Solar and Stellar Astrophysics
TIC 366240660 - A Dynamically Active Triple With a Very Short Outer Period of 30.5 Days
S.A. Rappaport, T. Borkovits, G. Torres et al. (+17 more)
Methods: We analyze TESS photometric data, radial velocity measurements, and eclipse timing variation curves for the triple
star system, TIC 366240660, with a photodynamical code to infer the properties of all three
stars and orbital motions. Results: With an outer orbital period of only 30.5 d, this is the second most compact triple reported in the literature. We have determined the masses and $T_{\rm eff}$ values of the three
stars with an accuracy of about 1% and the radii to about 2%. The inclination angles of the two planes, and the mutual inclination angle are found with an accuracy of better than 1/3$^\circ$. The system is determined to be quite flat (to within 1/2$^\circ$), but with an outer eccentricity of $e_{\rm out} \simeq 0.33$. We find that the properties of the secondary
star of the inner binary are completely inconsistent with the
evolution of a single
star in isolation, and it must have transferred most of its envelope to the current primary
star in the inner binary during a prior episode of mass transfer. The eclipse timing variation (ETV) curve derived from the TESS photometric data shows that, in addition to a typical dynamical delay curve at the period of the outer orbit, there is also a much larger amplitude anomalous sinusoidal-like delay with a period of 840 d. This latter feature in the ETV curve is not yet describable in simple analytic terms, but it appears certain that it can be explained by the near integer ($\simeq$13:1) ratio of the outer to the inner orbital periods. Conclusions: We have extensively explored the exotic and anomalous ETVs of this highly compact triple system and found that they can exceed hours for the inner binary eclipses, and several days for the outer orbital eclipses. We provide a preliminary explanation for how these are related to the 13:1 mean motion resonance of the outer to inner orbits.
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All authors S.A. Rappaport, T. Borkovits, G. Torres, H.-L. Chen, P. Zasche, D. Vokrouhlický, B. Deme, M. Mašek, H. Kučáková, R. Uhlař, M. Wolf, Z. Garai, T. Pribulla, I.B. Bíró, I. Csányi, Z. Dencs, D. Latham, T. Mitnyan, V.B. Kostov, B.P. Powell
Solar and Stellar Astrophysics
Using Machine Learning to Model Stellar Collisions in our Galactic Center
Tristan C. Sand, Sanaea C. Rose, Elena González Prieto et al. (+9 more)
Direct collisions in the inner pc of the Galactic center can alter the orbits and properties of
stars. The outcome of a collision depends on a number of parameters, including the masses and ages of the
stars, the impact parameter, and the initial relative velocity. We utilize the newly developed $\verb|collAIder|$, a machine learning tool developed to predict the outcomes of stellar collisions, to bridge 3D hydrodynamic simulations of stellar collisions with a dynamical model of the Galactic center. Our results show a substantial population of stripped
stars, $\sim$$10\%$ of the initial stellar population, produced by mass loss during high-speed collisions. Stellar mergers are less frequent, with about $5\%$ of the
stars experiencing a collision-induced merger. We also find that high-speed, nearly head-on collisions can completely disrupt the
stars. These destructive collisions are usually preceded by 10 or more collisions, which gradually reduce the mass of the
star before it is ultimately destroyed. We estimate that mass loss during stellar collisions injects roughly $(2.5-8)\times 10^5$ M$_\odot$ of gas into the surrounding environment. Most of this gas is injected into the inner $0.1$ pc and about $90\%$ is retained within the cluster and may be accreted onto the supermassive black hole.
