Calibrations of alpha Centauri A & B

Detailed evolutionary models of the visual binary ct Centauri, including pr e main-sequence evolution, have been performed using the masses recently de termined by Pourbaix et al. (1999). Models have been constructed using the CEFF equation of state, OPAL opacities, NACRE thermonuclear reaction rates and microscopic diffusion. A chi (2)-minimization is performed to derive th e most reliable set of modeling parameters rho = {t(alpha Cen), Y-i, [Fe/H] (i), alpha (A), alpha (B)}, where t(alpha Cen) is the age of the system, Y- i the initial helium content, [Fe/H](i) the initial metallicity and, alpha (A) and alpha (B) the convection parameters of the two components. Using th e basic Bohm-Vitense (1958) mixing-length theory of convection, we derive r ho (BV) = {2710 Myr, 0.284, 0.257, 1.53, 1.57}. We obtain a noticeably smal ler age than estimated previously, in agreement with Pourbaix et al. (1999) , mainly because of the larger masses. If convective core overshoot is cons idered we get rho (OV) = {3530 Myr, 0.279, 0.264, 1.64, 1.66}. The use of C anuto & Mazitelli (1991, 1992) convection theory leads to the set rho (CM) = {4086 Myr., 0 271, 0.264, 0.964, 0.986} Using the observational constrain ts adopted by Guenther & Demarque (2000), and the basic mixing-length theor y, we obtain rho (GD) = {5640 Myr, 0.300, 0.296, 1.86, 1.97} and surface Li thium depletions close to their observed values. A seismological analysis of our calibrated models has been performed. The d etermination of large and small spacings between the frequencies of acousti c oscillations from seismic observations would help to discriminate between the models of alpha Cen computed with different masses and to confirm or r ule out the new determination of masses.