Absolute dimensions and masses of eclipsing binaries. III. CW CMa.

The eclipsing binary CW CMa has been found to be strongly double-lined on high signal-to-noise ratio digital spectral scans obtained with the Reticon and Digicon spectrometers of the 2.7 m reflecting telescope at McDonald Observatory. Absorption lines of both components are of nearly equal strength in the 4500 A region, and radial velocities of high precision have been obtained for both stars. Spectroscopic orbits derived from these data have been combined with the photometric orbit of Williamon to give very accurate masses and radii: (2.09 + or - 0.02 solar masses, 1.89 + or - 0.04 solar radii) for the primary and (1.98 + or - 0.02 solar mass, 1.79 + or - 0.07 solar radius) for the secondary. The uncertainties are conservatively estimated standard errors. An analysis of the line profiles of both components indicates that they are synchronously rotating with the orbital period. A limited range of theoretical evolutionary tracks can be fitted simultaneously to both stars of CW CMa. The approximate age of this system is 200-million years.