WIYN Open Cluster Study. XIX. Main-Sequence-Fitting Distances to Open Clusters UsingV-KColor-Magnitude Diagrams

We have combined existing optical magnitudes for stars in seven open clustersand 54 field stars with the corresponding JHKs photometry from the Two MicronAll Sky Survey (2MASS). Combining optical with near-IR photometry broadens thecolor baseline minimizing the influence of photometric errors and allows betterdiscrimination between cluster stars and contaminating foreground andbackground populations. The open clusters in this study include NGC 2516, M35,M34, NGC 3532, M37, M67, and NGC 188. The field stars we are using possess highquality Hipparcos parallaxes and well-determined metal abundances allowing usto empirically determine the dependence of (V-K) color on metal abundance inthe range -0.45<=[Fe/H]<=+0.35. Using this relation along with the parallaxesof the field stars, we are able to construct an unevolved main sequence in the[Mv,(V-K)o] diagram for a specific abundance. These diagrams are then used tofit to the cluster main sequences in the [V,V-K] color-magnitude diagram inorder to estimate a distance for each open cluster. We find that the resultantdistances are within the range of distances found in the literature via themain sequence fitting technique. It is hoped that this will spur an expansionof the current (limited) database of star clusters with high quality (V-K)photometry down to the unevolved main sequence.Comment: 17 pages, 7 figures, to appear in The Astronomical Journal - February 200