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Trace hydrogen in helium atmosphere white dwarfs as a possible signature of water accretion
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Gentile Fusillo, N. P., Gänsicke, B. T. (Boris T.), Farihi, Jay, Koester, Detlev, Schreiber, Matthias R. and Pala, Anna F. (2017) Trace hydrogen in helium atmosphere white dwarfs as a possible signature of water accretion. Monthly Notices of the Royal Astronomical Society, 468 (1). pp. 971-980. doi:10.1093/mnras/stx468
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Official URL: http://dx.doi.org/10.1093/mnras/stx468
Abstract
A handful of white dwarfs with helium-dominated atmospheres contain exceptionally large masses of hydrogen in their convection zones, with the metal-polluted white dwarf GD 16 being one of the earliest recognized examples. We report the discovery of a similar star: the white dwarf coincidentally named GD 17. We obtained medium-resolution spectroscopy of both GD 16 and GD 17 and calculated abundances and accretion rates of photospheric H, Mg, Ca, Ti, Fe and Ni. The metal abundance ratios indicate that the two stars recently accreted debris, which is Mg-poor compared to the composition of bulk Earth. However, unlike the metal pollutants, H never diffuses out of the atmosphere of white dwarfs and we propose that the exceptionally high atmospheric H content of GD 16 and GD 17 (2.2 × 1024 and 2.9 × 1024 g, respectively) could result from previous accretion of water bearing planetesimals. Comparing the detection of trace H and metal pollution among 729 helium atmosphere white dwarfs, we find that the presence of H is nearly twice as common in metal-polluted white dwarfs compared to their metal-free counterparts. This highly significant correlation indicates that, over the cooling age of the white dwarfs, at least some fraction of the H detected in many He atmospheres (including GD 16 and GD 17) is accreted alongside metal pollutants, where the most plausible source is water. In this scenario, water must be common in systems with rocky planetesimals.
| Item Type: | Journal Article | ||||||
|---|---|---|---|---|---|---|---|
| Subjects: | Q Science > QB Astronomy | ||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||
| Library of Congress Subject Headings (LCSH): | White dwarf stars, Cosmic abundances, Accretion (Astrophysics) | ||||||
| Journal or Publication Title: | Monthly Notices of the Royal Astronomical Society | ||||||
| Publisher: | Oxford University Press | ||||||
| ISSN: | 0035-8711 | ||||||
| Official Date: | 24 February 2017 | ||||||
| Dates: |
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| Volume: | 468 | ||||||
| Number: | 1 | ||||||
| Page Range: | pp. 971-980 | ||||||
| DOI: | 10.1093/mnras/stx468 | ||||||
| Status: | Peer Reviewed | ||||||
| Publication Status: | Published | ||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||
| Funder: | Seventh Framework Programme (European Commission) (FP7), European Research Council (ERC) | ||||||
| Grant number: | FP/2007-2013 (FP7), 320964 (ERC) |
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