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All authors Tristan C. Sand, Sanaea C. Rose, Elena González Prieto, James C. Lombardi, Jr., Charles F. A. Gibson, Fulya K{\i}roğlu, Kyle Kremer, Christopher E. O'Connor, Enrico Ramirez-Ruiz, Frederic A. Rasio, Tjitske Starkenburg
Solar and Stellar Astrophysics
The oldest low-$\alpha$ thin disc stars
Riano E. Giribaldi, Laura Magrini, Marco Palla et al. (+1 more)
The formation pathway of the $\alpha$-poor Milky Way thin disc remains under debate. The latest observational data indicates the presence of comparable numbers of old
stars in both the low- and high-$\alpha$ disc components, suggesting either coeval or overlapping formation epochs. Using GALAH DR4, we provide evidence that the $\alpha$-poor
stars coexist with $\alpha$-rich
stars up to $\sim$12.5 Gyr. Stellar ages of 0.5 Gyr precision were re-derived for nearly $30\,000$ subgiant
stars using accurate effective temperatures ($T_{\rm{eff}}$) from the infrared flux method (IRFM) together with distances based on Gaia parallaxes. About 22% of the sample constitutes a population peaking at 9.2 Gyr, with evidence for an extended old-age tail reaching 12.5 Gyr. Among
stars older than 10 and 11 Gyr, between 20 and 30% have relative low [$\alpha$/Fe] and solar-like
metallicities ($-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex). These
stars exhibit kinematics consistent with those of near solar-age $\alpha$-poor
stars in the thin disc. These
stars can be evolved Sun-like
stars, i.e. old solar analogues, whose $T_{\rm{eff}}$ and
gravity modified with the time. Comparison with a well-tested Galactic disc chemical
evolution model supports the presence of a significant fraction of old, $\alpha$-poor disc
stars, confirming the plausibility of our selection criteria. We provide a catalogue with the selected sample to facilitate spectroscopic follow-ups at high resolution.
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All authors Riano E. Giribaldi, Laura Magrini, Marco Palla, Carlos Viscasillas Vázquez
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Early NIR echo and the time variable mass loss history of Type IIn SN 2024kgi
Naveen Dukiya, Kuntal Misra, Andrea Pastorello et al. (+30 more)
We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn
Supernova (SN) 2024kgi. The SN reaches at peak an $r$-band absolute magnitude of $-19.81 \pm 0.06$ mag and a bolometric luminosity of $\sim 2 \times 10^{43}$ erg s$^{-1}$. We observe a break in the lightcurve at day $\sim 312$, after which the luminosity decline changes from $t^{-1.0}$ to $t^{-4.5}$, likely due to the shock sweeping the dense CSM. We introduce a semi-analytical lightcurve modeling approach for CSM-interaction in transients that accounts for variable
diffusion time. We hence estimate a CSM mass of $2.34^{+11.8}_{-1.6} M_{\odot}$ and with a density profile $\rho_{csm} \propto r^{-2.74}$, indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca II triplet lines, at day $\sim 80$, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new dust formation in the ejecta and/or in the post-shock gas. We observe an NIR excess from day $\sim 40$ onwards. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from pre-existing dust, as there are no other indications for new dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.
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All authors Naveen Dukiya, Kuntal Misra, Andrea Pastorello, Andrea Reguitti, Anjasha Gangopadhyay, Aravind P. Ravi, Brian Hsu, Noah Franz, David J. Sand, Nathan Smith, Jennifer E. Andrews, Moira Andrews, K. Azalee Bostroem, Collin Christy, Monalisa Dubey, Joseph R. Farah, Archana Gupta, Estefania Padilla Gonzalez, Emily Hoang, D. Andrew Howell, Curtis McCully, Darshana Mehta, Megan Newsome, Jeniveve Pearson, Nicolas Meza Retamal, Jeonghee Rho, Manisha Shrestha, Bhagya Subrayan, Giacomo Terreran, Lina Tomasella, Stefano Valenti, Giorgio Valerin, Kathryn Wynn
Solar and Stellar Astrophysics
The white dwarf binary pathways survey - XI. The Gaia-GALEX UV Excess Sample for systems within 350 pc
James A. Garbutt, S. G. Parsons, N. Gentile Fusillo et al. (+9 more)
White dwarfs (WDs) with F, G or K type binary companions are the last common ancestor to a zoo of exotic phenomena. Finding a clean sample of such systems is difficult, as WDs in such binaries are usually outshone at optical wavelengths by their non-degenerate companion. It is useful to have a sample of such binaries - they can be studied to investigate binary
evolution, as they may have undergone a previous phase of mass transfer. Using Gaia data release 3 and GALEX, we compile a sample of 2597 candidate WD + FGK systems within 350 pc. These were identified via their ultraviolet excesses relative to MESA Isochrones and Stellar Tracks (MIST) model predictions consistent with the Gaia parameters of their non-degenerate companions. We estimate the mass, surface
gravity and effective temperature of the WDs by fitting the excess ultraviolet flux to models, or through interpolation where only one ultraviolet band was available. We also estimate the age of the system where possible, by comparing against any wide WD companions in higher-order stellar systems, or by checking if the system is a member of a cluster. On comparing against Simbad, we estimate the level of contamination within our sample to be between 10-35 per cent. This is a valuable sample for investigating WD + FGK binaries, particularly those containing hotter WDs (Teff,WD >~ 25 kK), and systems with post-main sequence companions.
