Cyclic changes in the interacting binary RX Cassiopeiae

Abstract

We analyzed 109 years of published photometry and times of minima of the eclipsing interacting binary RX Cas. The inclusion of 171 previously unnoticed minima confirms the tendency of an increase in the orbital period at a rate of 1.84 s per cycle. We also find evidence of variations in the length of the previously reported long photometric cycle and changes in the shape of the orbital light curve. By modeling the orbital light curves at different epochs, and assuming symmetry in the system physical conditions during the first and second halves of the long cycle, we find that the changes in the orbital light curve can be explained by variations in the physical properties of the accretion disk. We find that epochs of maximum brightness are those of thicker and hotter disks. In addition, we explore the evolutionary history of the system using the Modules for Experiments in Stellar Astrophysics code and find that the binary can be the result of nonconservative evolution of two stars of very similar initial mass (around 5.5M⊙) and orbital period of 4 days, although less massive and conservative models of longer starting orbital periods cannot be discarded.