AL 3 (BH 261): A New Globular Cluster in the Galaxy

Abstract

AL 3 (BH 261), previously classified as a faint open cluster candidate, is shown to be a new globular cluster in the Milky Way, by means of B, V, and I color-magnitude diagrams. The main feature of AL 3 is a prominent blue extended horizontal branch. Its color-magnitude diagrams match those of the intermediate-metallicity cluster M5. The cluster is projected in a rich bulge field, also contaminated by the disk main sequence. The globular cluster is located in the Galactic bulge at a distance from the Sun dsolar=6.0+/-0.5 kpc. The reddening is E(B-V)=0.36+/-0.03, and the metallicity is estimated to be [Fe/H]~-1.3+/-0.25. AL 3 is probably one of the least massive globular clusters of the Galaxy. The observations were carried out at the European Southern Observatory, La Silla, Chile [proposal 64L-0212(A)].