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All authors James A. Garbutt, S. G. Parsons, N. Gentile Fusillo, B. T. Gänsicke, M. S. Hernandez, F. Lagos-Vilches, R. Raddi, A. Rebassa-Mansergas, J. J. Ren, M. R. Schreiber, O. Toloza, M. Zorotovic
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
CRIMSONS: An Online Tool for Modeling Chemical Enrichment with Stochastic IMF Sampling
Martina Rossi, Lapo Querci, Stefano Ciabattini et al. (+14 more)
Chemical enrichment is a universal process shaped by several interconnected factors, including stellar feedback, the nature of chemical polluters, and the underlying distribution of stellar masses. Three key ingredients are often difficult to treat simultaneously in chemical-
evolution models: the
stochastic sampling of the stellar IMF, uncertainties in stellar nucleosynthesis yields, and pre-enrichment from primordial PopIII
stars. In low
star-formation rate environments, incomplete IMF sampling makes enrichment sensitive to the random presence or absence of massive
supernova progenitors. Here, we present CRIMSONS, the first online tool designed to model chemical enrichment while self-consistently incorporating these three ingredients. The framework allows users to explore different IMFs, stellar population masses and
metallicities, and multiple stellar yield sets. It follows the
evolution of individual
stars and tracks 30 elements(H-Zn), including contributions from SN, AGB
stars, and TypeIa SNe. The current implementation adopts a closed-box framework, neglecting gas flows and spatial mixing, thus providing a controlled setup to isolate the effects of IMF sampling, stellar yields, and PopIII pre-enrichment. With CRIMSONS, we show that incomplete IMF sampling produces large abundance scatter, particularly in low-mass stellar populations. Different yield prescriptions introduce element-dependent variations, while some abundance ratios remain comparatively robust across models. Finally, comparison between models including primordial enrichment and those adopting only a
metallicity floor shows that PopIII pre-enrichment can significantly affect subsequent chemical
evolution. CRIMSONS therefore provides a controlled framework for quantifying the relative impact of
stochastic IMF sampling, nucleosynthetic uncertainties, and primordial pre-enrichment on predicted abundance patterns
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All authors Martina Rossi, Lapo Querci, Stefano Ciabattini, Stefania Salvadori, Irene Vanni, Davide Massari, Edoardo Ceccarelli, Donatella Romano, Viola Gelli, Raffaele Pascale, Alice Mori, Elka Rusta, Ioanna Koutsouridou, Ása Skúladóttir, Laura Magrini, Riano Giribaldi, Jose Schiappacasse-Ulloa
Solar and Stellar Astrophysics
Elemental Abundances of Cool Stars: A Spectroscopic Framework Applied to Five Planet-Host Stars
Nicole Gromek, Drew Weisserman, Ryan Cloutier et al. (+2 more)
Stellar elemental abundances provide important constraints on the chemical environments from which
planets form. M and late-K dwarfs are
prime targets for the characterization of small
exoplanets, yet their complex spectra make accurate elemental abundance measurements challenging. In this work, we present a spectral synthesis-based framework to derive detailed abundances for cool
stars from high-resolution, near-infrared spectra. We apply our framework to SPIRou YJHK spectra of five
planet-host
stars–GJ 9827, K2-18, TOI-1201, TOI-1685, and Barnard's
Star–and derive abundances of C, O, Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, and Fe for all five
stars, plus Sc, V, and Ni for a subset, with typical uncertainties of $\lesssim 0.1$ dex. Our recovered
metallicities and elemental abundances are broadly consistent with expected trends and previous literature analyses of these
stars. We derive stellar ratios of C/O, Mg/Si, Fe/Mg, and Fe/O and find that all five systems are broadly consistent with solar ratios, with the exception of the metal-poor Barnard's
Star ([M/H] $= -0.33 \pm 0.06$ dex), which is substantially iron-poor ([Fe/H] $= -0.722 \pm 0.085$ dex). Our results establish stellar chemical baselines for interior structure and atmospheric studies of these planetary systems with the Hubble Space
Telescope (HST) and James Webb Space
Telescope (JWST), while highlighting the remaining model-dependent limitations of precise abundance analyses for cool
stars.
