Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

1B. C. Kaiser,1J. C. Clemens,2S. Blouin,3,4P. Dufour,1R. J. Hegedus,1J. S. Reding,3A. Bédard
Science 371, 168-172 Link to Article [DOI: 10.1126/science.abd1714]
1Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC, USA.
2Los Alamos National Laboratory, Los Alamos, NM, USA.
3Département de Physique, Université de Montréal, Montreal, QC, Canada.
4Institut de Recherche sur les Exoplanètes, Université de Montréal, Montreal, QC, Canada.
Reprinted with Permission from AAAS

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.

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