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Flares and CMEs can have deleterious effects on their surroundings: they canerode atmospheres of orbiting planets over time and also have high importancein stellar evolution. Most of the CME detections in the literature are singleevents found serendipitously sparse for statistical investigation. We aimed togather a large amount of spectral data of M-dwarfs to drastically increase thenumber of known events to make statistical analysis possible in order to studythe properties of potential stellar CMEs. Using archive data we investigatedasymmetric features of Balmer-lines, that could indicate the Doppler-signatureof ejected material. Of more than 5500 spectra we found 478 with lineasymmetries--including nine larger events--on 25 objects, with 1.2-19.6events/day on objects with line asymmetries. Most events are connected withenhanced Balmer-line peaks, suggesting these are connected to flares similar tosolar events. Detected speeds mostly do not reach surface escape velocity: thetypical observed maximum velocities are in the order of 100-300km/s , while thetypical masses of the ejecta were in the order of $10^{15}-10^{18}$g.Statistical analysis suggests that events are more frequent on cooler starswith stronger chromospheric activity. Detected maximum velocities are lowerthan those observed on the Sun, while event rates were somewhat lower than wecould expect from the solar case. These findings may support the idea that mostof the CMEs could be suppressed by strong magnetic field. Alternatively, it ispossible that we can observe only an early low-coronal phase before CMEs areaccelerated at higher altitudes. Our findings could indicate that later-type,active dwarfs could be a safer environment for exoplanetary systems CME-wisethan previously thought, and atmosphere loss due to radiation effects wouldplay a stronger role in exoplanetary atmosphere evolution than CMEs.

astronomy and astrophysics

The quest for stellar coronal mass ejections in late-type stars: I.  Investigating Balmer-line asymmetries of single stars in Virtual Observatory  data