  The characteristics of the various types of B[e] stars are discussed and
compared with those of classical Be stars. Both groups of stars are
characterized by the presence of emission lines in their spectra, in particular
of hydrogen. However, there are also significant differences between these
classes. Classical Be stars lack hot circumstellar dust and strong forbidden
low-excitation emission lines, which are typical characteristics produced by
B[e]-type stars. While classical Be stars are a rather uniform group of
early-type stars, B[e]-type stars form a quite heterogeneous group, very often
of poorly known evolutionary status, comprising such diverse types of objects
as near main-sequence objects, evolved low-mass proto-planetray nebulae and
massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars
sometimes find their way into the group of B[e] stars. However, despite these
dissimilarities classical Be stars and B[e]-type stars, share a common
property, namely the non-sphericity of their circumstellar envelopes.

Astrophysics