Stellar coronae with EXOSAT : broad band spectroscopy of nearby coronal sources.

Abstract

Broad-band observations of stellar coronae obtained with the Low Energy experiment on board the Exosat satellite are presented, together with a technique for the analysis of Exosat low-energy data. The limitations of filter spectroscopy with Exosat are discussed. Specific relationships are provided for extracting physical quantities (temperature, emission measure, luminosities) from the observed count rates for the case of nearby coronal sources. A continuous temperature distribution exists in the coronae of late-type stars; the differential emission measure distribution extends to temperatures in excess of 10 million K for flare stars and RS CVn binaries, even during quiescent conditions. Coronal loop models, similar to those developed for magnetically confined structures on the sun, should be used for interpreting spatially integrated observations of stellar coronae.