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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Monday 5 October

Solar and Stellar Astrophysics

Magnetohydrodynamic coronal modelling with high-fidelity magnetograms

Haopeng Wang, Stefaan Poedts, Wensi Wang et al. (+16 more)

To resolve coronal structures in detail, it is essential to constrain the coronal model using high-fidelity magnetograms with minimal smoothing. In this paper, we improve the numerical stability of COCONUT to enable efficient coronal MHD simulations driven directly by photospheric magnetograms, including magnetic field strengths exceeding 1000 Gauss (G), and then use it to investigate the impact of small-scale magnetic field structures that are typically filtered out of photospheric magnetograms on the coronal simulation results. We constrain this model with two types of magnetograms: the high-fidelity HMI photospheric magnetogram with only minor preprocessing through Gaussian smoothing, which preserves magnetic field strengths reaching 1500 G, and one processed using 50th-order filtered spherical harmonics, where the magnetic field strength is limited to below 100 G. The results demonstrate that the COCONUT can reproduce the large-scale coronal structures revealed by pB and EUV observations. Compared with the coronal MHD simulation constrained by a conventionally filtered magnetogram, the simulation constrained by the high-fidelity magnetogram yields approximately $50\%$ more OMF and produces EUV images that are more consistent with the observations. Moreover, the results show that when viewed from low latitudes in certain EUV passbands, such as the 193~Å channel, open-field regions near the solar poles may appear as bright structures that are typically associated with closed-field regions. This finding highlights the need for solar polar-orbiting missions to overcome the limitations and ambiguities arising from the restricted view of the polar regions from the ecliptic plane and to provide more complete full-Sun observations.
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All authors Haopeng Wang, Stefaan Poedts, Wensi Wang, Rayan Dhib, Andrea Lani, Martina Condoluci, Tinatin Baratashvili, Quentin Noraz, Luis Linan, Hyun-Jin Jeong, Junyan Liu, Zhenguang Huang, Rui Liu, Lingyu Dong, Rui Zhuo, Liping Yang, Giovanni Alejandro Pinzón Estrada, Jasmina M. Magdalenić Zhukov, Brigitte Schmieder

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

Linking simulations and observations of star-forming regions I. Masses and temperatures of ALMAGAL-like cores

Birka Zimmermann, Álvaro Sánchez-Monge, Stefanie Walch et al. (+1 more)

Dense cores and clumps in massive star-forming regions are studied through (sub-)millimetre continuum observations, but inferred masses and temperatures can be biased by limited resolution, interferometric filtering, projection, and uncertain dust temperatures. We quantify how reliably core masses and temperatures can be inferred from ALMA-like continuum data using synthetic observations of such clumps. We post-processed radiation-hydrodynamic simulations of collapsing 1000 M$_\odot$ clumps with RADMC-3D and CASA to generate synthetic ALMAGAL-like images. Cores were defined around sink particles, enabling comparison of masses from the 3D simulations, idealised RADMC-3D maps, and synthetic ALMA images. We quantified how resolution, projection, and viewing angle affect core masses, and tested three dust-temperature estimators (clump-scale L/M, a L/M+flux model, and a supervised machine-learning estimate). Projection effects cause line-of-sight integrated core masses within 1500 au to exceed spherical masses by factors of two to three. The empirical L/M temperature prescription follows the global thermal evolution but misses the core-to-core scatter, producing core-mass errors of a factor of a few. Including local flux improves temperature and mass estimates, while a gradient-boosting machine-learning model suggests further improvement. Synthetic ALMAGAL-like images recover the global core structure, but flux-reconstruction uncertainties introduce mass errors up to a factor of three and limit reliable core-mass recovery to $\gtrsim 0.3$ M$_\odot$, comparable to the ALMAGAL completeness limit. Individual core masses are typically uncertain by a factor of three to five, mainly due to dust-temperature assumptions and flux reconstruction. Reducing these biases requires temperature estimates that include local core information rather than a single clump-scale L/M-based prescription.
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All authors Birka Zimmermann, Álvaro Sánchez-Monge, Stefanie Walch, Gary A. Fuller

Solar and Stellar Astrophysics

Coherent radio bursts, polarity reversal, and quiescent emission from the M4V dwarf WW PsA

Jackson Mitchell-Bolton, Laura Driessen, Tara Murphy et al. (+6 more)

Coherent radio emission from magnetically active M dwarfs is largely observed in two varieties: stochastic solar-like bursts and beamed, rotationally modulated emission including auroral pulses. Detailed monitoring of these stars is critical for probing the plasmas and magnetic fields driving the emission. We conducted a search for polarised radio emission from stars within 85 pc, covering $2.2\times10^4$ h of stellar dynamic spectra from the ASKAP Deep Investigation of Neutral Gas Origins (DINGO) survey. We report the discovery of coherent radio bursts from the M4V dwarf WW PsA. In addition to quiescent emission, we detect three long-duration ($\gtrsim$30 min) bursts, each ~100% circularly polarised, in 283.3 h of data. We also report a fourth burst in an epoch not covered by our search, detected using the VASTER pipeline. One of the bursts features a polarity reversal midway through, based on which we favour the electron cyclotron maser (ECM) mechanism over plasma emission. We tentatively propose the bursts are due to rotationally modulated ECM pulses of variable intensity. We infer the required physical properties of WW PsA, including a high obliquity $\beta = 74^{+6}_{-22}$ deg under an oblique rotator model.
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All authors Jackson Mitchell-Bolton, Laura Driessen, Tara Murphy, Joshua Pritchard, Barnali Das, Richard Dodson, Martin Meyer, Jonghwan Rhee, Yuanming Wang

Solar and Stellar Astrophysics

From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars

Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia et al. (+9 more)

