Millimeter-wave aperture synthesis imaging of Vega: Evidence for a ring arc at 95 AU

We present the first millimeter-wave aperture synthesis map of dust around a main-sequence star. A 3″ resolution image of 1.3 mm continuum emission from Vega reveals a clump of emission 12″ from the star at a position angle (P.A.) of 45°, consistent with the location of maximum 850 μM emission in a lower resolution James Clerk Maxwell Telescope/Submillimeter Common-User Bolometric Array (SCUBA) map. The flux density is 4.0 ± 0.9 mJy. Adjacent 1.3 mm peaks with flux densities of 3.4 ± 1.0 and 2.8 ± 0.9 mJy are located 14″ and 13″ from the star at P.A.'s of 67° and 18°, respectively. An arclike bridge connects the two strongest peaks. There is an additional 2.4 ± 0.8 mJy peak to the southwest, 11″ from the star at P.A. = 215°, and a marginal detection, 1.4 ± 0.5 mJy, at the stellar position, consistent with photospheric emission. An extrapolation from the 850 μm flux, assuming F_{1.3-0.85 mm} ∝ λ^-2.8, agrees well with the total detected flux for Vega at 1.3 mm and implies a dust emissivity index β of 0.8 We conclude that we have detected all but a very small fraction of the dust imaged by SCUBA in our aperture synthesis map and that these grains are largely confined to segments of a ring of radius 95 AU.