Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. I. Discovery of Prominence Eruptions Associated with Superflares

Abstract

Young solar-type stars frequently produce superflares, serving as a unique window into the young Sun-Earth environments. Large solar flares are closely linked to coronal mass ejections (CMEs) associated with filament/prominence eruptions, but observational evidence for stellar superflares remains scarce. Here, we present a 12-day, multiwavelength campaign observation of young solar-type star EK Draconis (G1.5V, 50–120 Myr age) utilizing the Transiting Exoplanet Survey Satellite, the Neutron star Interior Composition ExploreR, and the Seimei telescope. The star has previously exhibited blueshifted Hα absorptions as evidence for a filament eruption associated with a superflare. Our simultaneous optical and X-ray observations identified three superflares of 1.5 × 1033–1.2 × 1034 erg. We report the first discovery of two prominence eruptions on a solar-type star, observed as blueshifted Hα emissions at speeds of 690 and 430 km s−1 and masses of 1.1 × 1019 and 3.2 × 1017 g, respectively. The faster, massive event shows a candidate of post-flare X-ray dimming with the amplitude of up to ∼10%. Several observational aspects consistently point to the occurrence of a fast CME associated with this event. The comparative analysis of the estimated length scales of flare loops, prominences, possible dimming region, and starspots provides the overall picture of the eruptive phenomena. Furthermore, the energy partition of the observed superflares in the optical and X-ray bands is consistent with flares from the Sun, M-dwarfs, and close binaries, yielding the unified empirical relations. These discoveries provide profound implications of the impact of these eruptive events on early Venus, Earth, and Mars and young exoplanets.

Stellar Flares, Superflares and Coronal Mass Ejections – Entering the Big Data Era

“…Complementary, the final evolution of this event is presented in Leitzinger et al [129], revealing that the back-falling filament reaches zero velocity until it dissolves. Then also erupting prominences have been reported on EK Dra [130], where the maximal projected bulk velocity is close to the escape velocity of the star. There are coordinated X-ray observations of one optical event, revealing a possible post-flare dimming.…”

Simple Model for Temporal Variations of Hα Spectrum by an Eruptive Filament from a Superflare on a Solar-type Star

“…The results are summarized as follows. In future work, our model can be applied to various eruptive events on the Sun and solar-type stars, such as prominence eruptions and post-flare loops (Otsu et al 2022;Namekata et al 2024). In addition, the relation between spot locations deduced from the photometry and flare occurrence has been investigated for M-dwarf flare stars (Ikuta et al 2023) using a code to map starspots on the surface (Ikuta et al 2020).…”

“…Blueshifted spectral lines have been widely observed on M dwarfs during stellar flares (see, e.g., Houdebine et al 1990;Eason et al 1992;Gunn et al 1994;Crespo-Chacón et al 2006;Hawley et al 2007). In particular, the temporal variation of a blueshifted Hα spectrum associated with stellar flares has also been reported as a signature of mass ejections from such stars as M dwarfs (Fuhrmeister et al 2008(Fuhrmeister et al , 2011Vida et al 2016;Fuhrmeister et al 2018;Honda et al 2018;Vida et al 2019;Muheki et al 2020aMuheki et al , 2020bKoller et al 2021;Maehara et al 2021;Notsu et al 2024), K dwarfs (Flores Soriano & Strassmeier 2017, H. Maehara et al 2024, a G dwarf (Namekata et al 2022b(Namekata et al , 2024, and an RS CVn type star (Inoue et al 2023). It has also been discussed that the blueshifted Hα spectrum observed in the early phase of solar flares (Švestka et al 1962) could be a result of the cool upflow (see, e.g., Canfield et al 1990;Tei et al 2018) or an absorption by the cool downflow (see, e.g., Heinzel et al 1994), both of which are associated with chromospheric evaporation.…”

Multiwavelength Sun-as-a-star Analysis of the M8.7 Flare on 2022 October 2 Using Hα and EUV Spectra Taken by SMART/SDDI and SDO/EVE

“…Hence, superflares are actively investigated, not only from a physical viewpoint but also with respect to the habitability of exoplanets. In fact, recent observations have revealed various signatures associated with stellar (super)flares, suggesting that stellar flares are accompanied by various activities like solar flares (e.g., Vida et al 2019;Muheki et al 2020;Maehara et al 2021;Veronig et al 2021;Namekata et al 2022bNamekata et al , 2024Wu et al 2022;Inoue et al 2023;Namizaki et al 2023;Notsu et al 2024). Maehara et al (2021) analyzed temporally resolved Hα spectra of stellar flares on an M-type star and found a blueshifted excess emission, which might be arising from a prominence eruption.…”