The Gaia-ESO Survey: the 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 test a new set of PMS models including radius inflation
due to starspots or to 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 are combined with Gaia
EDR3 astrometry to obtain clean lists of high-probability members for the five
clusters. A Bayesian maximum likelihood method is adopted to derive the best
model parameters and the cluster reddening and age. Models are 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, with $\alpha_{ML}=2.0$ and no spots, except at
low masses: a 20% spot coverage seems to better reproduce the sequence of
M-type stars 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.