The Gaia-ESO survey: A lithium depletion boundary age for NGC 2232
  Astrometry and photometry from {\it Gaia} and spectroscopic data from the
{\it Gaia}-ESO Survey (GES) are used to identify the lithium depletion boundary
(LDB) in the young cluster NGC 2232. A specialised spectral line analysis
procedure was used to recover the signature of undepleted lithium in very low
luminosity cluster members. An age of $38\pm 3$ Myr is inferred by comparing
the LDB location in absolute colour-magnitude diagrams (CMDs) with the
predictions of standard models. This is more than twice the age derived from
fitting isochrones to low-mass stars in the CMD with the same models. Much
closer agreement between LDB and CMD ages is obtained from models that
incorporate magnetically suppressed convection or flux-blocking by dark,
magnetic starspots. The best agreement is found at ages of $45-50$\,Myr for
models with high levels of magnetic activity and starspot coverage fractions
$>50$ per cent, although a uniformly high spot coverage does not match the CMD
well across the full luminosity range considered.
