ROTATION IN MODERATE-MASS PRE-MAIN-SEQUENCE RADIATIVE TRACK-G STARS

The influence of rotation on the evolution of a star has been the subject of numerous investigations. In general, these studies deal with stars of the age of the Pleiades or older. In 1981, Vogel and Kuhi published an extensive study of the rotational velocity characteristics of stars in the very young cluster NGC 2264. This was followed by a similar study of the Orion Ic region by Smith, Beckers, and Barden. These studies suggest that the observed high-mass radiative track velocity histograms for pre-main-sequence stars differ significantly. In the Vogel and Kuhi study, these stars were found to possess a rather broad distribution of rotational velocities with a moderate peak at low velocities. In contrast, the above authors found a very sharply peaked distribution located at low values of v sin i. The difference in these velocity distributions is shown to be due to inadequate allowance for field stars in the Smith, Beckers, and Barden work. Once these stars are removed, the high-mass velocity distributions of the two regions are remarkably similar. This result suggests that one might be able to use a unique velocity distribution in modeling very young stars. Assuming that the Orion Ic proto-F stars continue to contract in a homologous fashion, their average current rotational velocity is in agreement with that expected for zero-age main sequence (ZAMS) F stars.