2010AJ....139..195Y

In this paper, we presented multicolor photometric observations for two eclipsing binaries, AO Camelopardalis and AH Tauri, obtained on 2008 December 16 and 17. Using the Wilson-Devinney Code, the photometric solution of AH Tau was determined from our new CCD data. The mass ratio and the fill-out factor are q = 0.503(±0.003) and f = 10.8%(±0.1%), respectively. This indicates that AH Tau is in weak contact. For the weak-contact binary AO Cam, BVI light curves clearly show a difference in the heights of the maxima (i.e., the O'Connell effect), which may be explained by spot activity. By analyzing the O - C curves for AO Cam and AH Tau, it is found that the orbital periods appear to show a secular period decrease with a cyclic variation. The observed period modulation is ΔP/P ∼ 10^–6. For AO Cam, the cyclic oscillation with a short period of 7.63(±0.07) yr and a low amplitude of 0.<SUP>d</SUP>0019(±0.<SUP>d</SUP>0003) may be preferably attributed to the cyclic magnetic activity. The period and amplitude of the cyclic variation for AH Tau are 45.8(±1.1) yr and 0.<SUP>d</SUP>0171(±0.<SUP>d</SUP>0005), which may more likely result from the light-time effect via a third body. The secular period decrease rates are dP/dt = -1.26(±0.04)x10^–7 days/yr for AO Cam and dP/dt = -6.98(±0.07)x10^–8 days/yr for AH Tau. This kind of period decrease can be plausibly explained by the mass transfer from the primary to the secondary, and may result in the system evolving into a deep contact configuration.