Astron. Astrophys. 336, 565-586 (1998)

5. Conclusions

Continuum mapping at 1.3 mm turned out to be extremeful helpful to uncover the circumstellar structure of the HAEBE and FU Orionis stars. Together with near-infrared imaging we were able to relate the dust emission to individual objects. In the case of V 376 Cas/LkH 198, MWC 137, CoD -42^o11721, and V 1685 Cyg/V 1686 Cyg, the millimetre emission is not related to the HAEBE stars. Four objects could not be detected up to a 3 flux density limit of about 25 mJy. These are the HAEBE stars HK Ori, HD 250550, LkH 25 and the FU Orionis star V 1515 Cyg.

The following conclusions can be drawn on the structure of the circumstellar environment:

• The dusty environment of HAEBE and FU Orionis stars show two markedly different structures which can be described as core and core/envelope regions. Objects associated with only compact structures include AB Aur and HD 163296 which are known to be surrounded by compact disks.

• The total masses obtained from the maps are usually much higher than obtained from pointed On-On observations, especially in the case of the objects associated with extended envelopes. The circumstellar masses show a relatively broad variation between 0.03 and 1100 . The lowest mass was derived for AB Aur with a value in quite good agreement with recent interferometry measurements. The average densities in the cores range from 10⁵ to 10⁸ cm^-3. The densities of the extended envelopes are of the order of 10⁴ to 10⁵ cm^-3.

• Radiative transfer calculations based on a spherically symmetric model were performed for 4 objects (AB Aur, V 1331 Cyg, VY Mon, LkH 234) in order to test if such models are able to represent the SED of both the core and the core/envelope sources. In all these cases including the compact-core objects AB Aur and V 1331 Cyg, a satisfactory fit could be reached. This clearly demonstrates that a good fit with a spherical model cannot be used as an argument against the existence of a small-scale disk which is known to exist in the case of AB Aur.

One of the selection criteria of Herbig (1960) for an HAEBE star was its association with reflection nebulosities. As demonstrated by this survey and already noted by Herbig (1994), this criterion can now be replaced by the association with molecular-line or dust emission. Future studies should address the kinematic relation between the HAEBE stars and the associated circumstellar environment. Additional interferometry searches are necessary to find out if more HAEBE stars are related to disks with Keplerian velocity structures.

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998
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