EDP Sciences
Free access
Volume 422, Number 2, August I 2004
Page(s) 555 - 562
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20047073

A&A 422, 555-562 (2004)
DOI: 10.1051/0004-6361:20047073

Discovery of three optical open clusters in the Galaxy

E. Bica1, C. Bonatto1 and C. M. Dutra2

1  Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil
    e-mail: charles@if.ufrgs.br
2  Universidade Estadual do Rio Grande do Sul, Unidade São Borja, Rua Bompland 512, São Borja 97670-000, RS, Brazil

(Received 14 January 2004 / Accepted 31 March 2004 )

We report the discovery of three optical open clusters in the Milky Way. Two clusters are in Scutum (Cluster 1 at $\ell=18.44^{\circ}$ and $b=-0.42^\circ$, and Cluster 2 at $\ell=19.60^{\circ}$ and $b=-1.02^\circ$), thus projected not far from the Galactic center direction, and the other is in Canis Major (Cluster 3 at $\ell=235.61^{\circ}$ and $b=-4.10^\circ$), 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  $\pm$ 5 Myr, a reddening $\mbox{$E(B-V)$ }=2.18$  $\pm$ 0.03 and a distance from the Sun $\mbox{$d_\odot$ }=1.64$  $\pm$ 0.19 kpc; for Cluster 2, t=500  $\pm$ 100 Myr, $\mbox{$E(B-V)$ }=0.91$  $\pm$ 0.03 and $\mbox{$d_\odot$ }=2.19$  $\pm$ 0.21 kpc; finally for Cluster 3, t=32-100 Myr, $\mbox{$E(B-V)$ }=0.94$  $\pm$ 0.03 and $\mbox{$d_\odot$ }=3.93$  $\pm$ 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 $147~\mbox{$M_\odot$ }$ and $89~\mbox{$M_\odot$ }$, respectively. Estimated total masses, by extrapolating the mass functions to $0.08~\mbox{$M_\odot$ }$, amount to  $382~\mbox{$M_\odot$ }$ and $614~\mbox{$M_\odot$ }$ for the two clusters. Cluster 3 has an observed mass of ~ $55~\mbox{$M_\odot$ }$. The present results indicate that further searches in the optical might still reveal new open clusters, especially in the infrared bands.

Key words: Galaxy: open clusters and associations: general -- Galaxy: structure

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© ESO 2004