Testing the Paradigm of Asteroidal Dust around White Dwarfs with the Prototype

At least one quarter of all white dwarfs are actively accreting debris from planetesimals or planetary fragments. The prototype system G29-38 was discovered at the IRTF in 1987. Yet despite the intervening decades and a complete paradigm shift in the explanation from interstellar material to exoplanetary debris, there remain fundamental questions. The common assumption now is that the dust debris is in a circumstellar disk, yet if so the geometry and vertical optical depth are observationally degenerate. Optically thin and thick cases vary in disk mass — and hence parent body mass — by orders of magnitude. The parent body masses have far-reaching implications for planetary system architecture and long-term dynamics. We report on our work to break this degeneracy and even to test whether the dust is in a disk at all or some other geometrical distribution based on the fact that the prototype system contains a well-studied, pulsating star. Using MORIS and SpeX at the NASA 3-meter Infrared Telescope Facility, we simultaneously monitored the optical stellar pulsations and the ensuing infrared dust response. These observations can distinguish among a range of dust configurations, based on the observed infrared response to the known geometry of the optical pulsations.