A Photometric Study of the Contact Binary EQ Tauri

Light curves and photometric solutions for the contact binary EQ Tauri are presented. The light curves appear to exhibit a typical O'Connell effect, with primary maximum being 0.030 mag (V) and 0.032 mag (B) brighter than secondary maximum. From the present times of minimum light and those collected from the literature, changes in the orbital period of the system are analyzed. The results reveal that the orbital period of the system oscillates with a cycle of about 23 yr and an amplitude of 8.5 × 10^-7 days. The light curves and recent radial velocity curves from Rucinski et al. are analyzed simultaneously using the latest version of the Wilson-Devinney code. The results suggest that EQ Tau is a W Ursae Majoris contact binary of subtype A. The asymmetry of the light curves is explainable by starspot models. The cyclical period change can most probably be attributed to a magnetic activity cycle in the secondary component. The absolute dimensions of EQ Tau are found to be M₁ = 1.32(3) M_⊙, M₂ = 0.59(2) M_⊙, R₁ = 1.16(3) R_⊙, R₂ = 0.82(3) R_⊙, L₁ = 1.35(12) L_⊙, L₂ = 0.64(6) L_⊙, and A = 2.55(3) R_⊙.