. Our sample includes 91 pre-main-sequence stars hosting a protoplanetary disk according to Spitzer photometry, of which 34 have complementary ALMA dust mass measurements. We derived stellar and accretion properties using a self-consistent multi-component fitting procedure. Our sample encompasses spectral types from K3 down to M5, corresponding to stellar masses within $\sim$0.8-0.1 $M_{\odot}$. The accretion-stellar luminosity ($L_{acc}-L_{\star}$) and the mass accretion rate-stellar mass ($\dot{M}_{acc}-M_{\star}$) scaling relations in Orion A are consistent with those of other star-forming regions (SFRs) that span a range of stellar densities, far-ultraviolet (FUV) irradiation fields, and ages, with all regions occupying the same locus in parameter space. For the 34 sources with complementary dust mass measurements, we present the first investigation of the $\dot{M}_{acc}$ and disk mass ($M_{disk}$) correlation in Orion A, recovering a spread consistent with that reported for other regions. Despite our sample spanning nearly five orders of magnitude in local FUV field strength, we find no statistically significant correlation between $\dot{M}_{acc}$ and FUV irradiation. However, by combining our sample with literature measurements in Lupus, the Orion Nebula Cluster, and $\sigma$ Orionis, we find a tentative population-level decrease of the inferred disk lifetime $t_{\rm disk} =M_{disk}/\dot{M}_{acc}$ toward stronger FUV environments, though large intrinsic scatter and limited sample sizes at intermediate and high FUV fields prevent firm conclusions. The homogeneous $\dot{M}_{acc}$ measurements reported here provide a solid foundation for future studies of accretion and disk evolution across the diverse environments of Orion A and other SFRs.
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All authors Lara Piscarreta, Giacomo Beccari, Carlo Manara, Rossella Anania, Sierk van Terwisga, Victor Almendros-Abad, Henri Boffin, Rik Claes, Aaron Empey, Barbara Ercolano, Tereza Jerabkova, Karina Maucó, Miguel Vioque

Solar and Stellar Astrophysics

Kinematic Relationship Between Solar Extreme Ultraviolet Waves and Type II Metric Radio Bursts

Ramesh Chandra, Apoorv Dashora, P. F. Chen et al. (+1 more)

Solar extreme-ultraviolet (EUV) waves are large-scale disturbances that manifest as bright wavefronts, often during coronal mass ejections (CMEs). According to the magnetic field line stretching model, this phenomenon comprises two components: a fast-mode CME piston-driven shock wave and a slower, nonwave component. They are often associated with solar type II radio bursts. It is expected the radio source and the fast-mode EUV wave should come from different parts of the same shock, i.e., the CME piston-driven shock, and their speeds should be strongly correlated. To investigate this relationship, we utilized high spatiotemporal resolution observations from the Solar Dynamics Observatory in conjunction with radio data from the Radio Solar Telescope Network. Our analysis reveals that there exists a linear correlation between the EUV fast-mode speeds ($v_{euv}$) and the shock speeds derived from metric (m) type II radio bursts ($v_{radio}$), which is $v_{radio}=0.89v_{euv}+51$ kms$^{-1}$, with a correlation coefficient of 0.77. This strong correlation suggests that original coronal EIT waves, which are about three times slower than type II radio bursts, are not fast-mode waves, and it is misleading to map type II radio bursts to EIT waves in the literature.
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All authors Ramesh Chandra, Apoorv Dashora, P. F. Chen, Pooja Devi

Solar and Stellar Astrophysics

On the photospheric abundances of the B-type fast rotator Regulus

Yoichi Takeda

A spectroscopic study of Regulus (late B-type rapidly-rotating star) was conducted with an aim of investigating its photospheric chemical abundances (especially for light elements), which has barely been challenged so far because of the considerable difficulty of abundance determination for such a very fast rotator (>~300 km/s). The atmospheric parameters were determined to be T_eff = 12345K (effective temperature) and log g = 3.58 (surface gravity) based on the spectral energy distribution, while the microturbulence was estimated as v_t = 0.5 km/s. The abundances of 14 elements (He, C, N, O, Ne, Mg, Si, S, Ca, Ti, Cr, Mn, Fe, and Ni) were derived by applying the spectrum-fitting technique, where the non-LTE effect was taken into account for lighter elements from He to Ca. The resulting relative-to-the-Sun abundances ([X/H]) revealed a remarkable trend that, while most elements indicate near-solar abundances (within +/-<~0.3dex), only C shows a marked deficiency ([C/H]~ -1.4) which is hard to explain. For example, a simple scenario of C underabundance caused by mixing of CN-cycled product (e.g., due to rapid rotation or binary mass transfer) is unlikely because any N enrichment is not observed. This problem remains yet to be further investigated.
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Solar and Stellar Astrophysics

