MAGNETIC ACTIVITY CYCLES IN LATE-TYPE STARS

An intensive monitoring of the H and K Ca II lines for a large number of late-type stars, carried out since 1966 from Mount Wilson (US), has allowed the study of activity cycles in this kind of stars (Baliunas and Vaughan, 1985; Saar and Baliunas, 1992). About 30% of the monitore d stars have clearly detected magnetic cycles, some of them showing mo re than one periodicity, the remaining objects having a chaotic or lon g trend behaviour. We present in this paper results from a model based on the dynamo action which attempts to reproduce the duration of the observed activity cycles and also link what the theory predicts on som e quantities in the stellar interior, with observational results for t he product fB, i.e. the mean magnetic flux at the stellar surface.