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

Abstract

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 uvbyβ 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 Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ 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.