The Activity Cycle and Interaction of Stellar Winds in the Capella System

Abstract

We present observations of the He I λ10830 line of Capella obtained between 1985 and 1994. An analysis of radial velocities shows that the main He I absorption is located in the outer atmosphere of the quiescent, cooler G6 giant. We confirm our earlier conclusion that the equivalent width (EW) of the He i line varies with the 104-day orbital period of the Capella system. The mean level of the EW changes from year to year, and is associated with a 5–6-year activity cycle. In addition, a longer 11-year cycle is traced in all our data sets since 1980 (Katsova & Shcherbakov 1998; Katsova 1997). The amplitude of the EW variations versus the phase of the 104-day orbit becomes lower when the mean EW is higher. During a season when the activity level of the Capella system was high, we were able to identify the fraction of the He I absorption formed in the chromosphere of the active, hotter F9 giant.