Vega is the fifth brightest star in the sky. It is twice the size of the Sun and fifty times more luminous. In the early 1980s, astronomers discovered that a cold and extended dust disk the size of our solar system surrounded the star. However, limited by the star's high luminosity and the need for high-resolution observations, little was known about its inner regions.
Recently, an international team of scientists, including researchers from the LESIA and LAOG research laboratories,1 has for the first time observed circumstellar material in the close vicinity of Vega.2 To do so, they used the CHARA array,3 a Y-shaped array of six 1m-diameter telescopes linked together so closely that individual light waves from each one can be combined to simulate a giant telescope. Vega's starlight was then fed to the interferometric beam combiner FLUOR4 built by LESIA at the Paris Observatory, which enables researchers to observe infrared sources at milliarcsecond resolution.
Using these powerful tools, astronomers discovered that the inner part of Vega's debris disk appeared to be composed of hot and sub-micronic highly refractive grains (such as graphites or amorphous carbons), but which were much smaller than the ones in our solar system (which are mostly silicate). These tiny grains are concentrated in the first AU5 around Vega and heated up to 1300°C by the star, radiating mostly in the near-infrared. But radiation pressure created by the intense stellar flux should prevent such small grains from surviving in the inner disk for more than a few years. Scientists therefore believe that the inner debris disk must experience a high dust production rate, from ongoing intense meteoritic or cometic bombardment. Such a bombardment could be explained by the migration of giant planets in Vega's outer disk, further fuelling theories to the existence of Vega's planetary system.
1. LESIA: Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (CNRS / Observatoire de Paris / Universités Paris-VI and VII joint lab). LAOG: Laboratoire d'astrophysique de Grenoble (CNRS / Université Grenoble-I joint lab)
2. O. Absil et al., “Circumstellar material in the Vega inner system revealed by CHARA/FLUOR,” Astronomy & Astrophysics. 452: 237-244. 2006.
3. Based at Mt. Wilson Observatory, Calif.
4. Fiber Linked Unit for Optical Recombination.
5. Astronomical Unit: 149,597,870.691 km, the mean distance between the Earth and the Sun.