Farihi, J; Koester, D; Zuckerman, B; Vican, L; Gansicke, BT; Smith, N; Walth, G; Farihi, J; Koester, D; Zuckerman, B; Vican, L; Gansicke, BT; Smith, N; Walth, G; Breedt, E; - view fewer (2016) Solar abundances of rock-forming elements, extreme oxygen and hydrogen in a young polluted white dwarf. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY , 463 (3) pp. 3186-3192. 10.1093/mnras/stw2182.

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Abstract

The Teff = 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 × 109 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.

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