A Two-Dimensional Classification for Galactic Globular Clusters

It is shown that all of the galactic globular clusters with available C-M diagrams fit into a two- dimensional classification with helium and heavy-element abundance as the two parameters. The classi- fication, which is based on the cluster's position in the S,(B - V)og, plane, results in systematic changes in the character of the horizontal branch from group to group Satisfactory agreement in interpretation is found from the limited theoretical models available