SIMBAD references

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. (1999A&A...344..172P). Models have been constructed using the CEFF equation of state, OPAL opacities, NACRE thermonuclear reaction rates and microscopic diffusion. A χ²-minimization is performed to derive the most reliable set of modeling parameters {wp}={t_α Cen_,Yi_,[(Fe)/(H)]i_,αA_,αB_}, where t_αCen is the age of the system, Y_i the initial helium content, [(Fe)/(H)]_i the initial metallicity and, α_A and α_B the convection parameters of the two components. Using the basic Boehm-Vitense (1958, Z. Astrophys. 54, 114) mixing-length theory of convection, we derive {wp}_BV={2710Myr, 0.284,0.257,1.53,1.57}. We obtain a noticeably smaller age than estimated previously, in agreement with Pourbaix et al. (1999A&A...344..172P), mainly because of the larger masses. If convective core overshoot is considered we get {wp}_ov={3530Myr, 0.279,0.264,1.64,1.66}. The use of Canuto & Mazitelli (1991ApJ...370..295C, 1992ApJ...389..724C) convection theory leads to the set {wp}_CM={4086Myr, 0.271,0.264,0.964,0.986}. Using the observational constraints adopted by Guenther & Demarque (2000ApJ...531..503G), and the basic mixing-length theory, we obtain {wp}_GD={5640Myr, 0.300,0.296,1.86,1.97} and 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 rule out the new determination of masses.