Magnetic Activity in Cool Stars

Aspects of magnetic activity of late-type stars are reviewed: first, results obtained through the comparison of emissions from various temperature regimes in the outer atmospheres of cool stars, then results from stellar soft X-ray spectroscopy. Spectra obtained with different instruments (Imaging Proportional Counter and Solid State Spectrometer onboard the EINSTEIN Satellite, and the Objective Grating Instruments onboard EINSTEIN and EXOSAT) are interpreted through fits with model spectra consisting of one or two temperature components. Particular attention is given to the analysis of EXOSAT spectra of Procyon, Capella, and σ² CrB. Finally various relations between rotation and different measures of activity are compared. The effective X-ray temperature, derived from single-temperature fits to soft X-ray IPC spectra, is shown to play a part in the relation between activity and rotation.