Coronal activity in F-, G-, and K-type stars - Empirical relations between stellar parameters

For a sample of 58 late type stars the authors analyse the relations between the soft X-ray flux density F_x, the Ca II H and K line-core flux density F_H+K, and parameters determining the global stellar structure. By analysing the soft X-ray spectra from 15 stars the authors determine the coronal temperatures T and specific emission measures per unit area ζ. They discuss the dependence of T on B-V, F_x and stellar radius R. The diagram of the specific emission measure ζ against the temperature T is interpreted in terms of a coronal model consisting of static loops. Also, a search for time variations in the X-ray flux has been performed.