Absolute Properties of the Upper Main-Sequence Eclipsing Binary Star MU Cassiopeiae

Abstract

We present 6151 differential observations in the V filter measured by a robotic telescope, as well as 29 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EA-type, 9.65 day period double-lined eclipsing binary star MU Cas. Absolute dimensions of the components are determined with good precision (better than 2% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 4.57 ± 0.09 M⊙ and 3.67 ± 0.04 R⊙ for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 4.66 ± 0.10 M⊙ and 4.19 ± 0.05 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: 15,100 ± 500 K for the primary, 14,750 ± 500 K for the secondary—corresponding to spectral types of B5 and B5—and 0.356 mag for Eb-y. The stars are located at a distance of about 1.7 kpc near the plane of the Galactic disk. The orbits of the stars are eccentric, and spectral line widths give observed rotational velocities that are synchronous with the mean orbital motion for both components. The components of MU Cas are upper main-sequence stars with an age of about 65 Myr according to models.