AL 3 (BH261) : 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 dʘ = 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.