WIYN open cluster study LII: Wide-field ccd photometry of the old open cluster NGC 6819

Abstract

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 (rc = 2.′80, rt = 38.′2, and rh = 7′) and tidal mass of the cluster (Mtid = 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. © 2013. The American Astronomical Society. All rights reserved.