Theory of cool loops and the dividing line

Abstract

Static models for coronal loops have been widely used to interpret observations of the coronae of cool stars. Although these models have been successful in explaining several features of the observations; they have been unsuccessful in accounting for two key features: (a) in dwarf stars they do not agree with the observed form of the differential emission measure at low temperatures, T 105 K (the so-called dividing line). It appears that in high gravity stars there is more cool material than the standard models of the transition region predict; whereas in low gravity stars there is less hot material than the loop models predict.