The Influence of Evaporation on the Formation and Evolution of Huntsman Systems

Hao-Ran Yang, Shi-Jie Gao, Xiang-Dong Li et al. (+2 more)

Huntsman systems are a recently identified and rare subclass of millisecond pulsar (MSP) binaries, characterized by a detached neutron star and an evolved giant companion in relatively wide orbits. Their formation has been proposed to involve red-bump-induced detachment, whereas the influence of MSP-driven evaporation during this evolutionary stage has not yet been quantitatively assessed. We quantify the influence of MSP-driven evaporation on the formation and evolution of Huntsman systems and assess its effects on their observable properties. We performed detailed binary evolution calculations including MSP-driven evaporation over a wide range of initial binary parameters and combined them with binary population synthesis to predict the observable population of Huntsman systems. We find that Huntsman systems originate primarily from binaries undergoing Case B mass transfer and red-bump-induced detachment, with initial donor masses of $1.0-2.5\ M_\odot$ and orbital periods above the bifurcation period. Evaporation has a secondary effect, slightly modifying the orbital evolution and the duration of the detached phase, but does not significantly alter the formation parameter space or the expected population, which contains about 10 Huntsman systems. We further show that evaporation can produce systematic shifts in the white dwarf mass-orbital period relation at the low-mass end, leading to systematically wider final orbits for a given white dwarf mass.
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All authors Hao-Ran Yang, Shi-Jie Gao, Xiang-Dong Li, Yun-Lang Guo, Wen-Shi Tang

Solar and Stellar Astrophysics

Discovery of the First-Ever Recorded Fading Event of the Wolf-Rayet Star WR 59

Rod Stubbings

This paper presents the visual discovery of the first-ever recorded fading event of the Wolf-Rayet star WR 59. Historically documented as a stable star with an approximate magnitude of 13.9, the star underwent a sudden major decline during high-cadence visual monitoring in May 2021. On 11 May 2021 (JD 2459346), I observed the star plunge 1.3 magnitudes to a deep minimum of magnitude 15.2. It remained in this faded state for roughly 1 day before undergoing a structured 14-day recovery back to its baseline. This episode was independently verified by NASA's Transiting Exoplanet Survey Satellite (TESS) during Sector 38. The satellite's calibrated data stream confirms that the timing, structure, and recovery of the fade matched the ground-based observations. While a close 11.7 V companion star masked the true depth of the drop for automated large-pixel survey pipelines, this event firmly establishes WR 59 as an active dust-producing system. It demonstrates how high-magnification visual monitoring can successfully resolve crowded stellar fields.
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Monday 31 August

Solar and Stellar Astrophysics

SPIRITS 19q: Dust Production by a Subsolar-metallicity Carbon-rich Wolf-Rayet Star in NGC 2403

Sam Rose, Ryan M. Lau, Jacob E. Jencson et al. (+20 more)

We present JWST/NIRSpec IFU observations of SPIRITS 19q, the highly dust-producing carbon-rich (WC) binary candidate located in a subsolar-metallicity region of the nearby spiral galaxy NGC 2403. The observations, taken in April of 2024, confirm the association of a dusty outburst observed in 2019 by the Spitzer Space Telescope with an early-type WC star. Using models from the Potsdam Wolf-Rayet (PoWR) LMC model grid we find that the WC star of SPIRITS 19q likely has an especially high mass-loss rate ($\gtrsim$ 10$^{-4}$ $M_{\odot}$ yr$^{-1}$). From the flux peak of the IR transient as measured by Spitzer/IRAC as well as constraints on dust composition and size from the JWST spectrum, we estimate a total dust mass formed in the outburst of 6.6 $\pm$ 0.4 $\times$ 10$^{-6}$ $M_{\odot}$. Assuming a minimum orbital period of 12 years, this corresponds to a period-averaged dust production rate of $\lesssim$ 5.5 $\times$ 10$^{-7}$ $M_{\odot}$ yr$^{-1}$. These observations suggest that even a single WC system can contribute to the dust budget at subsolar metallicities, and that such systems are an important source of carbonaceous dust grains in the early universe.
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All authors Sam Rose, Ryan M. Lau, Jacob E. Jencson, Mansi M. Kasliwal, Andreas A.C. Sander, Howard E. Bond, Michael F. Corcoran, Izumi Endo, Matthew J. Hankins, Olivia C. Jones, Viraj R. Karambelkar, Astrid Lamberts, Thomas Madura, Anthony F.J. Moffat, Patrick W. Morris, Takashi Onaka, Michael E. Ressler, Noel D. Richardson, Christopher M. P. Russell, Itsuki Sakon, J. Sanchez-Bermudez, Gerd Weigelt, Peredur M. Williams

