The V471 Tauri system: A multi-data-type probe

Abstract

V471 Tauri, a white dwarf–red dwarf eclipsing binary (EB) in the Hyades, is well known for stimulating development of common envelope theory, whereby novae and other cataclysmic variables form from much wider binaries by catastrophic orbit shrinkage. Our evaluation of a recent imaging search that reported negative results for a much postulated third body shows that the object could have escaped detection or may have actually been seen. The balance of evidence continues to favor a brown dwarf companion about 12 AU from the EB. A recently developed algorithm finds unified solutions from three data types. New radial velocities (RVs) of the red dwarf and BVR{sub C}I{sub C} light curves are solved simultaneously along with white dwarf and red dwarf RVs from the literature, uvby data, the Microvariability and Oscillations of Stars mission light curve, and 40 years of eclipse timings. Precision-based weighting is the key to proper information balance among the various data sets. Timewise variation of modeled starspots allows unified solution of multiple data eras. Light-curve amplitudes strongly suggest decreasing spottedness from 1976 to about 1980, followed by approximately constant spot coverage from 1981 to 2005. An explanation is proposed for lack of noticeable variation in 1981 light curves, in terms of competition between spot and tidal variations. Photometric–spectroscopic distance is estimated. The red dwarf mass comes out larger than normal for a K2 V star, and even larger than adopted in several structure and evolution papers. An identified cause for this result is that much improved red dwarf RV curves now exist.