Photometric study of the open cluster – II. Stellar population and dynamical evolution in NGC 559

Abstract

We present UBVRI photometry of stars in the field of the intermediate-age open cluster NGC 559. By determining the stellar membership probabilities derived through a photometric and kinematic study of the cluster, we identify the 22 most probable cluster members. These are used to obtain robust cluster parameters. The mean proper motion of the cluster is μx = −3.29 ± 0.35, μy = −1.24 ± 0.28 mas yr⁻¹. The radial distribution of the stellar surface density gives a cluster radius of 4.5 ± 0.2 arcmin (3.2 ± 0.2 pc). By fitting solar metallicity stellar isochrones to the colour–colour and colour–magnitude diagrams, we find a uniform cluster reddening of E(B − V) = 0.82 ± 0.02. The cluster has an age of 224 ± 25 Myr and is at a distance of 2.43 ± 0.23 kpc. From the optical and near-infrared two-colour diagrams, we obtain colour excesses in the direction of the cluster E(V − K) = 2.14 ± 0.02, E(J − K) = 0.37 ± 0.01 and E(B − V) = 0.76 ± 0.04. A total-to-selective extinction of RV = 3.5 ± 0.1 is found in the direction of the cluster which is marginally higher than the normal value. We derive the luminosity function and the mass function for the cluster main sequence. The mass function slope is found to be −2.12 ± 0.31. We find evidence of mass segregation in this dynamically relaxed cluster.