We report differential photometric observations and radial-velocity measurements of the detached , 1.69-day period , double-lined eclipsing binary AQ Ser .
Accurate masses and radii for the components are determined to better than 1.8 % and 1.1 % , respectively , and are M _ { 1 } = 1.417 \pm 0.021 M _ { \sun } , M _ { 2 } = 1.346 \pm 0.024 M _ { \sun } , R _ { 1 } = 2.451 \pm 0.027 R _ { \sun } , and R _ { 2 } = 2.281 \pm 0.014 R _ { \sun } .
The temperatures are 6340 \pm 100 K ( spectral type F6 ) and 6430 \pm 100 K ( F5 ) , respectively .
Both stars are considerably evolved , such that predictions from stellar evolution theory are particularly sensitive to the degree of extra mixing above the convective core ( overshoot ) .
The component masses are different enough to exclude a location in the H-R diagram past the point of central hydrogen exhaustion , which implies the need for extra mixing .
Moreover , we find that current main-sequence models are unable to match the observed properties at a single age even when allowing the unknown metallicity , mixing length parameter , and convective overshooting parameter to vary freely and independently for the two components .
The age of the more massive star appears systematically younger .
AQ Ser and other similarly evolved eclipsing binaries showing the same discrepancy highlight an outstanding and largely overlooked problem with the description of overshooting in current stellar theory .