INFRARED IMAGING AND MILLIMETER CONTINUUM MAPPING OF HERBIG AE BE ANDFU ORIONIS STARS/

The goal of this paper is a detailed analysis of the dusty environment Herbig Ae/Be stars and FU Orionis Objects jects. For this purpose we mapped 22 regions at 1.3 mm wavelength containing 25 target objects. W e found that it is indispensable to perform mapping in contrast to poi nted On-Gin measurements in order to obtain the correct distribution o f cold material around young stellar objects and to relate 1.3 mm flux densities to individual sources. To get reliable information about th e structure and shape of the dust configurations and their relation to the stellar sources, we superimposed the millimetre maps on near-infr ared 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 V 376 Cas/LkH alpha 198, MWC 137, CoD-42 degrees 11721, and V 1685 Cyg/V 1686 Cyg. We found two dif ferent morphologies of the dust envelopes: 6 regions show a compact st ructure, whereas 12 regions are characterized by a core/envelope struc ture. The ''disk'' objects AB Aur and HD 163296 show only a compact co re and are not surrounded by an extended envelope. We did not detect H K Ori, HD 250550, LkH alpha 25, and V 1515 Cyg which all have low IRAS luminosities. Based on the flux densities derived from the millimetre maps, we estimated characteristic physical parameters like density an d mass assuming optically thin emission. The total masses of the circu mstellar regions around the Herbig Ae/Be stars with core/envelope stru cture and with ''genuine'' point-like millimetre sources are 80+/-60 M . and 0.15+/-0.15 M. respectively. The lowest and highest masses of th e circumstellar material were found around AB Aur (0.03 M.) and CoD-42 degrees 11721 (1100 M.), respectively. The average densities in the c ores range from 10(5) to 10(8) cm(-3). The densities of the extended e nvelopes are of the order of 10(4) to 10(5) cm(-3). In addition, we co mbined the measured millimetre flux densities with infrared and optica l data and modelled the broad-band spectral energy distributions using spherically symmetric models. We found good fits for both the co.-e s ources (AB Aur, V 1331 Cyg) and the core/envelope objects (VY Mon, LkH alpha 234) we considered for modelling. The parameters derived this w ay are generally in good agreement with data directly derived from the maps. However, the possibility to fit the spectral energy distributio n of AB Aur which is known to be associated with a disk clearly demons trates that a good ''spherical'' fit cannot be used as an argument aga inst the presence of a disk.