Jura, M; Muno, MP; Farihi, J; Zuckerman, B; (2009) X-ray and infrared observations of two externally polluted white dwarfs. Astrophysical Journal , 699 (2) pp. 1473-1479. 10.1088/0004-637X/699/2/1473.

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Abstract

With XMM-Newton and the Spitzer Space Telescope, we obtain upper bounds to the X-ray fluxes from G29-38 and GD 362, and the 70 μm flux from G29-38. These data provide indirect evidence that G29-38 is accreting from a tidally disrupted asteroid: it is neither accreting large amounts of hydrogen and helium nor is its surrounding dusty disk being replenished from a reservoir of cold grains experiencing Poynting-Robertson drag. The upper bound to the X-ray flux from GD 362 is consistent with the estimated rate of mass accretion required to explain its pollution by elements heavier than helium. GD 362 also possesses 0.01 M ⊕ of hydrogen, an anomalously large amount for a white dwarf with a helium-dominated atmosphere. One possibility is that before the current disk was formed, this hydrogen was accreted either from 100 Ceres-like asteroids or one large object. An alternative scenario which simultaneously explains all of GD 362's distinctive properties is that we are witnessing the consequences of the tidal destruction of a single parent body that had internal water and was at least as massive as Callisto and probably as massive as Mars.

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