Among the compact binaries detected through gravitational wave (GW) emission, double neutron stars (DNSs) hold the unique distinction of having well-characterized local analogs in the Milky Way. However, understanding their broader cosmological population remains challenging due to the complex metallicity-dependent evolution of their progenitors. Using the detailed binary population synthesis code POSYDON, we model DNS formation across a cosmological range of metallicities. We find that while DNSs are predominantly formed through common envelope evolution, metallicity-dependent radial expansion and stellar wind mass loss bifurcates the pathway into distinct subchannels, producing systematically distinct merging populations at different metallicities. Notably, our best representative Galactic models predict local merger rates in broad agreement with the latest GWTC-5 constraints, suggesting that the populations observed via radio pulsar surveys and through GW emission need not be in tension. Contrary to previous studies, we demonstrate that the intrinsic merger efficiency increases toward low metallicities, a trend robust across varying binary evolution assumptions, although the magnitude and the underlying stellar processes driving this enhancement vary across metallicity regimes. When convolved with the cosmic star formation history, our models reveal that the majority of merging DNSs originate from progenitors in the range $\sim 0.1\,Z_\odot - Z_\odot$, with significant supersolar contributions. Furthermore, we show that weaker stellar winds at low metallicities produce DNS mergers with systematically more symmetric mass ratios ($q \gtrsim0.9$). Additionally, we assess detectability within proposed configurations for third-generation GW observatories. Our study provides a framework for interpreting the cosmological DNS population in the upcoming multi-messenger era.
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All authors Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia, Max M. Briel, Michael Zevin, Tassos Fragos, Emmanouil Zapartas, David R. Aguilera-Dena, Seth Gossage, Anarya Ray, Philipp M. Srivastava, Zepei Xing

Solar and Stellar Astrophysics

Unravelling the Nature of AT 2025abao: From Precursor to Final Fate

Zhuo Chen, Yingzhen Cui, Tianshu Wu et al. (+9 more)

Luminous red novae (LRNe) are potential signatures of common envelope evolution (CEE), a critical yet poorly understood phase in compact binary formation. AT 2025abao, an LRN in the Andromeda galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system's evolutionary fate remains unclear. Here, we unravel the binary nature of AT 2025abao by modeling its complete evolution, from precursor to final outcome. We show that the eight-year infrared precursor arises from a $\approx1.4^{+0.2}_{-0.3}\,M_{\odot}$ main-sequence companion inspiralling through the wind of a $\approx 6.9\,M_{\odot}$ AGB star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to $\approx 0.92\,M_{\odot}$ and energy to $\approx 1.25\times 10^{47}\,$erg, revealing that only $\approx 0.57\,M_{\odot}$ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT 2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact binary formation.
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All authors Zhuo Chen, Yingzhen Cui, Tianshu Wu, Yongzhi Cai, Hongwei Ge, Andrea Reguitti, Minxuan Cai, Lulu Fan, Ji-An Jiang, Tinggui Wang, Zelin Xu, Jie Lin

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

A Physically Motivated Compact Parameterization of Neutron Star Atmosphere Emission for Thermal X-ray Pulse-Profile Modeling

Tong Zhao and Renxin Xu

Thermal X-ray pulse-profile modeling depends on the angular and spectral properties of neutron star atmosphere emission. We construct a compact empirical approximation to the specific intensity using eight coefficients for the angular dependence and five for a normalized spectral kernel. The angular prescription is motivated by the formal solution of the radiative-transfer equation, while the spectral normalization preserves a specified bolometric flux. We calibrate this family to numerical atmosphere tables, focusing on return-current-heated and fully ionized hydrogen atmospheres. When incorporated into a semi-analytic pulse-profile model, the approximation reproduces profiles normalized by their phase-averaged flux to within approximately $4\%$ for antipodal hot spots and $5\%$ for non-antipodal hot spots in the tested heated-atmosphere configurations. We also analyze synthetic eXTP observations using different beaming prescriptions to test the conclusion in our previous work based on a linear description of the angular dependence of the emission. The comparisons suggest that the angular dependence of the intensity cannot be simply characterized by a linear function of the cosine value of the emission angle, because its detailed shape and energy dependence will affect the parameter inference. This parameterization can significantly increase the efficiency for analytic and numerical models, and provide a compact framework for examining how atmosphere assumptions affect neutron star pulse profiles and the inferred stellar properties.
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Solar and Stellar Astrophysics

Fast and Differentiable MHD Surrogate for Solar Wind using Neural Operator

Prateek Mayank, Enrico Camporeale, Thomas E. Berger et al. (+2 more)

Global magnetohydrodynamic (MHD) simulations provide the complete plasma state of the heliosphere, but their computational cost limits applications requiring repeated model evaluations. We introduce SNOW (Solar Neural Operator for Wind), a fast and differentiable surrogate for global MHD solar wind. SNOW combines a rotational ballistic approximation, a spherical harmonic neural operator, and causal radial context to autoregressively propagate all eight MHD variables from 20 to 240 Rs through consecutive shell to shell transitions. Trained and evaluated using AWSoM simulations spanning a solar cycle, SNOW remains stable across the complete rollout. The model successfully reproduces the large scale plasma and magnetic field structures, including fast and slow wind streams, magnetic polarity sectors, vector orientations, fieldline connectivity, and bulk-flow structures. Additionally, the magnetic divergence and induction diagnostics remain comparable to the reference MHD solutions. The complete three-dimensional solution is generated in less than one second on a single GPU. These results demonstrate the feasibility of fast neural emulation of global MHD solar wind solutions while retaining physically meaningful plasma and magnetic field structure.
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All authors Prateek Mayank, Enrico Camporeale, Thomas E. Berger, Zhenguang Huang, Gabor Toth

Sunday 4 October

Solar and Stellar Astrophysics

ZTF J191814.28+010850.2: An eclipsing cataclysmic-variable candidate in the SW Sextantis period range

Klaus Bernhard, Wolfgang Moschner, Christopher Lloyd et al. (+1 more)

We present a photometric study of ZTF J191814.28+010850.2, a short-period variable previously classified as an EA-type eclipsing binary. The analysis is based on ZTF observations in the g and r bands and additional time-series CCD photometry obtained on two nights. We derive an eclipse period of 0.1408529(3) d. The phased ZTF light curves show a deep primary eclipse, with an eclipse depth of about 2.8 mag in g and 2.0 mag in r, as well as indications of cycle-to-cycle variations outside eclipse. After excluding the primary eclipse and accounting for the remaining orbital modulation, robust locally weighted fits reveal a broad non-linear long-term brightness variation in both bands, with peak-to-peak ranges of about 0.56 mag in g and 0.46 mag in r. The deep eclipse, short orbital period and irregular variability suggest that the object is a cataclysmic-variable candidate and possibly a member of the SW Sextantis group. Time-resolved spectroscopy is required to confirm or refute the proposed classification and to test possible membership in the SW Sex class.
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All authors Klaus Bernhard, Wolfgang Moschner, Christopher Lloyd, Peter Frank

Solar and Stellar Astrophysics

AI Agents as a Research Team: A Human-Supervised Case Study in Stellar Spectroscopy

