Absolute Properties of the Eclipsing Triple Star CO Andromedae: Constraints on Convective Core Overshooting

Accurate absolute properties have been determined for the eclipsing triple star CO And (F8+F8) based on extensive differential photometry obtained by three robotic observatories and CfA spectroscopy. The eclipsing binary star orbit is circular with a period of 3.655 days. The triple nature of this system is revealed by more than a century of timings of minimum light, and by the presence of third light in the photometric orbits. The masses of the eclipsing pair are 1.289 ± 0.007 and 1.264 ± 0.007 solar masses, and the corresponding radii are 1.727 ± 0.021 and 1.694 ± 0.017 solar radii. These stars are synchronously rotating and are near the end of their main-sequence phase, at an age of about 3.6 Gyr. The much fainter widely separated third body appears to have a mass of about 0.8 solar masses. The distance to the system is 377 ± 25 pc.