Whole Earth Telescope Observations of the White Dwarf G29-38: Phase Variations of the 615 Second Period

An extensive set of high-speed photometric observations obtained with the Whole Earth Telescope network is used to show that the complex light curve of the ZZ Zeti (DAV) star G29-38 is dominated by a single, constant amplitude period of 615 s during the time span of these observations. The pulse arrival times for this period exhibit a systematic variation in phase readily explained by light-travel time effects produced by reflex orbital motion about an unseen companion. The best-fit model to the observations indicates a highly eccentric orbit, a period of 109 + or - 13 days and a minimum mass of 0.5 solar mass for the companion.