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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Thursday 10 September

Solar and Stellar Astrophysics

An unresolved extreme warm infrared excess toward a nearby low-mass star

Sahin Torlakcik

Gaia DR3 2981818948336660224 is a nearby low-mass star with a substantial warm mid-infrared excess. Identified in a Gaia-2MASS-WISE search, it lies at approximately 127 pc and has an AllWISE W3 signal-to-noise ratio of 33.1. We recover the emission in all 16 available cryogenic exposures over 1.26 d; removing any one exposure leaves the signal intact. The W3 emission is centred close to the propagated stellar position, and the known neighbour 6.1 arcsec away fails to reproduce its morphology. Nominal scene fits place 97-98 per cent of the W3 flux at the target position. This provides strong spatial support for association, although template uncertainty and a nearly coincident hidden source prevent a definitive decomposition. The excess can be described by a roughly 300-350 K component with L_IR/L_star ~ 0.022, assuming stellar association and retaining the weaker W4 detection. If produced by circumstellar dust, it falls in the extreme warm-debris regime around a dwarf with no established evidence of youth. Its origin remains unresolved. The repeatable excess and close spatial association make this a useful target for subarcsecond MIR imaging and spectroscopy to test the warm-dust interpretation.
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Solar and Stellar Astrophysics

Teleparallel torsion and white dwarf structure in \(f(T)=T+\Xi T^2\) gravity

Edson Otoniel, Jonathan A. Reboucas and Iarley P. Lobo

We investigate how quadratic torsion modifies the equilibrium structure of white dwarfs in covariant $f(T)=T+\Xi T^2$ gravity. Static spherical configurations are calculated with a fixed equation of state for cold carbon matter, including relativistic electron degeneracy and Coulomb lattice corrections. The stellar interior is matched to a vacuum exterior, and the mass is determined from the asymptotic geometry. At fixed central density, negative couplings produce more massive and more compact configurations than general relativity, whereas positive couplings give smaller masses and larger radii. The deviations increase with central density and are more pronounced in mass than in radius. The first limiting feature of each sequence depends on the coupling. For $\Xi=-10^{18}\,\mathrm{cm}^{2}$, the sequence remains monotonic up to the electron capture density and reaches $1.508\,M_\odot$. General relativity and $\Xi=+10^{18}\,\mathrm{cm}^{2}$ instead reach mass turning points at $1.385\,M_\odot$ and $1.366\,M_\odot$, respectively. The positive extreme can be continued as an equilibrium solution to the capture density, where its mass decreases to $1.24\,M_\odot$, but this configuration lies beyond the turning point and is not the maximum mass along that sequence. These results identify a density dependent structural response to torsion that changes the stellar mass scale without modifying the matter equation of state.
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Solar and Stellar Astrophysics

A Homogenized Catalogue of Variable Stars in the Globular Cluster M22: Membership, Physical Parameters, and Distance

M. A. Yepez, B. Moreno-Amaro, M. Ornelas-Castañeda et al. (+2 more)

We present a photometric analysis of the variable stars in the field of the globular cluster M22 (NGC 6656), using time-series photometry from the literature and from OGLE and Gaia-DR3 data. From a sample of 666 variable stars in the field, we identify 94 as cluster members, including 10 RRab, 17 RRc, 2 Type II Cepheids, 15 SX Phe, 15 SR stars and 22 eclipsing binaries. Fourteen of these members are not included in the Catalogue of Variable Stars in Globular Clusters. Through the Fourier decomposition of the RR Lyrae light curves, we derived $[\mathrm{Fe/H}] = -1.73 \pm 0.17$ dex and $d = 3.27 \pm 0.14$ kpc. Among the RRc stars, V15 shows an additional frequency with a frequency ratio $f_{0.61}/f_\mathrm{1O} = 0.6152$, consistent with the RR$_{0.61}$ phenomenon. Using P-L relations for member SX Phe stars, we obtained $d = 3.31 \pm 0.17$ kpc, consistent with the RR Lyrae distance. We constructed a CMD comprising only cluster members, which allows us to confirm the evolutionary status of the cluster's RR Lyrae stars. None of the fitted isochrones satisfactorily reproduces the CMD morphology, which is consistent with the presence of multiple stellar populations in M22.
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All authors M. A. Yepez, B. Moreno-Amaro, M. Ornelas-Castañeda, A. Arellano Ferro, D. Deras

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

Solar Neutrino Constraints on Inelastic Dark Matter Scattering in Light of Recent LUX-ZEPLIN Observations

Thong T.Q. Nguyen, Tim Linden and Dan Hooper

The LUX-ZEPLIN (LZ) Collaboration recently reported the detection of a single nuclear recoil candidate event with a very high recoil energy. The lack of any corresponding low-energy events motivates models in which dark matter scattering with nuclei has a nontrivial momentum dependence or proceeds inelastically, suppressing the rate of low-energy recoils. In this study, we consider the constraints on inelastic dark matter, including scenarios favored by the LZ event, from the absence of an excess of high-energy neutrinos from the Sun in IceCube observations. We confirm the results of Pospelov & Ramani and show, more generally, that the lack of an excess of high-energy neutrinos from the Sun strongly constrains the parameter space in this class of models.
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Solar and Stellar Astrophysics

The Dyn-Atmo Survey: JWST/NIRSpec spectroscopy of dynamical benchmark GJ 758 B

Alexander Madurowicz, Emily Rickman, Daniella Bardalez Gagliuffi et al. (+22 more)

We present new JWST/NIRSpec IFU high contrast spectroscopic observations of the brown dwarf companion GJ 758 B. Extensive radial velocity monitoring of the primary has enabled high-precision measurements of the companion mass through characterization of their joint orbital dynamics. The combination of prior space- and ground-based photometry and spectroscopic observations in concert with a spectral model-independent mass makes this target an ideal benchmark for calibrating evolutionary models with known mass-age-luminosity degeneracies. A template-matching analysis on the NIRSpec/IFU data (F290LP,G395H; $\lambda \in$ [2.87-5.27] $\mu$m) detects the companion at the expected orbital position with incredible significance (265.2$\sigma$). Comprehensive spectral analysis including published datasets over a variety of different spectral model families reveal that an inference using a uniform radius prior is plagued by inaccurate posteriors. The atmospheric model degeneracy between metallicity, gravity, and clouds pull the inferred mass/gravity/radius to an unphysical portion of parameter space for all model families tested. A constrained inference with a gaussian prior on the mass can mitigate this issue but models without clouds still struggle to accurately reproduce the K-band photometry and result in mass inferences which are inconsistent with the dynamics. We explore modifying the spectral models with custom post-processed clouds and molecular abundance perturbations of ammonia and hydrogen sulfide. We find the best-fitting model includes clouds with no patchiness (hole fraction f$_\mathrm{hole}$ = 0), a small fractional depletion in ammonia and moderate enhancement in hydrogen sulfide.
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All authors Alexander Madurowicz, Emily Rickman, Daniella Bardalez Gagliuffi, James Mang, Kim Ward-Duong, William O. Balmer, Brendan P. Bowler, Emily Calamari, Henry Dennen, Jacqueline K Faherty, Kyle Franson, Mark R. Giovinazzi, Lisseth Gonzales Quevedo, Kielan K. W. Hoch, Piper Lentz, Elena Manjavacas, Klara Matuszewska, Ashley Messier, Caroline V. Morley, Evert Nasedkin, Marshall Perrin, Laurent Pueyo, Jean-Baptiste Ruffio, Christopher A. Theissen, Jerry W. Xuan