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All authors Nicole Gromek, Drew Weisserman, Ryan Cloutier, Alexandrine L'Heureux, Charles Cadieux
Solar and Stellar Astrophysics · Cross-listed from nucl-th
Ruling out nucleonic direct Urca cooling in low-mass neutron stars using nuclear data
Gabriele Montefusco, Pietro Klausner, Marco Antonelli et al. (+3 more)
Connecting nuclear experiments to
neutron star composition requires controlling the extrapolation of experimental information beyond the densities probed in the laboratory. We combine a broad set of nuclear structure observables and INDRA-FAZIA isospin-transport data within a
Bayesian inference of the dense matter equation of state (EoS). To limit uncontrolled extrapolation to high density, we employ a flexible asymptotically causal metamodel whose
neutron star posteriors are comparable to those obtained with agnostic EoS models. The nuclear structure information is propagated through its full multidimensional distribution of correlated nuclear matter parameters, while the density-dependent INDRA-FAZIA likelihood is evaluated directly along each sampled metamodel
symmetry energy curve. These two sources of laboratory information give compatible constraints on the
symmetry energy, and their combination preserves agreement with finite nuclear observables. When combined with ab initio chiral effective field theory calculations and astrophysical observations, all these constraints substantially improve the determination of central
proton fractions in low-mass
neutron stars, while leaving larger uncertainties for massive
stars. Within the adopted nucleonic metamodel, the reduced probability of large
proton fractions strongly disfavors electronic direct-Urca onset at or below $1.4\,M_\odot$: its posterior probability falls from $\sim20\%$ with chiral and astrophysical constraints alone to below $1\%$ when the laboratory information is included.
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All authors Gabriele Montefusco, Pietro Klausner, Marco Antonelli, Caterina Ciampi, Diego Gruyer, Francesca Gulminelli
Solar and Stellar Astrophysics
The Role of Non-local Thermal Transport in Flare-Driven Chromospheric Evaporation
Thomas Parmenter, Tony Arber, Sergey Belov et al. (+1 more)
Thermal conduction plays an important role in energy transport during solar
flares.
Flares heat the solar atmosphere to tens of MK which, combined with mean free paths in excess of 1Mm, can cause the heat flux to become non-local. We use the magnetohydrodynamic Lare2d code to simulate a reconnective heating event with three different thermal conduction models: classical Spitzer-Harm (SH) along the
magnetic field, local transport with a heat flux limiter (FL), and the non-local Schurtz, Nicolai, Busquet (SNB) model which is routinely used in
laser-
plasma codes and has been bench- marked against full Vlasov-Fokker-Planck treatment. The
evolution of the atmosphere post heating is compared between simulations using each of these models. Due to a supressed heat flux, SNB gives rise to significantly higher peak temperatures than SH. Further, with SNB transport chromospheric evaporation occurs later and has stronger extreme ultraviolet emission intensity. FL simulations have similar temperature
evolution and chromospheric evaporation to SNB, however different values of the flux limiter work best for peak temperature, downflow velocity and EUV emission intensity, and so there is no one optimal value for all cases. We conclude that the SNB model provides a practicable solution to incorporate non-local thermal transport at MHD scales, which will be crucial to improve the realism and accuracy of the next generation of solar
flare simulations.
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All authors Thomas Parmenter, Tony Arber, Sergey Belov, Tom Goffrey
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Transit timing variation
Luca Borsato
The transit timing variation (TTV) method is a key approach to the confirmation, detection, and characterisation of exoplanetary systems. This review discusses the detection of TTVs from transit observations and the origins of TTVs, mainly due to gravitational interactions with perturbing
planets, whether transiting or not. Additionally, this work details methodologies for deriving planetary parameters, employing quasi-global and local optimisation
algorithms within a
Bayesian framework. By analysing TTVs, planetary orbital parameters and dynamical properties can be inferred, providing valuable insights into system formation and
evolution. The role of resonances and stability in shaping these systems is reviewed, along with sensitivity biases that influence mass determination. Comparative analyses highlight the unique demographic contributions of TTV systems. TTVs offer a window into the dynamical and physical properties of planetary systems, advancing our understanding of their diversity and stability.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744
Mingyu Li, Roberto Maiolino, Zheng Cai et al. (+26 more)
When Population III (Pop III)
star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the
lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic
metallicity constraints, it was identified as an extremely metal-poor or metal-free
galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low
metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor
galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf
galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III
star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar
metallicity to identify Pop III
galaxy candidates for spectroscopic follow-up.
