CCD Photometry of the Galactic Globular Cluster NGC 6535 in the B and V Passbands

The first CCD color-magnitude diagram (CMD) in B and V is presented for the Galactic globular cluster NGC 6535. From this CMD, which extends below the main sequence turnoff, we draw the following conclusions: (1) The horizontal branch (HB) is predominantly blue in nature with no RR Lyrae variables known to be cluster members. Nonetheless, based on a comparison with clusters which have blue HBs and RR Lyraes (M15 and M79), we infer a mean HB magnitude of < V_RR >= 15.73 +/- 0.11 for NGC 6535. (2) Again, via a direct comparison with the blue HBs of M15 and M79, we derive a cluster reddening of E(B-V)=0.44 +/- 0.02. (3) When combined with the apparent color of the red giant branch at the level of the HB, (B-V)_g = 1.18 +/- 0.02, the derived reddening yields a metal abundance of [Fe/H] = -1.85 +/- 0.10, similar to that of NGC 6397. (4) Application of the delta-V_TO-HB and delta(B-V)_SGB-TO cluster dating techniques reveals no perceptible age difference between NGC 6535 and NGC 6397. (5) A significant population of 9 blue straggler candidates is detected in NGC 6535. However, this is too few to facilitate a meaningful analysis of their radial distribution. (SECTION: Stellar Clusters and Associations)