Absolute Properties of the Main-Sequence Eclipsing Binary Star V885 Cygni

We present 4179 differential observations in the V filter measured by a robotic telescope, as well as 25 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EB-type, 1.69 day period double-lined eclipsing binary star V885 Cyg. Absolute dimensions of the components are determined with high precision (better than 1.5% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.005 ± 0.029 M ⊙ and 2.345 ± 0.012 R ⊙ for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 2.234 ± 0.026 M ⊙ and 3.385 ± 0.026 R ⊙ for the cooler, larger, more massive and more luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvby β photometry: 8375 ± 150 K for the primary, 8150 ± 150 K for the secondary—corresponding to spectral types of A3m and A4m—and 0.058 mag for E b - y . The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvby β photometry. The orbits are circular, and spectral line widths give observed rotational velocities that are synchronous with the orbital motion for both components. The components of V885 Cyg are main-sequence stars with an age of about 500 Myr according to models. Our estimate of the age of this system would seem to favor the hydrodynamic damping formalism of Tassoul & Tassoul in this particular case, since both the components' spins are synchronous and the orbit is circular.