NGC 6293 and NGC 6333 - Photometry of two clusters in the central bulge of the Galaxy

Abstract

A preliminary investigation is conducted of two metal-poor globular clusters, NGC 6293 and NGC 6333, which are projected against the central bulge of the Galaxy. The observations consist of CCD B and V images obtained on three nights when the seeing was between 0.6 and 0.8 arcsec. The clusters' color-magnitude diagrams, which reach just to the main-sequence turnoff, show a morphology that confirms their metal-poor nature; both clusters have well-defined giant branches and blue horizontal branches, similar to those of M92. A comparison of NGC 6293 and NGC 6333 with the latter yields probable reddening values of about 0.47 and 0.44 mag, and apparent distance moduli of about 16.0 and 15.8, respectively, placing the two clusters roughly 1-2 kpc from the Galactic Center. The giant branch of NGC 6293 is deficient in bright red giants, its tip being a full magnitude fainter than that of NGC 6333. This may be the consequence of the cluster having undergone core collapse. 18 refs.