On the spin-down of Be stars

Abstract

The spin-down of Be stars due to angular momentum transport from star to disc has been considered. This has been prompted by empirical studies of observed optical and IR line profile studies indicating that the disc is rotating in a Keplerian fashion. It is found that substantial spin-down may occur, especially for late B stars throughout their main-sequence lives for the ``strongest'' discs (most dense $\sim 10^{-11}$g cm$^{-3}$ with high radial velocity $\sim 1\kms$ at their inner edge and with large opening angle $\sim 15^\circ$). This is in conflict with studies of rotational velocity distributions for different luminosity classes, which show no significant evolution. The implications of this for Be star discs are considered.