Circumstellar environment of Herbig Ae/Be stars as seen by the IOTA

We have conducted the first systematic study of Herbig Ae/Be stars using the technique of long baseline stellar interferometry. The Infrared Optical Telescope Array resolves the source of the near-infrared excess flux characteristic of these systems in 11 of the 15 stars observed. A close companion to MWC 361-A (18 mas separation) has been detected interferometrically for the first time. The visibility data has been interpreted within the context of four models which represent the range of plausible representations for the brightness of the excess emission: a Gaussian distribution, a narrow uniform ring, an accretion disk, and an infrared companion. We find that the large sizes measured by the interferometer, 0.5 - 5.9 AU, essentially invalidate accretion disk models that had been previously used to explain the spectroscopic observations. Although a unique model can not be determined for each source due to limited spatial frequency coverage, the observed symmetry of the sources favors, for the ensemble of the data, models in which the circumstellar dust is distributed in spherical envelopes.