WIYN Open Cluster Study LII: Wide-field CCD Photometry of the Old Open Cluster NGC 6819

We present a comprehensive photometric study of the old open cluster, NGC 6819, using 1° × 1° field VI MOSAIC CCD imaging taken with the WIYN 0.9 m telescope. The resultant color-magnitude diagram (CMD) shows a well-developed main sequence (MS) extending from V ~ 14.5 mag down to our photometric limit of V ~ 21 mag. Fitting theoretical isochrones with the adopted values of the reddening and metallicity (E(B - V) = 0.14, [Fe/H] = +0.09 dex) to the observed CMD yields a distance modulus of (m - M)₀ = 11.93 ± 0.10 and an age of ~2.6 Gyr for NGC 6819. Our wide-field imaging reveals that NGC 6819 is larger in areal extent (R = 13') than previously thought. The wide field also benefits our estimate of the degree of field star contamination, and ultimately yields improved measurements of the structural parameters (r_c = 2.'80, r_t = 38.'2, and r_h = 7') and tidal mass of the cluster (M _tid = 3542.4 M _⊙). The flattened luminosity and mass functions indicate that NGC 6819 has experienced mass segregation as a result of its dynamical evolution. Our variability study of the cluster blue straggler star (BSS) population using the Welch-Stetson variability index (I _WS) has revealed a number of variable BSS candidates.