Hydrogen delivery onto white dwarfs from remnant exo-Oort cloud comets

Dimitri Veras, Andrew Shannon, Boris T. Gänsicke

Research output: Contribution to journalArticle

52 Scopus citations

Abstract

The origin of trace hydrogen in white dwarfs (WDs) with He-dominated atmospheres is a long-standing problem, one that cannot satisfactorily be explained by the historically favoured hypothesis of accretion from the interstellar medium. Here we explore the possibility that the gradual accretion of exo-Oort cloud comets, which are a rich source of H, contributes to the apparent increase of trace H with WD cooling age. We determine how often remnant exo- Oort clouds, freshly excited from post-main-sequence stellar mass loss, dynamically inject comets inside the WD's Roche radius. We improve upon previous studies by considering a representative range of single WD masses (0.52-1.00M⊙) and incorporating different cloud architectures, giant branch stellar mass loss, stellar flybys, Galactic tides and a realistic escape ellipsoid in self-consistent numerical simulations that integrate beyond 8 Gyr ages of WD cooling.We find that ~10-5 of the material in an exo-Oort cloud is typically amassed on to the WD, and that the H deposits accumulate even as the cloud dissipates. This accumulation may account for the relatively large amount of trace H, 1022-1025 g, that is determined frequently among WDs with cooling ages=1 Gyr. Our results also reaffirm the notion that exo-Oort cloud comets are not the primary agents of the metal budgets observed in polluted WD atmospheres.

Original languageEnglish (US)
Pages (from-to)4175-4185
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume445
Issue number4
DOIs
StatePublished - Sep 29 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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