Far-Infrared Constraints on Dust Shells Around Vega-Like Stars

We present results of observations at 47 and 95 μm from the Kuiper Airborne Observatory of several "Vega-like" stars. Spatial cuts and aperture photometry are presented for β Pictoris and Fomalhaut, and for HD 135344, HD 139614, HD 142527, and HD 169142, four stars that had been suggested to possibly represent more distant examples of the Vega phenomenon by Walker & Wolstencroft. We have modeled the dust around β Pic and Fomalhaut with a spatially and optically thin disk to determine the constraints our new observations place on the properties of the dust disks that are required to explain the infrared and optical properties of these two stars. For β Pic we find that models similar to those proposed by Backman, Gillett, & Witteborn can fit our data quite well. For Fomalhaut we find that very different models are required which have much "blacker" dust with a much shallower density distribution, surface density ∝r−0.5, than for β Pic. Our observations of the four HD stars are consistent with their being spatially unresolved. Because of their distance, this does not allow us to put any new constraints on their circumstellar shells.