Images of the Vega Dust Ring at 350 and 450 μm: New Clues to the Trapping of Multiple-Sized Dust Particles in Planetary Resonances

Abstract

We have used the SHARC II camera at Caltech Submillimeter Observatory to make 350 and 450 μm images of the Vega dust disk at spatial resolutions (FWHM) of 9".7 and 11".1, respectively. The images show a ringlike morphology (radius ~100 AU) with inhomogeneous structure that is qualitatively different from that previously reported at 850 μm and longer wavelengths. We attribute the 350/450 μm emission to a grain population whose characteristic size (~1 mm) is intermediate between that of the centimeter-sized grains responsible for emission longward of 850 μm and the much smaller grains (≲18 μm) in the extensive halo, visible at 70 μm, discussed by Su et al. We have combined our submillimeter images with Spitzer data at 70 μm to produce two-dimensional maps of line-of-sight optical depth (relative column density). These "tau maps" suggest that the millimeter-sized grains are located preferentially in three symmetrically located concentrations. If so, then this structure could be understood in terms of the Wyatt model in which planetesimals are trapped in the mean motion resonances of a Neptune-mass planet at 65 AU, provided allowance is made for the spatial distribution of dust grains to differ from that of the parent planetesimals. The peaks of the tau maps are, in fact, located near the expected positions corresponding to the 4 : 3 resonance. If this identification is confirmed by future observations, it would resolve an ambiguity with regard to the location of the planet.