DIAMETERS OF GALACTIC GLOBULAR-CLUSTERS

All published aperture photometry of Galactic globular clusters has been used to derive total magnitudes, V(t), and values of the diameter containing half the cluster light in projection, D0.5. For the 98 globulars for which this information is available, cluster diameter is found to correlate with Galactocentric distance. In this respect the Galactic globular cluster system resembles those associated with M31, NGC 5128, and the Large Magellanic Cloud, in which cluster diameters also increase with increasing Galactocentric distance. The observed correlation D0.5 proportional-to unroofed-radical R suggests that compact clusters formed preferentially from the dense gas clouds near the centers of galaxies, whereas more open clusters formed in the less dense halo regions of galaxies. Perhaps surprisingly, cluster diameter does not correlate with cluster luminosity (mass). Furthermore, cluster diameter does not appear to correlate with metallicity.