Probable detection of an eruptive filament from a superflare on a solar-type star

Abstract

Solar flares are often accompanied by filament/prominence eruptions (~104 K and ~1010−11 cm−3), sometimes leading to coronal mass ejections that directly affect the Earth’s environment1,2. ‘Superflares’ are found on some active solar-type (G-type main-sequence) stars3–5, but the filament eruption–coronal mass ejection association has not been established. Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of 2.0 × 1033 erg, and a blueshifted hydrogen absorption component with a high velocity of −510 km s−1 was observed shortly afterwards. The temporal changes in the spectra strongly resemble those of solar filament eruptions. Comparing this eruption with solar filament eruptions in terms of the length scale and velocity strongly suggests that a stellar coronal mass ejection occurred. The erupted filament mass of 1.1 × 1018 g is ten times larger than those of the largest solar coronal mass ejections. The massive filament eruption and an associated coronal mass ejection provide the opportunity to evaluate how they affect the environment of young exoplanets/the young Earth6 and stellar mass/angular momentum evolution7.

Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for H$α$ and White-Light Emissions

“…Through this campaign, we succeeded in obtaining optical spectroscopic data of two superflares on a solar-type star, simultaneously with TESS photometry. One event on April 5, 2020 was already reported by Namekata et al (2021), and another event on March 14, 2020 will be reported in this Letter.…”

“…The exposure time was set to be 30 sec for these nights. The data reduction follows the prescription in Namekata et al (2020bNamekata et al ( , 2021 with IRAF and PyRAF packages. Only the data of particular interest are shown in Figure 2.…”

“…Ichimoto & Kurokawa 1984;Kowalski et al 2013;Namekata et al 2020b;Maehara et al 2021, for solar and M-dwarf flares). Our previous study (Namekata et al 2021) reported the first detection of the optical Hα spectra of a superflare of ∼ 10 33 erg on the young solar-type star EK Dra. Surprisingly, the Hα spectra show a blueshifted absorption as evidence of a filament eruption, which has dramatically advanced our understandings.…”

“…It has Sun-like atmosphere with an effective temperature of 5560-5700 K, radius of 0.94 R , and mass of 0.95 M (Waite et al 2017;S ¸enavcı et al 2021). It is rapidly rotating with period of 2.77 d and exhibits frequent stellar flares, so it is considered as a good target of flare observations (Audard et al 1999;Ayres 2015;Namekata et al 2021). One UV spectroscopic observation of the decay phase of a superflare on EK Dra has been reported using the Hubble Space Telescope (Ayres 2015), which had been the only example of a spectral line observation for solar-type stars before.…”

“…Surprisingly, the Hα spectra show a blueshifted absorption as evidence of a filament eruption, which has dramatically advanced our understandings. However, the mechanism of the superflare radiation is still unknown because in the first event by Namekata et al (2021), the flare emission was short-lived (∼16 min) and had not been thoroughly investigated. In this Letter, we report detection of the optical spectra of another gigantic superflare event on EK Dra, which enables us to investigate the radiation mechanism.…”