A high fraction of Be stars in young massive clusters: evidence for a
  large population of near-critically rotating stars
  Recent photometric analysis of the colour-magnitude diagrams (CMDs) of young
massive clusters (YMCs) have found evidence for splitting in the main sequence
and extended main sequence turn-offs, both of which have been suggested to be
caused by stellar rotation. Comparison of the observed main sequence splitting
with models has led various authors to suggest a rather extreme stellar
rotation distribution, with a minority ($10-30$\%) of stars with low rotational
velocities and the remainder ($70-90$\%) of stars rotating near the critical
rotation (i.e., near break-up). We test this hypothesis by searching for Be
stars within two YMCs in the LMC (NGC 1850 and NGC 1856), which are thought to
be critically rotating stars with decretion disks that are (partially) ionised
by their host stars. In both clusters we detect large populations of Be stars
at the main sequence turn-off ($\sim30-60$\% of stars), which supports previous
suggestions of large populations of rapidly rotating stars within massive
clusters.
