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

Farihi, J; Koester, D; Zuckerman, B; Vican, L; Gansicke, BT; Smith, N; Walth, G; (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. Green open access

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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.

Type: Article
Title: Solar abundances of rock-forming elements, extreme oxygen and hydrogen in a young polluted white dwarf
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stw2182
Publisher version: http://dx.doi.org/10.1093/mnras/stw2182
Additional information: © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Keywords: Science & Technology, Physical Sciences, Astronomy & Astrophysics, stars: abundances, circumstellar matter, stars: individual: (WD 1536+520), planetary systems, white dwarfs, EXTRASOLAR MINOR PLANET, IA PROGENITOR SURVEY, CHEMICAL-COMPOSITION, DZ STARS, DEBRIS, PLANETESIMALS, RICH, ACCRETION, WATER, EVOLUTION
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery-pp.ucl.ac.uk/id/eprint/1546020
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