Solar and Stellar Astrophysics

The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU

Kielan K. W. Hoch, Alex Madurowicz, Evert Nasedkin et al. (+22 more)

We present the first spectral analysis from the JWST Cycle 3 GO Program #6362, the Dyn-Atmo Survey of dynamical-atmospheric benchmarks, characterizing the atmospheres of directly-imaged companions with dynamical masses and measured orbits. This program has obtained moderate-resolution spectra (R$\sim$2700, 3-5$\mu$m) using the NIRSpec/G395H IFU. We observe the T4-dwarf companion, HD 13724 B, companion to a G-type star at a projected angular separation of 0”2. Updated orbital monitoring constrains the mass to $38.3\pm0.6~M_{\rm{Jup}}$, which we use as a Gaussian prior when inferring the atmospheric state. We fit the continuum-subtracted spectrum using the BT-SETTL, Sonora Diamondback, Sonora Flame Skimmer, and NEWERA-PHOENIX self-consistent model grids, together with petitRADTRANS atmospheric retrievals. We adopt bulk parameter values of $T_\mathrm{eff}$=$1150\pm$195 K, $\log g$=5.1$\pm0.3$ dex, [M/H]=0.4$\pm$0.4, $\log_{10}(K_{zz})$=6.33$_{-2.22}^{+2.59}$, and C/O=$0.50\pm0.13$ using a bayesian average across model grids. We find degeneracies in the models between surface gravity, metallicity, and $K_{zz}$ for Sonora Diamondback and Flame Skimmer. The Flame Skimmer and NEWERA-PHOENIX vertical mixing strengths are incompatible, with Flame Skimmer finding a systematically lower value. The retrievals favor an atmosphere in chemical equilibrium, with enhanced metallicity and a solar C/O ratio, but with no detection of disequilibrium chemistry, and no detection of trace gases other than CH$_4$, CO$_{2}$, $^{12}$CO and H$_{2}$O. Ultimately, we identify critical challenges in forward modeling continuum-subtracted G395H spectra in the low signal-to-noise regime. We find that including independent dynamical mass measurements better constrains atmospheric parameters, but degeneracies between self-consistent model parameters limit accurate atmospheric parameter inferences.
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All authors Kielan K. W. Hoch, Alex Madurowicz, Evert Nasedkin, Emily Rickman, Daniella C. Bardalez Gagliuffi, James Mang, Caroline V. Morley, Christopher A. Theissen, William O. Balmer, Brendan P. Bowler, Emily Calamari, Henry Dennen, Jacqueline K. Faherty, Kyle Franson, Mark R. Giovinazzi, Lisseth Gonzales Quevedo, Elena Manjavacas, Piper Lentz, Klara Matuszewska, Ashley Messier, Marshall Perrin, Laurent Pueyo, Jean-Baptiste Ruffio, Kimberly Ward-Duong, Jerry W. Xuan

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

Planetary Accretion Is Less Frequent in Wide Binaries: Evidence from Metal-Enriched White Dwarfs in DESI DR1

Siyi Xu, Laura. K. Rogers, Joan Najita et al. (+32 more)

Binary stars are common in the Galaxy, and understanding how stellar binarity influences the formation and evolution of planetary systems is an active area of research. In this study, we use metal-enriched white dwarfs in wide binaries as tracers of long-lived planetary systems. With Data Release 1 from the Dark Energy Spectroscopic Instrument (DESI), we find that the fraction of cool metal-enriched white dwarfs in wide binaries is 9.8\,$\pm$\,2.1%, significantly lower (4.7\,$\sigma$) than the 20.5\,$\pm$\,0.9% in a control sample of single systems. Furthermore, we identify a tentative dependence of metal enrichment on projected separation and white dwarf effective temperature, where enrichment fraction decreases at smaller separations and lower temperatures. These findings indicate that, compared to single stars, binary systems either start with smaller initial planetary reservoirs due to suppressed planetesimal formation or undergo more rapid depletion of planetary material during the initial part of the white dwarf stage.
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All authors Siyi Xu, Laura. K. Rogers, Joan Najita, Boris T. Gänsicke, Paula Izquierdo, Sergey E. Koposov, Christopher J. Manser, Andrew Swan, Sandford Nathan, Wang Wenting, J. Aguilar, S. Ahlen, C. Allende Prieto, D. Bianchi, D. Brooks, T. Claybaugh, A. de la Macorra, J. E. Forero-Romero, Satya Gontcho A Gontcho, G. Gutierrez, R. Joyce, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, G. Tarlé, B. A. Weaver, R. Zhou

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

Testing Chemical Tagging with LAMOST: Intrinsic Abundance Dispersion of Subgiant Stars in the Galactic Disk

Wu Yaqian, Xiang Maosheng, Zhao Gang et al. (+4 more)

The scatter in elemental abundances among stars of similar age and metallicity reflects chemical inhomogeneity in their birth environments, making abundance scatter a key observable for chemical-tagging studies of Galactic formation and evolution. Using a large sample of subgiant stars with precise ages and elemental abundances derived from LAMOST low-resolution spectra, we investigate the intrinsic chemical abundance scatter of the low-$\alpha$ thin disk near the solar neighborhood ($7 < R < 10$ kpc). We model the abundance ratio [X/Fe], for each of the 19 elements of concern, as a function of age, [Fe/H], and [Mg/Fe], and deduce the intrinsic dispersions with a forward modelling technique. Our results confirm previous findings that the intrinsic scatters are small, typically $\lesssim0.05$~dex, for light elements (C, Al), $\alpha$-elements (O, Mg, Si, Ca, Ti), and iron-peak elements (Mn, Ni). A dedicated analysis of M67 yields similarly small scatter values for these elements, implying limited discriminatory power from light-element abundances alone. In contrast, neutron-capture elements exhibit substantially larger scatters, typically $\gtrsim$0.1 dex, which are significantly larger than those of M67 member stars ($\sim$0.07~dex). In particular, our analysis suggests that the abundance variations of individual neutron-capture elements cannot be explained by a single tracer such as [Ba/Fe]. These findings clarify the utility of neutron-capture elements for chemical tagging and highlight the potential of low-resolution spectroscopy in such studies.
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All authors Wu Yaqian, Xiang Maosheng, Zhao Gang, Jiang Ruizheng, Li Zhuohan, Bi Shaolan, Zhang Meng

