ROTATING GLOBULAR-CLUSTERS .2. RELAXATION AND EVAPORATION

This paper focuses on the influence of rotation on two-body relaxation in globular clusters during the evaporation phase. We derive the Fokk er-Planck equation for rotating clusters, in the approximation that th e radial anisotropy of the velocity distribution can be neglected; a s imple generalization of the King distribution function to rotating clu sters is shown to be an approximate solution to this equation. Evapora tion rates are computed by applying the Fokker-Planck collision term t o this distribution function. The cluster rotation can increase the ma ss loss rate by up to a factor of 3 to 4 for the most rapidly rotating clusters, although the half-mass relaxation time is lengthened (the t otal mass loss is smaller due to the decrease of rotational energy in the evolution). Stellar evaporation always produces a decrease of the cluster flattening for the class of cluster model studied here; this p rovides some support to the idea that the apparent decrease in cluster flattening with age is due to internal relaxation effects. We also sh ow that the evolution of the concentration is not directly driven by t he mass loss as soon as the rotational energy exceeds a few percents o f the total kinetic energy, in opposition to the behavior along the Ki ng sequence for nonrotating cluster. For clusters which rotate suffici ently fast, the concentration can remain constant or even slightly dec rease until enough angular momentum and rotational energy is lost.