(Abstract)

(Super)flares, Coronal Mass Ejections (CMEs), and energetic particles accelerated by CME-driven shocks are the most eruptive space weather events in solar and stellar systems. While superflares from magnetically active stars can be directly detected and characterized in X-ray, FUV/UV, optical, and radio bands, their associated CMEs and stellar energetic particles (StEPs) are relatively difficult to detect using current observations and remain poorly known. Thus, numerical physics-based models of these events are critically needed to understand their initiation mechanisms and properties.

In this talk, we will provide a brief overview of the current modeling capabilities and caveats in simulating stellar CMEs with limited data constraints. We will cover some of the state-of-the-art solar space weather modeling tools that can be applied to the environments of young solar-like stars. We will discuss the typical model inputs used by these models that are available through the current multi-wavelength observations, and what more observations we hope to obtain to improve the modeling performance further. We will explore the effects of the stellar CMEs on exoplanetary habitability and atmospheric chemistry from the modeling perspective, and how we can use the modeling results to guide our future CME-related observational campaigns. These modeling efforts can provide valuable and unique insights into stellar eruptive events and the consequential stellar radiation environments, which cannot be obtained in conventional approaches (direct observations or empirical extrapolations).

Aline Vidotto, Dag Evensberget, Markus Strickert 

Leiden University, Leiden, Netherlands

(Abstract)

AB Dor is a young, active solar-type star whose large-scale coronal magnetic field is 100-1000 times more intense than that of the Sun. Magnetic fields of such magnitude are believed to prevent stellar coronal mass ejections (CMEs) from erupting. It is, therefore, surprising that coronal dimming was recently observed in AB Dor, as coronal dimming is typically associated with CMEs. To address this apparent paradox, we propose that CMEs in AB Dor occur in high-latitude regions where parts of the star’s coronal magnetic field may be open. This hypothesis is bolstered by observations that suggest AB Dor hosts active polar regions. The prolonged duration of the dimming event further supports our theory, as only high-latitude regions may be continuously observable through a stellar rotation cycle. To test our theory, we conducted a parametric study, modelling the global coronal magnetohydrodynamics for twenty-one CMEs of varying intensities. Using a surface magnetic map of AB Dor acquired through Zeeman-Doppler imaging, we injected CMEs into high-latitude regions. Our models demonstrate that nearly 50% of the injected CMEs can erupt, suggesting that magnetic confinement of CMEs may be less common in young solar-type stars than previously assumed.

Kai Ikuta (1); Takato Otsu (2); Ayumi Asai (2); Kosuke Namekata (2); Kazunari Shibata (2,3)

(1) The University of Tokyo;  (2) Kyoto University;  (3) Doshisha University

(Abstract)

Recently, large filament and prominence eruptions associated with superflares on a young solar-type star EK Draconis (EK Dra) were discovered for the first time (Namekata et al. 2022 \& 2024). The absorption and emission of the H$\alpha$ spectrum associated with the eruptions initially exhibited a blueshift, and decelerated in time probably due to gravity. Stellar coronal mass ejections (CMEs) are thought to have occurred, although the filament eruption did not exceed the escape velocity. To investigate how such a filament eruption occurred and whether CMEs were associated with the filament eruption or not, we perform a one-dimensional hydrodynamic simulation of the flow along an expanding magnetic loop emulating a filament eruption under adiabatic and unsteady conditions. We find that (i) the temporal variations of the H$\alpha$ absorption for EK Dra can be explained by a falling filament eruption in the loop with longer time and larger spatial scales than that of the Sun, and (ii) the stellar CMEs are also thought to have been associated with the filament eruption from the superflare on EK Dra, because the rarefied loop unobserved in the H$\alpha$ spectrum needs to expand faster than the escape velocity (Ikuta \& Shibata 2024).  We also apply the simple model to the prominence eruption on EK Dra, and it is suggested that (iii) the temporal variation of H$\alpha$ emission can be also explained simply by changing the line of sight as in the case of the filament eruption.