Solar and Stellar Astrophysics

Age Discrepancy in Three Galactic Cepheid Binaries

Sashwat Prasadh, Hilding R. Neilson and Nancy Remage Evans

SV Per, RW Cam, and KN Cen are Galactic classical Cepheids found in binary systems along with B-type companions. Each system exhibits an “apparent age discrepancy", where the Cepheid appears significantly younger than its companion. We compute stellar evolution tracks using the MESA code and compare them with these stars on the Hertzsprung-Russell diagram to estimate the masses and the corresponding ages. We find that, for two of the systems, the companions appear to be between 1.5 times to double the age of the Cepheids, suggesting that the Cepheids may be rejuvenated merger products of two main-sequence stars that have since evolved. We find that the third system KN Cen is consistent with single star evolution when we reevaluate ultraviolet observations and find that the companion is hotter than previously measured. We test this idea using the MESA code for each system by evolving a single star model and rapidly accreting mass on the main sequence to emulate a merger, and then continuing the evolution until the model is consistent with the parameters of the Cepheids. The results are consistent with the hypothesis that the Cepheids were originally merger products. We conclude with a discussion of potential observational tests of the merger hypothesis.
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Solar and Stellar Astrophysics

The Formation of Very Close Binary Stars

Maxwell Moe

The majority of very close binaries (orbital periods P < 5 days) are in triples. Previous studies surmised that the tertiary hardened the inner binary via Kozai-Lidov cycles coupled with tidal friction. Alternatively, the trend could be due to a common origin, e.g., more massive molecular cores and protostellar disks are more likely to fragment twice into a triple and harden the inner binary to very short periods via disk migration. Disk migration occurs during the embedded Class I protostellar phase while secular evolution with a tertiary occurs on much longer timescales. To determine the dominant migration mechanism, I accurately measure the very close binary fractions of both late-type and early-type primaries in star-forming environments. After combining five surveys, the late-type Class II/III T Tauri very close binary fraction is F_VCB = 2.1_{-0.5}^{+1.0}%, which is consistent with the measurement for late-type field main-sequence stars (1.7% +/- 0.1%). More than 85% of very close late-type binaries hardened via disk migration during the Class I protostellar phase. I next measure the OGLE-III eclipsing binary (EB) fractions of young massive stars in the LMC. The very close EB fractions of massive young stellar objects (YSOs; F_VCEB = 8.3_{-3.2}^{+4.9}%), OB stars near massive YSOs (4.7% +/- 0.8%), and OB stars in small, young H II regions (6.4% +/- 1.5%) are consistent with each other and the measurement for OB stars in slightly older clusters (4.7% +/- 0.3%). More than 90% of very close massive binaries hardened via disk migration during the embedded protostellar phase.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Where planetary solids survive sublimation around young and hot white dwarfs

Dimitri Veras, Keiji Ohtsuki, Rafael Martinez-Brunner et al. (+2 more)

All observed planetary systems orbiting single white dwarfs have lived through the hot stellar transition from an asymptotic giant branch star. In this post-nebular transition period, the initial conditions for planetary system evolution throughout white dwarf cooling are established. The hottest ($\gtrsim$ 20,000 K) and youngest ($\lesssim$ 20 Myr-old) white dwarf planetary system host stars differ significantly from their canonical older and colder counterparts by failing to support solid body accumulation in the immediate vicinity (a few $R_{\odot}$) of the white dwarf. Here, we analyse the likely locations of both solid-body survival and the sublimated gaseous content during this pivotal epoch, and the consequences. We find that (i) reservoirs of iron-rich, rocky and water-rich asteroids of radius $R$ that later observably enrich, or pollute, the white dwarf need to remain parked for the first tens of Myr of white dwarf cooling beyond critical distances of (16 au)$\times(1 {\rm km}/R)^{1/2}$ (for iron), (30 au)$\times(1 {\rm km}/R)^{1/2}$ (for rock) and (130 au)$\times(1 {\rm km}/R)^{1/2}$ (for snow), (ii) sublimation acts much more quickly than radiatively-driven orbital drifts from Poynting-Robertson drag or the Yarkovsky effect, and (iii) although large asteroids ($R \approx$ 10-1000 km) that are kicked on highly eccentric orbits around newly born white dwarfs could survive sublimation, they may fragment into debris which will sublime before the white dwarf cools. These results support, but do not necessitate, dynamical origin scenarios of polluted white dwarfs that feature delayed gravitational instability subsequent to the host star's asymptotic giant branch phase at Kuiper Belt-like distances, and beyond.
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All authors Dimitri Veras, Keiji Ohtsuki, Rafael Martinez-Brunner, Takato Nishio, Ryo Tamon