Solar and Stellar Astrophysics

Evidence for CME–CME Interaction in a Magnetic-Cloud-Like Ejecta: Insights from Multipoint Observations and Polytropic Analysis

Jyoti Sheoran, Vaibhav Pant, Eva Weiler et al. (+5 more)

Using in-situ observations from Solar Orbiter, STEREO-A, and Wind, we investigate the heliospheric evolution of an interplanetary coronal mass ejection (ICME). The magnetic ejecta (ME) shows a magnetic-cloud-like (MCL) configuration: a front region in which the magnetic field rotates and its magnitude declines, followed by a weakly rotating "back region" of nearly constant field magnitude. Near-Sun EUV and white-light observations reveal two fast CMEs launched in rapid succession and interacting at low coronal heights, providing direct evidence that an MCL ejecta can arise from interaction between two closely spaced CMEs sampled near their apex. Using near-radially aligned Solar Orbiter and STEREO-A observations, we find that the sheath expands more rapidly than the ME, consistent with the "snow-plow" effect, while the ME properties broadly follow trends reported in previous ICME studies. Comparison of STEREO-A and Wind observations, separated by only 9.2 degrees in longitude, reveals measurable mesoscale variability within both the sheath and the ME. We identify dual polytropic behavior within both substructures, consistent with the merging of two interacting CMEs to form the observed MCL ejecta. This dual behavior in the ME is most pronounced in the inner heliosphere and weakens with heliocentric distance, indicating thermodynamic homogenization during radial expansion, whereas the sheath maintains thermodynamic contrasts from the inner heliosphere to 1 au. Our findings suggest that polytropic diagnostics can help reveal thermodynamically distinct plasma populations associated with interacting CMEs, providing additional evidence for CME-CME interaction in MCL ejecta where conventional in-situ signatures show no clear evidence of such interactions.
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All authors Jyoti Sheoran, Vaibhav Pant, Eva Weiler, Vivek Menon, Emma E. Davies, Christian Möstl, Dipankar Banerjee, M. Saleem Khan

Solar and Stellar Astrophysics

Evidence for plasmoid formation related to a hot UV burst in the solar atmosphere

Mats Ola Sand, Luc Rouppe van der Voort, Souvik Bose et al. (+4 more)

Magnetic reconnection in the solar atmosphere drives energetic phenomena such as Ellerman bombs, UV bursts, and surges. We used coordinated observations from the Swedish 1-m Solar Telescope (SST), IRIS, SDO, and the Hinode/X-ray Telescope (XRT) to analyze an active region with strong magnetic flux emergence. This region displayed long duration UV burst activity, occurrence of multiple Ellerman bombs, and recurrent ejection of surges. Chromospheric imaging show sthe presence of a dome-like structure that overarched the region where magnetic flux was emerging. The curved chromospheric fibrils were closely associated with bright and similarly curved extensions from a UV burst in the IRIS 1400 A channel. We observed an episode of formation of a bright sheet along the curved fibrils in H-beta that subsequently fragmented into plasmoid-like blobs with peak emission at a Doppler offset of +43 km/s. IRIS Si IV lines in the same region show complex and non-Gaussian line profiles that display asymmetric extensions to high Doppler offsets. Some profiles have clear components with Doppler offsets in excess of 150 km/s on both sides of the nominal line center. The optically thin SDO/AIA channels, including 94 A, show intermittent and repeated occurrences of the burst. Emission measure and filter ratio analysis indicate that the burst is multi-thermal and can attain temperatures beyond 1 MK. AIA and Hinode/XRT observations reveal a localized EUV and soft-X-ray counterpart of the burst/dome system, supporting the presence of intrinsically multithermal plasma that reaches coronal, and likely multi-MK, temperatures.
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All authors Mats Ola Sand, Luc Rouppe van der Voort, Souvik Bose, Daniel Nobrega-Siverio, Jonas Thoen Faber, Reetika Joshi, Ignasi Josep Soler Poquet

Solar and Stellar Astrophysics

Non-axisymmetric Transport of Magnetic Flux Tubes: A Mechanism for Joy's Law and Poloidal Field Generation via Meridional Flows

Andrey G. Tlatov

We present a new scenario for the solar $\alpha\omega$-dynamo based on the interaction of asymmetric magnetic flux tubes with the near-surface meridional flow. Standard thin flux tube simulations indicate that the radial gradient of differential rotation ($\partial\Omega/\partial r > 0$) breaks the spatial symmetry of emerging $\Omega$-loops. The leading (western) leg becomes nearly vertical, while the trailing (eastern) leg is heavily stretched and flattens along the longitude. Upon emergence at the photosphere, the horizontal meridional flow toward the poles acts more efficiently on the trailing leg because the efficiency of the hydrodynamic entrainment by the plasma (the “sail effect”) is directly proportional to the total spatial length of the magnetic flux tube arc elements. This creates a differential torque that drives the trailing sunspot poleward while the leading sunspot remains anchored due to its compact spatial geometry. Our model yields a tilt angle evolution rate of $\approx 0.3^\circ\,\mathrm{day}^{-1}$ at a latitude of $20^\circ$ for a bipolar separation of $15^\circ$, reproducing Joy's law without invoking the classical Coriolis-driven twist during the rise phase.
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Solar and Stellar Astrophysics

Statistical evidence for linear combination frequencies in {\gamma} Doradus stars being nonlinear resonant modes

Yanqi Mo, Weikai Zong, Xuan Wang et al. (+4 more)

The quest for the origin of linear combination frequencies in pulsating stars is critical for mode identification and subsequent seismic modeling. Hybrid {\gamma} Doradus (Dor) stars provide a crucial testbed for such investigations due to their rich frequency content in both gravity (g) and pressure (p) modes. Here, we performed a comprehensive survey of 608 Kepler {\gamma} Dor stars, detecting 81,265 frequencies, and identifying 1,895 harmonics and 45,968 combinations involving two parent frequencies. Our results suggest that the proportion of linear combinations increases with the frequency number in each {\gamma} Dor star, leveling off at approximately 75%. The majority of the parent-to-child amplitude ratios are distributed between 100 and 10,000, peaking between 2,000 and 4,000. Moreover, the amplitude ratios, involving two g-mode parents, are found to escalate with increasing combination frequency. These values are at least an order of magnitude higher than those predicted by nonlinearity distortion of the light curve, whereas they align well with those of nonlinear resonant coupling. Our findings suggest that a significant portion of combination frequencies are likely intrinsic modes under resonant conditions rather than products of surface geometric distortions, offering new insights that warrant systematic investigations across other types of pulsating star.
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All authors Yanqi Mo, Weikai Zong, Xuan Wang, Jian-Ning Fu, Xiao-Yu Ma, Mingfeng Qin, Stéphane Charpinet

