CONSTRAINING CIRCUMSTELLAR ENVIRONMENTS - FAR-INFRARED OBSERVATIONS OF HERBIG AE BE STARS/

we have observed six Herbig Ae/Be stars at 50 and 100 mu m with the Ku iper Airborne Observatory. All were classified as group I sources by H illenbrand et al. (1992), signifying that their spectral energy distri butions could be modeled with stars surrounded only by accretion disks . If the far-infrared emission is assumed to arise in a disk, it shoul d be unresolved at 100 mu m, regardless of the size of the disk. In co ntrast, we find that five out of six sources are clearly resolved at 1 00 mu m. Three sources were also observed at 50 mu m and at least two were resolved. Consequently the far-infrared emission must arise in an other component, most plausibly a circumstellar envelope. This suggest s that the group I sources may be less distinct from the group II sour ces than previously suggested. Since the presence of an envelope can a ffect both the actual temperature distribution in a disk and the tempe rature distribution derived from modeling the emission, more consisten t models, including both disks and envelopes, are needed for these sou rces.