Solar and Stellar Astrophysics

Direct Measurement of Polar Coronal Hole-like Solar Wind in its Acceleration Phase

Samuel T. Badman, Yeimy J. Rivera, Michael L. Stevens et al. (+38 more)

The early evolution of fast polar coronal hole (PCH) solar wind remains largely unconstrained by in situ measurements. In March 2025, Parker Solar Probe (Parker) at its closest approach of 9.86 Solar Radii ($R_\odot$) measured outflow from a large equatorial coronal hole (ECH) which was also measured at 1\,au and at intermediate distances by Solar Orbiter (also near its perihelion). At 1\,au the stream properties are consistent with PCH properties established by Ulysses. The stream was measured by Parker substantially below the Alfvén surface, with proton temperatures in excess of 2\,MK and a speed at $\sim$10\,$R_\odot$ which was only $\sim$60% of its asymptotic value. The Solar Orbiter data indicates that the acceleration is largely complete by 60~$R_{\odot}$. Spherically-polarized fluctuations in the stream are observed to develop from near-transverse and small-angle at Parker to full reversal “switchbacks” at Solar Orbiter. Comparison of the implied acceleration profile to historical doppler-dimming measurements suggests that the stream's low coronal acceleration is similar to that of PCH flows. Consistent with previous work, this acceleration requires significantly more energy than can be provided by the observed thermal pressure gradients, with a significant contribution likely from the abundant Alfvénic fluctuation energy observed at Parker. These observations provide unique constraints on models of the radial evolution of the fastest solar wind, and indicate that these wind streams experience gradual, steady acceleration over their first few tens of solar radii of evolution.
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All authors Samuel T. Badman, Yeimy J. Rivera, Michael L. Stevens, Mari Paz Miralles, Steven R. Cranmer, Andrea Verdini, Lynn B. Wilson III, Xiangyu Wu, Georgios Nicolaou, Jean-Baptiste Dakeyo, Kai Jaffarove, Tamar Ervin, Dominic S. Payne, Michael Terres, Kristopher G. Klein, Jasper S. Halekas, Sujan Prasad Gautam, William H. Matthaeus, Riddhi Bandyopadhyay, Srijan Bharati Das, Tatiana Niembro, Christopher J. Owen, Rungployphan Kieokaew, Ali Rahmati, Orlando M. Romeo, Federico Fraschetti, Marco Velli, Lorenzo Matteini, Kristoff W. Paulson, Lidiya Ahmed, Stuart D. Bale, Phyllis Whittlesey, Marc Pulupa, Nour E. Raouafi, Timothy S. Horbury, Jean Morris, Helen O'Brien, Roberto Livi, Davin E. Larson, Adam J. Finley, Philippe Louarn

Solar and Stellar Astrophysics

A Data-Driven Model for $r$-Process Production Patterns

Chen-Qi Li, Yong-Zhong Qian, Axel Gross et al. (+1 more)

Using the elemental abundances in 68 metal-poor (MP) stars, we present a data-driven model for $r$-process production patterns covering Sr to U. We show that essentially all the $r$-process patterns in those and other test stars can be adequately explained as mixtures of Patterns 1 and 2, which provides theoretical insights into the empirical categories of limited-$r$, $r$-I, and $r$-II stars. We carry out an extensive survey of the yield templates produced by parametric $r$-process calculations. We propose that Pattern 2 may be dominated by a single template and points to regularity in $r$-process production by a subset of neutron star mergers (NSMs), while Pattern 1 is the average superposition of multiple templates and reflects production by other NSMs and perhaps also some magneto-rotational supernovae. We raise possible systematic issues with abundance ratios for elements measured in different ionization states, and highlight the need for examining the Os, Ir, and Pt measurements for HD~122563, which is dominated by Pattern 1 with a prominent Pt peak in our model. If this result is confirmed, the meaning of the limited-$r$ category requires drastic revision. Further measurements of a wider range of $r$-process elements in a larger sample of MP stars are critical to test and improve our model.
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All authors Chen-Qi Li, Yong-Zhong Qian, Axel Gross, Zewei Xiong

Solar and Stellar Astrophysics

TESS Observations of Seven Newly Identified High-amplitude $\delta$ Scuti Stars

Chenglong Lv, Ali Esamdin, Amir Hasanzadeh et al. (+3 more)

