2003NewA....8..457Q

Orbital period variations of two chromospherically active binary systems, RT CrB and PW Her, are presented. It is shown that the orbital period of RT CrB undergoes a cyclic oscillation with a period of 53.9years. For PW Her, an alternate change, with a period of 42.7years, is found to superimpose on a rapid secular increase (dP/dt=+3.53*10-6 days/year). If the period oscillations of those two systems are caused by the light-time effect of a third body, the analysis for RT CrB indicates that the third body would be a low-mass main-sequence star, while, for PW Her, the mass of the third body should be no less than 7.8 M. Since no spectral lines of the third body were seen in PW Her from the spectroscopic study by Popper [AJ 100 (1990) 247], if there is a third body in the system, it can only be a black hole. However, as both components in the two binary stars were showing strong chromospheric activity, the alternate period variations are more plausibly explained as the result! of magnetic activity cycles. No secular period changes of RT CrB are found, which is in agreement with the detached evolved configuration of the system. The long-term period increase of PW Her may indicate that it is on an active phase of mass transfer (dm/dt=2.17*10-6 M/year).