We investigate lithium depletion in standard stellar models (SSMs) and main
sequence (MS) open clusters, and explore the origin of the Li dispersion in
young, cool stars of equal mass, age and composition. We first demonstrate that
SSMs accurately predict the Li abundances of solar analogs at the zero-age main
sequence (ZAMS) within theoretical uncertainties. We then measure the rate of
MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three
well-studied clusters, and comparing the detrended data. MS depletion is found
to be mass dependent, in the sense of more depletion at low mass. A dispersion
in Li abundance at fixed Teff​ is nearly universal, and sets in by
∼200 Myr. We discuss mass and age dispersion trends, and the pattern is
mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with
theoretical expectations but contrary to the findings of some previous studies,
and suggest Li as a test of cluster metallicity. Finally, we argue that a
radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li
destruction, is responsible for the spread in Li abundances and the correlation
between rotation and Li in young cool stars, most well known in the Pleiades.
We calculate stellar models, inflated to match observed radius anomalies in
magnetically active systems, and the resulting range of Li abundances
reproduces the observed patterns of young clusters. We discuss ramifications
for pre-MS evolutionary tracks and age measurements of young clusters, and
suggest an observational test.Comment: 29 pages, 20 Figures, 4 Tables. A short video discussing the key
results can be found at this link: http://youtu.be/8576JQ0WkY