Stellar Active Region Evolution – I. Estimated Lifetimes of Chromospheric Active Regions and Active Region Complexes

Abstract

The lifetimes of chromospheric active regions and active region complexes ('active longitudes') for 35 lower-Main-Sequence stars observed at Mount Wilson Observatory are estimated from the relative distribution of pooled variance at different time scales. The time scale of active region evolution (i.e., the lifetime of large active regions) is approximately 50 days, while the lifetime of active region complexes is on the order of 1 year. These estimates can be used to clarify the contribution of active regions to variance in short-term (i.e., <1 yr) time series data. Previously unpublished mean rotation periods are documented for several stars.