A search for proton beams during flares on AU Microscopii

Abstract

We report the results of a coordinated observing campaign on the active M dwarf star AU Mic. The purpose of the campaign was to search for evidence of proton beams during the impulsive phase of stellar flares and to determine whether the energy contained in these beams represented a significant fraction of the energy budget of the flare. During a total of 3.5 hr of monitoring a small flare was observed simultaneously by the HST, IUE, and the AAT. This event, which had a total optical + UV emission of 1.3 x 10 exp 32 ergs, occurred during the decay phase of a much larger event and showed no evidence for a proton beam with an energy greater than a few times 10 exp 29 ergs/s. This is comparable to the maximum energy flux released by the flare, though this energy release rate must occur over a time interval much shorter than that of the impulsive phase itself. We conclude that the proton beams may be capable of transporting some energy during the impulsive phase of a flare, but that they are unlikely to be the major contributor, at least for this particular event.