Marwan Gebran and Ian Bentley

We present a qualitative case study of a human-supervised team of specialized AI agents supporting an astronomy research project. The Bot Spectroscopist team, described in the project record as operating through Grok Bot powered by xAI Grok, divided work among orchestration, numerical implementation, data curation, spectroscopy critique, literature search, figure preparation, manuscript editing, and review. Human decisions determined scientific scope, model changes, and manuscript inclusion. The scientific application is CondGen, a deterministic label-to-spectrum network extending our previous work to five individual elemental abundances. The reported baseline assessment achieved a mean absolute error (MAE) of 0.003681 in continuum-normalized flux on 21,657 synthetic test spectra. Existing binned diagnostics show that reconstruction error varies with effective temperature and abundance. The bots also flagged a non-monotonic cool-star magnesium response for further investigation; a matched SYNSPEC abundance sweep is needed to assess its physical fidelity. Building on a pre-existing spectral database, notebooks, and research program, the authors estimate that the reported analysis, diagnostics, figure preparation, and initial manuscript drafting were assembled in less than a week through human prompting and exchanges among agents. No comparison with a human team starting from the same resources was performed, so this elapsed-time account does not establish a productivity or labor saving. The study illustrates task delegation, artifact exchange, critique, and correction under human supervision.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Large offsets of double-neutron-star mergers: degeneracies and implications for host associations

Xiao-Tian Xu, Bin-Bin Zhang, Wenjie Wu et al. (+1 more)

The projected offset of a Gamma-Ray Burst (GRB) from its host galaxy is an important diagnostic of its physical origin, where the host associations are usually evaluated through chance-coincidence probabilities. However, as shown by observations, the host associations given by this approach may be ambiguous in some cases. In this work, we revisit the modelling of the offsets of double-neutron-star (DNS) mergers with controlled numerical experiments using Monte Carlo simulations. To isolate the dynamical effects of the second supernova (SN) from uncertainties in the upstream binary evolution, we parametrise the direct progenitor of DNSs and integrate the post-SN trajectories in galactic potentials using galpy. Complementary to previous population synthesis calculations, our Monte-Carlo tool, GRB-offset, provides a lightweight framework to identify sensitivities and expose degeneracies in offset modelling. With GRB-offset, we have investigated the following physical ingredients, supernova physics (ejected mass and kick velocity), galactic potential (potential shape, galaxy virial mass), DNS birth location, star formation history, and redshift. The offset distributions given by our reference Monte-Carlo simulation peak at around 30 kpc and 1000 kpc for the DNSs bound to and unbound from the host galaxy, which sensitively depends on the considered physical ingredients. A given offset can arise from various combinations of these ingredients, introducing substantial degeneracies when interpreting observed offsets. Therefore, an observed offset alone can hardly constrain the properties of the DNS progenitor and of the host galaxies.
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All authors Xiao-Tian Xu, Bin-Bin Zhang, Wenjie Wu, Suoning Wang

Solar and Stellar Astrophysics

SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. II. Dynamics of the dust in the Mira wind and the Halpha gas in the jet

H.M. Schmid, E. Lagadec, J. Milli et al. (+17 more)

R Aqr is a resolved symbiotic Mira binary and a prototype target for the study of complex hydrodynamic processes including dust-driven mass loss, mass transfer, accretion, and jet outflows and the formation of strongly asymmetric structures. We investigate for R Aqr the central Halpha emission from the ionized gas and the polarization from scattering dust based on SPHERE/ZIMPOL maps with a resolution of about 25 mas (5 AU). Data for four epochs were taken, including the dust eclipse around 2021, to follow structural changes. The central Halpha gas traces the orbital motion of the hot component. The polarization from scattering dust shows interaction effects near the binary (<60 AU), including a flattened distribution in the orbital plane, corotating dust, and a reduction of the scattering signal during the dust eclipse. The polarization shows at >60 AU a steady outflow with about a dozen dust clouds, a few of which have a comet-like core and tail features. The dust velocity is about 20 km/s, and this is faster than for the CO gas measured with ALMA. Several prominent Halpha clouds also show scattering polarization because they are just partly ionized dust clouds from the Mira wind. We also found small faster-moving transient Halpha clouds, pointing to outflow instabilities and shocks. The observed angular shift of Halpha during the dust eclipse, can be explained by strong illumination changes from the hot component. At larger separation, the H$\alpha$ clouds move faster (>100 km/s), in agreement with previous studies. This acceleration is probably a result of gas heating by photoionization and shocks, and the produced overpressure gives rise to the two well-known jet-like features expanding in polar directions. The presented R Aqr data are very useful to clarify the complex hydrodynamics taking place in AGB binaries.
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All authors H.M. Schmid, E. Lagadec, J. Milli, C. Tschudi, J. Ma, N. Engler, J.L. Beuzit, A. Boccaletti, G. Chauvin, R. Claudi, S. Desidera, K. Dohlen, M. Feldt, R. Gratton, Th. Henning, M. Kasper, M. Langlois, F. Ménard, D. Mouillet, A. Vigan

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

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum, III: nuclei with $8 \leq Z \leq 120$

DRHBc Mass Table Collaboration: Peng Guo, Xiaojie Cao, Kangmin Chen et al. (+89 more)

