Flaring-associated Complex Dynamics in Two M-dwarfs Revealed by Fast, Time-resolved Spectroscopy

TL;DR

This study uses high-cadence spectroscopy to analyze stellar flares on two M-dwarfs, revealing potential stellar CMEs and their relation to flare energy, advancing understanding of stellar activity impacts on habitability.

Contribution

First detection of symmetric broad H-alpha emission linked to possible CMEs in M-dwarfs using time-resolved spectroscopy, and analysis of their properties and relation to flare energy.

Findings

Broad H-alpha emission suggests stellar CMEs with velocities up to 800 km/s.

CME masses estimated between 4×10^18 g and 2×10^19 g.

Larger flares correlate with higher CME masses.

Abstract

Habitability of an exoplanet is believed to be profoundly affected by activities of the host stars, although the related coronal mass ejections (CMEs) are still rarely detected in solar-like and late-type stars. We here report an observational study on flares of two M-dwarfs triggered by the high-cadence survey performed by the Ground Wide-angle Camera system. In both events, the fast, time-resolved spectroscopy enables us to identify symmetric broad H$\alpha$ emission with not only a nearly zero bulk velocity, but also a large projected maximum velocity as high as $\sim700-800\ \mathrm{km\ s^{-1}}$. This broadening could be resulted from either Stark (pressure) effect or a flaring-associated CME at stellar limb. In the context of the CME scenario, the CME mass is estimated to be $\sim4\times10^{18}$ g and $2\times10^{19}$ g. In addition, our spectral analysis reveals a temporal variation of the line center of the narrow H$\alpha$ emission in both events. The variation amplitudes are at tens of $\mathrm{km\ s^{-1}}$, which could be ascribed to the chromospheric evaporation in one event, and to a binary scenario in the other one. With the total flaring energy determined from our photometric monitor, we show a reinforced trend in which larger the flaring energy, higher the CME mass is.