Light-Curve Study and Physical Properties of the Contact Binary EQ Tauri

Abstract

New V, RC, and IC light curves of EQ Tau have been obtained in 2002 and 2003. These show the secondary minimum to be a total eclipse. These new light curves have been analyzed, together with the published radial velocity observations, using the Wilson-Devinney code. The binary has an overcontact configuration, with an orbital inclination of 85°, a difference in component temperature of 80 K, and an overcontact fill-out factor of 16%. Absolute parameters of the component stars have been determined: M1 = 1.28 M⊙, R1 = 1.17 R⊙, L1 = 1.39 L⊙, and M2 = 0.47 M⊙, R2 = 0.81 R⊙, L2 = 0.63 L⊙. The calculated distance is 180 ± 20 pc. A critical review of our new timings of minimum light together with previously published ones suggests a change from one constant period to another one around 1974 rather than a cyclical variation. When corrected for energy transfer in the common envelope, the physical parameters of the two components are in good agreement with those of unevolved single stars of similar masses.