Flares and coronal heating in the sun and stars

Abstract

Many forms of energy input into coronae have been proposed as the dominant heating mechanism. Here I review topical aspects of impulsive releases of magnetic energy. Several solar phenomena from bright points to coronal mass ejections are attributed to free magnetic energy apparently available in the corona. The possibility that magnetic energy release is the dominant energy input into the corona is discussed for the Sun with special emphasis on small radio events, with negative results. The evidence is better, however, for active stars where a correlation between thermal radiation and gyrosynchrotron emission by energetic electrons has been found recently. It suggests that a flare-like release of magnetic energy is the dominant coronal heating process of active, rapidly rotating stars. However, the required cadence of flares has not (yet) been found. The link between stellar coronal heating and magnetic energy release is not clear as long as the various flare-like phenomena in the solar corona are not better understood.