Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Thursday 24 September

Solar and Stellar Astrophysics

Coronal Green-Line Emission During a Solar Prominence Eruption: Spectroscopic Evidence of Its Correspondence with the EUV Late Phase

P. Vemareddy, R. Ramesh and V. Muttu Priyal

We report spectroscopic observations during a prominence eruption on 9 October 2025 from the Sun's west limb, associated with an M2.0 flare that commenced at 12:11 UT. The event was captured in sit-and-stare mode by the Visible Emission Line Coronagraph (VELC) onboard Aditya-L1, providing continuous observations of the Fe XIV 5303 Åcoronal greenline. The spatially averaged green-line emission exhibits a clear correspondence with the EUV late-phase (ELP) emission observed in multiple SDO/AIA channels. In particular, an enhanced 5303 Åemission peak at 15:24 UT coincides with secondary peaks in the AIA 211, 171, 193, and 335 Åpassbands, occurring $\sim173$ minutes after the X-ray peak. The 5303 Åline-width information provides important constraints on the mechanism responsible for the ELP. The line-width decreases progressively by about 28% toward the ELP peak, broadly consistent with the cooling of post-flare coronal loops. This behavior suggests that the ELP is predominantly associated with plasma cooling, with relatively weak additional energy input from magnetic reconnection, which does not produce a significant enhancement in line-widths. The estimated non-thermal velocity decreases from $\sim$36 km s$^{-1}$ during the impulsive phase to $\sim$21 km s$^{-1}$ during the gradual phase, indicating a reduction in turbulent plasma motions. And doppler velocities evolve from predominantly positive values during the eruptive rise phase to negative values during the later gradual phase, implying upward and subsequent downward plasma motions. To our knowledge, this study provides the first space-based spectroscopic evidence linking coronal green-line emission with the ELP and its origin during a solar flare.
Read the full abstract

Solar and Stellar Astrophysics

Formation of adducts of C$_6$H with Na$^+$, Mg$^+$ and Al$^+$ metal cations by radiative association

Niyazi Bulut, Octavio Roncero, Maria Mallo et al. (+6 more)

The Mg-bearing cations MgC$_4$H$^+$, MgC$_6$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$ have been recently observed in the carbon-rich envelope IRC\,+10216. These species are thought to form upon radiative association between Mg$^+$ and the corresponding neutral radical. This work aims to determine the radiative association rate coefficients for the cations Al$^+$, Mg$^+$, and Na$^+$ reacting with carbon chain radicals to estimate the relative importance of metal-bearing carbon cations for each of these metals. For this purpose we use statistical methods in combination with highly accurate ab initio calculations to obtain the radiative association rate coefficient. Moreover, anisotropic effects beyond mono-dimensional capture model are considered, providing a more reliable description of the simulated processes.} The radiative association rate coefficients to form Mg-, Al- and Na-C$_6$H$^+$, as well as MgC$_4$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$, are calculated with the new restrictions considered in this work. These new rate coefficients are included in a chemical model of the C-rich AGB envelope IRC\,+10216. The abundances of MgC$_4$H$^+$, MgC$_6$H$^+$, and MgC$_5$N$^+$ are consistent with observations, with differences no greater than one order of magnitude, corroborating radiative association as a plausible formation mechanism for these adducts. However, the calculated abundance of MgC$_3$N$^+$ is about two orders of magnitude lower than observed, which indicates that either the chemistry of this species is significantly different from the others or the calculated rate coefficient is too low. The abundances obtained for Na-C$_6$H$^+$ and Al-C$_6$H$^+$ are around two orders of magnitude lower than for Mg, making very difficult to detect the analogous metal-bearing cations in IRC\,+10216.
Read the full abstract

All authors Niyazi Bulut, Octavio Roncero, Maria Mallo, German Molpeceres, Marcelino Agundez, Maysa Yusef-Buey, Jose Cernicharo, Carlos Cabezas, Piotr Zuchowski

Solar and Stellar Astrophysics

DKIST unveils MHD-predicted sub-50 km photospheric vortices

S. Vargas Dominguez, O. A. Calvo Rebellon, J. S. Castellanos Duran et al. (+4 more)

Solar vortices are rotating plasma structures that play a key role in the transport of energy and magnetic helicity from the photosphere to the chromosphere and corona. While numerical simulations predict the existence of small-scale photospheric vortices with diameters of $50$–$100$ km, no direct observational evidence has been reported to date, primarily because of the limited spatial resolution of previous instrumentation. Here, we analyze high-resolution observations obtained with the 4-meter Daniel K. Inouye Solar Telescope (DKIST) at 416 nm, with a spatial resolution of 12.3 km. Using Fourier local correlation tracking and the swirling strength criterion ($\lambda_{\rm ci}$), we identify 201 vortex detections across a sequence of 143 reconstructed frames, spanning approximately 3.2 minutes, within a field of view of $4.92 \times 4.13$ Mm. The observations cover a photospheric plage region containing pore-like magnetic concentrations. The detected vortices have a median equivalent diameter of 38.6 km and a mean diameter of $39.5 \pm 3.3$ km. Virtually all detections are smaller than 50 km and therefore fall within the subgranular regime predicted by magnetohydrodynamic simulations but never previously observed. The median swirling period, $\tau_{\rm ci}=37.3$ s, satisfies the $\tau_{\rm ci}<100$ s criterion established by MURaM simulations. No statistically significant preference is found for prograde rotation (53.7%) over retrograde rotation (46.3%), consistent with the negligible influence of the Coriolis force at subgranular scales. These results demonstrate the unique capability of DKIST to resolve the population of photospheric convective vortices predicted by state-of-the-art magnetoconvection simulations, opening a new observational window into small-scale solar convective dynamics.
Read the full abstract

All authors S. Vargas Dominguez, O. A. Calvo Rebellon, J. S. Castellanos Duran, M. van Noort, F. Wöger, D. A. Rodriguez Torres, C. G. Bernal

Solar and Stellar Astrophysics

A Multiwavelength View of $\rho$ Oph II: Disentangling the Variability of the Multi-Star Component C

Sean J. Gunderson, Walter W. Golay, Jackson Codd et al. (+8 more)

We present a multiwavelength analysis of the star $\rho$ Oph C, covering X-ray, optical, near-infrared, and radio observations to test for the presence of interferometrically-detected cool star companions. The X-ray observations from Chandra, XMM-Newton, and NuSTAR show flare-like events lasting minutes or days in time and spectral properties consistent with those of cooler stars instead of the primary magnetic B star. The near-infrared data is also consistent with the proposed trinary system properties due to the presence of CO-band heads. After removing the primary B star's rotation, the optical data from TESS shows a residual signal at the level of 0.8 mmags, matching the variations expected from cool stars in orbit around a bright B star. Finally, multi-epoch radio data reveals that $\rho$ Oph C exhibits significant large scale flux variations that are atypical for a magnetic massive star. Taken as a whole, the multi-epoch and -wavelength data presents a consistent picture of $\rho$\,Oph\,C as a rare trinary system composed of a hot star and two cool stars.
Read the full abstract