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All authors Mingyu Li, Roberto Maiolino, Zheng Cai, Hannah Übler, Boyuan Liu, Qiao Duan, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Eiichi Egami, Bjorn H. C. Emonts, Xiaohui Fan, Yuki Isobe, Lucy R. Ivey, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, J. Xavier Prochaska, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Yunjing Wu, Fujiang Yu, Zijian Zhang
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
LATED: Ly$\alpha$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon
Mingyu Li, Zheng Cai, Roberto Maiolino et al. (+24 more)
Cosmological simulations allow a low-level tail of Population III (Pop III)
star formation to persist to $z=2-6$. Spectroscopic confirmation is expensive, so an efficient photometric pre-selection is needed. We present LATED (Lyman-Alpha
Tomography of Extremely Metal-poor Domains), which selects metal-free and extremely metal-poor candidates from a Ly$\alpha$-emitter parent sample using strong-line diagnostics. The method requires three bands and two colours, $x=m_{\rm OIII}-m_{{\rm H}\alpha}$ and $y=m_{{\rm H}\alpha}-m_{\rm cont}$, which trace oxygen abundance and the H$\alpha$ equivalent width, respectively. Requiring that the filters simultaneously contain [O III]+H$\beta$ and H$\alpha$, together with a Ly$\alpha$ parent selection, defines five windows spanning $z=1.92-6.60$ (four JWST/NIRCam, one Roman/WFI). The criteria, $x\geq x_{\rm min}(z)$ and $y\leq y_{\rm max}(z)$, are set by the per-
redshift extrema of a forward-modelled Pop III template locus. Ordinary metal-enriched
star-forming and AGN templates fall outside the selection region, and possible contaminants such as little red dots are flagged by their multi-band colours. To check contamination empirically, we apply LATED to 1126 JADES spectroscopic
galaxies, and no source is selected in the four NIRCam windows. We release a Python package which converts the same photometry into R3=[O III]/H$\beta$ as a measurement or upper limit, reproducing JADES spectroscopy with small 0.12 dex scatter. Applied to 85 archival MUSE Ly$\alpha$ emitters in Abell 2744, LATED recovers the confirmed extremely metal-poor
galaxy AMORE6 and reveals three new candidates at $z=3-5$. Photometry alone cannot establish a metal-free nature. LATED delivers prioritised candidates for spectroscopic follow-up, providing a scalable route toward a systematic census of late-time Pop III
star formation.
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All authors Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang
Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM
Premature re-entry of the FACSAT-2 nanosatellite: orbital decay and attribution to the maximum of solar cycle 25
Santiago Vargas Dominguez, Mara Valentina Angel and Brayan Nicolas Buitrago
FACSAT-2 Chiribiquete, the second satellite of the Colombian Aerospace Force and the first South American nanosatellite mission dedicated to greenhouse gases, re-entered on 27 October 2025, 926 days after its deployment into a Sun-synchronous orbit, against a declared service life of at least five years and an estimated orbital lifetime of fifteen. The orbital
evolution was built from the epochs of the TLEs (two-line elements) of NORAD ID 56205. We reconstruct its decay using its 3696 orbital elements, the solar and geomagnetic indices from the OMNI2 database, and NRLMSISE-00 densities sampled along the orbit. Inverting the drag yields a ballistic coefficient of 72.3 kg/m2 (6% statistical, 20% systematic), equivalent to an effective area of 0.047 m2, consistent with the declared geometry. With it, the model reproduces the trajectory with a root-mean-square error of 7.4 km and, calibrated on 2023-2024 alone, the re-entry with a 28-day out-of-sample error. F10.7 averaged 170.8 sfu over the mission, against the 139 sfu of the environmental scenario derived from the official 2019 forecast, which lengthens the orbital lifetime by x1.52; two co-launched CubeSats give x1.50 and x1.57, a consistency check across objects rather than independent evidence. Imposing quiet geomagnetic conditions returns 102 days, 22% of the shortening, with strong sensitivity to the adopted threshold; a superposed-epoch analysis over 149 storms gives a median drag enhancement of x1.92 for the intense events. We discuss the consequences for the design of FACSAT-3 and for the public communication of a mission's expected lifetime.
