Potassium and lithium on a white dwarf White dwarfs are dense stellar remnants left when a dying parent star throws off its outer layers. The high gravitational fields should cause heavy elements to rapidly sink below the white dwarf surface. Nevertheless some “polluted” white dwarfs have evidence for those materials on their surface, which is thought to be due to the recent accretion of rocky bodies from a surrounding planetary system. Kaiser et al. report a white dwarf with pollution by potassium and lithium. This observation provides a record of the composition of the accreted rocky bodies and of the Galactic lithium abundance when the planetary system formed, billions of years ago. Science, this issue p. 168 A white dwarf with pollution by lithium and potassium from accreted rocky bodies records the ancient Galactic abundance. Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

中文翻译：

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白矮星的锂污染记录了太阳系外星子的吸积

白矮星上的钾和锂 白矮星是垂死的母星脱离外层时留下的致密恒星残余物。高引力场会导致重元素迅速下沉到白矮星表面以下。然而，一些“受污染”的白矮星在其表面有这些物质的证据，这被认为是由于最近从周围行星系统中吸积了岩石天体。凯撒等人。报告一颗被钾和锂污染的白矮星。这一观察提供了数十亿年前行星系统形成时吸积岩石体的组成和银河锂丰度的记录。科学，这个问题 p。168 一颗被吸积岩体中锂和钾污染的白矮星记录了古代银河的丰度。潮汐干扰和随后白矮星对星子的吸积可以揭示系外行星系统中岩石天体的元素丰度。这些丰度提供了有关形成系统的星云组成的信息，这类似于陨石丰度如何告知我们对早期太阳系的理解。我们报告了在白矮星 Gaia DR2 4353607450860305024 的大气中检测到锂、钠、钾和钙，我们将其归因于小行星的吸积。使用模型大气，我们确定了这些元素的丰度比，除锂外，它们与太阳系中的陨石值一致。我们将测得的锂丰度与旧恒星的测量值以及大爆炸核合成的预期进行了比较。