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The Hyades K2V+WD system 471 Tau is a prototype post-common envelope systemand a likely cataclysmic binary progenitor. We present 10 days of nearlycontinuous optical photometry by the MOST (Microvariability & Oscillations ofSTars) satellite and partly simultaneous optical spectroscopy from DDO (DavidDunlap Observatory) of the binary. The photometric data indicate that the spotcoverage of the K dwarf component was less than observed in the past,suggesting that we monitored the star close to a minimum in its activity cycle.Despite the low spot activity, we still detected seven flare-like events whoseestimated energies are among the highest ever observed in V471 Tau and whosetimes of occurrence do not correlate with the binary orbital phase. A detailedO-C analysis of the times of eclipse over the last ~35 years reveals timingvariations which could be explained in several ways, including perturbations byan as-yet-undetected third body in the system or by a small orbitaleccentricity inducing slow apsidal motion. The DDO spectra result in improveddeterminations of the K dwarf projected rotation velocity, V_K sin i = 92 kms^-1, and the orbital amplitude, K_K=150.5 km s^-1. The spectra also allow usto measure changes in H_alpha emission strength and radial velocity (RV)variations. We measure a larger H_alpha velocity amplitude than foundpreviously suggesting that the source of the emission in V471 Tau was lessconcentrated around the sub-white-dwarf point on the K star than had beenobserved in previous studies.

MOST photometry and DDO spectroscopy of the eclipsing (white dwarf + red dwarf) binary V471 Tau