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Solar and Stellar Astrophysics
Oblique kink waves in solar coronal streamers
Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin et al. (+1 more)
Coronal streamer kink waves excited by an impact of coronal mass ejections (CMEs) are routinely used to estimate the coronal Alfvén speed. These estimates generally assume wave propagation parallel to the
equilibrium magnetic field directed radially outward to the Sun, in the plane of the sky. However, the geometry of CME impacts naturally allows for oblique propagation. We investigate the properties of obliquely propagating kink waves guided by a
plasma slab with a central current sheet representing a coronal streamer stalk. We consider both cold and warm streamer
plasmas and analyse influence of propagation obliquity on wave dispersion, eigenfunctions, and seismological diagnostics. We find that increasing the propagation obliquity reduces the phase speed owing to both projection effects and the intrinsic dependence of the phase speed on the propagation angle. The wave structure also undergoes a gradual transition from a body mode to a surface mode, leading to stronger perturbations at the slab boundaries and enhanced wave localization. Consequently, for a given energy deposited by a CME impact, oblique kink waves are expected to produce larger observable amplitudes than field-aligned waves. Applying the developed theory to streamer waves reported previously, we infer Alfvén speeds in the range of 50-500 km/s. We show that neglecting wave propagation obliquity may underestimate the Alfvén speed by up to a factor of 1.5. These results demonstrate that wave propagation obliquity should be taken into account in coronal seismology of streamer waves and that stereoscopic observations will be required to constrain the true propagation direction.
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All authors Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin, Ding Yuan
Solar and Stellar Astrophysics
Streamer slab eigenmode analysis with the Legolas code
Jordi De Jonghe, Daria Sorokina and Tom Van Doorsselaere
Context. Helmet streamers are large ray-like structures extending from the solar corona that thin further away from the solar surface, forming an extended current sheet. These structures are quasi-stable, and are observed to support kink waves travelling outward from the Sun, called helmet streamer waves. Aims. Limited analytical models identify streamer waves as fast body kink eigenmodes of the streamer slab. To bridge the gap between analytical models and numerical simulations, we investigate the eigenmode spectrum of more realistic streamer slab configurations, obtained from simulations, to retrieve the kink profiles and firmly establish that streamer waves are eigenmodes of the streamer. Methods. Using a streamer slab model extracted from numerical simulations, the Legolas code is applied to compute the eigenmode spectrum, for wavelengths observed in the simulation. In the spectrum we identify the mode matching the behaviour in the non-linear simulations by comparing to analytical and numerical results for the established Epstein profile. The identified modes's phase speeds are then compared to analytical, simulation, and observational results. Results. For each case, the spectrum is found to contain a mode matching the properties of a streamer wave. The phase speeds of the identified modes are compatible with those measured in observations, strongly suggesting that the observed streamer waves are fast body kink modes. Comparison to the analytical slab model is difficult due to the sensitivity of the analytical dispersion relation to the internal values.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
How dust particles orbiting white dwarfs can reveal undetected co-orbiting exoplanets I. Exoplanet on a circular orbit
Kyriaki I. Antoniadou and Dimitri Veras
Abridged. Mounting observations of transiting dusty debris orbiting WDs display complex signatures that often feature orbital period drifts. The asteroid or
planet progenitor of this debris might still be partly intact on a near-circular orbit that is inclined or coplanar, with a period that is similar to that of the dust. Alternatively, the debris could persist concurrently with other intact asteroids or
planets that had tidally circularised around the WD at a later time, but still remain directly unobservable. We sought to first improve the identification of this detectability threshold by expanding our previous investigation of the WD-secondary-dust co-orbital circular restricted three-body problem (CRTBP) to higher secondary masses corresponding to Ceres, Mercury, Earth, and Neptune. Next, we continued to explore the link between the analytic and numerical characterisations of the CRTBP. First, we computed families of periodic orbits in the 1/1 mean-motion-resonance (MMR) in both the planar and spatial CRTBP cases, where the dust is on an arbitrarily eccentric orbit. Second, we generated global phase space portraits. Third, we determined observational links with debris located in very close proximity to WDs via N-body simulations. For each method we applied, we report a novel set of results. These include 3 newly discovered bifurcation points, $B_T^4, B_{cs}^4$, and $B_{cs}^5$, 2 branches of asymmetric periodic orbits, called $A_2$ and $A_3$, at high dust eccentricity regime in the 2D-CRTBP, and 2 families of symmetric orbits in the 3D-CRTBP. The maps reveal stability domains as a function of the dust's eccentricity, argument of pericentre, and slight semi-major axis deviations from the 1/1 MMR. The N-body simulations reveal that over 10 yr, mass analogues of Mercury, Earth, and Neptune generate orbital period deviations in the dust of, respectively, 1-10 s, 10-100 s, and over 100 s.
