Membership Probability via Control Field Colour-Magnitude Decontamination

The open clusters fundamental physical parameters are important tools to understand the formation and evolution of the Galactic disk and as grounding tests for star formation and evolution models. However only a small fraction of the known open clusters in the Milky Way has precise determination of distance, reddening, age, metallicity, radial velocity and proper motion. One of the major problems in determining these parameters lies on the difficulty to separate cluster members from field stars and to assign membership. We propose a decontamination method by employing 2MASS data in the encircling region of the clusters NGC1981, NGC2516, NGC6494 and M11. We present a decontaminated CMD of these objects showing the membership probabilities and structural parameters as derived from King profile fitting.