J. D. Alvarado-Gómez (1); J. J. Drake (2); O. Cohen (3); C. Garraffo (4); F. Fraschetti (5); K. Poppenhäger (1)

(1) Leibniz Institute for Astrophysics Potsdam ; (2) Lockheed Martin Solar and Astrophysics Laboratory; (3) U. of Massachusetts Lowell; (4) Center for Astrophysics | Harvard & Smithsonian; (5) U. of Arizona

(Abstract)

Coronal mass ejections (CMEs) are more energetic than any other type of solar phenomena. They arise from the rapid release of up to $10^{33}$ erg of magnetic energy mainly in the form of particle acceleration and bulk plasma motion. Their stellar counterparts, presumably involving much larger energies, are expected to play a fundamental role in shaping the environmental conditions around low-mass stars, in some cases perhaps with catastrophic consequences for planetary systems due to processes such as atmospheric erosion and depletion. Despite their importance, the direct observational evidence for stellar CMEs is extremely limited. In this way, numerical simulations constitute extremely valuable tools to shed some light on eruptive behavior in the stellar regime. In this talk, I will review recent results obtained from realistic 3D modeling of CMEs in active stars, highlighting their key role in the interpretation of currently available observational constraints. I will include studies performed on M-dwarf stars, focusing on how emerging signatures in different wavelengths related to these transient events vary as a function of the magnetic properties of the star. Finally, the implications and relevance of these numerical results are discussed in the context of future characterization of host star-exoplanet systems.

(Abstract)

The explosion in discovery and follow-up of exoplanets in our near solar neighborhood has re-ignited the quest to understand the various impacts that stars can have on their near stellar environment. These influences can be gravitational, radiation, or particle-induced. Especially for the latter two categories, observations spanning a range of wavelengths are necessary to interpret the exo-space weather environment for each system. I will summarize three main ways astronomers have accomplished simultaneous multi-wavelength observations (targeted observations of a single system, targeted observations of a cluster of stars, and serendipitously overlapping time domain surveys). I will provide some key takeaways from recent campaigns in the topics of stellar flares and evidence for eruptions to set the stage for further presentations and discussion in this splinter session.

 K. Namekata (1,2); V. Airapetian (3); P. Petit (4); H. Maehara (1); K. Ikuta (5); S. Inoue (2); Y. Notsu (6); R. Paudel (3); Z. Arzoumanian (3); A. Avramova-Boncheva (7); K. Gendreau (3); S. Jeffers (8); S. Marsden (9); J. Morin (10); C. Neiner (11); A. Vidotto (12); K. Shibata (2) (National K. Namekata (1,2); V. Airapetian (3); P. Petit (4); H. Maehara (1); K. Ikuta (5); S. Inoue (2); Y. Notsu (6); R. Paudel (3); Z. Arzoumanian (3); A. Avramova-Boncheva (7); K. Gendreau (3); S. Jeffers (8); S. Marsden (9); J. Morin (10); C. Neiner (11); A. Vidotto (12); K. Shibata (2) 

(1) Naional Astronomical Observatory of Japan, Tokyo, Japan; (2) Kyoto University, Kyoto, Japan; (3) NASA Goddard Space Flight Center, MD, USA; (4) Universit´e de Toulouse, Toulouse, France; (5) The University of Tokyo, Tokyo, Japan; (6) University of Colorado Boulder, CO, USA; (7) Bulgarian Academy of Sciences, Sofia, Bulgaria; (8) Max Planck Institute for Solar System Research, G¨ottingen, Germany; (9) University of Southern Queensland, Queensland, Australia; (10) Universit´e de Montpellier, Montpellier, France; (11) Universit´e Paris Cit´e, Meudon, France; (12) Leiden University, Leiden, The Netherlands

(Abstract)

Recent discoveries have revealed exoplanets orbiting young Sun-like stars, offering a window into the early solar system. The young stars are known to produce extreme magnetic explosions, called superflares, about once a day, potentially triggering fast and massive coronal mass ejections (CMEs). Recent studies suggest such ejections could induce atmospheric loss and chemical reactions in early exoplanet atmospheres. However, the association of CMEs with superflares is still unexplored. Here we present the results of 5-years multi-wavelength observations of young Sun-like stars, providing the critical clues to the common picture of solar and stellar CMEs. First, through optical spectroscopic observations, we found four of eleven superflares are associated with fast prominence eruptions, precursors to CMEs. The stellar data greatly resemble solar counterparts, indicating a common picture of solar/stellar eruptions. Second, one of the eruptions is associated with potential coronal dimming in X-rays, indicating that the prominence eruptions evolved into stellar CMEs propagating through interplanetary space. Furthermore, the extension of solar MHD model supports the above indication and suggests that the eruption originates from the observed magnetic active region. This comprehensive study suggests that further advancing the use of solar model could provide the first empirical inputs into calculations of atmospheric escape and chemical reactions for young planets.

