The horizontal branches of globular clusters .1. The color-magnitude diagram of NGC 6426

A color-magnitude diagram of the globular cluster NGC 6426 has been constructed from photometry in the V and I passbands. The cluster has the steep giant branch indicative of a very metal-poor composition. Following the technique of Sarajedini [AJ, 107, 618 (1994)], we derive [Fe/H]=-2.31+/-0.10 and E(V-I)=0.54+/-0.03 [E(B-V)=0.40+/-0.02] from a comparison with the giant branches of other globular clusters. These values are very close to the ones obtained from photometry of the cluster's integrated light, and the weighted means of our results and the previous ones are [Fe/H]=-2.281+/-0.09 and E(B-V)=0.41+/-0.02. The mean V magnitude of the horizontal branch (HE) at the instability strip is 18.12+/-0.05, from which we estimate that NGC 6426 lies 17.4 kpc from the Sun, 11.5 kpc from the galactic center, and 4.9 kpc from the galactic plane. NGC 6426 resembles NGC 5466 and M68 in both [Fe/H] and HB morphology. The HB of NGC 6426 overlaps the one in M15 from the red HB to M15's gap in the blue HB, but there is no evidence of significant numbers of faint blue HB stars in NGC 6426 that are analogous to the ones constituting the ''extended HB'' in M15. (C) 1996 American Astronomical Society.