WIYN Open Cluster Study : 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 1x1 degree field VI MOSAIC CCD imaging taken with the WIYN 0.9m
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 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(sun)). 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.
