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Flares and CMEs can have deleterious effects on their surroundings: they can erode atmospheres of orbiting planets over time and also have high importance in stellar evolution. Most of the CME detections in the literature are single events found serendipitously sparse for statistical investigation. We aimed to gather a large amount of spectral data of M-dwarfs to drastically increase the number of known events to make statistical analysis possible in order to study the properties of potential stellar CMEs. Using archive data we investigated asymmetric features of Balmer-lines, that could indicate the Doppler-signature of ejected material. Of more than 5500 spectra we found 478 with line asymmetries--including nine larger events--on 25 objects, with 1.2-19.6 events/day on objects with line asymmetries. Most events are connected with enhanced Balmer-line peaks, suggesting these are connected to flares similar to solar events. Detected speeds mostly do not reach surface escape velocity: the typical observed maximum velocities are in the order of 100-300km/s , while the typical masses of the ejecta were in the order of $10^{15}-10^{18}$g. Statistical analysis suggests that events are more frequent on cooler stars with stronger chromospheric activity. Detected maximum velocities are lower than those observed on the Sun, while event rates were somewhat lower than we could expect from the solar case. These findings may support the idea that most of the CMEs could be suppressed by strong magnetic field. Alternatively, it is possible that we can observe only an early low-coronal phase before CMEs are accelerated at higher altitudes. Our findings could indicate that later-type, active dwarfs could be a safer environment for exoplanetary systems CME-wise than previously thought, and atmosphere loss due to radiation effects would play a stronger role in exoplanetary atmosphere evolution than CMEs.
The stellar magnetic field completely dominates the environment around late-type stars. It is responsible for driving the coronal high-energy radiation (e.g. EUV/X-rays), the development of stellar winds, and the generation transient events such as f
Type II radio bursts are observed in the Sun in association with many coronal mass ejections (CMEs. In view of this association, there has been an expectation that, by scaling from solar flares to the flares which are observed on M dwarfs, radio emis
Coronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum and mass loss of late-type stars, and also shape the environment in which planets fo
Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermody
Coronal Mass Ejections (CMEs) may have major importance for planetary and stellar evolution. Stellar CME parameters, such as mass and velocity, have yet not been determined statistically. So far only a handful of stellar CMEs has been detected mainly