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As part of our study of the old (~2.5 Gyr) open cluster NGC 6819 in theKepler field, we present photometric (Kepler and ground-based BVRcIc) andspectroscopic observations of the detached eclipsing binary WOCS 24009 (Auner665; KIC 5023948) with a short orbital period of 3.6 days. WOCS 24009 is atriple-lined system, and we verify that the brightest star is physicallyorbiting the eclipsing binary using radial velocities and eclipse timingvariations. The eclipsing binary components have masses M_B =1.090+/-0.010 Msunand M_C =1.075+/-0.013 Msun, and radii R_B =1.095+/-0.007 Rsun and R_C=1.057+/-0.008 Rsun. The bright non-eclipsing star resides at the clusterturnoff, and ultimately its mass will directly constrain the turnoff mass: ourpreliminary determination is M_A =1.251+/-0.057 Msun. A careful examination ofthe light curves indicates that the fainter star in the eclipsing binaryundergoes a very brief period of total eclipse, which enables us to preciselydecompose the light of the three stars and place them in the color-magnitudediagram.  We also present improved analysis of two previously discussed detachedeclipsing stars in NGC 6819 (WOCS 40007 and WOCS 23009) en route to a combineddetermination of the cluster's distance modulus (m-M)_V=12.38+/-0.04. Becausethis paper significantly increases the number of measured stars in the cluster,we can better constrain the age of the color-magnitude diagram to be2.21+/-0.10+/-0.20 Gyr. Additionally, using all measured eclipsing binary starmasses and radii, we constrain the age to 2.38+/-0.05+/-0.22 Gyr. The quoteduncertainties are estimates of measurement and systematic uncertainties (due tomodel physics differences and metal content), respectively.

Determining the Age of the Kepler Open Cluster NGC 6819 With a New Triple System and Other Eclipsing Binary Stars