The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for nuclei with $8 \leq Z \leq 120$, extended from the previous works for even-even nuclei [Zhang et al. (DRHBc mass table collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)] and for even-$Z$ nuclei [Guo et al. (DRHBc mass table collaboration), At. Data Nucl. Data Tables 158, 101661 (2024)]. The calculated binding energies, two- and one-nucleon separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, neutron and proton Fermi surfaces, and the blocked neutron (proton) orbitals of odd-$N$ ($Z$) nuclei are tabulated and compared with the available experimental data. A total of 9495 nuclei are predicted to be bound, with an rms deviation of 1.444 MeV from the 2380 mass data. Good agreement with the available experimental pairing gaps, $\alpha$ decay energies, and charge radii is also achieved. The accuracies of the calculated nuclear masses and nucleon separation energies as well as the prediction for drip lines are compared with those obtained by other relativistic and nonrelativistic density functional calculations. It turns out that the DRHBc theory with PC-PK1 provides one of the best microscopic descriptions for nuclear masses. The systematics of nucleon separation energies, pairing gaps, pairing energies, two-nucleon gaps, $\alpha$ decay energies, rms radii, quadrupole deformations, potential energy curves, neutron density distributions, and neutron mean-field potentials are discussed.
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All authors DRHBc Mass Table Collaboration: Peng Guo, Xiaojie Cao, Kangmin Chen, Qibo Chen, Myung-Ki Cheoun, Yongbeom Choi, Wenmin Deng, Jianmin Dong, Pengxiang Du, Xiaokai Du, Kangda Duan, Xiaohua Fan, Wei Gao, Lisheng Geng, Xi Guo, Yixin Guo, Eunja Ha, Xiao-Tao He, Jinniu Hu, Rongyan Hu, Jingke Huang, Kun Huang, Yanan Huang, Zidan Huang, Xiaofei Jiang, Seonghyun Kim, Youngman Kim, Chang-Hwan Lee, Jenny Lee, Jian Li, Minglong Li, Zhipan Li, Zhengzheng Li, Zhanjiang Lian, Haozhao Liang, Boran Liu, Lang Liu, Xiao Lu, Chenjun Lv, Jie Meng, Myeong-Hwan Mun, Yifei Niu, Zhongming Niu, Cong Pan, Panagiota Papakonstantinou, Jing Peng, Xiaoying Qu, Tianshuai Shang, Xinle Shang, Caiwan Shen, Guofang Shen, Ting Sun, Tingting Sun, Wei Sun, Xiang-Xiang Sun, Chen Wang, Peng Wang, Sibo Wang, Yiran Wang, Yuanyuan Wang, Yumeng Wang, Jiawei Wu, Liang Wu, Xinhui Wu, Xuewei Xia, Yingfeng Xu, Yonghe Xue, Jiangming Yao, Yaochen Yang, Guixiang Ye, Lian Ye, To Chung Yiu, Jianghan Yu, Yangyang Yu, Wentao Zeng, Kaiyuan Zhang, Jinzhe, Zhang, Ning Zhang, Shijie Zhang, Shuangquan Zhang, Wei Zhang, Xiaoyan Zhang, Yanxin Zhang, Ying Zhang, Yingxun Zhang, Zhenhua Zhang, Qiang Zhao, Ruyou Zheng, Chang Zhou, Shan-Gui Zhou, Lianjian Zou

Saturday 3 October

Solar and Stellar Astrophysics

The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc

Ian Baeza, L. Monaco, H. Frelijj et al. (+8 more)

Mass-Loss (ML) is a critical process that remains poorly understood despite its broad implications across astrophysics. Our current knowledge is insufficient to reproduce ML consistently across stars, particularly in cool, low-mass giants, where the time-variable nature of chromospheres (CHR) —the region where most physical phenomena powering ML in this regime are expected to occur— is poorly constrained. We characterize the relevant timescales of CHR variability in red giants and explore correlations with intrinsic stellar properties. We analyze the first large temporal spectroscopic monitoring of CHR variability using the H$\alpha$ line in red giants belonging to the globular cluster NGC 104 (47 Tuc) using FLAMES/GIRAFFE data. We find that H$\alpha$ variations increase on average and span a wider range of values with luminosity, together with a systematic blueshift of the line core indicative of outflows for $\log(L/L_\odot) \gtrsim 2.4$, alongside deeper cores consistent with increased CHR optical depth. The characteristic timescale required to observe variations in the H$\alpha$ profile is approximately one day, showing a flat trend with luminosity. While shorter-timescale variations remain consistent with statistical uncertainties, a possible increase toward dimmer stars is found. These trends appear similarly correlated with luminosity and effective temperature. No further correlation is found with different cluster populations, nor are significant differences observed between AGB and RGB stars. The outflow trends closely match previous observations across a wide metallicity range. We discuss whether these observations reflect changes in H$\alpha$ sensitivity to the winds, a genuine atmospheric transition driven by changes in heating efficiency, or continued CHR expansion with geometrically dominated H$\alpha$ formation.
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All authors Ian Baeza, L. Monaco, H. Frelijj, Y. Momany, L. Sbordone, S. Zaggia, I. Yegorova, I. Saviane, A. Mucciarelli, K. Ohnaka, M. Gómez

Solar and Stellar Astrophysics

Deriving the Continuous $\beta$-FPUT Model for Decayless Solar Coronal Oscillations Directly from Resistive MHD

D. Tsiklauri

We present an analytical framework deriving the fluid-continuum $\beta$-Fermi-Pasta-Ulam-Tsingou ($\beta$-FPUT) system directly from a third-order resistive magnetohydrodynamics (MHD) expansion to explain persistent, decayless transverse oscillations observed in solar coronal loops. For a continuous wave field propagating along a longitudinal magnetic field with cross-field density variations, a multi-scale expansion demonstrates that quadratic $\mathcal{O}(2)$ advective and Maxwell tension terms vanish identically due to out-of-plane polarization symmetry. Instead, the quadratic longitudinal ponderomotive force drives field-aligned density modulations that back-react on the primary transverse wave, yielding a cubic $\mathcal{O}(3)$ restoring force. In the long-wavelength limit, the governing equations reduce to a fluid-continuum Modified Korteweg-de Vries (mKdV) system where cross-field profile variation provides the non-linear dispersive mechanism. We prove that this internal fluid mechanism establishes stable, amplitude-dependent frequency self-focusing, which phase-locks adjacent elements and prevents phase-mixing wave attenuation without requiring external steady driving parameterizations. This framework enables macro-scale coronal seismology, providing closed-form expressions to invert observed decayless wave-packet durations to compute the unresolved cross-field density gradient scale length ($L_x$) and the internal volumetric filling factor ($f_V$) without relying on traditional emission measure or spectroscopic line-ratio diagnostics. Much like famous Enrico Fermi's historic use of macro-scale displacements to estimate complex atomic explosion yields, this framework establishes a paradigm where monitoring macroscopic oscillation durations empowers observers to extract fine-scale, otherwise unresolvable waveguide properties.
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Solar and Stellar Astrophysics · Cross-listed from nucl-th

Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars

Zhi-yao Li, Wei-zhou Jiang and Dian Sun

The radius of a neutron star is closely related to the equation of state (EOS) of asymmetric nuclear matter, particularly to the nuclear symmetry energy. At fixed stellar mass, the neutron-star radius and the nuclear-matter pressure near saturation density approximately satisfy a pressure–radius (R-P) scaling relation, linking stellar geometry to strong-interaction matter. In the presence of dark matter (DM), changes in the stellar geometry can modify this relation. We investigate how GeV- and sub-GeV-scale DM affects the R-P relation in DM-admixed neutron stars (DANSs) within a gravity-only two-fluid framework. We extend the Buchdahl analytic solution to a two-fluid configuration to demonstrate this scaling and then use 21 nuclear EOSs to fit the relation $R_{\rm NM}=\bar C P_{\rm NM}^{\eta}$ for $1M_\odot$ and $1.4M_\odot$ DANSs. The exponent $\eta$ and coefficient $\bar C$ jointly quantify the DM-induced modification and depend on the DM particle mass, stellar DM content, and self-interaction strength. For bosonic DM, changes in $\eta$ and $\bar C$ occur mainly in the sub-GeV range, whereas significant fermionic-DM effects persist up to about 1.5 GeV. Increasing the DM content or strengthening a repulsive self-interaction generally increases $\eta$ and decreases $\bar C$. The modified R-P relation therefore encodes information about the DM particle mass, abundance, and self-interaction, and affect the extraction of the nuclear EOS from celestial observations. At DM masses of several hundred MeV, both fermionic and bosonic DM can also produce DM-dominated low-mass ($1M_\odot$) DANSs with large radial extensions, for which the conventional scaling relation ceases to apply.
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Solar and Stellar Astrophysics

Measured energy exchange in coronal hole solar wind from its solar origins to the heliosphere

Yeimy J. Rivera, Alin R. Paraschiv, Samuel T. Badman et al. (+33 more)

Coordinated ground- and space-based remote observations are used to provide a comprehensive, multi-perspective view of the solar atmosphere that we connect with in situ measurements in the heliosphere centered around the April 8 2024 Total Solar Eclipse observed across North America. These near-contemporaneous, multi-wavelength datasets are used to directly derive the plasma parameters and compute an energy budget of a solar wind stream at its low-coronal birthplace (at an altitude of 1.05Rsun). The energy budget is also independently computed at and beyond the Alfvén surface from the in situ observations of the same stream. The total wave energy flux dominates the low-coronal budget (11 W m-2 Alfvén, 7 to 23 W m-2 in compressive MHD modes), while enthalpy (13 W m-2) and work done against gravity from 1.0Rsun (2.5 W m-2) make up the remainder. The total coronal energy budget is consistent with the total measured in situ by Parker Solar Probe if and only if compressive energy flux is included and attributed to the fast magnetosonic mode. Nearly all this thermal and wave energy is converted to ion heating, acceleration and gravitational potential energy within the Alfvén surface. The stream evolution is well-described as a thermal-pressure driven wind with additional energy deposited by MHD fluctuations. The observed evolution of the Alfvénic component of these fluctuations follows a near-dissipation-free curve below the Alfvén surface while deviating from it more strongly above this critical surface.
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All authors Yeimy J. Rivera, Alin R. Paraschiv, Samuel T. Badman, Alberto M. Vasquez, Federico A. Nuevo, Ryan J. French, Momchil Molnar, Roberto Susino, Zihao Yang, Marco Romoli, Richard A. Frazin, Michael L. Stevens, Stuart D. Bale, Deborah Baker, Jasper Halekas, Thomas A. Schad, Christopher J. Owen, Philippe Louarn, Jenna Samra, Giuliana de Toma, Daniela A. Lacatus, Giulio Del Zanna, Chad A. Madsen, Enrico Landi, Manolis K. Georgoulis, Amir Caspi, Éric Buchlin, Nour E. Raouafi, Luca Franci, Miho Janvier, Cooper Downs, Roberto Livi, Phyllis Whittlesey, Ali Rahmati, Davin Larson, Nikos Sioulas

Solar and Stellar Astrophysics

Global solar compressible convection simulations on non-Cartesian mappings

Grégoire Doebele, Allan Sacha Brun and Maxime Delorme

Context. Modeling the global dynamics of the Sun requires numerical frameworks capable of simulating the highly turbulent convective envelope and its coupling with the stable radiative interior. Simulating such spherical domains in standard cartesian finite-volume codes presents significant topological challenges. Aims. The goal is to extend the cartesian Adaptive Mesh Refinement (AMR) framework Dyablo to non-cartesian geometries in order to perform global solar convection simulations that extend all the way down to the stellar core. Methods. We introduced a mapped grid approach within the Dyablo framework to build Dyablo Whole Sun (DWS) code. We implemented an $\alpha-\beta$ well-balanced scheme to preserve hydrostatic equilibrium. Furthermore, we present a robust methodology to generate fully integrated solar background profiles from $r=0$ to the surface. Results. We validated the implementation using standard hydrodynamic tests and ran high-resolution 2D global solar convection simulations on a disk grid. Conclusions. Our models successfully capture the turbulent convective broad slow upflows and narrow fast downflows and the excitation of acoustic waves and p modes. The interaction of strong downflowing plumes with the top of the radiative zone, successfully excites internal gravity waves in the radiative interior.
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Solar and Stellar Astrophysics

SWAN-SF-V2: A Multivariate Time Series Dataset for Space Weather Data Analytics; Now with AIA and Weighted SHARP Parameters

Dustin Kempton, Griffin Goodwin, Reet Gupta et al. (+4 more)

Since its original publication in 2020, the SWAN-SF dataset has been cited in over 300 research publications. Here we describe a comprehensive update to the original multivariate time series (MVTS) dataset extracted from solar photospheric vector magnetograms in the Spaceweather HMI Active Region Patch (SHARP) series. As was performed in the original release, our dataset includes a cross-checked NOAA solar flare catalog that facilitates the comparative evaluation of methods designed for solar flare prediction. We discuss the methods used for data collection, cleaning, and pre-processing of the solar active region and flare data, which includes improvements to the data integration and sampling methodology. Additional parameters have been derived from the Solar Dynamics Observatory's Atmospheric Imaging Assembly to augment the original features derived from magnetogram data. Our dataset expands the period of observations to cover 7,730 MVTS data collections from active regions occurring between May 2010 and December 2025, each of which is composed of 182 flare-predictive parameters. We continue to integrate flare reports, with over 39,000 multi-source verified flare reports providing flaring history information about the source active regions. The primary tasks enabled by the disseminated dataset continue to include optimization of solar flare prediction and detailed investigation for elusive flare predictors or precursors, with both operational (research-to-operations), and basic research (operations-to-research) benefits.
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All authors Dustin Kempton, Griffin Goodwin, Reet Gupta, Viacheslav M Sadykov, Rafal A. Angryk, Berkay Aydin, Manolis K. Georgoulis

Solar and Stellar Astrophysics

Cross-Modal Solar Image Synthesis: Adapting the Surya Foundation Model from He I 10830 Å to EUV Translation and Coronal Hole Segmentation

