The CFHT Open Star Cluster Survey. II. Deep CCD Photometry of the Old Open Star Cluster NGC 6819

We present analysis of deep CCD photometry for the very rich, old open starcluster NGC 6819. These CFH12K data results represent the first of nineteenopen star clusters which were imaged as a part of the CFHT Open Star ClusterSurvey. We find a tight, very rich, main-sequence and turn-off consisting ofover 2900 cluster stars in the V, B-V color-magnitude diagram (CMD).Main-sequence fitting of the un-evolved cluster stars with the Hyades starcluster yields a distance modulus of (m-M)v = 12.30 +/- 0.12, for a reddeningof E(B-V) = 0.10. These values are consistent with a newly calculatedtheoretical stellar isochrone of age 2.5 Gyrs, which we take to be the age ofthe cluster. Detailed star counts indicate a much larger cluster extent (R =9.5' +/- 1.0'), by a factor of ~2 over some previous estimates. Incompletenesstests confirm a slightly negatively sloped luminosity function extending tofaint (V ~ 23) magnitudes which is indicative of a dynamically evolved cluster.Further luminosity function and mass segregation tests indicate that low massobjects (M < 0.65Mo) predominate in the outer regions of the cluster, 3.5 < R <9.5. The estimation of the number of white dwarfs in NGC 6819 are in goodagreement with the observed number. For those white dwarf candidates which passboth a statistical and image classification tests, we show comparisons to whitedwarf isochrones and cooling models which suggest the need for spectroscopy toconfirm the white dwarf nature of the brighter objects.Comment: 15 Figures and 6 Tables available in higher resolution from ADS. Accepted for Publication in AJ -- Kalirai et al. 2001b, 122, 266. Update