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

Evidence for the binary nature of the long-period radio transient ASKAP/DART J1832-0911

Csanád Horváth, Natasha Hurley-Walker, Ziteng Wang et al. (+2 more)

Long-period transients are a class of periodic pulsed radio source repeating on the minute to hour timescale. Recently, an increasing number of them are being identified as binary systems, specifically white dwarfs with low-mass main-sequence companions. In this work we analyse the most luminous long-period transient discovered to date, ASKAP/DART J1832-0911, with two years of radio data, and propose that it, too, may be a white dwarf system, although in a far more compact orbit than the aforementioned. The pulses are composed of quasi-periodic components which evolve in a systematic way over days and months. The source is highly linearly or elliptically polarised and its brightness enabled very high signal-to-noise measurement of the time-resolved Faraday rotation measure, which was found to vary across pulse phase. The linear polarisation position angle, circular polarised fraction, and spectral index also varied systematically in ways not typical of pulsars and magnetars. We show that an ultra-compact asynchronous polar explains much of the phenomenology of ASKAP/DART J1832-0911, in particular the evolution of the pulse morphology, rotation measure variation, and periodic X-ray emission, although we cannot conclusively prove a binary nature. However, our model makes testable predictions.
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All authors Csanád Horváth, Natasha Hurley-Walker, Ziteng Wang, Andrew Zic, Emil Lenc

Solar and Stellar Astrophysics

Uncovering the Origin of Slow Rotators among Intermediate-Mass Stars in the Star-Forming Cluster Trumpler 14

Khushboo K. Rao, Wen-Ping Chen, Hsiang-Yu Chen et al. (+2 more)

Intermediate-mass (about 1.5-8 M$_{\odot}$) stars exhibit a wide range of rotation rates and have gained attention for their roles in the extended main-sequence turnoffs (eMSTO) seen in some young and intermediate-age clusters (ages $< 2$ Gyr). Although rapid rotation is expected due to their radiative envelopes, the presence of slow rotators remains puzzling. In this study, we examine disk and X-ray signatures among the intermediate-mass members of the star-forming cluster Trumpler 14. Of the 118 intermediate-mass members, 24 are considered disk-bearing on the basis of their infrared spectral indices derived from spectral energy distributions. The majority of these reside outside the heavily irradiated cluster core and are all slow rotators ($\lessapprox 100$ km s$^{-1}$) except for three fast-rotating Class III objects. Additionally, in the same sample of 118, 37 are X-ray sources, and 22 having available $v \sin i$ data show a systematically slower rotation than X-ray quiet sources. Our findings suggest that, while young stellar disks in intermediate-mass stars contribute to early spin-down, high-energy processes traced by X-ray emission during this phase could be an additional channel for angular-momentum loss in these stars.
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All authors Khushboo K. Rao, Wen-Ping Chen, Hsiang-Yu Chen, Kristen Dage, Stella S. R. Offner

Solar and Stellar Astrophysics

A prolonged plateau-to-tail transition in the Type II supernova SN2025abyc

Luhan Li, Bo Wang, Jujia Zhang et al. (+6 more)

We present optical photometric and spectroscopic observations of the Type II supernova SN2025abyc. During the optically thick phase between approximately 10 and 70 d after explosion, its light curves show strongly wavelength-dependent decline rates of approximately 2.7, 2.1, 0.9, and 0.8 mag/100d in the g, c, r, and o bands, respectively. At approximately 70 d, the light curves begin to depart from their nearly linear plateau evolution and gradually transition toward the radioactive tail. A Fermi-Dirac fit to the well-sampled ATLAS o-band light curve yields a transition midpoint of t_PT ~ 100.5d. The interval between the end of the linear plateau and this transition midpoint is approximately 30 d, indicating a prolonged plateau-to-tail transition. This timescale is comparable to those measured for SN2013by, SN2013ej, and SN2014G. Spectroscopically, at +13 d post-explosion, the Halpha profile appears weak and broad, whereas Hbeta and Hgamma display clear P-Cygni profiles. This morphology can be explained by the normal early spectroscopic evolution of SNe II, although partial filling of the Halpha absorption trough by emission associated with circumstellar interaction cannot be excluded. SN2025abyc otherwise follows the general photospheric velocity evolution of SNe II, while remaining toward the high-velocity side of the comparison distribution in Halpha, Hbeta, and FeII. Exploratory light-curve modelling suggests a synthesized Ni mass of approximately 0.03-0.04 solar mass. We suggest that the extended circumstellar environment, Ni distribution, and hydrogen-envelope structure could all play a role in shaping the observed light-curve evolution, particularly the prolonged plateau-to-tail transition.
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All authors Luhan Li, Bo Wang, Jujia Zhang, Zhengyang Zhang, Xinjie Luo, Shiyang Dong, Saien Xu, Zhengwei Liu, Zhanwen Han

Solar and Stellar Astrophysics

Science operation, data handling, and ground support system of the SOLAR-C mission

Shin Toriumi, Mari Nishiyama, Keiichi Matsuzaki et al. (+16 more)

SOLAR-C is an international solar-observing satellite mission led by Japan Aerospace Exploration Agency (JAXA). It aims to elucidate mass and energy transport in solar atmospheres through extreme ultraviolet (EUV) spectroscopy. The mission carries the EUV High-throughput Spectroscopic Telescope (EUVST) and the Solar Spectral Irradiance Monitor (SoSpIM), enabling comprehensive observations across a wide temperature range (10^4 K to 10^7 K) with minimum temperature gaps and high spatial and temporal resolution. To achieve its science objectives regarding atmospheric heating and solar flare eruptions, SOLAR-C implements a flexible and responsive operational procedure and a data processing system, while building on the heritage of the Hinode and IRIS satellites. The Chief Observer creates observation timelines that include core observation plans and approved proposed plans while taking into account the solar activity levels. A SpaceWire communication architecture is employed onboard the spacecraft, and a method is implemented in which the mission instrument temporarily acts as the network master during data transfer to support the high data rate requirements. Telemetry is downlinked at ground stations worldwide and gathered at the Institute of Space and Astronautical Science, JAXA. The EUVST data are calibrated at the SOLAR-C Science Center at Nagoya University, while the SoSpIM data are calibrated at the Processing and Archiving Facility before being integrated into the science data products. The data will be made publicly available immediately. The integrated operational scheme for this mission is expected to advance our understanding of solar atmospheric heating and flare processes.
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All authors Shin Toriumi, Mari Nishiyama, Keiichi Matsuzaki, Toshifumi Shimizu, Hideki Kato, Jun Matsumoto, Mizuho Uchiyama, Kota Miyoshi, Daiki Yamasaki, Hirohisa Hara, Yukio Katsukawa, Masahito Kubo, Ryohko Ishikawa, Takenori J. Okamoto, Shinsuke Imada, Satoshi Masuda, Kyoko Watanabe, Yusuke Iida, Ayumi Asai

