Publications of the Astronomical Society of the Pacific
106: 404-412, 1994 April

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

                                ATA SARAJEDINI
   Kitt Peak National Observatory, National Optical Astronomy Observatories,
                  P.O. Box 26732, Tucson, Arizona 85726-6732
                         Electronic mail: ata@noao.edu


    ABSTRACT.  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 nine blue-straggler candidates is detected in
    NGC 6535.  However, this is too few to facilitate a meaningful analysis
    of their radial distribution.