All authors Sean J. Gunderson, Walter W. Golay, Jackson Codd, David P. Huenemoerder, Felipe Navarete, Christiana Erba, Alexandrea Moreno, John M. Cannon, Richard Ignace, Pragati Pradhan, the MACRO consortium

Solar and Stellar Astrophysics

Quantum Phase Transitions in Nuclei and the Origin of Rhodium

P. Agarwal, H. Schatz, A. Francis et al. (+3 more)

The astrophysical rapid neutron capture process (r-process) is a major nucleosynthesis process responsible for the production of elements heavier than copper. Prominent features in the observationally inferred r-process abundance distributions provide critical clues for astrophysical conditions and possible r-process sites. The lack of clear features for the r-process elements lighter than tellurium has led to a broad range of proposed possible scenarios and alternative processes that may produce these elements. Here we show that the enhancement found in the solar system of rhodium and ruthenium isotopes compared to neighboring isotopes can serve as such a feature. The enhancement can be traced back to sudden changes in shape of unstable rare isotopes in the path of the light element r-process. Such shape changes have been described as quantum phase transitions. This finding points to r-process scenarios with relatively high neutron densities and temperatures for the origin of rhodium and ruthenium in the solar system. Rhodium and ruthenium abundances observed in r-process enhanced stars can now be used as diagnostics for the r-process conditions that produce these lighter r-process elements. Observational data for these elements indicate that different types of r-processes may have operated in the early Galaxy, and that the conditions do not necessarily align with the weak and main r-process classifications used in the past.
Read the full abstract

All authors P. Agarwal, H. Schatz, A. Francis, F. Montes, B. Pol, L. Roberts

Solar and Stellar Astrophysics

Estimates of magnetic field strength in the solar corona using observations of thermal radio emission at low frequencies

Shaik Sayuf, Kathiravan C and Ramesh C

Measurements of the magnetic field strength in the solar corona at heliocentric distances $r\,{\gtrsim}\,1.1\,R_{\odot}$, using observations other than transient radio bursts, are rare. Circular polarization observations of thermal bremsstrahlung radio emission at frequencies $<$ 100 MHz, which typically originate at $r\,{>}\,1.1R_{\odot}$ in the solar corona, can be effectively used for this purpose. The thermal bremsstrahlung emission is randomly polarized, but in the presence of a magnetic field it propagates in two oppositely polarized circular modes whose differential absorption in the medium results in an observable circular polarization. We report a case study of two-dimensional imaging observations of the above mentioned circular polarization in the solar corona at 51\,MHz using the Gauribidanur RAdioheliograPH (GRAPH), and estimates of the associated coronal magnetic field strength. The peak degree of circular polarization ($dcp$), calculated from the observed total and circularly polarized intensity images with the GRAPH, is ${\approx}$2.7%. Using ray-tracing simulations we find that the observed peak $dcp$ corresponds to a radio source located at $r\,{\approx}\,1.65\,{\pm}\,0.15\,R_{\odot}$ at 51 MHz, and its field strength is ${\approx}\,1.55\,{\pm}\,0.3\,$Gauss.
Read the full abstract

Solar and Stellar Astrophysics

JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure

Aaron M. Meisner, Adam J. Burgasser, Chih-Chun Hsu et al. (+15 more)

We present JWST NIRSpec and MIRI observations of the metal-poor T dwarf WISEA J155349.96+693355.2. The combined NIRSpec/prism plus MIRI/LRS spectrum (R ~ 100) provides 0.6-12 $\mu$m spectroscopic coverage that reveals the presence of H$_2$O, CH$_4$, and NH$_3$ absorption features, enhanced collision-induced H$_2$ absorption, and weak or absent CO and CO$_2$ absorption, all indicators of a metal-poor low-temperature atmosphere. Comparison of the spectral data to a suite of atmosphere models yields an effective temperature $T_{\rm eff}$ = 960$^{+28}_{-32}$ K and a solar-scaled metallicity of [M/H] = -1.16$^{+0.28}_{-0.25}$ dex. We find indications that the uncertain trigonometric parallax, likely subject to Lutz-Kelker bias, may be overestimated. Adopting the photometric distance yields a bolometric luminosity log$_{10}L_{bol}/L_{\odot}$ = -5.29 $\pm$ 0.10, from which we infer $T_{\rm eff}$ = 974 $\pm$ 56 K, consistent with the temperature derived via our atmospheric model fits. From the moderate-resolution (R ~ 3,000) NIRSpec/G395H spectrum, we measure a radial velocity of -163 $\pm$ 5 km/s, which combined with the source's measured proper motion and estimated distance indicates a highly eccentric (e $\geq$ 0.9) Galactic orbit consistent with an accreted halo object. The UVW kinematics of WISEA J155349.96+693355.2, its bulk metallicity, and its modest alpha enrichment ([$\alpha$/Fe] = +0.15$^{+0.04}_{-0.06}$ dex) are all equivalent to stars identified in the Gaia-Enceladus Milky Way substructure, making it the first brown dwarf with kinematic and chemical evidence of association.
Read the full abstract

All authors Aaron M. Meisner, Adam J. Burgasser, Chih-Chun Hsu, Sherelyn Alejandro Merchan, Jacqueline K. Faherty, Genaro Suárez, ZengHua Zhang, Roman Gerasimov, Christian Aganze, Nicolas Lodieu, Eileen C. Gonzales, Adam C. Schneider, Stanimir A. Metchev, Dan Caselden, Michael C. Cushing, Christopher A. Theissen, Jason J. Wang, Harshil Kothari

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

A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes

Jian-Guo He, Yong Shao, Yu-Dong Nie et al. (+5 more)

