Do Young Suns Produce Frequent, Massive CMEs? Results from Five-year Dedicated Optical Observations of EK Draconis and V889 Hercules
Journal Article
Overview
abstract
Abstract; ; We report results from a five-year (132-night) dedicated observational campaign targeting two nearby young solar-type stars, EK Draconis (∼50–125 Myr age) and V889 Hercules (∼30 Myr age), using the 3.8 m Seimei Telescope and Transiting Exoplanet Survey Satellite. The aim is to observationally constrain statistical properties of flaring radiation/heating, as well as coronal mass ejections (CMEs), through high time-cadence H; α; spectroscopy. We obtained an unprecedented sample of 15 H; α; superflares, including two blueshifted absorption, two blueshifted emission, one redshifted emission, and nine line broadening events. We obtain the following results: (1) larger flares exhibit broader H; α; line widths, up to 14.1; ±2.4; Å, indicating higher chromospheric heating than solar flares; (2) the long-lasting redshifted event at ∼100 km s; −1; may indicate dense postflare loops; (3) H; α; blueshifted absorptions/emissions provide evidence of massive filament/prominence eruptions, the core structures of CMEs. One newly identified event showed an unexpected rapid decrease in velocity; (4) the lower limit of the CME/eruption association rate with superflares is 27; ; ; ; ; ; ; ; ; −; 16; ; ; +; 25; ; ; ; ; %, yielding occurrence rates of 0.21; ±0.12; and <0.32; ; ; ; ; ; ; ; ; −; 0.32; ; ; +; 0.46; ; ; ; ; events per day for EK Draconis and V889 Hercules, respectively; and (5) we derived the first direct estimate of the lower limit of the mass-loss rate driven by super-CMEs (≳10; 33; erg) for EK Dra as 4 × (10; −13; –10; −12; ); M; ⊙; yr; −1; , comparable to the stellar wind mass loss at a similar age. This study provides critical observational constraints on the radiation and plasma environment around young solar-type stars and the early Sun, which can drive planetary space weather and stellar mass/angular momentum loss.;
