Constraining stellar CME occurrence with optical spectroscopy – updated results for M dwarfs

Optical spectroscopic observations sometimes show asymmetrically broadened wings and/or transient extra-emissions in chromospheric lines during or shortly after flares. Such events appear most commonly on active M dwarfs. These signatures could be due to prominence eruptions, which are closely related to CMEs on the Sun. Here we present an updated semi-empirical model which combines predictions of intrinsic stellar CME rates with radiative transfer calculations in the Balmer lines. Although Balmer signatures of (eruptive) prominences are typically dominated by scattering of the incident radiation on the Sun, we find that for M dwarfs the contribution of thermal emission should not be neglected. Its inclusion can lead to modified visibility compared to our previous study which assumed only scattering. Our updated model also predicts that filaments (i.e. prominences located in front of the stellar disk) can appear in emission for a wide range of plasma parameters on M dwarfs, in contrast to the Sun. This finding is consistent with existing observations of M dwarfs, which show typically blue asymmetries/blue-shifted line components in emission, but reports of absorption signatures are uncommon.