The ionising cluster of 30 Doradus - IV. Stellar kinematics

On the basis of multislit spectroscopy of 180 stars in the ionising cluster of 30 Doradus we present reliable radial velocities for 55 stars. We calcu late a radial velocity dispersion of similar to 35 km s(-1) for the cluster and we analyse the possible influence of spectroscopic binaries in this ra ther large velocity dispersion. We use numerical simulations to show that t he observations are consistent with the hypothesis that all the stars in th e cluster are binaries, and the total mass of the cluster is similar to5 x 10(5) M-circle dot. A simple test shows only marginal evidence for dynamica l mass segregation which if present is most likely not due to dynamical rel axation.