Marco Marena, Andrés Muñoz Jaramillo, Qin Li et al. (+8 more)

The long observational record of He I 10830 Å offers a means to investigate solar morphology before modern extreme-ultraviolet (EUV) imaging. We adapt the Surya solar foundation model to predict Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) 94, 193, and 304 Å images and a coronal hole (CH) probability map from full-disk helium observations. A convolutional input adapter, low-rank backbone updates, and dedicated output decoders learn from temporally paired, geometrically registered observations, with Spatial Possibilistic Clustering Algorithm (SPOCA) catalog polygons providing CH supervision. On observations held out from downstream fine-tuning, the selected dedicated models achieve disk-restricted correlation coefficients (CCs) of 0.8196, 0.8885, and 0.8398 for the three AIA channels, respectively; the CH model achieves an intersection over union (IoU) of 0.4360. The predictions recover broad solar structure, although local agreement varies substantially by channel. An optional residual refiner addresses spatial detail, and its application on pre-SDO dates improves the correlation of synthetic AIA 304 with Solar and Heliospheric Observatory/Extreme-ultraviolet Imaging Telescope (SOHO/EIT) 304 references from 0.6511 to 0.7085. Together, these results support the feasibility of helium-conditioned EUV morphological proxies and motivate their use in historical reconstruction, within the scope of the downstream test and cross-instrument evaluation.
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All authors Marco Marena, Andrés Muñoz Jaramillo, Qin Li, Haodi Jiang, Jinghao Cao, Wen He, Ziyang Zhang, Chenxi Yuan, Chao Wang, Haimin Wang, Bo Shen

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

Stellar magnetic activity and rocky planets in cool dwarf stars

A. K. Stefanov

Exoplanetary astronomy has entered its Golden Age, with humanity having found over 6000 exoplanets to date. The majority of these discoveries have been achieved through transit-photometry and radial-velocity (RV) techniques. While transit surveys lead in discovery numbers, the RV method persists as a vital and indispensable technique in exoplanetary science, particularly in the most prevalent stellar population – M dwarfs. Their low masses make them the theoretical favourites for RV detections, since exoplanet signals are stronger over the same period, and are therefore easier to detect and measure accurately. Nevertheless, the stellar activity M dwarfs exhibit introduces significant challenges, particularly when seeking RV semi-amplitudes to the order of 1 m$\,$s$^{-1}$, or lower. Stellar activity is known to mimic or suppress planetary signals, and its effects manifest across all time scales: from short-lived signals due to convective motion (lasting minutes to days), through active regions on the stellar surface (days to months), to long-term magnetic cycles (years to decades). These issues highlight the urgent need for robust methodologies that are capable of reliably disentangling stellar variability from genuine planetary signals. This doctoral dissertation explores these challenges through the application of Gaussian-process (GP) modelling. I present three distinct but interconnected publications that integrate high-precision spectroscopy and photometry with a unified GP-based approach in two cases, and that enable robust disentanglement of planetary signals from stellar activity. Together, these three studies illustrate how observations of different origin can be combined with appropriate statistical machinery for the sake of detecting exoplanets, with the possibility of interpreting stellar activity.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Fast X-ray Transient EP260321a: Shock Breakout through an Extended Circumstellar Matter

Maokai Hu, Yi Yang and Xiaofeng Wang

The Einstein Probe (EP) has discovered a fast X-ray transient, EP260321a, whose optical counterpart was subsequently classified as a broad-lined Type Ic supernova. Its observed rise time of about 690 seconds is inconsistent with theoretical predictions for shock breakout (SBO) from a Wolf-Rayet star, which is typically regarded as the progenitor of envelope-stripped supernovae. In this paper, we propose that EP260321a arose from a SBO within extended circumstellar matter (CSM), where breakout photons were initially trapped, then diffused out of the unshocked CSM as the ejecta expanded and the opacity decreased. We modeled this photon diffusion process using both Monte Carlo simulations and an analytical approach to describe the temperature evolution. Through Markov Chain Monte Carlo sampling, we obtain the best-fit CSM parameters of log10(Mcsm/Msun) = -3.3 for the total CSM mass, Rin = 160 Rsun for the inner CSM radius, and Rout = 612 Rsun for the outer CSM radius. The presence of such a dense CSM indicates that the progenitor of EP260321a underwent episodic mass loss just days before the explosion, providing new observational constraints on the late-stage evolution of massive stars.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

How dust particles orbiting white dwarfs can reveal undetected co-orbiting exoplanets II. Exoplanets on elliptic orbits

Kyriaki I. Antoniadou and Dimitri Veras

Abridged. We aim to extend Paper I to the eccentric secondary orbit case and now analyse the elliptic restricted three-body problem (ERTBP). Our secondary masses include Ceres, Mercury, Earth, and Neptune so that we can help infer the presence of both large asteroids and planets through our analysis. We study dust particles on both planar (2D-ERTBP) and non-coplanar (3D-ERTBP) orbits. We computed families of 1/1 resonant symmetric and asymmetric periodic orbits in the 2D-ERTBP and 3D-ERTBP. Doing so produces novel results in their own right and diagnostic tools for precise guidance for our next steps. Based on them, we generated detailed phase portraits. Finally, we run suitably seeded $N$-body simulations to compare with the periodic orbits, and to provide observational links with debris close to WDs. New families of asymmetric periodic orbits, called $E^A_{41}$, $E^A_{42}$, and $E^A_{43}$ in the high-eccentricity 2D-ERTBP regime were discovered. They are generated by the new bifurcation point, $B_T^4$, along the new $A_2$ family, showcased in Paper I. Moreover, new isolated families of asymmetric periodic orbits, namely $E^A_{44}$, $E^A_{45}$, and $E^A_{46}$ were discovered. Families of short- and long- period asymmetric orbits starting from $L_4$, called $E^A_S$ and $E^A_L$, were also computed. In both the 2D- and 3D-ERTBP regimes, highly eccentric motion is exhibited for the dust particles in the majority of the families of either symmetric or asymmetric periodic orbits. The $N$-body simulations reveal that over ten years, the orbital period deviations of the dust are higher than in the circular restricted three-body problem (Paper I); in some architectures, Mercury-mass planets can regularly generate deviations exceeding $\sim$100 s, which potentially aids observational inferences of hidden asteroids or planets orbiting WDs.
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Solar and Stellar Astrophysics

Stellar parameters and abundances for 3.2 million DESI DR1 spectra using machine learning

