Astronomy and Astrophysics, volume 336, 565-586 (1998/8-2)
Infrared imaging and millimetre continuum mapping of Herbig Ae/Be and FU Orionis stars.
HENNING T., BURKERT A., LAUNHARDT R., LEINERT C. and STECKLUM B.
Abstract (from CDS):
The goal of this paper is a detailed analysis of the dusty environment of Herbig Ae/Be stars and FU Orionis objects. For this purpose we mapped 22 regions at 1.3mm wavelength containing 25 target objects. We found that it is indispensable to perform mapping in contrast to pointed On-On measurements in order to obtain the correct distribution of cold material around young stellar objects and to relate 1.3mm flux densities to individual sources. To get reliable information about the structure and shape of the dust configurations and their relation to the stellar sources, we superimposed the millimetre maps on near-infrared images. The comparison of the data demonstrated that some of the Herbig Ae/Be stars are not associated with the peak of the millimetre emission. This is obviously the case for V376 Cas/LkHα 198, MWC 137, CoD -42°11721, and V1685 Cyg/V1686 Cyg. We found two different morphologies of the dust envelopes: 6 regions show a compact structure, whereas 12 regions are characterized by a core/envelope structure. The ``disk'' objects AB Aur and HD 163296 show only a compact core and are not surrounded by an extended envelope. We did not detect HK Ori, HD 250550, LkHα 25, and V1515 Cyg which all have low IRAS luminosities. Based on the flux densities derived from the millimetre maps, we estimated characteristic physical parameters like density and mass assuming optically thin emission. The total masses of the circumstellar regions around the Herbig Ae/Be stars with core/envelope structure and with ``genuine" point-like millimetre sources are 80±60M☉ and 0.15±0.15M☉, respectively. The lowest and highest masses of the circumstellar material were found around ABAur (0.03M☉) and CoD -42°11721 (1100M☉), respectively. The average densities in the cores range from 105 to 108cm–3. The densities of the extended envelopes are of the order of 104 to 105cm–3. In addition, we combined the measured millimetre flux densities with infrared and optical data and modelled the broad-band spectral energy distributions using spherically symmetric models. We found good fits for both the core sources (AB Aur, V1331 Cyg) and the core/envelope objects (VY Mon, LkHα 234) we considered for modelling. The parameters derived this way are generally in good agreement with data directly derived from the maps. However, the possibility to fit the spectral energy distribution of AB Aur which is known to be associated with a disk clearly demonstrates that a good ``spherical'' fit cannot be used as an argument against the presence of a disk.
stars: formation - stars: pre-main-sequence - ISM: clouds - dust, extinction - radio continuum: ISM - circumstellar matter
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