The Gaia-ESO Survey: Constraining evolutionary models and ages for young
  low mass stars with measurements of lithium depletion and rotation
  A growing disquiet has emerged in recent years that standard stellar models
are at odds with observations of the colour-magnitude diagrams (CMDs) and
lithium depletion patterns of pre main sequence (PMS) stars in clusters. In
this work we select 1,246 high probability K/M-type constituent members of 5
young open clusters (5--125\,Myr) in the Gaia-ESO Survey to test a series of
models that use standard input physics and others that incorporate surface
magnetic fields or cool starspots. We find that: standard models provide
systematically under-luminous isochrones for low-mass stars in the CMD and fail
to predict Li-depletion of the right strength at the right colour; magnetic
models provide better CMD fits with isochrones that are $\sim 1.5-2$ times
older, and provide better matches to Li depletion patterns. We investigate how
rotation periods, most of which are determined here for the first time from
Transiting Exoplanet Survey Satellite data, correlate with CMD position and Li.
Among the K-stars in the older clusters we find the brightest and least
Li-depleted are the fastest rotators, demonstrating the classic "Li-rotation
connection" for the first time at $\sim 35$ Myr in NGC 2547, and finding some
evidence that it exists in the early M-stars of NGC 2264 at $<10\,$Myr.
However, the wide dispersion in Li depletion observed in fully-convective
M-dwarfs in the $\gamma$ Vel cluster at $\sim 20$ Myr appears not to be
correlated with rotation and is challenging to explain without a very large
($>10$ Myr) age spread.
