We analyze extensive BVR _ { c } I _ { c } time-series photometry and radial-velocity measurements for WOCS 40007 ( Auner 259 ; KIC 5113053 ) , a double-lined detached eclipsing binary and a member of the open cluster NGC 6819 .
Utilizing photometric observations from the 1-meter telescope at Mount Laguna Observatory and spectra from the WIYN 3.5-meter telescope , we measure precise and accurate masses ( \sim 1.6 % uncertainty ) and radii ( \sim 0.5 % ) for the binary components .
In addition , we discover a third star orbiting the binary with a period greater than 3000 days using radial velocities and Kepler eclipse timings .

Because the stars in the eclipsing binary are near the cluster turnoff , they are evolving rapidly in size and are sensitive to age .
With a metallicity of [ Fe/H ] = +0.09 \pm 0.03 , we find the age of NGC 6819 to be about 2.4 Gyr from CMD isochrone fitting and 3.1 \pm 0.4 Gyr by analyzing the mass-radius ( M - R ) data for this binary .
The M - R age is above previous determinations for this cluster , but consistent within 1 \sigma uncertainties .
When the M - R data for the primary star of the additional cluster binary WOCS 23009 is included , the weighted age estimate drops to 2.5 \pm 0.2 Gyr , with a systematic uncertainty of at least 0.2 Gyr .
The age difference between our CMD and M - R findings may be the result of systematic error in the metallicity or helium abundance used in models , or due to slight radius inflation of one or both stars in the WOCS 40007 binary .