Gravitational-wave observations have revealed hundreds of stellar-mass black holes, yet only about two dozen are known in the Milky Way, almost all in binaries. We present POPKIN, a Python framework that couples single- and binary-star evolution with Galactic orbital dynamics to trace black-hole progenitors from the zero-age main sequence to the present-day isolated black-hole (IBH) population. Across ten models varying the supernova (SN) prescription, mass-transfer efficiency, and common-envelope ejection efficiency, the total IBH abundance is controlled primarily by the SN prescription. Our fiducial model, with a recently proposed metallicity- and stripping-history-dependent SN prescription, predicts $\sim4\times10^7$ IBHs in the Galaxy, including $\sim8\times10^4$ within $1\,\rm{kpc}$ of the Sun; alternative SN prescriptions predict $\sim(1-2)\times10^8$ IBHs. The fiducial model yields a bimodal mass distribution, peaking near $9\,M_{\odot}$ and $20\,M_{\odot}$, with a deficit at $13-17\,M_{\odot}$. This distinguishes it from alternative prescriptions, some of which populate the $2-5\,M_{\odot}$ mass-gap region. Non-kicked IBHs follow nearly circular orbits near the Galactic plane, with typical peculiar velocities of $20-30\,\rm{km\,s^{-1}}$, whereas kicked systems undergo stronger radial migration and span a broader velocity range. We estimate $\sim5\times10^3$ accreting IBHs with $F_{\rm X}>10^{-14}\,\rm{erg\,s^{-1}\,cm^{-2}}$, nearly all non-kicked; this estimate is sensitive to the adopted radiative-efficiency and hot-flow treatments. For a Roman-like bulge survey, our fiducial model predicts $\sim360$ intrinsic IBH microlensing events over five years in a $1.70\,\rm{deg^2}$ effective area, before survey-selection effects. We propose that long-timescale microlensing events from IBHs can strongly constrain the SN physics governing stellar-mass black hole formation.
Read the full abstract

All authors Jian-Guo He, Yong Shao, Yu-Dong Nie, Gui-Yu Wang, Xiao-Tian Xu, Chen Wang, Xiao-Jie Xu, Xiang-Dong Li

Solar and Stellar Astrophysics

Metal-Poor Stars as Metal-Rich Impostors via Planet Engulfment

Zongheng Li, Shi Jia, Jie Su et al. (+2 more)

Planet engulfment leads to planetary mass accretion and angular momentum deposition into the stellar envelope. This study uses MESA models to investigate the long-term impact of engulfment on stellar metallicity and rotational velocity, as well as the effect of rotational mixing on metal enrichment. Our models show that engulfment occurring during the late main-sequence (MS) stage yields significantly higher surface enrichment than at the ZAMS. Rotational mixing generally suppresses enrichment; however, metal-poor stars can sustain super-solar abundances for several Gyr, whereas high-metallicity stars remain largely unaffected. Although engulfment causes an instantaneous spin-up, this angular momentum injection is transient, and the star quickly re-converges to its standard rotational evolution. Thus, MS spin-up cannot serve as a long-term observational indicator. Because convective envelope thickness and MS lifetime dictate the magnitude and duration of enrichment, identifying engulfment signatures requires balancing the long-lived but diluted signals in 0.7 M_sun stars against the strong yet short-lived enrichment in 1.2 M_sun stars. Consequently, 1.0 M_sun stars offering both substantial enrichment and a relatively long MS lifetime represent optimal targets for observational searches.
Read the full abstract

All authors Zongheng Li, Shi Jia, Jie Su, Shang-Fei Liu, Jianheng Guo

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

SN 2025aedz: A typical short-plateau type IIP supernova with rapid post-peak decline

Bo Wang, Luhan Li, Chengyuan Wu et al. (+5 more)

Type IIP supernovae (SNe IIP) are the most common subclass of core-collapse SNe in observations. However, SNe IIP with short plateaus of the order of tens of days are rarely observed. The progenitors for this kind of SN can help to address the red supergiant issue in stellar evolution. In this article, we report optical photometry and spectroscopy of SN\,2025aedz, a rapidly post-peak declining SN IIP with a typical short plateau. It exhibits a peak absolute magnitude of $M_r=-17.16\pm0.03$\,mag. The $r$-band light curve shows a steep early post-peak decline of $\sim5\,\mathrm{mag}\,(100\,\mathrm{d})^{-1}$ followed by a relatively short plateau, with a plateau duration of $\sim50\pm3$\,d. The overall spectral evolution is consistent with that of normal SNe~IIP, showing a blue continuum with prominent Balmer P-Cygni profiles during the photospheric phase, followed by the gradual strengthening of hydrogen and metal lines as the ejecta cools down, although the metal lines remain weak and the expansion velocities decline rapidly. SN\,2025aedz is similar to the short-plateau SN\,2018gj in its overall evolution, whereas its pronounced early decline resembles that of SN\,2023ufx, which has the shortest plateau duration known so far. The radioactive tail of the bolometric light curve implies a synthesized $^{56}$Ni mass of $\sim0.03\pm0.01\,M_\odot$. Motivated by the steep early decline, we performed radiation hydrodynamic simulations by exploring different circumstellar material configurations to reproduce its early bolometric light curve. These simulations indicate that SN\,2025aedz originated from a progenitor with a relatively low-mass hydrogen envelope, possibly produced through enhanced mass loss or binary interaction, while the steep early decline is likely explained by additional luminosity from circumstellar interaction.
Read the full abstract

All authors Bo Wang, Luhan Li, Chengyuan Wu, Jujia Zhang, Yongzhi Cai, Yize Dong, Xuefei Chen, Zhanwen Han

Solar and Stellar Astrophysics

On the altitude profile of lower ionospheric D-region response time delay during solar flares

Sayak Chakraborty, Rakhi Paul and Tamal Basak

The D-region ionosphere is sluggish in nature while responding to the incoming solar radiation. We study the altitude (h) profile of mid-latitude D-region response time delay (Delta t) during three chosen solar flares, namely, C5.2, M5.2, and X2.2 classes. We solve "electron continuity equation" numerically at each and every h to obtain Delta t-h profile. We investigate the 1) latitudinal variation (over both Northern and Southern hemispheres) and 2) seasonal variation (throughout the year) of Delta t-h profiles of each of these solar flares separately. We go over noteworthy variations of Delta t-h profile for both 1) and 2) with reasonably different results over different hemispheres. Also, we study some contrasting behaviours of Delta t-h profile of X2.2 class for both 1) and 2) in comparison to C5.2 or M5.2 classes. We conclude the outcome with possible explanations.
Read the full abstract

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

Uber-calibration-based Two-level Radial-velocity Zero-point Correction for APOGEE

Jinming Zhang, Haibo Yuan and Zhijia Tian

APOGEE delivers high-resolution, near-infrared spectroscopy and highly precise radial velocities (RVs), with extensive repeat observations spanning more than a decade. Long-term RV repeatability is nevertheless limited by instrumental zero-point systematics: exposure-to-exposure drift and fiber-dependent offsets that are only partially tracked by lamp-based wavelength calibration, and that can evolve as fibers are serviced or replaced. We infer and remove these zero points directly from the published per-visit RVs using an uber-calibration framework based on shared repeat observations. We solve sequentially for two sets of minimal calibration units: (plate, night) exposure-level offsets and time-dependent (fiber, observing year) offsets. We apply the method independently to APO and LCO DR17 and to APO DR19. After correction, the same-fiber repeatability within two days reaches a limiting precision of ~14 m/s, and the long-baseline single-visit precision improves by a factor of two from 98.2 to 44.7 m/s. We release per-visit, value-added RV catalogs for DR17 (APO+LCO) and DR19 (APO) containing 3,501,727 visits (3,336,141 fully corrected) of 930,519 unique stars, enabling more reliable RV variability, binary, and Galactic-dynamics studies.
Read the full abstract

