Advances in Astronomy and Space Physics, Volume 2, Issue 2 (2012)

Period changes of the sample of eclipsing binaries with active chromospheres

D. Jableka1, S. Zola1,2, B. Zakrzewski2, T. Szymanski1, A. Kuzmicz1, S. N. de Villiers3, M. Zejda4, D. Koziel-Wierzbowska1

1Astronomical Observatory of the Jagiellonian University, ul. Orla 171,30-244 Krakow, Poland
2Mt. Suhora Astronomical Observatory, Cracow Pedagogical University, Podchorazych 2, 30-084 Krakow, Poland
3Private Observatory, 61 Dick Burton Road, Plumstead, Cape Town, South Africa
4Department of Theoretical Physics and Astrophysics, Masaryk University, Brno, Czech Republic

Abstract
In this work we present results derived from analysis of the O-C behaviour of ten eclipsing binary systems: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. It was proved on the basis of moments of minima compiled from the literature and new ones determined from recent observations, that these binaries show long term (19-91 years) modulations of their orbital periods, clearly visible in their O-C diagrams. Two possible explanations for this effect are considered: (1) the light-travel time effect due to the presence of a third body orbiting the eclipsing systems; (2) the Applegate mechanism predicting period modulation by changes in the distribution of angular momentum as a star goes through its activity cycles. It was found that in the case of four systems the existence of a third star, orbiting the binary, is a more plausible explanation of observations.

Keywords:
stars: binaries: eclipsing, stars: magnetic field, stars: chromospheres