Evidence for external plasma around the K dwarf component of the eclipsing binary V471 Tauri

New, higher resolution, time-resolved spectra of the Hα profile of V471 Tauri are presented in which transient appearances of emission components are detected at the level of 5σ. Measurements of the radial velocity of these components relative to the rest center of the K dwarf reveal unambiguously that they cannot originate on the surface of that star. The same measurements also rule out the white dwarf, or an accretion disk around the white dwarf, as a source of the emission. Furthermore, these external emission components are greatly enhanced immediately following the detection of a flare on the surface of the K dwarf, leading to an inference of causality.