Gaia-ESO Survey: Role of magnetic activity and starspots on pre-main
  sequence lithium evolution
  Pre-main sequence models with inflated radii are needed to simultaneously
reproduce the colour-magnitude diagram and the lithium depletion pattern in
young open clusters. We tested a new set of PMS models including radius
inflation due to starspots or magnetic inhibition of convection, using five
clusters observed by the Gaia-ESO Survey, spanning the age range ~10-100 Myr
where such effects could be important. Gaia-ESO radial velocities were combined
with Gaia EDR3 astrometry to obtain clean lists of high-probability members for
the five clusters. A Bayesian maximum likelihood method was adopted to derive
the best model parameters and the cluster reddening and age. Models were
calculated for different values of the mixing length parameter
($\alpha_{ML}=2.0$, 1.5 and 1.0), without spots or with effective spot coverage
$\beta_{spot}=0.2$ and 0.4. To reproduce the CMD and the Li depletion pattern
in Gamma Vel A and B and in 25 Ori we need both a reduced convection efficiency
$\alpha_{ML}=1.0$ and an effective spot coverage of ~20%. We obtained ages of
18 Myr and 21 Myr for Gamma Vel A and B, respectively, and 19 Myr for 25 Ori.
However, a single isochrone is not sufficient to account for the Li dispersion,
and an increasing level of spot coverage as mass decreases seems to be
required. The older clusters (NGC2451B at 30 Myr, NGC2547 at 35 Myr, and
NGC2516 at 138 Myr) are consistent with standard models ($\alpha_{ML}=2.0$ and
no spots) except at low masses: a 20% spot coverage seems to reproduce the
sequence of M-type stars better and might explain the observed abundance
spread. The quality of Gaia-ESO data combined with Gaia allows us to gain
important insights on PMS evolution. Models including starspots can provide a
consistent explanation of the cluster sequences and Li abundances of young
clusters, although a range of starspot coverage is required to fully reproduce
the data.
