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ASTRONOMY AND ASTROPHYSICS Calibrations of αCenA & B

Detailed evolutionary models of the visual binary α Centauri, including pre main-sequence evolution, have been performed using the masses recently determined by Pourbaix et al. (1999). Models have been constructed using the CEFF equation of state, OPAL opac-ities, NACRE thermonuclear reaction rates and microscopic diffusion. A χ 2-minimization is performed to derive the most reliable set of modeling parameters ℘ = {t α Cen , Y i , [ Fe H ] i , α A , α B }, where t α Cen is the age of the system , Y i the initial helium content, [ Fe H ] i the initial metal-licity and, α A and α B the convection parameters of the two components. Using the basic Böhm-Vitense (1958) mixing-length theory of convection, we derive ℘ BV = {2710 Myr, 0.284, 0.257, 1.53, 1.57}. We obtain a noticeably smaller age than estimated previously, in agreement with Pourbaix et al. (1999), mainly because of the larger masses. If convective core overshoot is considered we get ℘ ov surface lithium depletions close to their observed values. A seismological analysis of our calibrated models has been performed. The determination of large and small spacings between the frequencies of acoustic oscillations from seismic observations would help to discriminate between the models of α Cen computed with different masses and to confirm or rules out the new determination of masses.