Rotational velocities of low mass stars in young open clusters

Abstract

Reviews of stellar rotation written prior to 1980 included essentially no information on the rotational velocities of stars later than G0 other than that they were generally slow rotators. Due to the advent of new instrumental capabilities, a large body of data on the rotational velocities of low mass stars is now available. In particular, several nearby clusters have good rotational velocity data for low mass stars, allowing us to estimate the evolution of rotation on and near the main sequence. Somewhat unexpectedly, many low mass stars have very large rotational velocities when they arrive on the main sequence. However, these stars spin down rapidly so that by the age of the Hyades essentially all of the low mass stars are relatively slow rotators. This paper provides a brief review of the “classical” rotation studies of the 1960’s, an outline of the new discoveries of the 1980’s and their current interpretation, and a description of the outstanding problems that remain.