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Astron. Astrophys. 331, 231-243 (1998)

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Period variation and surface activity of the contact binary VW Cephei

G. Kaszás 1, J. Vinkó 1, K. Szatmáry 2, T. Hegedüs 3, J. Gál 2, L.L. Kiss 2 and T. Borkovits 3

1 Department of Optics, JATE University, P.O. Box 406, Szeged, H-6701 Hungary
2 Department of Experimental Physics, JATE University, Dóm tér 9., Szeged, H-6720 Hungary
3 Baja Astronomical Observatory, P.O. Box 766, Baja, H-6500 Hungary

Received 28 August 1997 / Accepted 13 November 1997

Abstract

Long-term behavior of the well-known contact binary VW Cephei is discussed based on new multicolor (BV) photometry made over 8 years and high-resolution spectroscopy. The existence of an at least 7 year-long activity cycle is confirmed using light curve disturbances as the indicator of surface brightness variations. The orbital period of the system has been decreased further in accordance with previous predictions. It is shown that the cyclic component of the period variation ([FORMULA]) curve has an amplitude too large to be fully due to the light-time effect of the astrometric 3rd companion. It is suspected that the magnetic activity cycle of the primary component affects the orbital period significantly. Simultaneous solution of light- and velocity curves (obtained during the "quiet" stage) resulted in new parameters of the system. The mass ratio ([FORMULA]) is considerably larger than the previous spectroscopic value given by Hill (1989). High resolution optical spectroscopy made at the beginning of the new active cycle reveals [FORMULA] emission arising from the chromosphere of the primary whereas the secondary lacks such emission. This fact gives further support to the theoretical prediction that the primary component drives the activity of contact binaries. Fitting cool spots ([FORMULA]  K) to the surface of the primary, the minimum spot coverage was found to be 12 % at the active stage, while it is about 1-2 % at the quiet stage. An anticorrelation of [FORMULA] emission and spot position has been pointed out.

Key words: stars: individual: VW Cep – binaries: eclipsing – stars: activity – stars: variables

Send offprint requests to: kaszas@physx.u-szeged.hu

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© European Southern Observatory (ESO) 1998

Online publication: February 4, 1998
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