On the Mass Ratio of Capella

High-dispersion spectrograms of Capella have been measured by cross correlation with a similar spectrogram of beta Aquarii in order to determine the velocity amplitudes of both components. A mass ratio of 1.025 +/- 0.028, the component with the sharper spectral lines being marginally the more massive, is found. The total mass of the system is found to be 5.05 solar mass +/- 0.12 solar mass, which is acceptably close to the value found by combining the orbital semiaxis major derived from speckle interferometry with the trigonometrical parallax. Individual masses of 2.56 solar mass +/- 0.08 solar mass and 2.49 solar mass +/- 0.09 solar mass are deduced. Stellar models that include convective overshooting are needed to interpret the observations and it is found, by comparison with such models, that the age of Capella is 8 x 10 to the 8th years.