Stellar rotation on the zero age main sequence

Analysis of rotational velocities of unevolved members in clusters indicates that for a given mass the dispersion in the true rotational velocities is small for normal, single main-sequence stars. The envelope of highest rotation of rich clusters and associations is utilized to derive the rotational velocities on the zero age main sequence. It is suggested (1) that the zero age main-sequence rotation curve defines the star's stability against fission and (2) that the frequency of spectroscopic binaries in a cluster is determined by the total angular momentum available to the gas cloud before fragmentation. (author)