UvbyCaHβ CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71

Abstract

CCD photometry on the intermediate-band uvbyCaHβ system is presented for the anticenter, intermediate-age open cluster Melotte 71. Restricting the data to probable single members of the cluster using the color-magnitude diagram and the photometric indices alone generates a sample of 48 F dwarfs on the unevolved main sequence. The average E(b - y) = 0.148 ± 0.003 (standard error of the mean [s.e.m.]) or E(B - V) = 0.202 ± 0.004 (s.e.m.), where the errors refer to internal errors alone. With this reddening, [Fe/H] is derived from both m1 and hk, using Hβ and b - y as the temperature index, with excellent agreement among the four approaches and a final weighted average of [Fe/H] = -0.17 ± 0.02 (s.e.m.) for the cluster, on a scale in which the Hyades has [Fe/H] = +0.12. When adjusted for the higher reddening estimate, the previous metallicity estimates from Washington photometry and from spectroscopy are now in agreement with the intermediate-band result. From comparisons to isochrones of appropriate metallicity, the cluster age and distance are determined as 0.9 ± 0.1 Gyr and (m - M) = 12.2 ± 0.1 or (m - M)0 = 11.6 ± 0.1. At this distance from the Sun, Mel 71 has a galactocentric distance of 10.0 kpc on a scale in which the Sun is 8.5 kpc from the Galactic center. Based on its age, distance, and elemental abundances, Mel 71 appears to be a less populous analog to NGC 3960.