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Issue A&A
Volume 404, Number 3, June IV 2003
Page(s) 1087 - 1097
Section Stellar atmospheres
DOI 10.1051/0004-6361:20030570



A&A 404, 1087-1097 (2003)
DOI: 10.1051/0004-6361:20030570

The diameters of $\alpha$ Centauri A and B

A comparison of the asteroseismic and VINCI/VLTI views
P. Kervella1, F. Thévenin2, D. Ségransan3, G. Berthomieu2, B. Lopez4, P. Morel2 and J. Provost2

1  European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
2  Département Cassini, UMR CNRS 6529, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
3  Observatoire de Genève, 1290 Sauverny, Switzerland
4  Département Fresnel, UMR CNRS 6528, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France

(Received 20 January 2003 / Accepted 9 April 2003 )

Abstract
We compare the first direct angular diameter measurements obtained on our closest stellar neighbour, $\alpha$ Centauri, to recent model diameters constrained by asteroseismic observations. Using the VINCI instrument installed at ESO's VLT Interferometer (VLTI), the angular diameters of the two main components of the system, $\alpha$ Cen A and B, were measured with a relative precision of 0.2% and 0.6% respectively. Particular care has been taken in the calibration of these measurements, considering that VINCI is estimating the fringe visibility using a broadband K filter. We obtain uniform disk angular diameters for $\alpha$ Cen A and B of $\rm\theta_{\rm UD}[A] = 8.314 \pm 0.016$ mas and $\rm\theta_{\rm UD}[B] = 5.856 \pm 0.027$ mas, and limb darkened angular diameters of $\rm\theta_{\rm LD}[A] = 8.511 \pm 0.020$ mas and $\rm\theta_{\rm LD}[B] = 6.001 \pm 0.034$ mas. Combining these values with the parallax from Söderhjelm (1999), we derive linear diameters of $D[{\rm A}] = 1.224 \pm 0.003\ D_{\odot}$ and $D[{\rm B}] = 0.863 \pm 0.005\ D_{\odot}$. These values are compatible with the masses published by Thévenin et al. (2002) for both stars.


Key words: techniques: interferometric -- stars: binaries: visual -- stars: evolution -- stars: oscillations -- stars: fundamental parameters -- stars: individual: $\alpha$ Cen

Offprint request: P. Kervella, pierre.kervella@eso.org

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© ESO 2003


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