FAR-INFRARED OBSERVATIONS OF MAIN-SEQUENCE STARS SURROUNDED BY DUST SHELLS

We present 50 and 100 pm photometry and size information for several m ain sequence stars surrounded by dust shells. The observations from NA SA's Kuiper Airborne Observatory include the ''Vega-like'' stars, Beta Pic, Fomalhaut, as well as four stars suggested by Walker and Wolsten croft to belong possibly to the same class. The results of our observa tions are best interpreted as upper limits to the far-infrared sizes o f the dust clouds around all of the stars except Fomalhaut and Beta Pi c. We have also fit simple, optically thin models to the Beta Pic data to explore the range of shell parameters consistent with our limits a nd with previous observations.