High-resolution spectroscopy of flares and CMEs on AD Leonis^★,★★

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
e-mail: pmuheki@must.ac.ug
² Mbarara University of Science and Technology, PO Box 1410, Mbarara, Uganda

Received: 11 October 2019
Accepted: 20 March 2020

Abstract

Context. 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 previous studies have therefore modelled their occurrence frequency by scaling up solar relations. However, because 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.

Aims. We used a large number of high-resolution spectra to study flares, CMEs, and their dynamics of the active M dwarf star AD Leo. The results can then be used as reference for other M dwarfs.

Methods. We obtained more than 2000 high-resolution spectra (R ~ 35 000) of the highly active M dwarf AD Leo, which is viewed nearly pole on. Using these data, we studied the behaviour of the spectral lines H_α, H_β, and He I 5876 in detail and investigated asymmetric features that might be Doppler signatures of CMEs.

Results. We detected numerous flares. The largest flare emitted 8.32 × 10³¹ erg in H_β and 2.12 × 10³² erg in H_α. 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.

Conclusions. 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.