COMPOSITION AND EVOLUTION PATTERNS IN THE OLD OPEN CLUSTER MELOTTE-66- PHOTOELECTRIC (U)BV(RI) PHOTOMETRY OF 71 STARS

New photoelectric (U)BV(RI) data for 71 red giants and turnoff stars i n the old open cluster Melotte 66 are presented and discussed. The pho tometry confirms the broad color range exhibited by giants at and abov e the level of the clump. UBV analysis of turnoff stars yields [Fe/H]= -0.53+/-0.08 assuming a cluster E(B-V)=0.16+/-0.02. A nearly identical [Fe/H] is implied by the giants' ultraviolet excesses, but with a sig nificantly higher dispersion. Previously published CCD vby data have b een transformed to the BV system to permit an analysis of the cluster color-magnitude diagram with reference to isochrones which incorporate convective core overshoot. Main-sequence fits imply an age of 4.5+/-0 .5 Gyr and an apparent modulus (m-M)=13.75. Further support for these reddening and distance values is provided by comparison of the red-gia nt clump to other old open clusters and of the M(I),(V-I) data to a sa mple of globular and old open clusters. The giant branch of Mel 66 is shown to extend to an extreme in both luminosity and color currently m atched only by old open clusters NGC 6791 and Cr 261.