Deirdre Ní Chonchubhair; Aaron Golden 

University of Galway, Galway, Ireland

(Abstract)

EQ Peg is a nearby (6.26 pc) M3.5/M4.5 dwarf flare star binary system with a period of $\sim 180$ years. We present results of a 6.7 hour observation of EQ Peg obtained with the I:IO photometer on the Liverpool Telescope in the SDSS-U passband and compare these with simultaneous radio observations at 4.5-7.5 GHz, part of a campaign involving the eMERLIN and LOFAR radio telescopes to distinguish coronal against stellar magnetospheric emission with U band data used to identify any 'white light' flare events associated with the latter. Of the two components, EQ Peg A was found to be particularly active with a complex pattern of flare events occurring towards the end of the optical observations. These flares had a U' band energy of up to $2.7 \times 10^{31}$ erg. Crosley \& Osten (2018), give a threshold of $8.38 \times 10^{29}$ erg in SDSS U' for a stellar flare to have an accompanying CME, if stellar and solar flares occur at the same flare energy. We see quiescent emission with no flares detected in the eMERLIN data for both EQ Peg A and EQ Peg B. Taken together these data suggest a complex interplay of coronal physical processes resulting in the observed multi-wavelength emission.

Adriana Valio (1), Paulo J. A. Simões (1,2), Alexandre Araújo (1), Lyndsay Fletcher (2)

(1) Centro de Rádio Astronomia e Astrofísica Mackenzie, Escola de Engenharia, Universidade Presbiteriana Mackenzie, São Paulo, Brazil; (2) SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, UK

(Abstract)

The study of stellar flares has increased with new observations from space missions, revealing the broadband visible emission from these events. Typically, stellar flares have been modelled as 10000 K blackbody plasma to obtain estimates of their total energy. Solar white light flares (WLFs) are much fainter than their stellar counterparts. Identifying the radiation mechanism for the formation of the visible spectrum from solar and stellar flares is crucial to understand the energy transfer processes during these events, but spectral data for WLFs are relatively rare, and insufficient to remove the ambiguity of their origin: photospheric blackbody radiation and/or Paschen continuum from hydrogen recombination in the chromosphere. We employed an analytical solution for the recombination continuum of hydrogen instead of the typically assumed 10000 K blackbody spectrum to study the energy of stellar flares and infer their fractional area coverage. We investigated 37 events from Kepler-411 and 5 events from Kepler-396, using both radiation mechanisms. We find that estimates for the total flare energy from the H recombination spectrum are about an order of magnitude lower than the values obtained from the blackbody radiation. Given the known energy transfer processes in flares, we argue that the former is a physically more plausible model than the latter to explain the origin of the broadband optical emission from flares.

Abstract submission has been closed.

Deadline: March 11th, 2024 (Monday), 11:59pm PDT  March 18th, 2024 (Monday), 11:59pm PDT (Extended since the selection results of the plenary session talks have not been announced yet on the original deadline date).

Notes for the contributed talks in this splinter session

• Cool Stars 22 adheres to the "one person - one contribution" rule, where "contribution" in this context includes: 1) Invited talk; 2) Contributed talk; 3) Splinter Session presentation; or 4) poster.

• We (organizers) plan to organize the proceeding document summarizing the discussions in this splinter session. The organizers and the invited speakers will lead writing the summary. We will also ask all the speakers to contribute this by submitting the summary slides which can be incorporated into the proceeding pdf.

• The session will be in hybrid mode, as the same as the main plenary session.

• (Additional note on Mar 13th): As notified from the conference organizors, all the abstracts not selected for the contributed oral talks are now transferred into the splinter session organizors. They would be also taken into consideration, but if the same author submit the abstracts both into plenary session and the splinter session, the abstract submitted directly into the splinter session will be taken into consideration for the talk selection of this splinter session.