The T-eff = 20 800 K white dwarf WD 1536+520 is shown to have broadly solar abundances of the major rock-forming elements O, Mg, Al, Si, Ca, and Fe, together with a strong relative depletion in the volatile elements C and S. In addition to the highest metal abundances observed to date, including log (O/He) = -3.4, the helium-dominated atmosphere has an exceptional hydrogen abundance at log (H/He) = -1.7. Within the uncertainties, the metal-to-metal ratios are consistent with the accretion of an H2O-rich and rocky parent body, an interpretation supported by the anomalously high trace hydrogen. The mixed atmosphere yields unusually short diffusion time-scales for a helium atmosphere white dwarf, of no more than a few hundred years, and equivalent to those in a much cooler, hydrogen-rich star. The overall heavy element abundances of the disrupted parent body deviate modestly from a bulk Earth pattern, and suggest the deposition of some core-like material. The total inferred accretion rate is 4.2 x 10(9) g s(-1), and at least four times higher than for any white dwarf with a comparable diffusion time-scale. Notably, when accretion is exhausted in this system, both metals and hydrogen will become undetectable within roughly 300 Myr, thus supporting a scenario where the trace hydrogen is related to the ongoing accretion of planetary debris.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/622949 |
| Date | 11 December 2016 |
| Creators | Farihi, J., Koester, D., Zuckerman, B., Vican, L., Gänsicke, B. T., Smith, N., Walth, G., Breedt, E. |
| Contributors | Univ Arizona, Steward Observ |
| Publisher | OXFORD UNIV PRESS |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society |
| Relation | https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw2182 |
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