1. R. F. Webbink, in IAU Symposium 113: Dynamics of Star Clusters, Ed. by J. Goodman and P. Hut (Reidel, Dordrecht, 1985), p. 541.
2. W. E. Harris, Astron. J. 112, 1487 (1996).
3. A. Sandage and R. Wildey, Astrophys. J. 150, 469 (1967).
4. R. Buonanno, F. Fuse Pecci, E. Cappellaro, et al., Astron. J. 102, 1005 (1991).
5. Y.-W. Lee, P. Demarque, and R. Zinn, in Calibration of Stellar Ages, Ed. by A. G. D. Philip (Davis, Schenectady, 1988), p. 149.