A constraint on the angular momentum evolution of Be stars

The Be star sample of Steele et al. (1998) has a distribution of v sin i's that is luminosity dependant, with giants having lower projected rotational velocities than dwarfs. We show that this effect can be understood simply in terms of angular momentum conservation during the evolution from dwarf to giant. Any decretion disk or other angular momentum losing mechanism for such objects must cause a loss of no more than 15 per-cent of the stellar angular momentum over the Be phase lifetime.