Spatial structure of the globular cluster system and the distance to the galactic center

Harris, W.E. 1976, A. J. 81, 1095.

Distance moduli for 111 globular clusters are presented which were obtained from color-magnitude diagrams or on the basis of horizontal-branch magnitudes, 25 brightest cluster stars, photographic measurements of RR Lyrae variables, cluster luminosities, or the degree of visual resolution of cluster stars. The space coordinates of the clusters are calculated, and the distance information is applied to determine the true centroid of the cluster system as well as the distance to the galactic center. A value of 8.5 kpc is adopted for the latter, uncertainties in this determination are evaluated, and the total number of globular clusters in the Galaxy is estimated to be about 170. The space distribution of metallicity groups among the clusters is investigated along with the ellipticity of the cluster system, the three-dimensional density distribution in the system, and the relation between this distribution and metallicity. The relation of the outermost halo objects to the normal cluster system is briefly discussed, and a rough estimate of the total halo mass is obtained by assuming that the mass distribution of Population II halo stars is similar to the space distribution of the globular clusters.