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

A Collisional Origin for Ice-rich Iapetus and Titan's Anomalous Eccentricity

Ignacio Mosqueira

We test whether collisions involving Titan can eject enough water-rich material onto sufficiently distant Saturn-bound orbits to form Iapetus, while also accounting for Titan's orbital eccentricity. Three-dimensional impact calculations and post-impact trajectories examine initially Saturn-unbound and bound impactors. In the oblique unbound case with a differentiated impactor roughly a tenth the mass of Titan at a speed of 10 km s\(^{-1}\), outgoing predominantly icy material from a selected population totaling about 3.5 times Iapetus's mass remains Saturn-bound for days after impact. We track an icy sample whose orbital apoapsis extends beyond Iapetus's distance. After impact, Titan's eccentricity increases to near 0.13, while the impactor's rocky core escapes Saturn. In another case, a bound companion one quarter Titan's mass collides at \(45^\circ\) and about 3.7 km s\(^{-1}\), ejecting 0.60 Iapetus masses of ice. The rocky impactor core initially skips past Titan; an orbital continuation reaches return contact after 6.9 yr. This run also retains 0.48 Iapetus masses of ice. Titan's eccentricity evolves due to the initial impact and debris scattering. The merger results in a Titan with an eccentricity of about 0.10. These results establish the collisional production of an icy debris reservoir, with some material on orbits of large semimajor axis; raising Iapetus's periapse would require gas drag or dynamical friction.
Read the full abstract

Solar and Stellar Astrophysics

Study of Chromospheric Global-Scale Flows using Local Correlation Tracking Across the past 10 Solar Cycles

Qin Li, Yan Xu, Keiji Hayashi et al. (+2 more)

Global-scale solar surface flows, including differential rotation and meridional circulation, provide key observational constraints on the solar dynamo. We investigate these flows using local correlation tracking (LCT) of chromospheric intensity structures in digitized \ion{Ca}{2}~K observations from the Kodaikanal Solar Observatory covering Solar Cycles (SC) 14 to 23 (1907 – 2007). The most valuable data coverage are from cycles 14 to 19 for two reasons: (1) it provided record for early cycles that are not commonly available; (2) it had much better duty cycle than the data of cycles 20-23, therefore the measurements had much less errors. On the other hand, the information loss in cycles 20-23 are compensated by other modern space observations. The recovered differential rotation shows relatively small cycle-to-cycle variations and remains close to the Howard reference profile. Recurring zonal-flow residual bands at low and middle latitudes are broadly associated with the activity belts during the well-sampled SC~15–19. The meridional flow is predominantly poleward in the earlier record and exhibits larger relative cycle-to-cycle variations and uncertainties. Incomplete coverage of SC~14 and sparse sampling during SC~21–23 limit detailed comparisons to the better-covered SC~15–20. Compared with its immediate successor SC~19, the strongest cycle in the record, SC~18 exhibits a stronger and continuous northern poleward meridional branch, peaking two to three years before its sunspot maximum. SC~19 shows a minor enhancement that peaks earlier prior to its own maximum. An independent comparison using PSPT observations yields a full-period correlation of $r=0.91$ between the LCT and SDO/HMI meridional-flow profiles. These results extend the observational context for solar-cycle-related flows over a century and motivate further refinement through data-driven reconstruction.
Read the full abstract

All authors Qin Li, Yan Xu, Keiji Hayashi, Chunlei Liang, Haimin Wang

Solar and Stellar Astrophysics

Central stars of newly discovered infrared nebulae: eruptive Be stars PY Gem and HD253659

Olga Maryeva, Julieta Sánchez Arias, Sergey Karpov et al. (+3 more)

The presence of a nebula around massive hot stars often works as an indicator that the object is either in an advanced evolutionary stage or a rare product of close binary interaction. Here, we focus on two Be stars - PY Gem and HD253659 - whose nebulae were detected with the Wide-field Infrared Survey Explorer. We estimated their basic physical parameters from modelling the spectral energy distribution and examined their variability. We combined archival photometric data from several ground-based survey telescopes and from the Transiting Exoplanet Survey Satellite (TESS) with our own data from dedicated multi-colour photometric and spectroscopic monitoring, and concluded that, despite having similar stellar properties, the photometric variability of the two objects is strikingly different. For HD253659 we detected continuous eruptive variability and a major outburst that took place between 2016 and 2022 along with numerous flicker events seen in the TESS data. HD253659 also exhibits loop-like behaviour in the colour-magnitude diagram, consistent with build-up and dissipation phases of a circumstellar disk seen close to pole-on. In contrast, during the past ~20 years PY Gem has lost its eruptive variability and shows only small-amplitude p and g-mode pulsations classifying PY Gem as \beta Cephei hybrid pulsator. An incoherent low-frequency signal is identified as a Štefl frequency, which seems to be supported by the cyclic variation of the emission-line profiles. Detailed analysis of these stars indicates that both objects are inconsistent with evolved massive stars, and that the origin of their nebulae is more likely linked to the physics of the Be phenomenon.
Read the full abstract

All authors Olga Maryeva, Julieta Sánchez Arias, Sergey Karpov, Michaela Kraus, Michalis Kourniotis, Sabina Mammadova

Solar and Stellar Astrophysics · Cross-listed from cs.LG

Image Fidelity is Not Field Fidelity: Joint Thermodynamic Reconstruction and Error Localization in Neural Tomography

Alan Hsu, Jenna Samra, Alin Razvan Paraschiv et al. (+1 more)

Neural fields for scientific tomography are optimized from 2D images, but the actual quantity of interest is often a latent 3D physical field. Because the forward map is many-to-one, low 2D image error need not certify a correct 3D field. Moreover, the latent field is not directly supervised during training, and its error cannot be evaluated against truth at deployment. We develop CoroNeRF to jointly optimize 3D electron density and temperature fields directly from multiview, multiline intensities through a differentiable atomic-emission renderer. Using solar coronal tomography as a controlled testbed, we evaluate physical-field recovery and test whether cross-seed instability provides a ground-truth-free-at-inference indicator of local physical-field error. We underscore the following two observations. (i) Image fidelity is not field fidelity: spectral ablations show that limited-channel reconstructions can fit their available observations well while recovering substantially worse fields, whereas evaluation on a common richer probe exposes the discrepancy. (ii) Cross-seed instability ranks local physical-field error across tested matched-model conditions, supported by sparsification and physical signal-strength controls. Seed-deviation projections provide complementary directional validation, but shared forward-model mismatch can still produce incorrect cross-seed consensus. These results characterize joint thermodynamic recovery and the usefulness and limits of seed-based error localization in a controlled, single-scene solar tomography testbed.
Read the full abstract