We report seven newly identified high-amplitude $\delta$ Scuti (HADS) stars. Among them, two stars (TIC 30977864 and TIC 387379145) exhibit pure radial pulsation without the excitation of non-radial modes. TIC 30977864 is classified as a double-mode HADS star, while the other four stars potentially show triple-mode HADS behavior. TIC 112682462 and TIC 255603395 closely resemble RR Lyrae stars based on their light curves, position in the period-luminosity diagram, and the period-ratio diagram. However, without spectral observations, it is challenging to ascertain whether these two stars are HADS or RR Lyrae stars. TIC 281695001 exhibits a fundamental frequency amplitude smaller than that of the first overtone, suggesting the presence of intriguing phenomena that necessitate further analysis. We analyzed the relationship between metallicity and period using data provided by Netzel & Smolec. The metallicities of the 176 stars display a broad distribution ranging from -2.0 dex to 0.5 dex, with periods spanning 0.05 to 0.20 days. This random distribution of metallicities may contribute to the dispersion observed in the $P_1/P_0$ ratio. To derive more accurate conclusions, future spectroscopic observations of a larger sample of HADS stars are crucial. These observations will provide precise rotational velocities and more accurate determinations of metallicities.
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All authors Chenglong Lv, Ali Esamdin, Amir Hasanzadeh, Shuguo Ma, TaoZhi Yang, Rivkat Karimov

Solar and Stellar Astrophysics

Statistical analysis of asteroseismic indices and stellar parameters of TESS-observed $\delta$ Scuti stars

C. Lv, A. Esamdin, A. Hasanzadeh et al. (+4 more)

We analyze the statistical properties and asteroseismic indices of delta Scuti stars observed during TESS Cycle 4. Using 2 minute cadence photometry and Fourier analysis, we identified 765 delta Scuti stars in Sectors 40-55, including 179 objects with low-resolution stellar parameters from LAMOST. We examined the distributions of their pulsation and stellar parameters using values from the TESS Input Catalog and LAMOST. Most targets lie within the classical instability strip, follow the period-luminosity relation, and show periods, amplitudes, temperatures, surface gravities, and luminosities consistent with delta Scuti stars. For the LAMOST subsample, we estimated the large frequency separation ($\Delta\nu$), $\nu_{\rm max}$, and $\nu({\rm Amax})$ using an empirical relation and a two-dimensional autocorrelation method. We also derived relations among these asteroseismic indices. This catalog provides a useful sample for future studies of the internal structure and evolution of delta Scuti stars.
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All authors C. Lv, A. Esamdin, A. Hasanzadeh, M. Ghazinejad, J. Pascual-Granado, G. M. Mirouh, R. Karimov

Solar and Stellar Astrophysics

Discovery and Characterization of Three New High-amplitude delta Scuti Stars from TESS Observations

Chenglong Lv, Ali Esamdin, J. Pascual-Granado et al. (+5 more)

We report the discovery and detailed analysis of three new high-amplitude {\delta} Scuti (HADS) stars, TIC 408074920, TIC 189714989, and TIC 34137913, identified from Transiting Exoplanet Survey Satellite short-cadence observations. Fourier analysis reveals dominant radial modes accompanied by rich harmonic structures in all three stars, confirming their HADS classification. In addition, TIC 189714989 exhibits clear symmetric side peaks around the radial harmonics, indicative of amplitude and/or phase modulation. Broadband spectral energy distribution (SED) fitting constrained by Gaia DR3 parallaxes provides independent estimates of the stellar effective temperatures and radii. These are compared with results from stellar evolutionary and seismic modeling based on MESA and GYRE. For two targets, the SED-derived and seismic radii are mutually consistent, while TIC 408074920 displays a significant discrepancy, plausibly attributable to the different sensitivities of the two methods and additional systematic effects. These findings highlight the diversity of amplitude variability among classical HADS and emphasize the importance of the long-term monitoring that future missions such as PLATO will allow in order to explore the underlying physical mechanisms of this variability.
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All authors Chenglong Lv, Ali Esamdin, J. Pascual-Granado, Guojie Feng, Haozhi Wang, Rivkat Karimov, Bolkin Juraev, Shuhrat A. Ehgamberdiev

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

A JWST transiting survey of FGK stellar limb darkening: empirical evidence for quadratic laws and atmospheric model comparisons

David K. Sing, Joshua D. Lothringer, Jeff A. Valenti et al. (+11 more)

