Deep, Low Mass Ratio Overcontact Binary Systems. III. CU Tauri and TV Muscae

Abstract

New CCD photometric light curves in the B and V bands of the neglected W UMa–type eclipsing variable star CU Tauri are presented. The O'Connell effect in the V light curve obtained in 2001 by Yang and Liu was about ΔV = +0.015, but it vanished in our 2004 observations. The variations in the levels of both minima were seen. Our two epochs of light minimum and others compiled from the literature were used for the period study. It is shown that the types of some eclipse times were incorrect and the values of the period obtained by previous investigators were aliases that prevented formation of a plausible O - C curve. A new linear ephemeris was derived, and it is discovered that the orbital period of CU Tau shows a continuous decrease at a rate of dP/dt = -1.81 × 10-6 days yr-1. The present symmetric light curves were solved with the 2003 version of the Wilson-Devinney (W-D) code. Both our solutions and those derived by Yang and Liu reveal that CU Tau is a deep (f = 50.1% ± 3.2%), low mass ratio (q = 0.1770 ± 0.0017) overcontact binary system.