A TECHNIQUE FOR SIMULTANEOUS DETERMINATION OF THE METALLICITY AND REDDENING OF OLD OPEN CLUSTERS USING (V,B-V) COLOR-MAGNITUDE DIAGRAMS

A technique similar to that originally developed by Sarajedini [AJ, 10 7, 618 (1994)] for the simultaneous determination of [Fe/H] and E(B - V) in globular clusters, is applied to seven old open clusters in our Galaxy (NGC 6791, Be 32, Mel 66, M67, NGC 2420, To 2, and IC 4651). Wi th these clusters we prove that there exist linear relationships betwe en [Fe/H] and Delta V-1.2 and [Fe/H] and (B - V)(0.g). From these rela tions we derive a general technique for the determination of metallici ty and color excess. The success obtained with its application support s it as a general-use technique. This procedure is also applied to the clusters Be 39, King 11 and NGC 1193. The results obtained for the me tallicity and color excess values, are in excellent agreement with tho se published in the literature. Clusters Be 29 and Be 22, for which ve ry uncertain values for metallicity and color excess are published, ar e used with our technique. We determine values for [Fe/H] = -0.30, -0. 42 and E(B - V) = 0.01, 0.70, respectively. It seems that there is a t ransition region between, globular and old open clusters around [Fe/H] similar to-0.4. (C) 1997 American Astronomical Society.