The form of the galactic globular cluster system and the distance to the Galactic Centre

Abstract

By choosing samples limited in galactic latitude which can be assumed to be complete, considering the distance-independent information contained in the positions of clusters separately, and taking into account the information contained in their apparent three-dimensional distribution, new quantitative methods for analyzing the structure of the galactic globular cluster system are developed. It is found that the cluster system is slightly flattened, and there is no evidence for any variation in flattening as a function of metallicity. A Hubble law describes its density as lying in the 0.2-5 solar radii range. A systematic difference in distance scale of about 0.5 magnitudes is needed to reconcile the centroid of this distribution with that of the metal-poor clusters, with the shift being of the same kind and size as that predicted by theoretical pulsation models of RR Lyrae stars. The effects of an estimated Galactic Center distance of 6.8 plus or - 0.8 kpc on an earlier dynamical analysis of the cluster system are considered, and judged to be small.