NGC 6535 BV CCD photometry

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.