Orbital Period Changes and Their Evolutionary Status for Weak-Contact Binaries. II. CC Comae Berenices and BV Draconis
Based on O - C curves, we present detailed period investigations of two weak-contact binaries CC Com and BV Dra. It is found that the periods of these two binaries have varied in a cyclic variation way superposed on a secular period change. The periods and amplitudes of the cyclic variations are P 3 = 23.6(±0.4) yr and A = 0fd0028(±0fd0003) for CC Com and P 3 = 23.8(±0.6) yr and A = 0fd0029(±0fd0003) for BV Dra. The cyclic oscillations for these two stars may be attributed to the light-time effect via an unseen third body, which could extract angular momentum from the central system. If the existence of the additional body is true, CC Com and BV Dra may be triple system stars. For CC Com, the secular period decrease rate is dP/dt = -0.20 × 10-7 d yr-1, which suggests that the mass transfers from the more massive component to the less massive one, accompanied with the angular momentum loss due to mass outflow from L 2. A decrease in its orbital period will result in the shrinking of the inner and outer critical Roche lobes, and then cause the contact degree to increase. This kind of weak-contact binary with a long-term period decrease may evolve into a deep contact configuration. For BV Dra, the continuous period increase rate is dP/dt = +0.29 × 10-7 d yr-1, indicating that the mass transfers from the less massive component to the more massive one. An increase in its orbital period may cause the separation between both components to increase, and thus the contact configuration will break, as predicted by thermal relaxation oscillation theory. Therefore, this kind of weak-contact binary with a secular period increase will evolve into a broken-contact configuration.