INFRARED-EMISSION FROM DUST STRUCTURES SURROUNDING HERBIG AE/BE STARS

We present IR observations in J, H, K, L, M, and 8-13 mum bands of Herbig Ae/Be stars located in the southern hemisphere. These results enlarge an already existing data base, increasing the significance of the correlations which can be obtained from observational parameters. Silicate features detected both in emission and in absorption indicate the presence of dust around these objects. A first analysis based on two-color diagrams, polarization, and luminosity suggests that the spherical geometry for the dust distribution is a more common feature, with respect to the flattened structure. An emission model in which the central object is surrounded by a circumstellar envelope of gas and dust is introduced and the continuum spectrum is computed taking into account radiative properties both of gas (free-free, free-bound, electron scattering) and dust. The numerical results, compared with the observations, suggest that anisotropic dust distributions are not necessarily required to account for the emitting properties of the circumstellar envelopes around Herbig Ae/Be stars.