Orbital period variation in close binaries from radial velocity data and magnetic activity cycles

Abstract

We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most bright members of the RS CVn class of magnetically active binary systems. Intermediate-resolution optical spectroscopy and IUE archive spectra were used to build radial-velocity curves yielding epochs of superior conjunction with an accuracy of 0.01 days. The final database ranged from 1976 to 2002 and allowed us a better assessment of the amplitude of the orbital period variation and its timescale. On the basis of such results, the mechanisms proposed to explain the observed period change were briefly discussed giving further support to the possible connection between the orbital period modulation and the change of the gravitational quadrupole moment of the Kl subgiant component, in the framework of the model elaborated by Lanza et al. (1998).