metallicity estimates and RVs, are described in §4.

Likely Member Star Selection for Open Clusters
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Since the fields of nearby open clusters are not as crowded as those of globular clusters, the signal-to-noise ratio between the cluster region and the background region is not sufficiently high to select likely cluster members by means of the CMD mask algorithm. As an alternative, we first obtain a fiducial line for an open cluster (including its main sequence and sub-giant branch, if it exists) by use of an robust polynomial fitting procedure. As an example, Figure 4 shows the CMD of the NGC 2420 field inside a radius of 0.3 degrees from the center of the cluster. According to the open cluster catalog of Dias et al. (2002), the apparent diameter of this cluster is only 5$^{'}$ on the sky, but we prefer to adopt a 20$^{'}$ radius, in order to include as many member stars as possible. The red line is the fiducial line derived from the robust polynomial fit. The blue lines are the upper and lower limits (fiducial $\pm$ 0.06 dex in $(g-r)_{0}$), determined by eye. Stars from the spectroscopic sample that fall within the 20$^{'}$ radius and inside 