  An analysis of solid-state features in infrared spectra of 46 Herbig Ae/Be
stars is presented. The presence of solid-state emission bands is compared to
other indicators of circumstellar material, such as Halpha emission, optical
variability and sub-mm continuum fluxes. The correlation between these
different indicators is weak, if present at all, in our sample. However, a
strong dependence on spectral type of the central star seems to be present:
stars with spectral type earlier than B9 show either amorphous silicate in
absorption or infrared spectra dominated by PAH emission, whereas more than 70%
of the stars of later spectral type show silicate emission. We conclude that
the infrared spectrum of Herbig Be stars is in general dominated by emission
from the circumstellar envelope, whereas the lower-mass Herbig Ae stars show a
spectrum that is dominated by a disk that is passively heated by the central
star.
