Exploring the role of binarity in the origin of the bimodal rotational
  velocity distribution in stellar clusters
  Many young and intermediate age massive stellar clusters host bimodal
distributions in the rotation rates of their stellar populations, with a
dominant peak of rapidly rotating stars and a secondary peak of slow rotators.
The origin of this bimodal rotational distribution is currently debated and two
main theories have been put forward in the literature. The first is that
all/most stars are born as rapid rotators and that interacting binaries brake a
fraction of the stars, resulting in two populations. The second is that the
rotational distribution is a reflection of the early evolution of pre-main
sequence stars, in particular, whether they are able to retain or lose their
protoplanetary discs during the first few Myr. Here, we test the binary channel
by exploiting multi-epoch VLT/MUSE observations of NGC 1850, a 100Myr massive
cluster in the LMC, to search for differences in the binary fractions of the
slow and fast rotating populations. If binarity is the cause of the rotational
bimodality, we would expect that the slowly rotating population should have a
much larger binary fraction than the rapid rotators. However, in our data we
detect similar fractions of binary stars in the slow and rapidly rotating
populations (5.9+/-1.1% and 4.5+/-0.6%, respectively).Hence, we conclude that
binarity is not a dominant mechanism in the formation of the observed bimodal
rotational distributions.