We present a study of stellar limb-darkening using JWST transit observations of seven exoplanets orbiting FGK host stars, spanning 4200-6800 K. The wide wavelength coverage and high S/N of NIRISS/SOSS and NIRSpec/PRISM enable precise constraints on the wavelength-dependent limb-darkening. Using Bayesian model selection, we find that the quadratic limb-darkening law is statistically preferred over higher-order laws for most FGK stars, recovers consistent intensity profiles for $>$95% of the stellar disk area, and introduces a minimal bias in the derived transit depths of only $\sim$14 ppm (1$\sigma$) for 6/7 targets. This contrasts with previous studies relying on stellar models. We compare the empirically derived quadratic coefficients to predictions from the PHOENIX, MPS-ATLAS, MURaM, and Stagger stellar atmosphere grids. We introduce a quadratic limb-darkening parameterization in terms of limb intensity ($\ell$) and curvature at mid-$\mu$ ($\delta$), finding that empirical FGK limb darkening is generally more linear than models predict ($\delta \lesssim 0.1$). We identify wavelength-independent offsets between data and model quadratic coefficients, minimized by adopting $\mu_{\rm min} = 0.2$ in intensity calculations; we attribute this in part to models overpredicting limb-darkening near the limb where the plane-parallel approximation breaks down. For spherical PHOENIX models, we derive a $\mu$ rescaling method using a $\tau = 1$ photospheric radius. With these corrections, residual offsets are minimized and all stellar models achieve statistically acceptable fits. We provide recommended limb-darkening offset priors for use in JWST transit analyses, enabling more accurate constraints on exoplanet transmission spectra while accounting for residual stellar model uncertainties.
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All authors David K. Sing, Joshua D. Lothringer, Jeff A. Valenti, Natalie H. Allen, Katherine A. Bennett, Carlos Gascón, Mei Ting Mak, Patrick McCreery, Sagnick Mukherjee, Lakeisha M. Ramos Rosado, Stephen P. Schmidt, Kevin B. Stevenson, Daniel P. Thorngren, Le-Chris Wang

Solar and Stellar Astrophysics

A Probabilistic Framework for Incorporating Helioseismic Far-Side Active Regions into SFT Models

Bibhuti Kumar Jha, Lisa A. Upton, K. D. Leka et al. (+5 more)

Surface Flux Transport (SFT) models are routinely used to model the Sun's photospheric magnetic field and provide inner boundary conditions for coronal and heliospheric models, yet they remain fundamentally limited by the lack of direct information about flux emergence on the far side of the Sun. To address this, we develop a framework for incorporating helioseismic images of far-side active regions (HIFAR), into the Advective Flux Transport (AFT) model. Using near-simultaneous magnetic flux maps (HIFARM) inferred from HIFAR, and STEREO/EUVI 304 A observations from 2010 May 13 to 2014 August 18, we develop a logistic regression model to estimate the probability that a helioseismic detection corresponds to an AR based on descriptors of magnetic flux, field strength, and location. The model achieves a precision of 0.93 for active region (AR) detections at a probability threshold of 0.73, selected to reject 90% of "ghost" ARs. We also derive an empirical scaling relationship between HIFARM and AFT flux to place HIFARM on the AFT flux scale and demonstrate that the framework reproduces the flux evolution of ARs consistent with near-side observations over multiple solar rotations. At the global scale, we find that conventional near-side-driven AFT simulations underestimate the total unsigned magnetic flux by ~10-20% of the Sun's total magnetic flux budget. The probabilistic AR detection model and the complete framework developed in this work provide a practical pathway for incorporating helioseismic far-side ARs into SFT models, a step toward realistic modeling of full-Sun magnetic field.
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All authors Bibhuti Kumar Jha, Lisa A. Upton, K. D. Leka, Ruizhu Chen, Junwei Zhao, Shea Hess Webber, Ignacio Ugarte-Urra, Kiran Jain

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

Portraits of the young and old in X-ray: New millisecond pulsar detections and updated characterization of young neutron stars

Wynn C. G. Ho, Patrick H. Wang and Sebastien Guillot

We present analyses of new and archival Chandra and NuSTAR data on two old millisecond pulsars, a young highly-energetic pulsar, and a young neutron star. PSR J1810-0623 is a recently-discovered 4.55 ms radio pulsar in a binary with a possible carbon-oxygen white dwarf companion. We tentatively detect the pulsar for the first time in X-ray using a new short Chandra HRC-I observation. Its faintness suggests a distance more in accord with the further (~1 kpc) of its dispersion measure-inferred distances. PSR J1933-6211 is a 3.54 ms radio pulsar also with a carbon-oxygen white dwarf companion. Our first-time X-ray detection in an archival HRC-S image indicates its X-ray luminosity is similar to that of the 1.9 Msun pulsar PSR J1614-2230. Next, PSR J1813-1749 is a 1-2 kyr pulsar with one of the highest known spin-down luminosities. We measure its spin period of 44.7 ms using 2025 NuSTAR and 2026 Chandra ACIS-S data and update its spin evolution model. We show for the first time the pulse profile of PSR J1813-1749 at 3-79 keV, and we find that the spectra of the pulsar and pulsar wind nebula at these energies did not change significantly between observations in 2018 and 2025. Finally, for the 5-10 kyr neutron star CXOU J182913.1-125113 in the supernova remnant G18.95-1.1, we combine ACIS-I observations from 2009 and 2024 to better measure the neutron star's spectrum.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Evidence for a luminosity-class dichotomy in the supergiant donors of persistent high-mass X-ray binaries and supergiant fast X-ray transients

