Evidence for Activity of Capella

Abstract

Results of observations of Capella in the infrared He I λ10830 Å line obtained with the Shajn 2.6 m telescope of the Crimean Astrophysical Observatory over 10 years are analyzed. The He I equivalent width varies with the 104-day orbital period, and the amplitude of these variations in September 1993-March 1994 was significantly lower than during our observations in 1985-1988. A comparison of these observations with those obtained by us since 1985 suggests the presence of an activity cycle with a period of at least 5 years. The main He I absorption forms in the chromosphere of the quiescent G6 giant, but near the maximum of the activity cycle, helium absorption forming on the more active, hotter F9 giant becomes observable. These helium data, together with the EUV results for the high-temperature Fe XX-Fe XXIII lines can be explained using a model in which an enhanced magnetized stellar wind originating from the hot corona on the active F9 giant reaches the Lagrangian point and then forms a shock wave in the corona of the quiescent G6 giant.