Discovery of three optical open clusters in the Galaxy

Abstract

We report the discovery of three optical open clusters in the Milky Way. Two clusters are in Scutum (Cluster 1 at = 18.44° and b = −0.42°, and Cluster 2 at l= 19.60° and b = −1.02°), thus projected not far from the Galactic center direction, and the other is in Canis Major (Cluster 3 at l= 235.61° and b = −4.10°), near the anti-center direction. Cluster 3 is less populous than Clusters 1 and 2, but presents evidence of being a physical system. The objects were found optically by inspecting maps obtained from the Guide Star Catalogue and images from the Digitized Sky Survey. No previous identification of a cluster has been reported in any of these areas so far. The analysis was carried out with 2MASS photometry in J and H. For Cluster 1 we derive an age of t = 25 ± 5 Myr, a reddening E(B − V) = 2.18 ± 0.03 and a distance from the Sun dʘ = 1.64 ± 0.19 kpc; for Cluster 2, t = 500 ± 100 Myr, E(B − V) = 0.91 ± 0.03 and dʘ = 2.19 ± 0.21 kpc; finally for Cluster 3, t = 32−100 Myr, E(B − V) = 0.94 ± 0.03 and dʘ = 3.93 ± 0.35 kpc. Luminosity and mass functions are derived for Clusters 1 and 2 which, in turn, allow us to estimate their observed masses as 147 Mʘ and 89 M , respectively. Estimated total masses, by extrapolating the mass functions to 0.08 Mʘ , amount to 382 Mʘ and 614 Mʘ for the two clusters. Cluster 3 has an observed mass of ∼55 Mʘ. The present results indicate that further searches in the optical might still reveal new open clusters, especially in the infrared bands.