Lara Sidoli and Vito Sguera

We have investigated the properties of the supergiant donors in two types of high-mass X-ray binaries (HMXBs, i.e. the so-called supergiant fast X-ray transients (SFXTs) and the classical X-ray sources), by collecting all available information from the literature. A prevalence of O-type versus B-type supergiant donors in SFXTs was previously suggested in the literature, possibly indicative of faster winds in SFXTs than in classical, persistent sources. Our aim is to investigate whether there is evidence for a dichotomy in the stellar luminosity class, since B-type supergiants are also known to be hosted in SFXTs. Our collection of the relevant literature allowed us to build a robust sample of both types of HMXBs with a secure stellar classification. We have found that the SFXTs showing the most extreme, transient X-ray emission host only O-type or B-type stars with a Ib and Iab luminosity class, whereas classical sources have mostly Ia donors. This is robust evidence that might explain the two different behaviours of HMXBs at X-rays since the stellar luminosity class appears to be linked to the wind properties (the supergiant wind terminal velocity, the mass-loss rate, and the wind strength Q parameter), indicative of faster and less dense winds in SFXTs than in classical sources.
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2609.00175 · 31 Aug · Accepted for publication in Astronomy & Astrophysics (received May 18, 2026; accepted August 11, 2026). The manuscript comprises 11 pages, 5 figures, and 4 tables. The version submitted here also includes all supplementary tables (B.1, C.1, C.2, and D.1), which in the published A&A article are provided exclusively in electronic form via the CDS

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

Self-induced edge rings in protoplanetary disks

Massimiliano Bolchini, Haochang Jiang and Jiaqing Bi

Observations with a high angular resolution by ALMA have revealed that substructures are ubiquitous in protoplanetary disks. Axisymmetric dust rings are the most common morphology. The profiles of some observed disks, including young disks, are smooth overall, with a localized dip or bump near the outer edge of the continuum disk that manifests as an edge ring. While embedded planets might contribute to these structures, their physical origin remains unclear. We investigated the possibility that these edge rings arise purely from radiative transfer effects at the outer edge of a protoplanetary disk. A steep surface density dust gradient at the outer edge of the disk allows stellar irradiation to penetrate more efficiently beyond the disk edge, producing a non-monotonic temperature profile characterized by a dip that is followed by a bump. We tested whether this non-monotonic temperature structure can generate and maintain a localized continuum enhancement. We coupled radiative transfer and dust evolution by iterating between the Monte Carlo radiative transfer code RADMC-3D and the dust evolution code DustPy. This framework self-consistently follows the coupled evolution of temperature, grain growth, and dust dynamics. Thermodynamic feedback at the disk edge can naturally generate and maintain localized dust enhancements resembling the edge rings that are observed in some extremely young disks. Without invoking planets or additional dynamical perturbations, this mechanism offers a plausible explanation for the first-generation ring formation. Our results highlight the importance of coupling thermodynamics and dust evolution when modeling protoplanetary disks, suggesting that thermodynamic feedback probably plays a role in shaping disk substructures.
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Solar and Stellar Astrophysics

Conspicuous Gas, Cryptic Dust: Spectroscopy and Chromaticity of Complex Periodic Variables

Luke G. Bouma, Facundo Perez Paolino, Lynne A. Hillenbrand et al. (+17 more)

