Analysis of α Centauri AB including seismic constraints

Abstract

Detailed models of α Cen A and B based on new seismological data for α Cen B by Carrier & Bourban (2003) have been computed using the Geneva evolution code including atomic diffusion. Taking into account the numerous observational constraints now available for the α Cen system, we find a stellar model which is in good agreement with the astrometric, photometric, spectroscopic and asteroseismic data. The global parameters of the α Cen system are now firmly constrained to an age of t = 6.52 ± 0.30 Gyr, an initial helium mass fraction Yi = 0.275 ± 0.010 and an initial metallicity (Z/X)i = 0.0434 ± 0.0020. Thanks to these numerous observational constraints, we confirm that the mixing-length parameter α of the B component is larger than the one of the A component, as already suggested by many authors (Noels et al. 1991; Fernandes & Neuforge 1995; Guenther & Demarque 2000): αB is about 8% larger than αA (αA = 1.83 ± 0.10 and αB = 1.97 ± 0.10). Moreover, we show that asteroseismic measurements enable to determine the radii of both stars with a very high precision (errors smaller than 0.3%). The radii deduced from seismological data are compatible with the new interferometric results of Kervella et al. (2003) even if they are slightly larger than the interferometric radii (differences smaller than 1%).