2003PASP..115..748Y

From the present times of minimum light and those collected from the literature, changes in the orbital period of the two W UMa-type contact binaries RW Com and CC Com are analyzed. The results reveal that the period changes of these two systems show the same natures, with a short-term oscillation superposed on the secular decrease. For RW Com, its period shows a secular decrease at a rate of dP/dt=0.43x10^–7 days.yr^–1. An oscillation with a periodicity of 13.7 yr and an amplitude of ΔP=5.4x10^–7 days is superposed on the secular decrease. For CC Com, its period shows a secular decrease at a rate of dP/dt=0.40x10^–7 days.yr^–1. An oscillation with a periodicity of 16.1 yr and an amplitude of ΔP=2.8x10^–7 days is superposed on the secular decrease. The period secular decreases of the two systems may be explained by a mass-transfer rate of dm/dt=0.29x10^–7 M_☉.yr^–1 for RW Com and dm/dt=0.52x10^–7 M_☉.yr^–1 for CC Com. The period short-term oscillations of the two systems may be explained by the magnetic activity cycle model given by Applegate, and the parameters for the magnetic activity cycle model are presented.