Solar and Stellar Astrophysics

Classical Nova V1405 Cas Had $M_{\rm ejecta}$$>$$M_{\rm accreted}$ and so is Unlikely to be a Type Ia Supernova Progenitor

Bradley E. Schaefer

Nova 2021 Cassiopeia (V1405 Cas) was an ordinary J(175) neon nova with the white dwarf mass estimated to be $M_{\rm WD}$=0.60$\pm$0.10 $M_{\odot}$. I found an orbital period of $P$=0.1884 days, and have tracked 20 times of photometric minima from 2013–2025. I measure that $P$ increased from before to after the eruption with $P_{\rm pre}$=0.1883919$\pm$0.0000018 days and $P_{\rm post}$=0.1884043$\pm$0.0000018 days, for $\Delta P$/$P$=66$_{-18}^{+21}$ parts-per-million. With correction for the angular momentum loss by the binary during the eruption, I derive that the nova ejected $M_{\rm ejecta}$=7.5$\times$10$^{-4}$ $M_{\odot}$, with an extreme range of (2.9–40)$\times$10$^{-4}$ $M_{\odot}$. The mass accreted during the previous eruption cycle comes from the trigger mass, and is $M_{\rm accreted}$=(1.6$\pm$0.4)$\times$10$^{-4}$ $M_{\odot}$. V1405 Cas provides counterexamples against five claims about CV evolution that have dominated since the 1980s. First, V1405 Cas has positive $\dot{P}$, and this is contrary to the Magnetic Braking Model. Second, the $\Delta P$ is 20$\times$ too small to allow the system to fade into a hibernation state. Third, $M_{\rm WD}$ is decreasing over time, as shown by $M_{\rm ejecta}$$>$$M_{\rm accreted}$ and by being a neon nova. Fourth, V1405 Cas is not a Type Ia supernova progenitor, for the same reasons. Fifth, the orbital period of V1405 Cas increased by $+$75 ppm from 2013–2025, as a counterexample to the pervasive idea that cataclysmic variables are universally declining in period from evolution. V1405 Cas is the latest of recent measures of $\Delta P$ and $\dot{P}$ for 52 cataclysmic variables and 25 X-ray binaries that have together refuted all five claims.
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2609.10990 · 10 Sep · 7th in a series of ApJ papers, each proving that popular progenitor candidates cannot become Type Ia supernovae: 1. V445 Pup (arXiv:2412.17286), 2. T CrB (arXiv:2510.01587), 3. U Sco (arXiv:2510.01589), 4. FQ Cir (arXiv:2511.16594), 5. all symbiotic stars (arXiv:2511.19948), 6. T Pyx (arXiv:2602.09377), 7. V1405 Cas (ApJ in press)

Abstract PDF $EVO ×2$SNOV ×2$MAG ×1

Solar and Stellar Astrophysics

Eclipse Properties and Superhump Evolution in the SU UMa-Type Dwarf Nova Z Cha

Qi-Bin Sun, Sheng-Bang Qian, Li-Ying Zhu et al. (+10 more)

The advent of large-scale time-domain surveys provides both opportunities and challenges for understanding accretion disk evolution in cataclysmic variables (CVs). Using high-cadence photometry from the Transiting Exoplanet Survey Satellite (TESS), we investigate the eclipsing SU UMa-type dwarf nova Z Cha. Leveraging eclipses as a natural probe, we examine the evolution of the accretion disk through variations in eclipse depth, O–C of eclipse minima, and positive superhump (PSH) amplitude. During superoutbursts, all three quantities exhibit quasi-periodic modulations with a common period of $\sim$2 days, consistent with the precession period of an eccentric disk. We interpret these correlated variations as evidence of an eccentric, precessing disk: O–C traces the periodic shift of the system's brightness center, while eclipse depth and PSH amplitude vary with the orientation of the disk bulge relative to the line of sight. In quiescence (Sectors 13 and 93), PSHs with periods of $\sim$0.0762 days show linearly decreasing amplitudes and periods, indicating gradual shrinkage of the eccentric disk and a slowing precession. Remarkably, a coherent signal with a period of $\sim$0.0729~days ($\epsilon^{-}\approx-0.02$) appears in the same quiescent intervals. This signal may represent negative superhumps (NSHs) coexisting with PSHs, although an orbital sideband of the PSH cannot presently be excluded with the available data. If confirmed as NSHs, their coexistence with PSHs would challenge the classical tilted-disk model, and could be explained by retrograde apsidal precession of an eccentric disk, where the inner disk precesses retrogradely (NSHs) and the outer disk progradely (PSHs); this interpretation remains to be tested by further observations.
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All authors Qi-Bin Sun, Sheng-Bang Qian, Li-Ying Zhu, Qin-Mei Li, Wen-Ping Liao, Fu-Xing Li, Wen-xu Lin, Min-Yu Li, Ping Li, Zi-Mo Li, Tao Wang, Mao-Han Zhang, Eduardo Fernandez-Lajus

Wednesday 9 September

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

Constraining Tidal Migration with the Hot Jupiter Population

Linhao Ma, Yubo Su, Samuel W. Yee et al. (+3 more)

