Study of FK Comae Berenices

Abstract

Aims. We investigate the spot evolution and the surface differential rotation of the single late-type giant FK Com. Methods. A total of 18 new surface temperature maps of FK Com are calculated with the Doppler imaging technique for the years 1993–2003. Photometric observations from 2002–2004 are also given. The new and previously published spectroscopic and photometric observations are used to study the spot locations and lifetimes, and to estimate the value of the surface differential rotation. Results. The phases of the active regions determined from the Doppler images follow closely the active longitudes determined earlier from the long-term photometric observations. One active longitude can remain active for several years, but the exact spot configuration within the active longitude changes on much shorter time scales, indicating that the spot lifetime is months instead of years. There are periods during which the spot configuration changes even within days. Measurements using spot latitudes from the Doppler images and spot rotation periods from the photometric observations yield a surface differential rotation law of Ω= (151.30 ◦ /day ± 0.09 ◦ /day) − (1.78 ◦ /day ± 0.12 ◦ /day) sin 2 ψ and the relative differential rotation coefficient α = 0.012 ± 0.002 for FK Comae.