ACCURATE DIAMETER MEASUREMENT OF BETELGEUSE USING THE VLTI/AMBER INSTRUMENT

The apparent size and greater luminosity of Red Super Giant stars (RSGs) make them ideal targets for astrometry experiments. Since the observation of Betelgeuse by Michelson & Pease (1921), several other works have been carried out improving the precision on the measurement of the diameter of the star (e.g., (Weiner et al. 2000; Young et al. 2000)). We present preliminary results of the observations of the super giant star Betelgeuse carried out with the AMBER (Astronomical MultiBEam Recombiner) instrument. AMBER is one of the first generation instruments of the VLTI able to combine the beams of two or three telescopes simultaneously, and brings spectral dispersion. The a priori knowledge of the angular size of Betelgeuse, gives us a well established reference to indirectly probe the stability of AMBER. Furthermore, we demonstrate the AMBER ability to measure low contrast visibilities under high flux conditions.