Flare energetics: Analysis of a large flare on YZ CMi observed simultaneously in the ultraviolet, optical and radio

Abstract

. The results of coordinated observations of the dMe star YZ CMi at optical, UV and radio wavelengths during 3 - 7 February 1983 are presented. YZ CMi showed repeated optical flaring with the largest flare having a magnitude of 3.8 in the Uband. This flare coincided with an IUE exposure which permits a comparison of the emission measure curves of YZ CMi in its flaring and quiescent state. During the flare a downward shift of the transition zone is observed while the radiative losses in the range 10 4 \Gamma 10 7 K strongly increase. The optical flare is accompanied with a radio flare at 6 cm, while at 20 cm no emission is detected. The flare is interpreted in terms of optically thick synchrotron emission. We present a combined interpretation of the optical/radio flare and show that the flare can be interpreted within the context of solar two-ribbon/whitelight flares. Special attention is paid to the bombardment of dMe atmospheres by particle beams. We show that the characteristic t..