Stellar Rotation in Galactic Clusters.

Rotational velocities are derived for the brighter stars in the I Lacerta and I Orion associations and the a Persei and Pleiades clusters. These, as well as published data on four other clusters, show that each group has a distinctive dependence of mean rotational velocity on luminosity. For field stars the irregularities in the dependence of mean rotational velocity on luminosity and its dips at B2 and A2 are seen as being due to large admixtures of stars from certain groups which have distinctive rotational velocities, such as the Ursa Major stream and the Cassiopeia-Taurus stars There is evidence in four groups for a strong inverse correlation between binary frequency and mean rotational velocity.