The spectra of peculiar Be star with infrared excesses.

The paper presents a spectroscopic survey of the Be stars with infrared excesses. A variety of spectral features are found, characteristic of objects ranging from almost conventional Be stars to high-density planetary nebulae. In many stars, the dominant spectral features are emission lines of singly ionized iron. The circumstellar dust which produces the infrared excess is found preferentially in the denser envelopes and probably forms in condensations within them. Hot dust, detected at 2 microns, is most often found around stars of spectral types B and early A, but also occurs in a few high-density planetary nebulae. Three mechanisms of mass loss may explain the formation of the shells: formation of planetary nebulae as a single event, interaction of an OB star with a late-type companion, and direct ejection from a particularly massive Be or Oe star.