Color-magnitude diagrams for three distant globular clusters
Color-magnitude diagrams are presented for three distant galactic globular clusters (NGC 5466, NGC 6229, and NGC 7006). In each case the photometry reaches below the main-sequence turnoff; the ages deduced by comparison with stellar evolutionary isochrones are indistinguishable from those of the well-studied nearby clusters. The luminosity functions derived from computer-generated star counts complete to a well-defined limiting magnitude in selected fields support identical ages for the three clusters with maximum differences between NGC 5466 and NGC 6229 of 10% of the age, and between NGC 5466 and NGC 7006 of 25%. The previously published claims of an exceptionally bright turnoff for NGC 7006 are shown to be spurious. The horizontal branch of NGC 6629 is unusually red for its metallicity. Star counts and tidal radii are discussed for NGC 6229 and NGC 7006.
Additional Information© American Astronomical Society • Provided by the NASA Astrophysics Data System. Received 17January 1985; revised 5 August 1985. This research was supported by NSF Grant No. AST 82-12270. I am grateful to Alain Porter for a useful software routine, and especially to Keith Shortridge, who wrote the basic image-processing software package in use at Caltech. To Jim Gunn and the entire crew who built the 4-Shooter— bravissimo. I also thank the referee for critical and thoughtful comments on the original version of this manuscript that forced me not to be lazy.
Published - 1985AJ_____90_2254C.pdf