All authors Alan Hsu, Jenna Samra, Alin Razvan Paraschiv, Liam Connor

Wednesday 23 September

Solar and Stellar Astrophysics

Metal-poor Brown Dwarf Kinematics from JWST NIRSpec Spectroscopy

Chih-Chun Hsu, Christopher A. Theissen, Adam J. Burgasser et al. (+14 more)

Galactic archaeology relies on stellar kinematics and chemical abundances to identify various stellar populations and associations. With JWST, Galactic archaeology of ancient metal-poor brown dwarfs is now possible through high-sensitivity, medium-resolution spectroscopy. We present the first metal-poor brown dwarf radial velocity (RV) survey using JWST/NIRSpec G395H spectra ($\lambda/\Delta\lambda \sim$ 3,000) for a sample of 23 LTY dwarfs across a wide range of temperatures and metallicities. We introduce a forward-modeling framework to measure robust RVs for brown dwarfs by focusing on the CO fundamental band at $\sim$4.5 $\mu$m. By comparing to sources with existing high-resolution RV measurements, we demonstrate that G395H RVs can achieve a systematic uncertainty of 5 km s$^{-1}$, sufficient to examine their Galactic space motions. We identify kinematic members of the Milky Way's thin disk, thick disk, and halo populations in this sample. We also confirm WISE J155349.98$+$693355.2 as likely associated with the Gaia-Enceladus merger remnant, and 2MASS J05325346$+$8246465 is likely associated with the Thamnos stream. Our study systematically demonstrates that JWST G395H spectroscopy can provide robust RVs in addition to detailed chemical abundances, necessary for Galactic archaeology studies. Future discoveries and characterization of brown dwarfs associated with Galactic halo substructures and streams will enable a stringent test of stellar/substellar formation and evolutionary models for diverse metallicities.
Read the full abstract

All authors Chih-Chun Hsu, Christopher A. Theissen, Adam J. Burgasser, Adam C. Schneider, Christian Aganze, Aaron M. Meisner, Jonathan Gagné, Nicolas Lodieu, Zenghua Zhang, Genaro Suárez, Eileen C. Gonzales, Jacqueline K. Faherty, Jason J. Wang, Stanimir Metchev, Dan Caselden, Michael C. Cushing, Roman Gerasimov

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

Triggering star formation by free-floating planets

Yu. N. Eroshenko

Recently, a population of free-floating planets has been discovered in the Galaxy. This paper examines the influence of the planets trapped within a protostellar hydrogen clouds on the processes of gravitational instability in the gas. A sufficiently massive planet can become an alternative dynamic center for the contracting cloud. This occurs due to rapid mass growth from accretion onto the planet within the cloud. Owing to residual velocity and density gradients in the cloud, the planet that triggers star formation is likely to end up in a distant orbit around the newborn star. Some second- and subsequent-generation stars in the Galaxy may have formed via this mechanism.
Read the full abstract

Solar and Stellar Astrophysics

A comprehensive multi-wavelength study of two X-ray emitting Be stars

Hema Anilkumar, Blesson Mathew, Savithri H. Ezhikode et al. (+4 more)

We present a multi-wavelength study of two X-ray-emitting Be stars, CXOU J052218.4+332820 (Star 1) and CXOU J052304.2+332846 (Star 2), identified from the LAMOST DR5 Hot emission-line stars catalog. Our spectroscopic and photometric analyses indicate that Star 1 is a main-sequence B5e star, whereas Star 2 is a pre-main-sequence B7e star. The LAMOST spectrum of Star 1 exhibits shell-type Feii, Paschen, and Oi emission from circumstellar regions extending to ~ 3 - 5Rstar. TESS period analysis reveals a rapid rotational period of ~ 0.355 d and an inclination angle of ~ 68 deg, confirming the Classical Be nature of Star 1. In contrast, Star 2 shows strong accretion signatures, including inverse P-Cygni Feii and redshifted Hei absorption features. Its ZTF light curves display irregular dimming events of up to ~ 3 mag and quasi-periodic variability on timescales of ~ 50 - 110 d, consistent with circumstellar obscuration in an accreting Herbig Be star. To further investigate the high-energy properties of the two systems, we analyzed their Chandra X-ray spectra. Chandra spectroscopy yields moderate plasma temperatures (kT ~ 1.7-1.8 keV) and X-ray luminosities of logL_X ~ 30.4-30.6 erg/s, comparable to those observed in magnetically active coronae. Furthermore, the positional agreement between the Chandra and Gaia coordinates indicates that the X-ray emission is spatially associated with the optical systems rather than a nearby resolved companion. These results suggest that the observed X-ray emission originates from magnetically influenced circumstellar activity, consistent with magnetically confined wind-shock (MCWS) or magnetically torqued disk scenarios.
Read the full abstract

All authors Hema Anilkumar, Blesson Mathew, Savithri H. Ezhikode, Sreeja S. Kartha, Suman Bhattacharyya, Sneha Nedhath, Ajith N

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

Tomography analysis of the intermediate-luminosity Type Iax SN 2024pxl

Barnabás Barna, Mridweeka Singh, Lindsey A. Kwok et al. (+90 more)

We present an abundance tomography analysis of SN 2024pxl, an intermediate luminosity Type Iax supernova ($M_{r}=-16.82 \pm 0.19$ mag), with the most-detailed follow-up in the Type Iax subclass to-date. As one of the few intermediate luminosity Type Iax objects, SN 2024pxl may link the two extremes of the peculiar thermonuclear supernova subclass. To test this hypothesis, we analyze its spectral evolution through the first 100 days after the explosion and aim to probe the structure of its ejecta. We conduct an abundance tomography analysis using synthetic spectra produced with the one dimensional radiative transfer code TARDIS. The fit of the spectral time series provides a radial scan of physical properties and probes the stratification of chemical elements throughout most of the SN ejecta. The observed spectral evolution is well fit with the final model, similar to the general predictions of the pure deflagration scenarios, but significant modifications are required in the density function of the inner ejecta and in the chemical profiles of the outermost regions. The constrained physical characteristics, such as the photospheric velocities and the time of maximum light, are also consistent with other SNe~Iax. Despite their small number, intermediate luminosity Type Iax SNe are not outliers in the subclass but demonstrate the continuous nature of SNe Iax through their luminosity range. Following this observation, we argue that all SNe~Iax share the same progenitor and explosion origin.
Read the full abstract

