Context : Capella is among the few binary stars with two evolved giant components .
The hotter component is a chromospherically active star within the Hertzsprung gap , while the cooler star is possibly helium-core burning .

Aims : The known inclination of the orbital plane from astrometry in combination with precise radial velocities will allow very accurate masses to be determined for the individual Capella stars .
This will constrain their evolutionary stage and possibly the role of the active star ’ s magnetic field on the dynamical evolution of the binary system .

Methods : We obtained a total of 438 high-resolution échelle spectra during the years 2007–2010 and used the measured velocities to recompute the orbital elements .
Our double-lined orbital solution yields average residuals of 64 m s ^ { -1 } for the cool component and 297 m s ^ { -1 } for the more rapidly rotating hotter component .

Results : The semi-amplitude of the cool component is smaller by 0.045 km s ^ { -1 } than the orbit determination of Torres et al .
from data taken during 1996–1999 but more precise by a factor of 5.5 , while for the hotter component it is larger by 0.580 km s ^ { -1 } and more precise by a factor of 3.6 .
This corresponds to masses of 2.573 \pm 0.009 M _ { \odot } and 2.488 \pm 0.008 M _ { \odot } for the cool and hot component , respectively .
Their relative errors of 0.34 % and 0.30 % are about half of the values given in Torres et al .
for a combined literature-data solution but with absolute values different by 4 % and 2 % for the two components , respectively .
The mass ratio of the system is therefore q = M _ { A } / M _ { B } = 0.9673 \pm 0.0020 .

Conclusions : Our orbit is the most precise and also likely to be the most accurate ever obtained for Capella .