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Astron. Astrophys. 360, 1067-1076 (2000)


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Study of FK Comae Berenices

II. Spot evolution from 1994 to 1997 *

H. Korhonen 1, S.V. Berdyugina 1, T. Hackman 2, K.G. Strassmeier 3 and I. Tuominen 1

1 Astronomy Division, P.O. Box 3000, 90014 University of Oulu, Finland
2 Observatory, P.O. Box 14, 00014 University of Helsinki, Finland
3 Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria

Received 5 May 2000 / Accepted 5 July 2000

Abstract

We present new surface (Doppler) images of the late-type single giant FK Com for June-July 1996, July-August 1996, April 1997 and June 1997. These images are compared with the previously published images from 1994 and 1995. The consecutive maps are cross-correlated to see the possible migration of the spots and the effects of differential rotation. The cross-correlation confirms an average longitudinal spot migration of [FORMULA] in phase within a year. This movement is probably an artifact caused by a difference between the accepted rotation period and the real photometric period for these years. If this is true, then the photometric rotation period for these years is [FORMULA]. Measurements from these four years and six maps limit the surface differential rotation to [FORMULA], where [FORMULA] is the difference between polar and equatorial angular velocities relative to the equatorial angular velocity.

Key words: stars: activity – stars: imaging – stars: individual: FK Comae – stars: late-type – stars: starspots

* Based on the observations obtained at the Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Canary Islands, Spain; the National Astronomical Observatory, Rozhen, Bulgaria; the Kitt Peak National Observatory, USA; the Automatic Photometric Telescope, Phoenix 10, Arizona, USA.

Send offprint requests to: H. Korhonen (heidi.korhonen@oulu.fi)

© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000

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