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Solar and Stellar Astrophysics
Stellar flare detection and characterization in ZTF High-cadence light curves
Aratrika Ghosh, Shravan Hanasoge, Matthew J. Graham et al. (+1 more)
Stellar
flares are brief, intense increases in brightness resulting from
magnetic reconnection events in stellar atmospheres. In this paper, we have developed a pipeline to detect and characterize
flares in short-duration (approximately 6.2-hour) light curves from the Zwicky Transient Facility (ZTF) Extended Deep-Drilling survey. This method involves robust detrending with Tukey's biweight
estimator, followed by sigma-based thresholding and visual scrutiny to identify
flare candidates. It is applied to 28 million light curves, and we found 331 flaring events from 310
stars across evolutionary stages and spectral types. We estimated
flare energies by assuming a blackbody emission model for 234
flares with reliable distance, and
flare morphologies were classified based on
flare modeling using the template by Mendoza et al.(2022). We obtained a power law correlation between energy and duration with an index of $0.19 \pm 0.01$. We also find similar power law correlation between the
flare energy and $T_{decay}$, $T_{rise}$ and FWHM. This study demonstrates the power of high-cadence ground-based surveys for statistical and morphological
flare studies across a broad stellar sample.
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All authors Aratrika Ghosh, Shravan Hanasoge, Matthew J. Graham, Ashish Mahabal
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Impact of accretion variability on the CO emission of a disk around a very-low-mass star with JWST
C. Bergez-Casalou, B. Tabone, Y. Aoyama et al. (+14 more)
Studying the structure of very-low-mass
stars ($M_\star<0.2M_\odot$) protoplanetary disk is crucial to understand the formation of Earth-like
planets. In this paper, we characterize the innermost regions of the disk around a known very-low-mass
star, 2MASS J16053215-1933159 (J1605 hereafter), by analyzing new JWST/NIRSpec observations taken in 2024, 2 years after a first observation with JWST/MIRI. We find that between the two epochs (2022 & 2024), the CO flux is reduced by a factor $\sim 3$, the flux of the HI 10-6 line seen by both NIRSpec and MIRI is reduced by a factor $\sim13$, and the total continuum density flux is reduced by $\sim 15 \%$. The
accretion rate derived from individual HI lines is consistent with a decrease of a factor $\sim13$ in 2 years. After correcting the spectrum from the CO absorption present in J1605 stellar photosphere, we find that the decrease of the disk's CO emission is consistent with a CO gas of same column density and temperature at each epoch, but originating from a smaller emitting area when the
accretion rate is low. While warm hydrocarbons ($\simeq 500~$K) are detected with MIRI-MRS with extremely high column densities of $\rm C_2H_2$, no hydrocarbons features are seen with NIRSpec. We propose that non-LTE effects quench the near-IR emission of hydrocarbons in the warm reservoir. The variation of the
accretion luminosity of J1605 correlates with the variation of its fundamental CO luminosity in a similar way as in T-Tauri
stars, supporting the idea that very-low-mass
stars could be seen as scaled-down versions of T-Tauri
stars. The detection of the emission of the fundamental band of CO in disks around cold objects is challenging because of the presence of CO absorption in their photosphere. Future observations (e.g., with ELT/METIS) looking for such emission will require robust ways to constrain the photosphere emission.
