The interferometric diameter and internal structure of Sirius A

The interferometric observations of dwarf stars in the solar neighbourhood, combined with HIPPARCOS parallaxes provide very precise values of their linear diameters. In this paper, we report the direct measurement of the angular diameter of the bright star Sirius A with the VINCI/VLTI instrument. We obtain a uniform disk angular diameter of (theta) UD= 5.936 (plus-minus) 0.016 mas in the K band and a limb darkened value of (theta) LD= 6.039 (plus-minus) 0.019 mas. In combination with the HIPPARCOS parallax of 379.22 (plus-minus) 1.58 mas, this translates into a linear diameter of 1.711 (plus-minus) 0.013 D(odot). Using the VINCI/VLTI interferometric diameter and the published properties of Sirius A, we derive internal structure models corresponding to ages between 200 and 250 (plus-minus) 12 Myr. This range is defined mainly by the hypothesis on the mass of the star, the overshoot and the metallicity.