  We discuss spectral energy distributions of a sample of Herbig Ae/Be stars in
the context of a passive irradiated disk model. The data have been presented
earlier by Meeus et al (2001), and preliminary interpretations of these data
were given in that paper. While the spectra of Herbig Ae stars all show
similarities, there is significant variation between the spectra, in particular
in the shape of the mid-IR rise and in the presence or absence of a silicate
feature. We explore the hypothesis that all these different spectra can be
interpreted as pure disk spectra without additional components. Using the model
of Dullemond, Dominik and Natta (2001) we deduce the disk parameters of a
number of the sources, and find that for a large fraction of investigated
sources, satisfactory fits can be obtained. The derived model parameters show
that some group Ia sources can only be fit with radially increasing surface
densities, indicating the presence of depleted inner disk regions. The
steep-sloped SEDs of group IIa sources can be fit with very compact disks,
probably representing disks with collapsed outer regions. The largest
difficulties arise from sources that do not show significant silicate emission
features. Our attempts to explain these objects with a pure geometric effect
are only partially successful. It seems that these stars indeed require a
strong depletion of small silicate grains.
