Heating of chromospheres and coronae present status of theory

Abstract

Three aspects of the theory of the non-radiative heating of stellar atmospheres are treated in this review. First, the transient brightenings seen in the inter-network quiet chromosphere are discussed, and their importance to the basal heating rate of stellar chromospheres is emphasized. Second, recent investigations of simple models for magnetostatic flux tubes are described, and the possible importance of current filamentation as a heating process in such tubes is noted. It is also pointed out that departures from simple magnetic topology in and beneath the photosphere can exert a marked effect on the atmospheric field structure. Third, an account is given of recent work on models of electrodynamic heating in stellar coronae, including the mechanisms of topological heating and resonant absorption, and the use of circuit models to describe the coupling between the generation and dissipation regions in the star.