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arXiv 0905.0117astro-ph.SR
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两颗外部污染的白矮星的X射线和红外观测

X-ray and Infrared Observations of Two Externally-Polluted White Dwarfs

M. Jura, M. P. Muno, J. Farihi, B. Zuckerman

备注：
ApJ, in press
发表信息：
Astrophys.J.699:1473-1479,2009
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摘要：

利用XMM-Newton和斯皮策空间望远镜，我们得到了G29-38和GD 362的X射线通量的上界，以及G29-38的70微米通量。这些数据提供了间接证据，证明G29-38是从一颗潮汐破裂的小行星吸积而来：它既没有吸积大量的氢和氦，也没有从经历坡印廷-罗伯逊阻力的冷颗粒库中补充周围的尘埃盘。GD 362的X射线通量的上限与解释其被比氦重的元素污染所需的质量吸积的估计速率是一致的。GD 362还拥有0.01个地球质量的氢，对于一个以氦为主的大气层的白矮星来说，这是一个非常大的数量。一种可能性是，在目前的圆盘形成之前，这些氢是从大约100颗谷神星一样的小行星或一个大型物体中吸积而来的。另一种同时解释GD 362所有独特性质的情况是，我们正在目睹一个内部有水的单一母体的潮汐破坏的后果，它至少和木卫四一样大，可能和火星一样大。

英文摘要：

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 micron 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 of an Earth's mass 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 from either about 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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