VLTI near-IR interferometric observations of Vega-like stars - Radius and age of $\alpha$ PsA, $\beta$ Leo, $\beta$ Pic, $\epsilon$ Eri and $\tau$ Cet

We report in this paper the direct interferometric measurement of the angular diameter of five nearby Vega-like stars: alphaPsA, betaLeo, betaPic, epsilonEri and tauCet. The near-infrared (K and H bands) observations were conducted at the VLTI during the commissioning period with the VINCI instrument and three different baselines ranging from 66 m to 140 m. The five stellar photospheres are resolved and we derive their angular diameters with a 1 to 2% accuracy, except for beta Pic (14%). We discuss the detectability and the influence of a possible small amount of warm circumstellar dust on our measurements. In addition, we have used the stellar evolution code CESAM ( Morel 1997) to compare the computed fundamental parameters to the observed values ( linear diameter, luminosity, temperature and chemical abundance). As a result of the simulation, the age of the stars is inferred and found to be in good agreement with previous estimates from various other methods.