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All authors C. Bergez-Casalou, B. Tabone, Y. Aoyama, G. Herczeg, A. Caratti o Garatti, E. Habart, E. F. van Dishoeck, I. Chemerynska, T. Henning, S. L. Grant, M. Guedel, A. M. Arabhavi, J. Kanwar, G. Olofsson, G. Perotti, L. Tychoniec, L. B. F. M. Waters
Solar and Stellar Astrophysics
Companion masses of Gaia DR3 AstroSpectroSB1 binaries: a Bayesian forward-modelling framework
Prasid Sandave and Raghuveer Garani
Gaia Data Release 3 (DR3) has substantially expanded the study of unresolved binaries by providing combined astrometric and spectroscopic orbital solutions for a large sample of non-single
stars. We present a
Bayesian forward-modelling framework for estimating companion masses in Gaia DR3 AstroSpectroSB1 systems. The method samples the physical parameters of each binary, predicts the corresponding astrometric Thiele-Innes constants and spectroscopic orbital coefficients, and evaluates their likelihood using the full covariance
matrix published by Gaia. An external prior on the primary mass is incorporated to resolve the remaining degeneracy between the component masses and orbital inclination in single-lined systems. We apply this framework to 1035 AstroSpectroSB1 systems with primary-mass estimates drawn from the Gaia DR3 astrophysical\_parameters table. Of these, 760 systems also have Gaia-reported estimates for both component masses and are used as a validation sample. The remaining 275 systems constitute an inference sample for which the mass of the fainter, unresolved companion is estimated. For systems with well converged posteriors, the inferred parameters reproduce the Gaia orbital observables, while the companion masses recovered for the validation sample are consistent with the Gaia estimates. In the inference sample we find 113 well converged systems for which the companion masses are meaningfully inferred. We find that the population is dominated by ordinary
stars, together with a smaller high-mass tail that may contain massive white dwarfs or other compact-object candidates. Our framework provides a scalable approach for converting Gaia AstroSpectroSB1 solutions into companion-mass posterior distributions, identifying promising systems for targeted follow-up, and preparing for the larger and more precise orbital samples anticipated with Gaia DR4.
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Solar and Stellar Astrophysics
The Common Envelope Evolution Outcome. III. the Improvement of Stellar Binding Energy with the Envelope Residual
Lifu Zhang, Hongwei Ge, Dylan Hebrail et al. (+7 more)
Common-envelope
evolution (CEE) is a key process in the
evolution of close binary systems. Many important astrophysical objects and evolutionary stages are closely related to CEE, including white dwarf binaries, hot subdwarfs, and gravitational wave mergers. In the standard energy formalism of CEE, the binding energy of the donor envelope plays a crucial role, as it directly affects the final orbital period after CEE and serves as a key physical parameter in binary population synthesis studies. However, the currently adopted binding energy suffers from large uncertainties, mainly because the envelope binding energy of giant-branch
stars varies strongly near the helium-core boundary. In addition, the expansion of the
star during CEE can also affect the binding energy. To address these issues, we introduce an improved binding energy for the envelope mass residual. Based on adiabatic mass loss models, we recalculate the distribution of the CEE binding-energy parameter lambda for
stars with different masses and at different evolutionary stages, and we analyse the effects of envelope mass residual and adiabatic expansion. Due to the envelope mass residual, the lambdas of some donors can increase by one to two orders of magnitude at the late red giant branch and asymptotic giant branch stages. Furthermore, we provide interpolation grids and fitting formulae for these results, which can be readily applied to various binary population synthesis codes.
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All authors Lifu Zhang, Hongwei Ge, Dylan Hebrail, Ross Church, Mingkuan Yang, Zhenwei Li, Hailiang Chen, Dengkai Jiang, Xuefei Chen, Zhanwen Han
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Satellite Survival through Gas Redistribution in a Low-viscosity Disk
Ignacio Mosqueira
We investigate satellite survival through gas redistribution in a dense circumplanetary disk with a low dimensionless viscosity parameter $\alpha \sim 10^{-6}$. The model combines modal Lindblad excitation, launch-dependent shock deposition, 3D effects, and an instantaneous Rayleigh adjustment that conserves angular momentum and suppresses sharp density gradients. An isolated Ganymede-mass satellite depletes the disk outside its orbit and stalls under a calibrated three-dimensional Lindblad torque. This behavior is consistent with the non-feedback branch of Rafikov's stalling criterion. The inward migration stalls near 15 Jupiter radii ($R_J$) when the gas depletion exterior to the satellite's orbit reduces the outer torque by the amount required to balance the torque of the undepleted inner disk, even when we adopt a transport prescription that begins smoothing density gradients halfway to Rayleigh marginality. Likewise, two Callisto masses form an extended depleted region and stall in nearly steady orbits before a late close encounter; however, a self-consistent disk response to satellite eccentricity remains to be modeled. A simulation of a Ganymede-mass satellite adds a specified source of unsaturated local angular momentum deposition by buoyancy torques, reducing the late radial oscillations indirectly caused by non-local shock deposition. Lastly, we redistribute gas while conserving angular momentum to proactively inhibit Rossby-wave unstable pressure bumps at the gap edges. We find that this approach preserves gap clearing and strong migration suppression for Ganymede and the two Callisto masses. In the pressure-adjusted run, the two Callisto masses are captured in a 7:5 resonance and retain eccentricities below 0.06.
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