Nagaraj Vernekar, Michael Hayden and Sara Lucatello

We present a machine-learning pipeline for determining stellar parameters and chemical abundances from spectra observed by the Dark Energy Spectroscopic Instrument (DESI). Building on the model-driven Payne framework, we train an artificial neural network on ~370,000 synthetic spectra spanning FGK stars, and fit the network directly to the flux-calibrated, un-normalised spectral energy distribution (SED) of each star, rather than to a continuum-normalised spectrum as done by DESI's official Stellar Parameter (SP) pipeline. Internal accuracy tests show a median interpolation error of less than 0.3% for 90% of a synthetic verification sample, and the full fitting workflow recovers input labels to high accuracy even at low signal-to-noise ratio (S/N). Validating our method on cross-matched samples of 6719 APOGEE and 3455 GALAH stars observed by DESI with S/N > 20, we recover Teff and logg with smaller systematic offsets than the DESI SP pipeline, an improvement we attribute to fitting the full SED shape rather than a normalised spectrum. We further recover 12 elemental abundances (Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Ba, and Y) to an accuracy that matches or exceeds SP where a comparison is possible, and provide four abundances, Mn, V, Ba, and Y, that SP does not report at all. Applying this pipeline to the DESI Data Release 1 stellar sample, we deliver a catalogue of stellar parameters and abundances for 3.2 million stars.
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Friday 2 October

Solar and Stellar Astrophysics

A forest of emission lines observed by Sunrise III/SUSI above the solar limb

J. S. Castellanos Durán, F. A. Iglesias, S. K. Solanki et al. (+31 more)

We present off-limb spectroscopy using low-straylight data from the Sunrise Spectropolarimeter and Imager (SUSI) onboard the Sunrise III stratospheric solar observatory. A spatial scan with SUSI's slit almost parallel to the local limb reached from within the solar disc to 6.5 Mm off-limb. The wavelength range spanned from 407.6 to 410.25 nm. We detected a total of 174 spectral lines in emission off-limb, a 2.5-fold increase over previous reports. Surprisingly, 122 of these lines begin to appear in emission already on the disc, although close to the limb. In addition, one-fifth of relatively prominent emission lines are due to rare-earth and heavy elements and molecules, where the absorption lines of these transitions are typically weak on-disc.
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All authors J. S. Castellanos Durán, F. A. Iglesias, S. K. Solanki, A. Lagg, I. Milic, H. N. Smitha, D. Vukadinović, T. L. Riethmüller, A. Gandorfer, A. Feller, J. Blanco Rodríguez, D. Orozco Suárez, Y. Katsukawa, J. Hölken, J. C. del Toro Iniesta, S. Rao, M. Sánchez Toledo, K. Singh, P. Bernasconi, T. Berkefeld, A. Alvarez-Herrero, M. Kubo, V. Martínez Pillet, B. Grauf, M. Carpenter, A. Bell, H. Strecker, A. L. Siu-Tapia, P. Santamarina Guerrero, Y. Kawabata, T. Matsumoto, R. T. Ishikawa, E. Harnes, T. Oba

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

Stars Would Remember a Recent Gravitational Transition: Testing G-step Resolutions of the Hubble Tension with Red Dwarfs

Jeremy Sakstein and Harry Desmond

We test the hypothesis that Newton's gravitational constant underwent a rapid transition approximately $73$-$130\,{\rm Myr}$ ago, as proposed in some resolutions of the Hubble tension. Fully convective red dwarf stars with masses below $\sim0.35\,M_\odot$ have thermal timescales comparable to the proposed transition look-back times, so an appreciable present-day memory can remain. We show that a rapid step in $G$ induces measurable changes in their radii and confront these predictions with mass-radius measurements of eight red dwarfs in detached eclipsing binaries. We find that the $G$-step models proposed to resolve the Hubble tension, corresponding to a $4\%$ change in $G$ at a look-back time of $73\,{\rm Myr}$ and an $11\%$ change at $130\,{\rm Myr}$, are excluded at significances of $3.1\sigma$ and $4.0\sigma$, respectively.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

A concordance model of neutron star kicks

Cheyanne Shariat, Kareem El-Badry and Smadar Naoz

Neutron stars (NSs) receive natal kicks during supernovae that affect their survival in binaries and motion through the Galaxy. The global distribution of these kick velocities across the NS population remains uncertain. Here, we combine the orbital properties and birth rates of Gaia NS and Be+NS binaries with velocity constraints from young isolated pulsars to construct a concordance model of NS natal kicks. We find that all three populations can be jointly described by a shared bimodal kick distribution. The low-velocity component follows a lognormal distribution with $\mu_{\ln v}=1.87^{+0.65}_{-0.53}$ and $\sigma_{\ln v}=0.55^{+0.85}_{-0.44}$, corresponding to a median speed of $6.5^{+5.9}_{-2.7}~{\rm km~s^{-1}}$. The high-velocity component is consistent with the distribution inferred from young pulsars, which peaks near $200~{\rm km~s^{-1}}$. The low-velocity component contributes only $\sim10\%$ of all NS births, but produces most Gaia NS binaries and roughly half of Be+NS binaries. The same model predicts systemic recoil velocities consistent with the observed kinematics of Gaia NSs, Be+NS binaries, and NS low-mass X-ray binaries. For Gaia NSs, whose formation history remains unknown, we use this kick distribution to constrain their progenitors. We favor pre-supernova binaries containing intermediate-mass stripped stars with $\sim1~{\rm M_\odot}$ companions in au-scale orbits, and predict $\sim300$ such binaries in the Milky Way today, $\sim40$ in the LMC, and $\sim30$ in the SMC. Finally, we consider the implications of these kicks for NSs in hierarchical triples. We find that 2-10$\%$ of Gaia NS triples and 3-23$\%$ of Be+NS triples retain their tertiary after the supernova. Overall, our results suggest that a shared natal kick law can account for isolated pulsars and surviving NS binaries, where most NSs receive large kicks and low kicks are common among surviving binaries.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

A Unified Multi-Band Secular Framework for the Hierarchical Triple PSR J0435+3233 System

Achamveedu Gopakumar, Vidit Singh, Abhimanyu Susobhanan et al. (+9 more)

