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M.F. Campbell (Colby C.), L.K. Deutsch (BU/CfA)
Recognition that high-mass stars form only in clusters has motivated us to make new radiative transfer models for infrared emission from compact, dense cloud cores surrounding very young high-mass stars. We assume outer cloud radii are limited by the formation of stars in clusters to 0.1 pc. Since there is a high efficiency of conversion of gas into stars within clusters, we assumed the mass of gas and dust in the cloud models is equal or less than the mass of the central star. We assumed Draine and Lee (1984) dust properties with 100:1 gas to dust mass ratio, and used the Egan, Leung, and Spagna (1988) radiative transfer code. The central star in all models is an O8 ZAMS type at 1700 pc distance (the distance to NGC6334). The dust emitting clouds were assumed to have inner cavities of radius 0.006 pc, just outside an ultracompact HII region. Density distributions were taken as uniform or proportional to r-3/2. Except for the highest mass clouds, the models showed the 10 micron silicate feature in emission rather than self absorption. All models' spectral energy distributions peak shortward of 50 microns. The lack of silicate self absorption and the SEDs peaking shortward of 50 microns are apparently due to the small size of these models. In order to match observed silicate absorption in UCHIIs, an external cold absorbing component must be added to the models. The results suggest that individual high mass star-formation cores should be searched for in mid-infrared rather than far-infrared wavelengths, and that SEDs which peak in the far- infrared are at least partly produced by separate, larger outer cloud envelopes.
Draine, B. T. & Lee, H. M. 1984 ApJ, 285, 89; Egan, M.P., Leung, C.M., & Spagna, G.F, Jr. 1988 Comput. Phys. Comm., 48, 271
The author(s) of this abstract have provided an email address for comments about the abstract: mfcampbe@colby.edu