Hot Jupiters with orbital periods shorter than a few days have probably been affected by tidal orbital migration. We develop an analytical framework for constraining tidal migration from the present-day hot Jupiter period distribution, taking into account the uncertain rate and period distribution of hot Jupiters produced by mechanisms such as high-eccentricity migration or disk-driven migration. Assuming the tidal migration timescale is proportional to $P^{\chi_\tau}$, solutions with $\chi_\tau \simeq 3, 1.7,$ and 5.6 are all compatible with the present-day period distribution. The $\chi_\tau \simeq 3$ solution is consistent with equilibrium tides with suppression of dissipation at short periods, and implies that newly circularized hot Jupiters have periods concentrated near $3-4$ days, as predicted in some high-eccentricity migration models. The $\chi_\tau \simeq 1.7$ solution is also compatible with the $3-4$ day peak but has no clear counterpart in existing tidal theories and is more finely tuned. The $\chi_\tau \simeq 5.6$ solution is compatible with enhanced short-period equilibrium tidal dissipation or weakly nonlinear gravity-wave dissipation, but requires circularization at unexpectedly short periods. Thus, we find the model with $\chi_\tau \simeq 3$ most appealing. Transit timing of individual systems and observational constraints on the rate of hot Jupiter engulfment provide additional constraints, which are presently inconclusive but should improve with future data. Improved measurements of the occurrence of short-period planets as a function of planet mass and system age could also help to sharpen the constraints on tidal migration.
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All authors Linhao Ma, Yubo Su, Samuel W. Yee, Caleb Lammers, Eliot Quataert, Joshua N. Winn

Solar and Stellar Astrophysics

Frozen-composition effects on rotational failure of neutron-star crusts

Elia Giliberti

The elastic response of a neutron-star crust to rotational loading depends on whether weak interactions can restore chemical equilibrium during the deformation. We quantify this effect using unified equations of state and compare chemically equilibrated and frozen-composition responses within the same Newtonian hydro-elastic framework. Frozen composition increases the effective bulk modulus and redistributes the strain throughout the inner crust rather than producing a simple global rescaling. For BSk24, the breaking frequency decreases from $0.4997\Omega_K$ to $0.3912\Omega_K$, a reduction of 21.7 per cent, while the location of first failure moves to higher density. Comparable reductions are obtained for BSk21, whereas SLy4 gives a smaller effect of 16.7 per cent. For BSk24 the relative reduction remains close to 21–22 per cent over the mass range $1.2$–$2.0,M_\odot$. A density-resolved perturbation analysis shows that the result is controlled by the radial overlap between the microphysical frozen-composition stiffening and the mechanical susceptibility of the crust, with most of the linear sensitivity in the BSk models arising from $0.01<n_B<0.03,{\rm fm}^{-3}$. These results show that chemical non-equilibrium can substantially modify both the rotational failure threshold and the layer in which crustal failure begins.
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Solar and Stellar Astrophysics

UX Men: Detached Eclipsing Binary as a Benchmark Candidate

Ganesh N. Pawar, Krzysztof G. Hełminiak, Nicola J. Miller et al. (+5 more)

We present ultra-precise fundamental parameters for the detached eclipsing binary UX Men based on 31 TESS sectors ($\sim$882 d) and radial velocities from HARPS, FEROS, CORALIE, and UCLES. The light curves were detrended for spot-induced variability and modelled independently with JKTEBOP and ALLESFITTER, while radial velocities were extracted via TODCOR and fitted with a Keplerian orbit. Spectral disentangling yielded individual component spectra analysed with iSpec to determine $T_{\rm eff}$ and $\mathrm{[M/H]}$. Multi-band photometry was used to determine the fluxes, flux ratios and ultimately to measure photometric $T_{\rm eff}$. We obtain the masses $M_{\rm A}$ = $1.2300 \pm{0.0012}$ M$_{\odot}$, $M_{\rm B}$ = $1.1946\pm{0.0012}$ M$_{\odot}$ and radii $R_{\rm A}$ = $1.3605\pm{0.0031}$ R$_{\odot}$, $R_{\rm B}$ = $1.2801\pm{0.0069}$ R$_{\odot}$ with sub-percent precision. Uncertainties were found to be dominated by systematic effects coming from (weak) stellar activity. $T_{\rm eff,A}$ = $6302\pm{77}$, $T_{\rm eff,B}$ = $6292\pm65$ & Metallicity estimates are $[M/H]_{\rm A} = 0.02\pm{0.13}$ dex and $[M/H]_{\rm B}= 0.07\pm{0.10}$ dex. Isochrone fitting yields a consistent age of $\tau$ = $2.75\pm{0.13}$ Gyr. The system exhibits a $\sim$ 673-day periodicity in eclipse-timing variations, likely due to stellar activity, with no evidence for a third body. Results are independent of the modelling code used, but without proper treatment of activity-induced systematics the uncertainties would be underestimated. UX Men is a high-precision benchmark binary providing stringent tests of stellar models and a robust calibration source for PLATO. Expanding the sample of well-characterised detached eclipsing binaries will strengthen the empirical foundations for stellar physics and the calibration of future photometric missions
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All authors Ganesh N. Pawar, Krzysztof G. Hełminiak, Nicola J. Miller, Frédéric Marcadon, Ayush Moharana, Tilaksingh B. Pawar, Anish Kalsi, Maciej Konacki

Solar and Stellar Astrophysics

Solar Flare Prediction Using a Hybrid Convolutional Neural Network and Transformer Model

Mason Cao and Junwei Zhao

Solar flares are intense bursts of electromagnetic radiation that occur when stored magnetic energy in the Sun's atmosphere is suddenly released. They are categorized into five classes – from least to most powerful: A, B, C, M, and X – with each successive class representing a ten-fold increase in energy output. The electromagnetic radiation emitted by the stronger classes (C, M, and X) is capable of causing significant disruptions to communication systems, satellites, and power grids on Earth. Accurate prediction of solar flares is crucial for mitigating their adverse effects and ensuring the functionality of critical infrastructure. This research introduces a novel model named ResNet-Transformer, which combines a convolutional neural network (CNN), ResNet50, with a standard Transformer architecture. The hybrid model effectively processes both spatial and time-series data derived from solar images to predict the occurrence, class (C, M, and X), and probability of solar flares within 24-hour, 36-hour, and 72-hour windows. This hybrid deep learning model represents the first of its kind in the domain of image-based, multiclass solar flare prediction. We evaluated the model's performance using a comprehensive set of metrics, including weighted precision, recall, and F1 score, together with balanced accuracy, the Matthews correlation coefficient (MCC), Cohen's kappa, and the area under the receiver operating characteristic curve (ROC-AUC). Results show that ResNet-Transformer surpasses traditional machine learning methods, such as support vector machines (SVMs) and standalone CNN models, across all evaluated metrics. This study highlights the potential of integrating convolutional neural networks with Transformers to enhance predictive capabilities in solar physics, paving the way for more reliable and timely solar flare forecasting.
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Solar and Stellar Astrophysics

Hbeta Spicules, Small-scale Jets, and Hbeta Microflashes: Sub-arcsecond Dynamic Events and their Magnetic Origins in the Lower Solar Chromosphere Observed by DKIST

Navdeep K. Panesar, V. Aparna, Sanjiv K. Tiwari et al. (+3 more)

