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 fr om Vega reveals a clump of emission 12" from the star at a position angle ( P.A.) of 45 degrees, consistent with the location of maximum 850 mum emissi on in a lower resolution James Clerk Maxwell Telescope/Submillimeter Common -User Bolometric Array (SCUBA) map. The flux density is 4.0 +/- 0.9 mJy. Ad jacent 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 degrees and 18 degree s, 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 a t P.A. = 215 degrees, and a marginal detection, 1.4 +/- 0.5 mJy, at the ste llar position, consistent with photospheric emission. An extrapolation from the 850 mum flux, assuming, F1.3-0.85 mm proportional to lambda (-2.8), ag rees well with the total detected flux for Vega at 1.3 mm and implies a dus t emissivity index beta 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 m ap and that these grains are largely confined to segments of a ring of radi us 95 AU.