Detection of Flare-associated CME Candidates on Two M-dwarfs by GWAC and Fast, Time-resolved Spectroscopic Follow-ups

Abstract

The flare-associated stellar coronal mass ejection (CME) in solar-like and late type stars is quite essential for the habitability of an exoplanet. In this paper, we report detection of flare-associated CMEs in two M-dwarfs, thanks to the high cadence survey carried out by the Ground Wide-angle Camera system and the fast photometric and spectroscopic follow-ups. The flare energy in $R-$band is determined to be $1.6\times 10^{35}\mathrm{erg}$ and $8.1\times 10^{33}\mathrm{erg}$ based on the modeling of their light curves. The time-resolved spectroscopyic observations start at about 20 and 40 minutes after the trigger in both cases. The large projected maximum velocity of $\sim 500-700\mathrm{km}{\mathrm{s}}^{-1}$ suggests that the high velocity wing of their H$\alpha$ emission lines are most likely resulted from a CME event in both stars, after excluding the possibility of chromospheric evaporation and coronal rain. The masses of the CMEs are estimated to be $1.5-4.5\times 10^{19}\mathrm{g}$ and $7.1\times 10^{18}\mathrm{g}$.

15 pages, 10 figures and 5 tables, accepted by ApJ

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