The GALAH Survey: Accreted stars also inhabit the Spite Plateau
  The ESA Gaia astrometric mission has enabled the remarkable discovery that a
large fraction of the stars near the Solar neighbourhood appear to be debris
from a single in-falling system, the so-called Gaia-Enceladus-Sausage (GSE).
One exciting feature of this result is that it gives astronomers for the first
time a large sample of easily observable unevolved stars that formed in an
extra-Galactic environment, which can be compared to stars that formed within
our Milky Way. Here we use these stars to investigate the "Spite Plateau" --
the near-constant lithium abundance observed in metal-poor dwarf stars across a
wide range of metallicities (-3<[Fe/H]<-1). In particular our aim is to test
whether the stars that formed in the GSE show a different Spite Plateau to
other Milky Way stars that inhabit the disk and halo. Individual galaxies could
have different Spite Plateaus -- e.g., the ISM could be more depleted in
lithium in a lower galactic mass system due to it having a smaller reservoir of
gas. We identified 76 GSE dwarf stars observed and analyzed by the GALactic
Archeology with HERMES (GALAH) survey as part of its Third Data Release.
Orbital actions were used to select samples of Gaia-Enceladus stars, and
comparison samples of halo and disk stars. We find that the Gaia-Enceladus
stars show the same lithium abundance as other likely accreted stars and in
situ Milky Way stars, strongly suggesting that the "lithium problem" is not a
consequence of the formation environment. This result fits within the growing
consensus that the Spite Plateau, and more generally the "cosmological lithium
problem" -- the observed discrepancy between the amount of lithium in warm,
metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to
have been produced by Big Bang Nucleosynthesis -- is the result of lithium
depletion processes within stars.