We examine an on-disk solar quiet region of enhanced magnetic network using Hbeta images from Daniel K. Inouye Solar Telescopes (DKISTs) Visible Broadband Imager (VBI) and line-of-sight magnetograms from DKISTs Visible Spectro-Polarimeter (ViSP). We also compare the ViSP magnetograms with co-aligned co-temporal line-of-sight magnetograms from the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI). We find:(i) Two types of chromospheric jet-like features: Hbeta spicules, and small-scale jets. Both are rooted near edges of magnetic network lanes. Several sit close to ViSP-detected tiny islands of either minority-polarity flux or dips in majority-polarity flux. Hence, those several plausibly stem from mixed-polarity magnetic flux, and are caused by chromospheric magnetic reconnection. For He̱ta} spicules, the average width, length, lifetimes, and speeds are 420$\pm$400 km, 2600$\pm$1600 km, 4.3$\pm$0.25 min, and 12$\pm$4.7 kms. For small-scale jets, those are 385$\pm$100 km, 620$\pm$40 km, 5$\pm$3min, and 4.4$\pm$1.5 kms. (ii) H$\beta$ microflashes sit in evidently unipolar flux. Their widths, lengths, lifetimes, and speeds are 180$\pm$65 km, 365$\pm$100 km, 4.3$\pm$2.6 min, and 3.1$\pm$0.2 kms. (iii) At the base of a coronal plume, due to its higher spatial resolution than HMI, ViSP shows both some very strong (>800 G) majority-polarity flux not shown by HMI and some sub-arc-second minority-polarity-flux inclusions not shown by HMI. These sub-arcsecond chromospheric transients carry sufficient energy (10^{24}erg) to transiently heat the local chromosphere and corona and potentially contribute to solar-wind acceleration. They may represent the small-scale end of a continuum of magnetic-reconnection-driven activity, highlighting the importance of DKIST's high-resolution magnetic-field measurements for understanding small-scale chromospheric dynamics.
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All authors Navdeep K. Panesar, V. Aparna, Sanjiv K. Tiwari, Alphonse C. Sterling, Ronald L. Moore, J. M. da Silva Santos

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

Predictions for astrometric microlensing in Gaia

Zofia Kaczmarek, David Sweeney, Łukasz Wyrzykowski et al. (+1 more)

ESA's astrometric space mission Gaia is uniquely positioned for microlensing studies thanks to its all-sky coverage and simultaneous astrometric and photometric observations. In Gaia Data Release 4 (DR4), astrometric time series will be published for the first time, providing a rich dataset for isolated stellar remnant searches. In anticipation of DR4, we prepared tools for fitting photometric and 1D astrometric measurements. We tested the recovery of true event parameters and population distributions with Gaia-like observations. We created a mock survey of microlensing events mirroring Gaia DR4's design. The events were generated using dedicated Galactic simulations to provide realistic expectations on stellar and dark lens yields. For selected events, we simulated observations following Gaia's scanning law and precision, using the astromet package. Such simulations are needed to interpret forthcoming data; they also enable testing inference tools with known ground truth. We used nested sampling to infer full posterior distributions and compare them with the true lens parameters. Our simulation predicts $322 \pm 70$ microlensing events with astrometric signals above Gaia precision thresholds; $209 \pm 57$ of them have detectable photometric signals. Among those, $82 \pm 9$ and $49 \pm 7$, respectively, have remnant lenses. To assess Gaia's capabilities in constraining remnant mass distributions, we modelled $49$ events from this sample. We recovered the true Einstein times and radii for most events. Microlensing parallax measurements are consistent with true values but uncertain, limiting mass determination. We recommend focusing on events with bright sources or anomalous fits to optimize dark lens searches. We make available the mock Gaia time-series dataset, as well as a toolkit repository for working with the data format, fitting models, and visualizing results.
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All authors Zofia Kaczmarek, David Sweeney, Łukasz Wyrzykowski, Ulrich Bastian

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

Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture

Qinxun Li and Shengyi Liu

The recent 248-keV nuclear recoil candidate reported by LUX-ZEPLIN has renewed interest in endothermic inelastic dark matter, motivating us to examine its capture in primordial dark stars. Relative to the conventional elastic-capture picture in dark star evolution, endothermic capture adds two qualitative features. First, it opens only after the growing star crosses a compactness threshold, expressed as a kinematic radius $R_{\rm kin}\propto\mu_{\chi}M_\star/\delta$ set by the stellar mass, the dark-matter–nucleus reduced mass and the mass splitting. The accreting growth carries the star through the threshold, and the capture rate turns on quadratically above it. Second, although newly captured particles generically begin on nonthermal bound orbits, endothermic kinematics can keep this normally transient population spatially extended, turning it into a persistent reservoir rather than an intermediate step toward a thermal core. Following complete chains of state-changing collisions, we find that the reservoir compacts sharply and then stalls, because a ground state particle below a compactness-dependent orbital energy has no allowed up-scatter anywhere in the star. A percent-level radius contraction reopens the relaxation. These kinematic results do not depend on whether the excited state decays promptly or is long-lived. As a result, inelastic capture does not replenish a thermal annihilation core. The captured population forms an evolving orbital distribution that sets up the co-evolutionary dynamics between the star and the dark matter in the core and the reservoir, which we develop in a companion paper.
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Solar and Stellar Astrophysics

Wave Emission and Absorption in a Near-Sun Proton-Cyclotron Wave Storm

Kristopher G Klein, Daniel Verscharen, Mihailo Martinovic et al. (+5 more)

Quantification of energy transport and dissipation in weakly collisional heliospheric plasmas that are far from local thermodynamic equilibrium is an outstanding scientific problem. A central challenge is determining how non-Maxwellian velocity-space structure affects damping and emission of coherent ion-scale waves, especially compared to simplified analytical models for background plasma velocity distributions. In this work, we study the damping and emission of parallel-propagating proton cyclotron waves for two models of proton velocity distributions measured by the SPAN-I instrument on board Parker Solar Probe during an extended storm of waves with left-hand polarization in the solar wind at a heliocentric distance of 30.1 solar radii. Using the measured velocity distribution rather than a two-component bi-Maxwellian model predicts instabilities consistent with the observed coherent waves. For intervals in which both models predict net damping, the observed VDF model yields weaker damping in 90% of cases, with a reduction in the integrated heating rate of 0.44 relative to the bi-Maxwellian model. These results suggest that simplified analytical velocity distribution models may overestimate cyclotron damping and underestimate wave emission in the near-Sun solar wind.
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All authors Kristopher G Klein, Daniel Verscharen, Mihailo Martinovic, Niranjana, Ali Rahmati, Roberto Livi, Davin Larson, Michael Stevens

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

From spirals to rings: dust dynamics in gravitoturbulent protoplanetary discs after late infall

