SUBMILLIMETER OBSERVATIONS OF AN ASYMMETRIC DUST DISK AROUND FOMALHAUT

New submillimeter images of the cold dust emission around the nearby main-sequence star Fomalhaut are presented. Observations at a wavelength of 450 lm, where the telescope beam size is equivalent to a resolu-tion of 50 AU, reveal that Fomalhaut is encircled by a signicantly nonaxisymmetric inclined ring. Smooth axisymmetric models of the ring images suggest the existence of a least one clump with an estimated ux of about 5 % of the total from the disk, thus implying a clumpmass of 0.075 lunar masses. At the resolution of the data, this clump could instead be a ring arc. Themost plausible explanation is that this feature is produced by dust trapped in a resonance with a large planet. The observed structures around Fomalhaut and other Vega-excess stars qualitatively resemble features seen in numerical simulations with a gas giant perturber. Subject headings: circumstellar matter planetary systems stars: individual (Fomalhaut) 1