All authors Barnabás Barna, Mridweeka Singh, Lindsey A. Kwok, Saurabh W. Jha, R. Dastidar, Conor Larison, Alexei V. Filippenko, J. P. Anderson, Jennifer E. Andrews, Moira Andrews, G. C. Anupama, Prasiddha Arunachalam, Katie Auchettl, Dominik Bánhidi, K. Azalee Bostroem, Thomas G. Brink, Régis Cartier, Ping Chen, T.-W. Chen, Collin T. Christy, David A. Coulter, Sofia Covarrubias, Kyle W. Davis, Connor B. Dickinson, Yize Dong, Joseph Farah, Andreas Flörs, Ryan J. Foley, Noah Franz, Christoffer Fremling, Lluís Galbany, Anjasha Gangopadhyay, Aarna Garg, Elinor L. Gates, Or Graur, Mariusz Gromadzki, Daichi Hiramatsu, Emily Hoang, D. Andrew Howell, Brian Hsu, Joel Johansson, Arti Joshi, Lordrick A. Kahinga, Ravjit Kaur, Sahana Kumar, Piramon Kumnurdmanee, Hanindyo Kuncarayakti, Chang Liu, Keiichi Maeda, Kate Maguire, Bailey Martin, Curtis McCully, Darshana Mehta, Luca M. Menotti, Anne J. Metevier, A. A. Miller, Kuntal Misra, Erika Mochnács, T. E. Müller-Bravo, Megan Newsome, Estefania Padilla Gonzalez, Kishore C. Patra, Jeniveve Pearson, Anthony L. Piro, Abigail Polin, Aravind P. Ravi, Armin Rest, Nicolas Meza Retamal, O. M. Robinson, César Rojas-Bravo, Devendra K. Sahu, David J. Sand, Brian P. Schmidt, Steve Schulze, Michaela Schwab, Manisha Shrestha, Matthew R. Siebert, Sunil Simha, Nathan Smith, Jesper Sollerman, Shubham Srivastav, Bhagya M. Subrayan, Tamás Szalai, Kirsty Taggart, Rishabh Singh Teja, Jacco H. Terwel, Samaporn Tinyanont, Stefano Valenti, József Vinkó, Aya L. Westerling, J. Craig Wheeler, Yi Yang, WeiKang Zheng

Solar and Stellar Astrophysics

The physics of deep-interior convective shell boundaries in a massive pre-supernova star: Internal gravity wave mixing at the $N^2$ peak

Praneet Pathak, Falk Herwig, Simon Blouin et al. (+2 more)

The physics of convective boundary mixing involves concepts such as penetration and overshooting and has been mostly characterized for envelope and core convection. For the burning shells deep inside massive stars in their final stages, the convective boundary remains poorly understood. 1D stellar-evolution codes typically place a steep entropy gradient and the corresponding narrow \brunt{} ($N^2$) peak at a lower convective shell boundary. Based on high-resolution 3D hydrodynamic simulations of a $25 \rm{M_\odot}$ star 11 days before core collapse, we find that convection excites high-frequency internal gravity waves at the $N^2$ peak representing the C-shell convection bottom. These waves efficiently mix entropy and species and the $N^2$ peak erodes by ${\sim}40\%$ within hours, correspondingly reducing the entropy gradient. The wave-driven diffusion coefficient is $D\approx 5\text{--}6\times 10^{9} \rm{cm}^2 \rm{second}^{-1}$ at the $N^2$ peak in numerically converged simulations. Our simulations show that the dominant physics at this boundary is mixing due to internal gravity waves. Extrapolated with the time-dependent $D$ coefficient from the 3D simulations, the entropy step across the peak decreases by 40–85% within half a day, thereby reducing the density, temperature and entropy gradients that set the accretion-rate drop a stalled supernova shock encounters. This physics is not included in present-day 1D models and enters the structural parameters that predict explodability. Flattening the gradients days before collapse favors an O–C shell merger, which could reshape pre-collapse nucleosynthesis. Without this physics 1D models carry too sharp gradients that introduce previously unaccounted systematic errors into the explodability surveys, yield tables and chemical-evolution studies built on them.
Read the full abstract

All authors Praneet Pathak, Falk Herwig, Simon Blouin, Paul R. Woodward, Joshua Issa

Solar and Stellar Astrophysics

3D Radiation Hydrodynamics of Blue Supergiant Envelopes

Linhao Ma, Lars Bildsten and Yan-Fei Jiang

We present the first 3D radiation hydrodynamical simulation of the outer envelope of a blue supergiant. These near Eddington limited massive stars in the Hertzsprung gap exhibit substantial photometric variability and have spectroscopic line widths indicating unexplained macroturbulent velocity fields. Our Athena++ simulations find that the convection associated with the opacity peak from iron directly extends to the photosphere, as found in previous 3D simulations of massive main sequence stars. Unlike 1D stellar models, this single convecting region imprints a velocity field that is consistent with spectroscopic models of macroturbulence. In addition, the convection in the outermost layer leads to such large density variations that the exiting radiation varies on large ($\lesssim 10 \% $) amplitudes and short ($\sim$ days) timescales. This leads to stochastic low frequency (SLF) photometric variability, with amplitudes and power spectra broadly consistent with observations.
Read the full abstract

Solar and Stellar Astrophysics

External photoevaporation in the center of Tr14

Katia Gkimisi, Da Eun Kang, Dominika Itrich et al. (+11 more)

Most stars form in massive stellar clusters, where intense far-ultraviolet (FUV) radiation from OB stars can accelerate the dispersal of protoplanetary disks through external photoevaporation. Quantifying the impact of this process on disk evolution remains challenging, particularly in distant and crowded star-forming regions. We investigate the low-mass stellar population in the highly irradiated center of Trumpler 14 and examine how the local FUV radiation field influences circumstellar disk evolution. We extracted stellar spectra from VLT/MUSE observations using an enhanced background-optimized extraction method, carefully corrected for instrumental response as a function of wavelength and finally derived the stellar parameters with the SAPSAL deep-learning framework. We combined these results with a probabilistic estimate of the local FUV field and near-infrared photometry to identify disk-bearing stars. We identify 310 bona fide cluster members with an age of $0.66^{+0.73}_{-0.35}$ Myr and local radiation fields spanning $\log(FUV)\simeq4.2-6.0\ G_{\mathrm{0}}$. The fraction of stars exhibiting near-infrared excess decreases from 30% at the lowest FUV fluxes to under 5% at $\log(FUV)\gtrsim5.6 \ G_{\mathrm{0}}$, while no significant correlation is found between our simplified estimate of the optical veiling and the local FUV field. The pronounced decline in the disk fraction with ambient FUV flux provides strong evidence for external photoevaporation rapidly dispersing circumstellar disks in the core of Trumpler 14. Our results confirm previous disk dispersal estimates and extend to higher values of the FUV field strength.
Read the full abstract

