Rotation in T Tauri stars. I. Obervations and immediate analysis.

The authors obtained rotational velocities for 28 T Tauri stars down to a resolution limit of a few km s^-1. They find that the distribution of rotational velocities for low-mass T Tauri stars (M < 1.25 M_sun;) is narrow and well-peaked around 15 km s^-1 whereas high-mass T Tauri stars have rotational velocities covering a range from 15 to 75 km s^-1. Comparison between the rotational velocity distribution of low-mass T Tauri stars and of main-sequence Pleiades K-stars supports the hypothesis that pre-main-sequence low-mass stars spin up on their radiative evolutionary tracks during contraction toward the main-sequence. The lack of very slow rotators (v sin i ≤ 6 km s^-1) among the authors' sample of T Tauri stars suggests that a minimum rotational velocity may be necessary for the T Tauri phenomenon to turn-on.