Constraining stellar CME occurrence with optical spectroscopy

Our knowledge on coronal mass ejections (CMEs) on stars other than the Sun is still sparse. Spectroscopic observations in the optical sometimes show asymmetrically broadened wings and/or transient extra-emissions in chromospheric lines during or shortly after flare events. These may be interpreted as signatures of prominence eruptions, which are closely related to CMEs on the Sun. Dedicated searches for these signatures have, however, mostly yielded non-detections. Here we present a semi-empirical model which combines predictions of intrinsic stellar CME rates with simple radiative transfer calculations in the Balmer lines. We find that typical observations have most likely been too short and/or they had a too low signal-to-noise ratio to detect CMEs. We predict the minimum observing time needed to detect CMEs in the Balmer lines for stars with different spectral types and activity levels.