Spectroscopic orbit of Capella

The hotter component is a chromospherically active star within the Hertzsprung gap, while the cooler star is possibly helium-core burning. 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. We obtained a total of 438 high-resolution echelle 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 64m/s for the cool component and 297m/s for the more rapidly rotating hotter component.