Clément Baruteau, Steven Rendon Restrepo, Gaylor Wafflard-Fernandez et al. (+7 more)

Substructures appear to be a common trait of all extended protoplanetary discs. They are found notably in discs still surrounded by ambient, possibly infalling material. In this study, we revisit the observational signatures of gravitational instability (GI) in the dust and gas emission of protoplanetary discs. We focus on discs undergoing a short-lived episode of late infall that triggers spirals via GI, in order to investigate the long-term dynamics of millimetre-sized dust. We performed 2D hydrodynamical simulations modelling gas and millimetre-sized dust in a self-gravitating disc, with a simplified treatment of stellar irradiation and infall. Results were post-processed by 3D radiative transfer calculations. During infall, GI sets in and the disc develops a gravitoturbulent state characterised by the continuous formation of spirals. Shortly after infall ends, the millimetre-sized dust remains well coupled to the gas, and the dust emission exhibits large-scale spirals in both near-infrared scattered light and continuum emission. Even long after infall has ceased, two-armed spirals are persistently excited by GI in specific regions of the disc. Their dissipation entails the formation of multiple long-lasting pressure maxima, which can be viewed as vestiges of shocks induced by the spirals. They form persistent dust rings that are more or less axisymmetrical. Consequently, once late infall ends, a massive disc can gradually evolve from a disc with spirals in the continuum into one featuring multiple, potentially lopsided bright rings in the continuum. In near-infrared scattered light, the disc initially displays multiple spirals during infall or shortly after it ceases, before ultimately exhibiting multiple rings. The persistent excitation of spirals implies, however, that the residual line-of-sight velocity, derived from line emission, shows large-scale spirals across the disc.
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All authors Clément Baruteau, Steven Rendon Restrepo, Gaylor Wafflard-Fernandez, Sebastián Pérez, Zhaohuan Zhu, Hans Baehr, Farzana Meru, Jean-François Gonzalez, Sergei Nayakshin, Sahl Rowther

Solar and Stellar Astrophysics

On the 3D Magnetic Structure of Coronal Mass Ejections Through the Solar Corona

Erika Palmerio, Michal Ben-Nun, Tibor Török et al. (+2 more)

The magnetic fields that make up the internal structure of coronal mass ejections (CMEs) are thought to be organised in a flux rope configuration, consisting of twisted magnetic fields that wind about a central axis. Remote-sensing observations of CMEs show a wide range of morphologies, dynamics, and evolution, including rotation, non-uniform expansion, deflection, and interaction with the ambient solar wind. In-situ measurements, however, typically consist of a single 1D spacecraft trajectory through a large 3D structure (or few at best), restricting our ability to determine how CME magnetic structure varies in space and time. In this work, we analyse the magnetic configuration of two idealised CMEs during their early evolution in the range 1-30 $R_{\odot}$ using the Magnetohydrodynamic Algorithm Outside a Sphere code. The initial flux ropes differ only in their orientation with respect to the global dipole and erupt from a bipolar active region below the streamer belt in a simplified coronal environment. We deploy a fleet of synthetic spacecraft throughout the CMEs' paths at different combinations of latitudes, longitudes, and heliocentric distances. We identify and examine flux rope signatures in the synthetic in-situ profiles to characterise radial variations as well as latitudinal/longitudinal ones. We find that, even in a simplified CME erupting under solar minimum-like conditions, the sampling location significantly affects the global structure that would be deduced from common flux rope reconstruction and analysis techniques used for in-situ measurements. Additionally, we consider possible in-situ signatures that may serve as indicators of the source region's topology.
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All authors Erika Palmerio, Michal Ben-Nun, Tibor Török, Cooper Downs, Viacheslav S. Titov

Solar and Stellar Astrophysics

MHD Modelling of magnetic reconnection heating and jets in the solar corona

P. Pagano, C. Argiroffi, F. Reale et al. (+3 more)

Magnetic reconnection is seen as the lead mechanism to explain the persistent and bursty heating of the solar corona that keeps its thermal structure. Lately the observations and modelling of magnetic reconnection outflows, i.e. nanojets, has empowered our capabilities to scrutinise this mechanisms, however more needs to be understood on the relation between the energetic and kinematic events. The aim of this paper is to study in details the properties of the heating events (nanoflare) and the kinematic counterparts (nanojets) in order to augment detection capabilities of magnetic reconnection events. We use MHD simulations of the interaction of two magnetic flux tubes where magnetic reconnection occurs and such reconnection outflows are generated. We vary key parameters, such as the critical current and the size of the domain to study the heating and slingshot mechanisms. We find that the properties of the nanojets can give away much information on the magnetic reconnection that generated it, while it is difficult to directly link the amount of heating and the jet speeds. We also find that such reconnection model can explain a wide range of heating events. Magnetic reconnection still is invariably linked to both heating and outflows and our simulations show the complex interplay between these two byproducts of the magnetic reconnection and how their properties can be studied in observations.
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All authors P. Pagano, C. Argiroffi, F. Reale, A. Petralia, G. Cozzo, P. Testa

Solar and Stellar Astrophysics

Untangling EIT Waves: What a Measured Speed Actually Traces

Olena Podladchikova

Nearly three decades after the first SOHO/EIT observations, reported EUV-wave speeds still range from a few tens to more than 1000 km/s. This Perspective asks what those numbers actually trace. A measured image speed depends on passband and line-of-sight weighting, cadence, difference imaging, the selected crest or leading edge, propagation sector, fitted interval, and projection geometry. Same-event comparisons quantify this observation-operator effect. In events common to the Nitta and Muhr analyses, early or fastest-sector measurements were typically higher; five of six directly shared events differed by about 30%. For 19 May 2007, the 171 Angstrom peak speed was 475 +/- 47 km/s, compared with 238 +/- 20 km/s in 304 Angstrom, while the 171 Angstrom cadence was four times faster than the 195 Angstrom cadence. A sampling audit of the 1 April 2017 SWAP event shows that a repeated speed near 834 km/s is almost exactly one 91.6-Mm radial ring per 110-s image interval. In a reconstructed 3 April sector, AIA 171 Angstrom gives about 405 km/s, compared with the published SWAP mean of 484 km/s; an independently selected AIA 193 Angstrom ridge gives about 250 km/s under strongly shortened exposures. Such differences are not automatic evidence for different MHD modes. A same-event energy pilot separates compact-source heating, dimming/ejecta, and one weak-compression front segment. The current data do not justify a universal power law, but define a falsifiable question: is the fraction of released energy carried by the front scale invariant from compact quiet-Sun events to global waves and shocks? Establishing this dependence would show which eruption scales can contribute materially to coronal heating.
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