ROTATING GLOBULAR-CLUSTERS .1. ONSET OF THE GRAVOTHERMAL INSTABILITY

Rotation in globular clusters can a priori influence their dynamical e volution prior to core collapse in two different ways. First, the rate of evaporation of stars is increased; second, the limit of stability of the cluster with respect to the gravothermal catastrophe can be dis placed. We have investigated these two processes with the help of a si mple cluster model, which generalizes the King distribution function t o rotating clusters. We find that the critical concentration for the o nset of the gravothermal instability is not much modified by the clust er rotation, as it is reduced by at most 15%. The effect of rotation o n the total mass loss in the evaporation phase is much more noticeable , and amounts to a factor of similar to 1.5 to 2 for cluster models in which the rotational energy initially represents 15% to 20% of the to tal kinetic energy. Surprisingly, this increased mass loss is not acco mpanied by an increase of the evolution rate of the cluster concentrat ion, which is found to be more or less insensitive to the cluster rota tion.