We present an extensive set of photometry and radial velocities for the detached eclipsing binary KV 29 in the intermediate-aged open cluster M11 ( NGC 6705 ) .
Spectroscopy shows that the system is double-lined and all available evidence ( proper motion , photometry , and position on the CMD ) indicates it is a member of the cluster .
We find the period of the binary to be 4.64276 \pm 0.00001 days .
We find masses 3.604 ^ { +0.002 } _ { -0.011 } M _ { \sun } and 1.837 ^ { +0.001 } _ { -0.006 } M _ { \sun } , and radii 5.392 ^ { +0.018 } _ { -0.035 } R _ { \sun } and 1.656 ^ { +0.007 } _ { -0.044 } R _ { \sun } for the primary and secondary stars , respectively .
Because the primary star in the binary is rapidly evolving and is brighter than the cluster turnoff in a color-magnitude diagram , the measurement of its radius leads to a strong constraint on the cluster age .
We find the age of M11 to be 222 ^ { +2 } _ { -3 } \pm 15 Myr , where the quoted uncertainties come from statistical errors in the calculated masses and radii , and systematic uncertainties due to the ambiguity of the metallicity of the open cluster and variations within the isochrone models concerning heavy elements and convective overshooting .