August 11-15, 2014


Is the oxygen-rich white dwarf SDSSJ1242+5226 accreting water-abundant debris?

Roberto Raddi (University of Warwick)

B.Gaensicke (University of Warwick), D.Koester (University of Kiel), J.Farihi (University College London), J.J.Hermes (University of Warwick), S.Scaringi (University of Leuven, MPE), E.Breedt (University of Warwick), J.Girven (University of Warwick)

The detection of metals in white dwarf atmospheres unambiguously signals recent, or ongoing accretion, with debris from planetary systems currently being the favoured origin of the polluting material. We report the discovery of SDSS1242+5226 as one of the most heavily metal-polluted white dwarfs with He-dominated atmospheres. This white dwarf displays in its near-UV to near-IR spectrum strong absorption features of H, O, Na, Mg, Si, Ca, and Fe, indicating that the circumstellar debris is rich in refractory elements. Our analysis reveals a very large amount of H in the convection zone of the star, ~1e24g, which makes it similar to GD362 and GD16. Assuming that the metal-oxydes composition of the accreted debris is similar to the one observed in solar system meteorites, we find a nominal excess of oxygen that leads us to argue that SDSS1242+5226 as well as GD362 and GD16 are currently accreting water-rich planetary debris, or did it in the past. This evidence is also supported by the much larger amounts of H compared to typical He-dominated white dwarfs in the same temperature range.

Mode of presentation: oral