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Astron. Astrophys. 360, 272-280 (2000)


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The long-period RS CVn binary IM Pegasi

II. First surface images *

S.V. Berdyugina 1, A.V. Berdyugin 1,2, I. Ilyin 1 and I. Tuominen 1

1 Astronomy Division, P.O. Box 3000, 90014 University of Oulu, Finland
2 Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland

Received 10 April 2000 / Accepted 25 May 2000

Abstract

New high-resolution, high signal-to-noise ratio spectroscopic observations and UBV photometry carried out in 1996-1999 were analysed with the surface imaging technique. A total of 8 images of IM Peg was obtained for the first time. A huge high-latitude active region was found to dominate the stellar surface and decreased in area during the period of the observations. At the same time, on the opposite hemisphere (in longitudes), smaller spots were developing. The spots were migrating in the orbital reference frame, the period of spot rotation being of [FORMULA][FORMULA][FORMULA]. The spots constitute two active longitudes on opposite stellar hemispheres, similar to other RS CVn stars. The evolution of the spot areas within the active longitudes indicates a stellar activity cycle, during which one active longitude dominates the stellar activity, to be about 6.5 years. Then, a total cycle, comprising two consecutive periods of activity of both active longitudes, is about 13 years. In 1999, the activity switched to the other active longitude. This declared the beginning of a new (half-) cycle.

Key words: stars: imaging – stars: starspots – stars: activity – stars: late-type – stars: individual: IM Peg

* based on observations collected at the Nordic Optical Telescope (NOT), La Palma, Spain; the 2.6 m and 1.25 m telescopes of the Crimean Astrophysical Observatory, Ukraine; the 2m telescope of the National Astronomical Observatory, Rozhen, Bulgaria.

Send offprint requests to: S.V.Berdyugina (sveta@ukko.oulu.fi)

© European Southern Observatory (ESO) 2000

Online publication: July 27, 2000

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