Differential emission measure distributions of Capella and σ2 CrB

The active late-type stars Capella (α Aur G6III+F9III) and σ² CrB (F6V+GV) (X-ray candidate emitters underlined) were observed with the EXOSAT Transmission Grating Spectrometer (TGS) in the region 10-200 Å. We have made an analysis of the differential emission measure (DEM) distribution. The derived DEM peaks between 3 and 7 MK and above 10 MK. The results disagree with models for static loops as developed by Rosner, Tucker and Vaiana [1, hereafter referred to as RTV]: the contrast in emission between the maximal and lower temperatures in the loop is larger than predicted by the RTV model. Other models which predict DEM distributions falling off more steeply towards lower temperatures are briefly discussed: e.g. quasi-static loops with varying cross-sectional area or dynamic loops with strong downward flows.