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Issue A&A
Volume 417, Number 1, April I 2004
Page(s) 235 - 246
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20034203



A&A 417, 235-246 (2004)
DOI: 10.1051/0004-6361:20034203

Analysis of $\alpha$ Centauri AB including seismic constraints

P. Eggenberger1, C. Charbonnel1, 2, S. Talon3, G. Meynet1, A. Maeder1, F. Carrier1 and G. Bourban1

1  Observatoire de Genève, 51 chemin des Maillettes, 1290 Sauverny, Suisse
2  Laboratoire d'Astrophysique de Toulouse, CNRS UMR 5572, OMP, 14 Av. E. Belin, 31400 Toulouse, France
3  Département de Physique, Université de Montréal, CP 6128, Station centre-ville, 2900 Bld. Édouard-Montpetit, Montréal PQ H3C 3J7, Canada

(Received 15 August 2003 / Accepted 6 December 2003 )

Abstract
Detailed models of $\alpha$ Cen A and B based on new seismological data for $\alpha$ Cen B by Carrier & Bourban ([CITE]) have been computed using the Geneva evolution code including atomic diffusion. Taking into account the numerous observational constraints now available for the $\alpha$ 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 $\alpha$ Cen system are now firmly constrained to an age of $t=6.52 \pm 0.30$ Gyr, an initial helium mass fraction $Y_{\mathrm{i}}=0.275 \pm 0.010$ and an initial metallicity $(Z/X)_{\mathrm{i}}=0.0434 \pm 0.0020$. Thanks to these numerous observational constraints, we confirm that the mixing-length parameter $\alpha$ of the B component is larger than the one of the A component, as already suggested by many authors (Noels et al. [CITE]; Fernandes & Neuforge [CITE]; Guenther & Demarque [CITE]): $\alpha_{\mathrm{B}}$ is about 8% larger than $\alpha_{\mathrm{A}}$ ( $\alpha_{\mathrm{A}}=1.83 \pm 0.10$ and $\alpha_{\mathrm{B}}=1.97 \pm 0.10$). 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. ([CITE]) even if they are slightly larger than the interferometric radii (differences smaller than 1%).


Key words: stars: binaries: visual -- stars: individual: $\alpha$ Cen -- stars: evolution -- stars: oscillations

Offprint request: P. Eggenberger, Patrick.Eggenberger@obs.unige.ch

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© ESO 2004


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