All authors Katia Gkimisi, Da Eun Kang, Dominika Itrich, Rossella Anania, Eleonora Fiorellino, Sacha Gavino, Ralf S. Klessen, Victor F. Ksoll, Giuseppe Milazzo, Anna McLeod, Thomas Preibisch, Veronica Roccatagliata, Leonardo Testi, Claudia Toci

Solar and Stellar Astrophysics

Detection of new Galactic Wolf-Rayet stars with SPHEREx

Paul A. Crowther and Erin L. Smith

We assess the potential for the NASA Explorer SPHEREx mission in adding to the Milky Way census of Wolf-Rayet (WR) stars by extracting 0.75–5micron spectrophotometry of 30 candidate WR stars previously identified using Gaia XP spectra. We confirm an additional Galactic 13 WR (8 WN and 5 WC) stars, identify 3 probable [WC]-type central stars of Planetary Nebulae, plus 2 He emission line sources. SPHEREx has the potential to detect additional relatively isolated WR stars on the far size of the Milky Way by combining Machine Learning techniques with a judicious choice of candidate selection criteria. Indeed SPHEREx is sufficiently sensitive to identify bright Magellanic Cloud Wolf-Rayet stars.
Read the full abstract

Solar and Stellar Astrophysics · Cross-listed from hep-ph

Finite-Temperature Axion-Admixed Neutron Stars in a Quarkyonic Crossover Framework

S. K. Patra, D. Dey, Jeet Amrit Pattnaik et al. (+1 more)

We analyze the effect of axion contribution on the mass, radius and dimensionless deformability of a neutron star (NS) at finite temperature. Although the cooling of an NS is mainly due to the emission of neutrinos, additional cooling cannot be ruled out due to the emission of axions. The existence of an axion is needed for addressing the strong CP problem within the standard model. The Peccei-Quinn (PQ) symmetry breaking mechanism generates axions. They are pseudo-Nambu-Goldstone bosons. Their mass is extremely small but non-zero. This naturally resolves the fine-tuning problem of the strong CP-violating parameter ${\theta} \lesssim 10^{-10}$. We propose that a finite temperature NS feature a quark core surrounded by a baryonic medium admixed with the axions, which are pseudo scalar Goldstone bosons and are considered as strong candidates for the dark matter (DM). Unlike the original quarkyonic model, we formulate a quarkyonic-inspired smooth crossover equation of state (EoS) at finite temperatures. This smooth crossover avoids thermodynamic instabilities found in sharp first-order constructions. We add the axionic EoS to the finite temperature quarkyonic one and solve the Tolman-Oppenheimer-Volkoff equations to estimate the properties of the NS both with and without taking the axion into account at different temperatures. We find that the production of axions is maximum within a radius of $5-11$ km in the star's interior; however, the impact on the mass is significant, i.e., $\sim 60\%$ of axion mass concentrated in the central region of the star. We also find that the effect of temperature on the mass of NS is marginal unlike the radius. In general, the influence of axions is significant for the observational properties of NS. These results highlight the pivotal role of axion physics in neutron star phenomenology.
Read the full abstract

All authors S. K. Patra, D. Dey, Jeet Amrit Pattnaik, R. N. Panda

Solar and Stellar Astrophysics

A Search For Stellar-mass Black Holes Via Astrometric Microlensing II: 2012-2015 Keck Candidates

Mace J. Huston, Jessica R. Lu, Casey Y. Lam et al. (+55 more)

The Milky Way is expected to host $\sim$10$^8$ stellar-mass black holes with an uncertain binary fraction. The only proven method to detect isolated stellar mass black holes is gravitational microlensing. Here we report the results of a microlensing search for black holes with photometry and astrometry. By combining 10 years of seeing-limited photometry from OGLE and MOA with diffraction-limited photometry and astrometry from adaptive optics imagers at the W.~M.~Keck Observatory, we constrain lens masses for OGLE-2012-BLG-0169, OGLE-2014-BLG-0613/MOA-2015-BLG-041, OGLE-2015-BLG-0029/MOA-2015-BLG-170, and OGLE-2015-BLG-0211. Of the four long-duration microlensing events monitored, we ruled out black hole lenses in 3 events, which likely have stellar or white dwarf lenses. OGLE-2015-BLG-0211 remains a black hole candidate with a poorly constrained lens mass with a 1$\sigma$ upper mass limit of 3.2$M_\odot$ and a 3$\sigma$ upper mass limit of 21.6$M_\odot$. This event suffered from poor observing conditions and significant astrometric reference frame uncertainties, but its analysis may benefit from additional astrometric data in the upcoming Gaia Data Release 4. Of the six long-timescale ($t_E>100$ days) microlensing events from this work and previous studies, one black hole has been confirmed with a second not ruled out. We briefly examine Galactic model simulations and find that our result agrees with current expectations. Ultimately, we need a larger sample of isolated black holes to constrain their formation processes. This will be possible in the coming years with Rubin and Roman, as well as improved astrometry from JWST and large, ground-based telescopes equipped with adaptive optics.
Read the full abstract

All authors Mace J. Huston, Jessica R. Lu, Casey Y. Lam, J. Nijaid Arredondo, Natasha S. Abrams, Shep Brooke, Sage H. Remulla, Eran Ofek, Michael S. Medford, Fatima Abdurrahman, Shrihan Agarwal, Edward Broadberry, Matthew Freeman, Matthew W. Hosek Jr., Siyao Jia, Sean K. Terry, The OGLE Collaboration: Andrzej Udalski, Przemek Mroz, Radoslaw Poleski, Jan Skowron, Michal K. Szymanski, Igor Soszynski, Pawel Pietrukowicz, Szymon Kozlowski, Krzysztof Ulaczyk, Krzysztof A. Rybicki, Patryk Iwanek, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mroz, Michal Malkowski, The MOA Collaboration: Fumio Abe, David P. Bennett, Aparna Bhattacharya, Ian A. Bond, Kotaro Daimon, Ryusei Hamada, Yuki Hirao, Shuma Makida, Stela Ishitani Silva, Shota Miyazaki, Yasushi Muraki, Tutumi Nagai, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Greg Olmschenk, Clement Ranc, Nicholas J. Rattenbury, Yuki K. Satoh, Takahiro Sumi, Daisuke Suzuki, Takuto Tamaoki, Chihiro Ueda, Paul J. Tristram, Aikaterini Vandorou, Hibiki Yama

