Coronal Activity in F-, G-, and K-Type Stars; Empirical Relations Between Stellar Parameters

For a sample of 58 late type stars we analyse the relations between the soft X-ray flux density Fx, the Ca II H and K line-core flux density FH+K, and parameters determining the global stellar structure. By analysing the soft X-ray spectra from 15 stars we determine the coronal temperatures T and specific emission measures per unit area ζ. We discuss the dependence of T on B-V, Fx 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.