The Gaia-ESO survey: Lithium abundances in open cluster Red Clump stars
  It has recently been suggested that all giant stars with mass below 2
$M_{\odot}$ suffer an episode of surface lithium enrichment between the tip of
the red giant branch (RGB) and the red clump (RC). We test if the above result
can be confirmed in a sample of RC and RGB stars that are members of open
clusters. We discuss Li abundances in six open clusters with ages between 1.5
and 4.9 Gyr (turn-off masses between 1.1 and 1.7 $M_{\odot}$). These
observations are compared with the predictions of different models that include
rotation-induced mixing, thermohaline instability, mixing induced by the first
He flash, and energy losses by neutrino magnetic moment. In six clusters, we
find about 35\% RC stars with Li abundances that are similar or higher than
those of upper RGB stars. This can be a sign of fresh Li production. Because of
the extra-mixing episode connected to the luminosity bump, the expectation was
for RC stars to have systematically lower surface Li abundances. However, we
cannot confirm that the possible Li production is ubiquitous. For about 65\% RC
giants we can only determine abundance upper limits that could be hiding very
low Li abundances. Our results indicate a possible production of Li during the
RC, at levels that would not classify the stars as Li rich. Determination of
their carbon isotopic ratio would help to confirm that the RC giants have
suffered extra mixing followed by Li enrichment. The Li abundances of the RC
stars can be qualitatively explained by the models with an additional mixing
episode close to the He flash.
