FAR-INFRARED CONSTRAINTS ON DUST SHELLS AROUND VEGA-LIKE STARS

We present results of observations at 47 and 95 mu m from the Kuiper A irborne Observatory of several ''Vega-like'' stars. Spatial cuts and a perture photometry are presented for beta Pictoris and Fomalhaut, and for HD 135344, HD 139614, HD 142527, and HD 169142, four stars that ha d been suggested to possibly represent more distant examples of the Ve ga phenomenon by Walker & Wolstencroft. We have modeled the dust aroun d beta Pic and Fomalhaut with a spatially and optically thin disk to d etermine the constraints our new observations place on the properties of the dust disks that are required to explain the infrared and optica l properties of these two stars. For beta Pic we find that models simi lar to those proposed by Backman, Gillett, & Witteborn can fit our dat a quite well. For Fomalhaut we find that very different models are req uired which have much ''blacker'' dust with a much shallower density d istribution, surface density proportional to r(-0.5), than for beta Pi c. Our observations of the four HD stars are consistent with their bei ng spatially unresolved. Because of their distance, this does not allo w us to put any new constraints on their circumstellar shells.