BVI CCD PHOTOMETRY OF THE BROAD MAIN-SEQUENCE GLOBULAR-CLUSTER NGC-1851

Three-color CCD color-magnitude diagrams have been obtained for NGC 1851 as a part of our continuing program of globular cluster photometry. The most remarkable aspect of these diagrams is the extreme breadth of the main sequence, reminiscent of that of ω Centauri. We find that the mainsequence turnoff points are located at VTO = 19.44 ± 0.10, with colors at B - V = 0.54 ± 0.02, V - I = 0.61 ± 0.02, and B - I = 1.15 ± 0.03. The best fit to the isochrones of VandenBerg and Bell (1985) is produced for all color-magnitude diagrams with Y = 0.20, [Fe/H] = -1.27, and (m - M)v = 15.45. We derive ΔVTO-HB = 3.34 ± 0.10 and an age of 16 ± 2 Gyr.