Solar abundances of rock-forming elements, extreme oxygen and hydrogen in a young polluted white dwarf

December 2016 • 2016MNRAS.463.3186F

Authors • Farihi, J. • Koester, D. • Zuckerman, B. • Vican, L. • Gänsicke, B. T. • Smith, N. • Walth, G. • Breedt, E.

Abstract • 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 × 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2016MNRAS.463.3186F
• PDF https://academic.oup.com/mnras/pdf-lookup/doi/10.1093/mnras/stw2182
• PREPRINT http://arxiv.org/abs/1608.07278
• ELECTR https://doi.org/10.1093%2Fmnras%2Fstw2182