As part of our study of the old ( \sim 2.5 Gyr ) open cluster NGC 6819 in the Kepler field , we present photometric ( Kepler and ground-based BVR _ { C } I _ { C } ) and spectroscopic observations of the detached eclipsing binary WOCS 24009 ( Auner 665 ; KIC 5023948 ) with a short orbital period of 3.6 days .
WOCS 24009 is a triple-lined system , and we verify that the brightest star is physically orbiting the eclipsing binary using radial velocities and eclipse timing variations .
The eclipsing binary components have masses M _ { B } = 1.090 \pm 0.010 M _ { \sun } and M _ { C } = 1.075 \pm 0.013 M _ { \sun } , and radii R _ { B } = 1.095 \pm 0.007 R _ { \sun } and R _ { C } = 1.057 \pm 0.008 R _ { \sun } .
The bright non-eclipsing star resides at the cluster turnoff , and ultimately its mass will directly constrain the turnoff mass : our preliminary determination is M _ { A } = 1.251 \pm 0.057 M _ { \sun } .
A careful examination of the light curves indicates that the fainter star in the eclipsing binary undergoes a very brief period of total eclipse , which enables us to precisely decompose the light of the three stars and place them in the color-magnitude diagram .

We also present improved analysis of two previously discussed detached eclipsing stars in NGC 6819 ( WOCS 40007 and WOCS 23009 ) en route to a combined determination of the cluster ’ s distance modulus ( m - M ) _ { V } = 12.38 \pm 0.04 .
Because this paper significantly increases the number of measured stars in the cluster , we can better constrain the age of the color-magnitude diagram to be 2.21 \pm 0.10 \pm 0.20 Gyr .
Additionally , using all measured eclipsing binary star masses and radii , we constrain the age to 2.38 \pm 0.05 \pm 0.22 Gyr .
The quoted uncertainties are estimates of measurement and systematic uncertainties ( due to model physics differences and metal content ) , respectively .