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Astron. Astrophys. 350, 626-634 (1999)


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The active RS Canum Venaticorum binary II Pegasi

IV. The spot activity cycle *

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

1 Astronomy Division, University of Oulu, P.O. Box 3000, 90401 Oulu, Finland
2 Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland

Received 21 May 1999 / Accepted 26 August 1999

Abstract

A total of 6 new surface images of II Peg obtained for the years 1997 and 1998 confirms the recently revealed permanent active longitude structure. The lower limit of the active longitudes' lifetime is now extended up to 25 years. A new "flip-flop" phenomenon, redefined as a switch of the activity between the active longitudes, has started in summer of 1998. It coincides reasonably well with the moment predicted from the activity cycle of the star. This confirms definitely the cyclic behaviour of the activity of II Peg we recently discovered. Therefore, we assign numbers to the cycles of 4.65 yr since the earliest photoelectric observations of II Peg and define the active longitudes as "odd" and "even" corresponding to odd and even numbers of cycles. With such a definition, in late 1998 the 7th cycle began and the "odd" active longitude became more active. From the analysis of the spot area evolution within the active longitudes we conclude that the activity cycle is developed as a rearrangement of the nearly constant amount of the spot area between the active longitudes. We discuss the "flip-flop" phenomenon as a tracer of stellar activity and the role of the unseen secondary in establishing the cycle.

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

* Based on observations collected at the Nordic Optical Telescope (NOT), La Palma, Spain; the 1.25 m telescope of the Crimean Astrophysical Observatory, Ukraine; the Phoenix 10 robotic telescope, APT Observatory, Arizona, USA.

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

© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999

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