Available formats: HTML | PDF | (gzipped) PostScript
Infrared imaging and millimetre continuum mapping of Herbig Ae/Be and FU Orionis stars *
Th. Henning 1,
A. Burkert 1,
R. Launhardt 1,
Ch. Leinert 2 and
B. Stecklum 3
Received 5 January 1998 / Accepted 27 April 1998
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 1.3 mm 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 1.3 mm 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 V 376 Cas/LkH 198, MWC 137, CoD-42o11721, and V 1685 Cyg/V 1686 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, LkH 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 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 8060 and 0.150.15 , respectively. The lowest and highest masses of the circumstellar material were found around AB Aur (0.03 ) and CoD-42o11721 (1100 ), respectively. 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.
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, V 1331 Cyg) and the core/envelope objects (VY Mon, LkH 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.
Key words: stars: formation stars: pre-main-sequence ISM: clouds dust, extinction radio continuum: ISM circumstellar matter
Send offprint requests to: Th. Henning
Online publication: July 20, 1998