Angular Momentum Loss in Pre-Main Sequence Objects and the Initial Angular Momentum of Stars

Abstract

Several lines of observational evidence point to angular momentum loss from pre-main sequence stars between the end of the dynamical collapse phase and arrival on the main sequence. The degree of angular momentum loss is a strong function of mass, with low mass stars (M<1.3M⊙) experiencing the most angular momentum loss. This angular momentum loss prevents the use of low mass main sequence stars in studies of primordial stellar angular momentum. However, intermediate mass stars (1.3M⊙<~6M⊙) have apparently lost little angular momentum and can be used to probe the initial distribution of angular momentum. While the angular momentum distribution is broad for a given spectral type, the mean angular momentum is a well determined function of the stellar mass. This relationship, derived for intermediate mass main sequence stars, is consistent with the measured rotation velocities of pre-main sequence stars of lower mass as well.