Lithium in red giants: the roles of the He-core flash and the luminosity
  bump
  Lithium abundances for red giants in the GALAH DR3 survey are studied. The
rare examples of Li-enriched stars with abundances A(Li) $\geq 1.5$ are
confirmed to be He-core burning stars belonging to or evolved from the red
clump with similar masses and metallicity: $M\simeq 1.1\pm0.2{\rm M_\odot}$ and
[Fe/H] $\simeq-0.3\pm0.3$. Li enrichment over the Li abundance present in a
star's predecessor at the tip of the red giant branch likely occurs in all
these red clump stars. Examination of the elemental abundances (C to Eu) in the
GALAH catalogue shows no anomalous abundances in red clump giants and, in
particular, no dependence on the Li abundance, which ranges over at least five
dex. Lithium synthesis is attributed to the He-core flash occurring in stars at
the tip of the red giant branch. Models from the Modules for Experiments in
Stellar Astrophysics (MESA) match the observed evolution of these stars along
the red giant branch and to the red clump but only at the low effective
temperature end of the observed spread of red clump giants. Run of Li abundance
on the red giant branch is fairly well reproduced by MESA models. A speculation
is presented that the series of He-core flashes not only leads to $^7$Li
synthesis from a star's internal reservoir of $^3$He but also may lead to
internal restructuring leading to the observed effective temperature spread of
red clump stars at about a constant luminosity. Giants exhibiting marked Li
enrichments are not found at other evolutionary phases and, in particular, not
directly associated with the luminosity bump on the red giant branch for which
the Li abundance increase does not exceed 0.3 dex.
