A VIC COLOR-MAGNITUDE DIAGRAM OF THE GLOBULAR-CLUSTER NGC-6352 FROM HUBBLE-SPACE-TELESCOPE PLANETARY CAMERA OBSERVATIONS

The globular cluster NGC 6352, which on the basis of its Galactic posi tion, radial velocity, and [Fe/H] is a member of the (thick) disk syst em of globular clusters, has been observed to below the main-sequence turnoff (MSTO) using the Hubble Space Telescope. These observations, w hich were obtained before the repair mission, were analyzed using the flux-conserving iterative/recursive deconvolution algorithm developed at the University of North Carolina. This algorithm can produce more p recise photometry than standard PSF-fitting methods with the aberrated images. The V, (V-I-C) color-magnitude diagram constructed from these observations places the cluster turnoff at V=18.80+/-0.10. Observatio ns with the CTIO 0.9 m telescope have been used to photometer the brig hter stars in the cluster, providing a calibration of the HST data and an estimate of the cluster's reddening, E(B - V)=0.21+/-0.03. From. s pectroscopic observations of the strengths of the Ca n triplet lines i n red giants in the cluster and from previous measurements in the lite rature, we find that NGC 6352 is only slightly more metal rich (Delta[ Fe/H]=0.08+/-0.05) than the prototypical disk globular cluster, 47 Tuc . From the difference in V magnitude between the horizontal branch and the MSTO, we find that NGC 6352 is essentially the same age as 47 Tuc (formally, older by 0.7+/-2.2 Gyr). Comparisons with the latest Yale isochrones support this result and yield 14.5+/-2 Gyr for the age of 4 7 Tuc from the photometry of Hesser et al. [PASP, 99, 739 (1987)], whi ch is consistent with other determinations. The old age obtained for N GC 6352 provides additional evidence that the disk system of globular clusters is very old and is in fact older or comparable in age to seve ral globular clusters populating the Galactic halo. (C) 1995 American Astronomical Society.