Pre-Mainsequence Stellar Evolution in N-Body Models

We provide a set of analytic fits to the radii of pre-mainsequence stars in the mass range 0.1 < M/M-circle dot < 8.0. We incorporate the formulae in N-body cluster models for evolution from the beginning of pre-mainsequence. In models with 1 000 stars and high initial cluster densities, pre-mainsequence evolution causes roughly twice the number of collisions between stars than in similar models with evolution begun only from the zero-age main sequence. The collisions are often all part of a runaway sequence that creates one relatively massive star.