The millisecond pulsar PSR J0435+3233, discovered by FAST, exhibits an unusually large apparent spin-down rate, potentially reflecting line-of-sight acceleration from a distant companion. Recent investigations reveal a hierarchical triple consisting of an inner pulsar-helium white dwarf binary with an orbital period of ~8 days, orbited by a G-type subgiant tertiary on an eccentric ~74 yr orbit. The current timing description admits two distinct geometrical solutions. We develop a singly averaged (SA) formulation that averages over the inner orbit while retaining the instantaneous phase of the eccentric outer orbit, thereby capturing the time-dependent quadrupolar perturbations induced by the tertiary. We show how this physical three-body description can be incorporated naturally into pulsar-timing analyses and use it to forward-propagate the two currently viable configurations, Tv1 and Tv2, to forecast when their timing signatures become distinguishable with FAST. The SA evolution predicts that the two configurations will become distinguishable in the coming years, with the effective projected semi-major axis, $x_{1,\mathrm{eff}}$, providing the earliest discriminating observable. We further extend the framework to predict the tertiary's spectroscopic radial-velocity and astrometric evolution, linking FAST timing with LAMOST time-domain spectroscopy and Gaia astrometry. This multi-band framework has the potential to establish PSR J0435+3233 as an exceptionally well-constrained laboratory for three-body dynamics, compact-binary and stellar evolution, and gravitational physics.
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All authors Achamveedu Gopakumar, Vidit Singh, Abhimanyu Susobhanan, Mauri J. Valtonen, Sayantan Bhattacharya, Di Li, Hong-Liang Yan, Jianping Yuan, Na Wang, Pei Wang, Qingdong Wu, De Zhao

Solar and Stellar Astrophysics

Spectroscopic monitoring of long secondary period variables. The case of J-type carbon stars

L. Planquart, A. Jorissen and H. Van Winckel

Long-secondary-period (LSP) variables are a subclass of long-period variables whose origin is a matter of debate. J-type carbon stars are a subclass of carbon stars enriched in 13C, and the origin of this chemical peculiarity is unclear. In this paper, we report on the discovery of a LSP in two J-type carbon stars: VZ Per and UV Cam. Methods. A decade-long spectroscopic monitoring was used to obtain a long-term radial-velocity curve for the two stars. From a frequency analysis, we isolated a LSP signal. The retrieved periodicity was then compared with changes in spectral profiles and available light-curve variability to further constrain the origin of the modulation. Results. For VZ Per, the LSP derived from the radial-velocity curve (~960 days) is correlated with the light-curve dimming event and a variation in the Balmer absorption line profile. These results translate into changes in the gas and dust column densities with the phase of the LSP, with the maximum gas column density occurring ahead of the dust. For UV Cam, the radial velocity monitoring yields a period of ~1178 d with an amplitude of about 1 km/s. Interpreting the RV modulation as a Keplerian signal for both stars, a low-mass (<0.1Msun) close companion is found. In this scenario, variations in gas and dust column densities with (orbital) phase trace the material in the expanding comet-like tail trailing the substellar companion. Conclusions. These observations provide time-dependent variations of the gas and dust in LSP variables that are consistent with the current binary scenario. Furthermore, the detection of LSP among J-type carbon stars anchors their current evolutionary status in the dust-producing region of the thermally-pulsing AGB phase.
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Solar and Stellar Astrophysics

The origin of dispersion in the wind mass-loss rate–luminosity relation of massive O stars

Jiri Krticka and Iva Krtickova

Stellar winds of hot stars are accelerated by the radiative force that mainly comes from the line transitions of heavy elements. As a result, the wind mass-loss rate is expected to scale mostly with the stellar luminosity. This scaling clearly emerges from the observational analysis of O stars and their winds, but with substantial scatter. The origin of this scatter is unclear. Part of the scatter of the observational relation between the hot star wind mass-loss rate and luminosity may originate from the sensitivity of the mass-loss rate to other stellar parameters besides the luminosity, such as the effective temperature, mass, and metallicity. We tested this possibility using our wind models. We calculated tailored wind models for stellar parameters corresponding to selected individual O stars from the Large Magellanic Cloud as derived from a previous analysis. To model the wind, we used our global wind code that calculates the radiative force from the solution of the radiative transfer equation in the comoving frame. Wind models calculated for particular stellar parameters reproduce the observational mass-loss rates better than simple scaling relations derived from model grids. This indicates that the dependence of the mass-loss rate on the other stellar parameters except the luminosity might explain part of the dispersion in the relation between the mass-loss rate and luminosity. However, some dispersion still remains, which might indicate that wind variability is another source of the dispersion.
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Solar and Stellar Astrophysics · Cross-listed from nucl-ex

First strength measurements of low-energy resonances in the $^{45}$Sc($p,\gamma$)$^{46}$Ti reaction and its astrophysical implications

R. S. Sidhu, R. J. deBoer, J. Görres et al. (+13 more)

The $^{45}$Sc($p,\gamma$)$^{46}$Ti reaction plays an important role in both hydrostatic and explosive nucleosynthesis. During hydrostatic oxygen and silicon burning in massive stars, including dynamic processes such as convective carbon-oxygen (C-O) shell mergers, it acts as a bottleneck that regulates the reaction flow in the Sc-Ti mass region. In oxygen-neon (ONe) novae, the ejecta indicate the production of elements up to the Fe group, as observed in V1974 Cygni, and the $^{45}$Sc($p,\gamma$)$^{46}$Ti reaction links nuclei above Ca to the Fe region. In core-collapse supernovae (CCSNe), it influences the production of the radioactive isotope $^{47}$Sc. At present, the thermonuclear reaction rate is based on statistical model calculations. In this work, we report on measurements of the $^{45}$Sc($p,\gamma$)$^{46}$Ti reaction performed using the 5~MV accelerator at the Nuclear Science Laboratory, University of Notre Dame, over a laboratory proton energy range of 526–1275~keV. We present the first direct measurements of the resonance strengths for six resonances at $E^{\rm lab}_{\rm R} = 917.4$, 1026.0, 1031.1, 1049.7, 1059.4 and 1257.5~keV, together with integrated resonance strengths at $E^{\rm lab} = 555$, 630, 700, 761 and 871~keV. For resonance energies below the lowest directly measured energy, available transfer-reaction data were used to estimate the resonance strengths. An updated thermonuclear reaction rate is derived, and its astrophysical implications are discussed.
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All authors R. S. Sidhu, R. J. deBoer, J. Görres, M. Wiescher, W. N. Catford, C. Dembski, C. R. Jones, Ó. E. López-López, G. Lotay, K. Manukyan, M. Matney, J. O'Neill, J. Rufino, A. T. Sanchez, M. Williams, L. Zimmer