EDP Sciences
Free access
Volume 434, Number 1, April IV 2005
Page(s) 257 - 274
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20034114

A&A 434, 257-274 (2005)
DOI: 10.1051/0004-6361:20034114

The circumstellar environments of high-mass protostellar objects

II. Dust continuum models
S. J. Williams1, G. A. Fuller1 and T .K. Sridharan2

1  School of Physics and Astronomy, The University of Manchester, Sackville Street, PO Box 88, Manchester, M60 1QD, UK
    e-mail: G.Fuller@manchester.ac.uk
2  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138, USA

(Received 24 July 2003 / Accepted 10 January 2005)

We analyse the dust continuum emission seen towards a sample of candidate high-mass protostellar objects, modelling the cores we recently observed at 850 $\mu$m with a one-dimensional radiative transfer code. Fitting radial slices in a range of directions across sources, we identify a number of objects that have non-spherical density profiles and show that for such sources fitting the azimuthal averaged emission produces erroneous estimates of the source properties. We find the majority of cores can be successfully modelled using envelopes of power-law density structure (where $\rho \propto r^{-\alpha}$), finding a mean power-law index of $\overline{
\alpha } = 1.3 \pm 0.4$. These envelopes extend considerably further, are more dense, and have a more shallow density profile than those bearing low-mass protostars. The majority of best-fit models have a SED resembling the cold-component dust bodies previously proposed for the sample, implying the short wavelength emission seen towards the HMPOs either originates from a separate hot dust component(s), or involves mechanisms such as accretion disks, stochastic heating and/or optically thin cavities not included in the radiative transfer model. We find evidence of smaller dust-free cavities towards some pre-UCHII sources. The modelling indicates a correlation between $\alpha$ and optical depth, suggesting that the densest cores also tend to have the most strongly peaked power-law density profiles.

Key words: stars: formation -- stars: circumstellar matter -- ISM: clouds -- ISM: dust, extinction

SIMBAD Objects

© ESO 2005