High-resolution spectroscopy of flares and CMES on AD Leo*

Priscilla Muheki, Eike. W. Guenther, Tom Mutabazi, Edward Jurua

Published 2020-03-13Version 1

Flares and coronal mass ejections (CMEs) are important for the evolution of the atmospheres of planets and their potential habitability, particularly for planets orbiting M stars at a distance < 0.4 AU. Detections of CMEs on these stars have been sparse and thus previous studies have modeled their occurrence frequency by scaling up solar relations. However, since the topology and strength of the magnetic fields on M stars is different from that of the Sun, it is not obvious that this approach works well. Our aim was to study, using a large amount of high resolution spectra, flares, CMEs and their dynamics of an active M dwarf star AD Leo. The results can then be used as reference for other M dwarfs. We obtained more than 2000 high-resolution spectra (R (35000)) of the highly active M dwarf AD Leo which is viewed nearly pole on. Using this data, we studied the behaviour of the spectral lines H(alpha) , H(beta) , and HeI 5876 in detail and investigated asymmetric features that could be Doppler signatures of CMEs. We detected numerous flares. The largest one emitted 8.32E31 erg in H(beta) and 2.12E32 erg in H(alpha) . Although the spectral lines in this and other events showed a significant blue asymmetry, the velocities associated with it are far below the escape velocity. Although AD Leo shows a high level of flare activity, the number of CMEs is relatively low. It is thus not appropriate to use the same flare to CME relation for M dwarfs as for the Sun.