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

TL;DR

This study detects lithium and other elements in a white dwarf's atmosphere, indicating accretion of a planetesimal, and compares the lithium abundance to stellar and cosmological benchmarks.

Contribution

It reports the first detection of lithium in a white dwarf accreting a planetesimal, providing insights into exoplanetary composition and nucleosynthesis.

Findings

Detected Li, Na, K, Ca in white dwarf atmosphere

Elemental ratios mostly match Solar System meteoritic values

Li abundance compared to stellar and Big Bang nucleosynthesis data

Abstract

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, analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of Li, Na, K and Ca in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and with the exception of Li, they are consistent with meteoritic values in the Solar System. We compare the measured Li abundance to measurements in old stars and to expectations from Big Bang nucleosynthesis.