August 11-15, 2014


A Variable Gaseous Disc Around a Metal Polluted White Dwarf

David Wilson (University of Warwick)

Boris Gaensicke (University of Warwick) Detlev Koester (University of Kiel)

In recent decades several dozen white dwarfs have been observed to have infrared excesses indicative of a close-in dust debris disc, formed by the tidal disruption of an asteroid. In a small number of these systems an additional gaseous disc is detected via observation of double peaked emission lines in the CaII 8600A triplet. Analysis of the morphology of the emission line has shown that the gaseous disc overlaps the dusty disc, instead of being confined to within the sublimation limit of the white dwarf. Here we present the discovery of a variable gaseous disc around a DA white dwarf. Time-series spectroscopy obtained during the period 2006-2014 has shown the appearance of very strong double-peaked CaII emission lines in 2008, that subsequently faded again over several years. The white dwarf is strongly metal polluted, requiring ongoing accretion, and exhibits infrared excess emission from circumstellar dust. Our observations represent the strongest evidence yet for real-time evolution of planetary debris discs around WDs, and we discuss potential scenarios including a secondary impact of a dense planetesimal onto the dusty disc, or the periodic passage of an object in a highly eccentric orbit.

Mode of presentation: oral