Submillimeter Emission from Small Dust Grains Orbiting Nearby Stars

Abstract

The most exciting discovery of the Infrared Astronomical Satellite (IRAS) was intense far-infrared radiation from various nearby main-sequence stars. This radiation, which is produced by numerous dust particles, is suggestive of solar-systemlike objects in orbit about the stars. We have detected and measured, at submillimeter wavelengths, properties of the particulate clouds around Vega, Fomalhaut, and Beta Pictoris. These measurements yield accurate estimates of particle size, spatial distribution, and minimum total mass for these three dusty clouds. In particular, the particles appear to be sufficiently small that they are probably being supplied continually by a very substantial population of much larger objects, perhaps comets or asteroids. The widespread occurrence of excess far-infrared emission from nearby stars (Backman and Gillett 1987; Aumann 1988) suggests, therefore, that a majority of single main-sequence stars are surrounded by vast clouds of comets and/or asteroids. A limited map of the submillimeter emission toward Fomalhaut is consistent with the possibility that the radiating particles are substantially depleted near the star, which could be due either to destruction of the grains or accumulation into larger objects such as planets.