The color-magnitude diagram of the metal-rich globular cluster NGC 6712

Abstract

The color-magnitude diagram is presented for NGC 6712 as obtained from two-color photographic photometry of 304 stars calibrated with a 25-star photoelectric sequence. The diagram differs from that of halo clusters in that (1) the giant branch at (B - V)0 = +1.4 rises only 2.2 mag. above the horizontal branch instead of the usual 3.0 mag.; (2) the horizontal branch is heavily populated on the red side of the variable-star gap; and (3) the giant and subgiant sequences are displaced redward in intrinsic color from the corresponding sequences in clusters having lower metal abundance. Point 3 is shown to be a general characteristic in clusters studied to date and is correlated with metal abundance. The reddening of the cluster is estimated to be E(B - V) = 0.48 + 0.01. The apparent visual distance modulus is (m - M) p,v = 15.6 if Mv = +0.5 for the RR Lyrae stars. The true modulus is (m - M)0 = 14.2 if the visual absorption is A = 3 E(B - V). The distance of NGC 6712 is 6750 pc from the Sun, 470 pc from the galactic plane, and 4900 pc from the galactic center, if R0 = 10 kpc.