P. Abraham 1, Ch. Leinert 1, D. Lemke 1, A. Burkert 2, & Th. Henning 2
1 Max-Planck-Institut für Astronomie Heidelberg, Germany
2 Astrophysikalisches Institut und Universitats-Sternwarte Jena, Germany
Many intermediate mass stars show signatures of circumstellar material. The young pre-main sequence Herbig Ae/Be stars often show flat or rising spectral energy distributions (SEDs) in the far-infrared, attributed to thermal emission of heated circumstellar dust, the remnant of star formation.
We observed 8 Herbig Ae/Be with ISOPHOT in order to derive their SEDs
and to learn about the spatial structure of their cold circumstellar
envelopes. In several cases we found that the observed flux densities at
were significantly higher than predicted from earlier
star+disk models. In these cases the ISOPHOT data reveal the peak of the
spectral energy distribution at wavelengths shorter than 100 micron, in spite
of the IRAS measurements which show increasing SEDs at 100 micron. The
difference is probably due to the larger beam of IRAS. The strong far-infrared
emission observed indicates that a large amount of very cold dust has to be
incorporated into the models of young intermediate mass stars. We model
the new SEDs by a radiative transfer code, in order to determine the density
and temperature structures of the circumstellar envelopes.
For the first time we mapped the circumstellar environment of several
Herbig Ae/Be stars at
.
The highly oversampled maps,
taken
at 120, 150 or 200 
with the C200 camera of ISOPHOT,
were able to resolve the cold dust envelopes of three stars (LkHa 233,
LkHa 234, MWC 1080), and to determine their spatial extensions.