Indirect evidence for short period magnetic cycles in overcontact binary stars

Borkovits, T. and Csizmadia, Sz. and Nuspl, J. and Biro, I. B. (2006) Indirect evidence for short period magnetic cycles in overcontact binary stars. In: 4th Workshop of Young Researchers in Astronomy & Astrophysics. Publications of the Astronomy Department of the Eötvös University (17). ELTE Sokszorosítóüzeme, Budapest, pp. 110-114.

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Abstract

Complex period variations of five W~UMa type binaries (AB~And, OO~Aql, DK~Cyg, V566~Oph, U~Peg) were investigated by the analysis of their O--C diagrams, and several common features were found. Four of the five systems show secular period variations at a constant rate in the order of $|\dot{P}_\mathrm{sec}/P|\sim10^{-7}$~y$^{-1}$. In the case of AB~And, OO~Aql and U~Peg a high-amplitude, nearly one-century long quasi-sinusoidal pattern was also found. It might be explained as light-time effect, or by some magnetic phenomena. The most interesting feature of the studied O--C diagrams is a low amplitude ($\sim2-4\times10^{-3}$ d) modulation with a period around 18--20 yr in four of the five cases. This phenomenon might be an indirect evidence of some magnetic cycle in late-type overcontact binaries as an analog to the observed activity cycles in RS~CVn systems.

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