Biperiodic orbital period modulation of the W UMa binary system CK Bootis

A study of the orbital period variation of the W UMa system CK Bootis is made using an extended observational time base. The biperiodicity of the orbital period modulation is emphasized. Both detected periodicities (24.14 yr and 10.62 yr) cannot be explained through the light-time effect unless the companion would be a white dwarf as suggested by other authors, too. Moreover, we also argue that, nowadays at least, it seems that there is no causal relation between the orbital period variation and the recently discovered visual companion. Consequently, we infer that at least one of the two periodicities may be related to the magnetic activity cycles in the component stars of CK Boo, while the other periodicity could be related to the presence of a fourth companion in the system.