A SEARCH FOR PROTON-BEAMS DURING FLARES ON AU MICROSCOPII

We report the results of a coordinated observing campaign on the activ e M dwarf star AU Mic. The purpose of the campaign was to search for e vidence of proton beams during the impulsive phase of stellar flares a nd to determine whether the energy contained in these beams represente d a significant fraction of the energy budget of the flare. During a t otal 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(32) ergs, occurred during the decay phase of a much larger event and showed no evidence for a proton beam with an e nergy greater than a few times 10(29) ergs s-1. This is comparable to the maximum energy flux released by the flare, though this energy rele ase rate must occur over a time interval much shorter than that of the impulsive phase itself. We conclude that the proton beams may be capa ble 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. More observations are required to establish whe ther this is a general characteristic of stellar flares.