Radio observations provide the ability to make observations with sub-arcsecond resolution. In August 1991 we observed the Be stars Psi Persei with the VLA at 15 GHz and resolved its circumstellar emission. The emitting region had a major axis dimension of 111+/-16 mas, and the minor axis was unresolved, with an upper limit of 68 mas. From brightness temperature arguments we expect that the minor axis size could be as small as 10 mas. Hence we predict that this circumstellar envelope could be highly flattened. This is the first time that the circumstellar envelope of a Be star had been resolved, and demonstrates that the envelope is highly flattened. This was first suggested in 1951, and remained a contentious issue in Be star research.
Radio and millimeter observations of six Be stars reveal that the continuum spectra of these stars exhibit a turndown longward of the IR wavelength region. These turndowns can be explained by a number of phenomena acting at large distances from the underlying stars, including: recombination of ions; acceleration of the circumstellar material; and changes in the geometry of the circumstellar envelope. At this time we cannot distinguish between these possibilities. Further observations are being obtained in order to relate the wavelength of the turndown to the physical parameters of the underlying stars.
We recently completed a multi-epoch near-IR survey of the majority of the Be stars in the Bright Star Catalogue, using the University of Calgary Infra-Red Telescope. This survey has been combined with other near-IR observations of Be stars from the last two decades in order to search for variations on a time scale of months to decades. Recently, an analysis of the near-IR colours of of these stars suggest that turndowns, first seen in the radio and millimeter data, maybe a common feature of the continuum spectra of Be stars.
For further information on the research in to Be stars at the University of Calgary, contact Dr. A. R. Taylor (email:russ@ras.ucalgary.ca) or Haiqi Chen.