Apparent Age Spreads in Clusters and the Role of Stellar Rotation
  We use the Geneva Syclist isochrone models that include the effects of
stellar rotation to investigate the role that rotation has on the resulting
colour-magnitude diagram (CMD) of young and intermediate age clusters. We find
that if a distribution of rotation velocities exists within the clusters,
rotating stars will remain on the main sequence (MS) for longer, appearing to
be younger than non-rotating stars within the same cluster. This results in an
extended main sequence turn-off (eMSTO) that appears at young ages
($\sim30$~Myr) and lasts beyond 1~Gyr. If this eMSTO is interpreted as an age
spread, the resulting age spread is proportional to the age of the cluster,
i.e. young clusters ($<100$~Myr) appear to have small age spreads (10s of Myr)
whereas older clusters ($\sim1$~Gyr) appear to have much larger spreads, up to
a few hundred Myr. We compare the predicted spreads for a sample of rotation
rates to observations of young and intermediate age clusters, and find a strong
correlation between the measured 'age spread' and the age of the cluster, in
good agreement with models of stellar rotation. This suggests that the 'age
spreads' reported in the literature may simply be the result of a distribution
of stellar rotation velocities within clusters.