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

The compressible liquid drop model with curvature included algebraically for the pasta phases in neutron stars

Dmitry Kobyakov

In the compressible liquid drop model (CLDM), the curvature energy term has been included in many works in the literature, and its effects on the presence of pasta phases have also been extensively investigated. However, the analytical part of the inclusion used to cease once a 4-order algebraic equation for the optimized size of the nucleus was written. In this paper, an optimization is suggested to the analytical part of the solution of the CLDM equations. Solving analytically the 4-order algebraic equation proves to be helpful for a straightforward identification of the denied parameter ranges in which the CLDM has no real-root solutions. Using a particular nuclear force derived from the chiral effective field theory, I investigate effects on the ground state of the nucleus curvature. Surprisingly, the inclusion has lead to a significant modification of the range of baryon density in which the bubble phases are found, disfavoring the bubble phases from the ground state. This shows a strong difference between the predictions of the CLDM with the nucleus size obtained when including the curvature term and that obtained from the $w_\mathrm{s} = 2w_{\mathrm{C+L}}$ approximation. The importance of the curvature energy in the CLDM is linked with its ability to change qualitatively the ground state. This paper presents an analytical extension to the CLDM solution, which is ready to be used with any other nuclear model in the future, in order to optimize the inclusion of the nuclear curvature energy, and is not limited to one nuclear model.
Read the full abstract

Solar and Stellar Astrophysics

Nature of small-scale Ca II H brightenings associated with weak fields in a quiet Sun region

Xiang Li, H. N. Smitha, S. K. Solanki et al. (+3 more)

Context. Chromospheric emission observed in the Ca II H and K resonance lines is generally positively correlated with photospheric magnetic fields. However, a fraction of strong Ca II H&K brightenings are found to occur over regions of low photospheric magnetic flux density. Aims. We aim to understand the origin of these chromospheric brightenings associated with weak fields in quiet Sun regions. Methods. We use Ca II H observations taken by the SuFI along with the photospheric magnetograms recorded by the IMaX, instruments onboard the first flight of the balloon-borne observatory Sunrise. We also use the atmospheric physical parameters inverted from IMaX data by the SPINOR code. Results. 217 Ca II H brightenings associated with weak fields are identified. 111 of these are located at the peripheries of strong field regions, in the magnetic canopies formed by the expansion of the kG flux tube. The other brightenings are associated with either weak unipolar magnetic patches, with interactions between weak mixed-polarity magnetic fields, or at locations with no clear magnetic features. For the latter two situations, the Ca II H intensity varies with a period of 3-5 mins, accompanied by variations in the line-of-sight velocity, the temperature, and the magnetic flux with a similar period. Conclusions. About half of the strong Ca II H brightenings associated with weak fields are located in magnetic canopies overlying very weak photospheric fields. About 10-12% are associated with magnetic bright points where the magnetic field is probably not spatially resolved. The remainder appears to be Ca II H grains, which are overwhelmingly associated with magnetic emergence or cancellation events. We conclude that although Ca II grains are mainly driven by (magneto-)acoustic shock waves, interactions between opposite-polarity magnetic fields also contribute to the formation of the brightest peaks.
Read the full abstract

All authors Xiang Li, H. N. Smitha, S. K. Solanki, T. L. Riethmüller, L. P. Chitta, S. Jafarzadeh

Solar and Stellar Astrophysics

High-Resolution Modelling of Coronae and Winds in Solar-type Stars with Varying Rotation Rates II. Stellar Winds

Yue-Hong Chen, Julián D. Alvarado-Gómez, Xin Cheng et al. (+6 more)

Observations suggest a connection between steady-wind mass loss and coronal X-ray activity in low-mass main-sequence stars. Interpreting this connection is challenging because the wind is controlled mainly by the large-scale open field, whereas X-ray emission traces heating in small-scale closed fields often unresolved in global wind models. Here we use Space Weather Modelling Framework-Alfvén-Wave Solar Model with global convective dynamo-generated magnetic maps and solar magnetograms. We model Alfvén-wave-heated winds for four solar-type stars plus the Sun, spanning rotation rates of $1.0$–$23.3$ times the solar rate, and magnetic field strengths of $6.0$–$1200$ G. Our models show that faster rotation yields a more tightly wound spiral, a larger Alfvén surface, higher terminal wind speeds, and a harsher wind-pressure environment for orbiting exoplanets, different from that of the present-day Sun. We estimate the mass- and angular-momentum-loss rates and find systematic differences from Zeeman-Doppler Imaging-based predictions. Building on the successful reproduction of X-ray coronae in our Paper~I, we obtain the first self-consistent activity–wind relation in a unified modelling framework: the mass-loss rate scales with the surface X-ray flux following a power law with an index of ${\sim}0.67$. We also re-examine magnetic braking via open-flux magnetisation, finding that the effective Alfvénic lever arm depends on the magnetisation parameter with a power-law index of ${\sim}0.35$. Finally, we quantify the stellar wind pressure at the orbits of several super-Earths. Together with our Paper~I, the series of results shows the distinct roles of multi-scale magnetic fields and provides physically grounded inputs for assessing habitable-zone space weather.
Read the full abstract

All authors Yue-Hong Chen, Julián D. Alvarado-Gómez, Xin Cheng, Victor See, Yu Dai, Maarit J. Korpi-Lagg, Jörn Warnecke, Chen Xing, Mingde Ding

Solar and Stellar Astrophysics · Cross-listed from cs.LG

PISCES: Physics-Informed Solar-wind Convolutional autoEncoder for Space-weather Anomaly Detection and Early Warning

Kevin Lee and Alison J. March

Space weather early warning depends on detecting solar wind transients in in-situ measurements at the first Sun-Earth Lagrange point (L1), before they reach Earth. Fixed thresholds can miss combined magnetic and plasma structure, and many learning methods provide a single anomaly score. We present the Physics-Informed Solar-wind Convolutional autoEncoder for Space-weather (PISCES), a convolutional autoencoder trained without catalog labels on OMNI solar wind measurements under physics constraints. Its loss includes magnetic field consistency, an empirical relation between temperature and velocity, the Parker spiral angle, and penalties on changes between consecutive one-minute samples in derived quantities calculated from the reconstruction. At inference, PISCES separates the anomaly score into magnetic and plasma reconstruction errors, physics relations, and residual corrections, and reports the magnitude of each contribution. Attenuation of the skip connections, selected on validation data, improves average precision for the trained models, while the untrained scores remain nearly the same. The trained models also give a more consistent ordering of these physical contributions. After smoothing with a trailing median, the alarms can precede independently observed sudden commencements, including positive sudden impulses.
Read the full abstract