Space Weather

Probable Detection Of An Eruptive Filament From A Superflare On A Solar-type Star

By Keith Cowing
December 9, 2021
Filed under
Probable Detection Of An Eruptive Filament From A Superflare On A Solar-type Star
Light curves (a-b) and spectra (c-e) of a superflare on EK Dra. (a) The light curve observed by TESS in white light (∼6000– 10,000 A) on BJD (Barycentric Julian Day) 2458945.2 (5 April 2020). The individual points represent the stellar flux normalized by ˚ the averaged value with the pre-flare level subtracted. The 1-σ value of the pre-flare light curve (-150 min to 0 min) is plotted in blue. (b) Light curves of the Hα equivalent width (E.W.) observed by the medium-dispersion spectroscopy MALLS at the Nayuta telescope (grey circles) and the low-dispersion spectrograph KOOLS-IFU installed at the Seimei telescope (red triangles) during the same observing period as in panel (c). The Hα emissions were integrated within ±10 A from the H ˚ α line center (6562.8 A) after dividing ˚ by the continuum level, and the pre-flare level is subtracted. The positive and negative values represent emission and absorption, respectively, compared to the pre-flare level. The 1-σ value of the pre-flare light curve (-150 min to 0 min) is plotted with red and black color for Seimei and Nayuta data, respectively. (c-d) Two-dimensional Hα spectra obtained by the Seimei Telescope (c) and the Nayuta Telescope (d). The red and blue colors correspond to emission and absorption, respectively. The dashed lines indicate the stellar surface gravity (g∗) and half of the surface gravity (0.5 g∗). The panels (c-d) share the upper color bar. (e) Temporal evolution of the pre-flare-subtracted Hα spectra observed by the Seimei telescope (red) and the Nayuta telescope (black), with the spectra shifted by constant values for clarity. The spectra are binned in time, and the integration periods correspond to the horizontal axes of panels (a-d). The intensities are normalized by the stellar continuum level. The vertical dotted line indicates the Hα line center, and the horizontal dotted lines indicate the zero levels for each spectrum. The 1-σ error bar around the line core is also plotted based on the residual scattering in the line wing.

Solar flares are often accompanied by filament/prominence eruptions (∼104 K and ∼1010−11 cm−3), sometimes leading to coronal mass ejections (CMEs) that directly affect the Earth’s environment.

`Superflares’ are found on some active solar-type (G-type main-sequence) stars, but the association of filament eruptions/CMEs has not been established.

Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals the evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of 2.0×1033 erg, and blue-shifted hydrogen absorption component with a large velocity of −510 km s−1 was observed shortly after. The temporal changes in the spectra greatly resemble those of solar filament eruptions. Comparing this eruption with solar f

ilament eruptions in terms of the length scale and velocity strongly suggests that a stellar CME occurred. The erupted filament mass of 1.1×1018 g is 10 times larger than those of the largest solar CMEs. The massive filament eruption and an associated CME provide the opportunity to evaluate how they affect the environment of young exoplanets/young Earth and stellar mass/angular-momentum evolution.

Kosuke Namekata, Hiroyuki Maehara, Satoshi Honda, Yuta Notsu, Soshi Okamoto, Jun Takahashi, Masaki Takayama, Tomohito Ohshima, Tomoki Saito, Noriyuki Katoh, Miyako Tozuka, Katsuhiro L. Murata, Futa Ogawa, Masafumi Niwano, Ryo Adachi, Motoki Oeda, Kazuki Shiraishi, Keisuke Isogai, Daikichi Seki, Takako T. Ishii, Kiyoshi Ichimoto, Daisaku Nogami, Kazunari Shibata

Comments: 40 pages, 4 figures, 4 extended data figures, published in Nature Astronomy (2021)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
DOI: 10.1038/s41550-021-01532-8
Cite as: arXiv:2112.04808 [astro-ph.SR] (or arXiv:2112.04808v1 [astro-ph.SR] for this version)
Submission history
From: Kosuke Namekata
[v1] Thu, 9 Dec 2021 10:01:42 UTC (1,026 KB)
Astrobiology, Space Weather,

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.