Photometric Metal Abundances for Twenty Clusters

Metal abundances, colour excesses and distance moduli have been determined for individual giant stars, using UBViyz photometry, in NGC 188, 559, 752, 1245, 1342, 1907, 1912, 2099, 5139 (ω Cen), 5316, 5617, 5822, 5823, 6067, IC 4651, 6819, 6940, 7142, 7261 and 7789. All six clusters with ages $$3-8 \times 10^{9}$$ yr have metal abundances agreeing with one another; their average value of [Fe/H] = –0·24±0·05, agrees with the average found for the bright K-giants near the Sun. All six clusters are at least 140 pc from the galactic plane. For the younger clusters less than ~ 10⁹ yr old, one-third are metal deficient. The very young cluster, NGC 559, is probably very metal weak.