  The binary star alpha Aurigae (otherwise known as Capella) is extremely
important to understand the core hydrogen and helium burning phases of the
stars, as the primary star is likely evolving through the core helium burning
phase, and the masses of the two components are 2.5 Msun and 2.6 Msun, which
fall into a mass range for which the extention of the core overshoot during the
main sequence phase is uncertain. We aim at deriving the extent of the core
overshoot experienced during the core burning phases and testing the efficiency
of the convective transport of energy in the external envelope, by comparing
results from stellar evolution modelling with the results from the
observations. We consider evolutionary tracks calculated on purpose for the
present work, for the primary and secondary star of Capella. We determine the
extent of the extra-mixing from the core during the main sequence evolution and
the age of the system, by requiring that the effective temperatures and surface
gravities of the model stars reproduce those derived from the observations at
the same epoch. We further check consistency between the observed and predicted
surface chemistry of the stars. Consistency between results from stellar
evolution modelling and the observations of Capella is found when extra-mixing
from the core is assumed, the extent of the extra-mixed zone being of the order
of 0.25 H_P. The age of the system is estimated to be 710 Myr. These results
allow to nicely reproduce the observed surface chemistry, particularly the
recent determination of the 12C/13C ratio based on LBT (Large Binocular
Telescope) and VATT (Vatican Advanced Technology Telescope) observations
