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 � = 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 � = 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 d� = 1.64 ± 0.19 kpc; for Cluster 2, t = 500 ± 100 Myr, E(B − V) = 0.91 ± 0.03 and d� = 2.19 ± 0.21 kpc; finally for Cluster 3, t = 32−100 Myr, E(B − V) = 0.94 ± 0.03 and d� = 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 Mand 89 M� , respectively. Estimated total masses, by extrapolating the mass functions to 0.08 M� , amount to 382 Mand 614 Mfor the two clusters. Cluster 3 has an observed mass of ∼55 M� . The present results indicate that further searches in the optical might still reveal new open clusters, especially in the infrared bands.