Complex periodic variables (CPVs) are young low-mass stars whose light curves show periodic dips indicative of transiting corotating material. The origin and composition of this material are unclear. Here we present new optical and near-infrared spectroscopy and photometry of four CPVs from Magellan, Keck, Hale, MuSCAT1, MuSCAT2, Tierras, KeplerCam, and TESS. The spectra imply that CPVs host magnetically bound circumstellar plasma clumps, on the basis of sinusoidal-in-time Balmer emission out of transit, and Balmer dimming during transit. Yet large night-to-night changes in circumstellar hydrogen emissivity occur without clear changes in light curve morphology, suggesting that the sharp flux dips are caused not by circumstellar plasma but by dust. Optical chromaticities (depth proportional to $\lambda^{-\beta}$, with $\beta$ = 0.79 $\pm$ 0.16) support this, but the power law breaks in the near-infrared, where a single power law under-predicts the depths observed at 2.1 microns. We therefore favor dips caused by dusty plasma clumps with opaque cores and optically thin halos, though we cannot rule out models in which the dust properties vary per-star or per-epoch. Observations at wavelengths greater than 2 microns and less than 0.4 microns would test this interpretation and clarify the dust's origin.
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All authors Luke G. Bouma, Facundo Perez Paolino, Lynne A. Hillenbrand, Juliana Garcia-Mejia, Allyson Bieryla, Patrick Tamburo, David Charbonneau, John H. Livingston, Keisuke Isogai, Norio Narita, Akihiko Fukui, Enric Palle, Felipe Murgas, Adolfo S. Carvalho, Howard Isaacson, Jessica J. Spake, Luisa M. Rebull, Moira M. Jardine, David R. Ciardi, Jeff A. Valenti

Solar and Stellar Astrophysics

Modeling Rotation in the Old, Cold Domain: Implications on Gyrochronology and the Stellar Magnetic Wind

Amanda L. Ash, Yuxi Lu and Marc H. Pinsonneault

Gyrochronology ties stellar rotation periods to ages. It is well studied in the young, open cluster age domain, but there are few constraints on gyrochronology in the old field star regime. In this work we use gyro-kinematic ages to explore the spin down of stars in this formerly inaccessible domain. Using forward modeling techniques which relax strict Rossby scaled assumptions, we find evidence for a departure from a standard spin down models. This departure can be explained with a mass-dependent term either in the global strength of the stellar wind or in the relationship between angular velocity and wind strength. Models with this additional mass- dependence help explain prior difficulty in fitting open cluster rotation distributions across the full mass range. Additionally, we use rotation models to identify an mass-dependent age domain over which wind driven stellar spin down can be isolated from other physical effects. For lower mass stars, this age domain is most affected by the core-envelope coupling timescale, where as higher mass stars are more subject to inertial effects late in their main sequence lifetimes. Using simple, analytic models of stellar spin down in this domain is unable to determine whether the stellar wind has a mass-dependence or if the stellar wind is strictly Skumanich-like in nature. In future studies of rotational and dynamo evolution we advocate for a forward modeling approach to gyrochronology over purely empirical approaches due to its superior ability to trace physical effects governing stellar spin down.
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Solar and Stellar Astrophysics

Exploring stellar evolution with Luminous Red Novae and Interacting Gap Transients

Nadejda Blagorodnova

Interacting gap transients encompass several families of astrophysical phenomena where eruptive mass loss and interaction play an important role in shaping the observational properties and energetics of the events. Composed of Luminous Red Novae (LRNe), Intermediate Luminosity Red Transients (ILRTs), Luminous Blue Variable (LBV) giant eruptions, and pre-supernova precursors, interacting gap transients offer crucial insights into unstable mass transfer, extreme stellar mass loss, and binary evolution. In these proceedings, I review the observational signatures, progenitors, physical origin, and classification challenges of these heterogeneous phenomena. Finally, I highlight how ongoing and future wide-field time-domain missions will revolutionize this field by compiling complete volume-limited samples, tracking faint pre-outburst precursors, and establishing statistical links between gap transient families and their progenitor populations.
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Solar and Stellar Astrophysics · Cross-listed from hep-ph

Solar Spin-Dependent Dark Matter-Neutron Cross Section Constraints: The Lost Case

Thong T.Q. Nguyen, Carlos Blanco and Tim Linden

The Sun has long served as a natural dark matter detector, capturing halo particles that scatter with solar nuclei and electrons and subsequently produce indirect signals from dark matter annihilation that can be probed by either neutrino or $\gamma$-ray instruments. Previous efforts have computed cross-section constraints for dark matter scattering with electrons, as well as spin-independent and spin-dependent dark matter-proton scattering. However, the spin-dependent dark matter-neutron scattering scenario has been neglected, despite its importance in direct detection. For the first time, we compute the capture and evaporation rates for spin-dependent dark matter-neutron scattering in the Sun, including odd-neutron isotope targets in the current standard solar model. Comparing the predicted annihilation signals against current neutrino and $\gamma$-ray observations, and projecting the reach of upcoming detectors, we find that solar constraints exceed direct detection limits for several annihilation channels. For models in which the dark matter annihilates into long-lived mediators, these constraints can extend below the neutrino fog.
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