On the rotational velocities of Be and Be-shell stars

Abstract

The identification of Be-shell stars as edge-on ‘normal’ Be stars is tested, whilst a new method for calculating the distribution of equatorial rotational velocities as a fraction of the break-up velocity is developed. This may be measured directly from complete samples of Be-shell stars. The derived distribution is highly consistent with the observed rotational distribution for a complete sample of all Be stars — indeed, the two cannot be statistically differentiated. This method supersedes any previous method in that it does not require any iteration process or ad hoc estimation of the intrinsic rotational velocities of Be stars. It is found that the distribution of rotational velocity as a function of (critical) break-up velocity is sharply peaked at ∼ 0.7vcrit, in accordance with previous studies. Future observational work should further constrain the function.