Absolute Properties of the Eclipsing Binary Star RW Lacertae

We present 3004 differential observations in the V bandpass measured by a robotic telescope, as well as 36 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, eccentric, EA-type, 10.37 day period, double-lined eclipsing binary star RW Lac. Absolute dimensions of the components are determined with excellent precision (better than 0.7% in the masses and 0.5% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain 0.928+/-0.006 M_solar and 1.186+/-0.004 R_solar for the hotter, larger, more massive, and more luminous photometric primary (star A) and 0.870+/-0.004 M_solar and 0.964+/-0.004 R_solar for the cooler, smaller, less massive, and less luminous photometric secondary (star B). A faint, third component contributes 2.6% of the light in V but is not detected in our spectrograms. The effective temperatures and interstellar reddening of the stars are accurately determined from UBV and uvbyβ photometry and from analysis of the spectrograms: 5760+/-100 K for the primary and 5560+/-150 K for the secondary, corresponding to spectral types of G5 and G7, and 0.050 mag for interstellar reddening E_b-y. The orbits are slightly eccentric, and spectral line widths give observed rotational velocities that are not significantly different from synchronous for both components. The components of RW Lac are old, somewhat metal-deficient, low-mass, main-sequence stars with an age of about 11 Gyr, according to models.