Rotational velocities of low-mass stars in the Pleiades

A spectroscopic rotational velocity survey was made of over 60 stars fainter than V = 11 mag in the Pleiades. Most of those stars have rotational velocities below the present detection limit of 10 km/s, but a significant number (18 stars) have v sin i's between 25 and 140 km/s. Based on photometry presented elsewhere, the rapidly rotating stars are identified as heavily spotted main-sequence stars. Thirteen of the 18 rapid rotators are concentrated to a relatively narrow range of color, V-I between 0.95 and 1.35. It is believed those stars stars have only recently arrived on the main sequence and that they owe their high rotational velocities to spin-up while on their radiative pre-main-sequence evolutionary tracks. The G stars in the cluster should also have spun up via that process. Since all of the stars observed with V-I between 0.5 and 0.95 have projected rotational velocities less than 20 km/s, the main sequence spin-down time must be short. The significant number of slow rotators (v sin i less than 10 km/s) in the same color range as the rapid rotators argues for a large range in initial angular momentum and/or an age spread of at least 30 million years among low-mass stars in the Pleiades.