Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.2604s&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #26.04; Bulletin of the American Astronomical Society, Vol. 26, p.1355
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The dust emission and distribution from two Galactic H II regions, the Rosette Nebula and the lambda Orionis H II region, have been modeled and compared with spatially resolved IRAS observations. The grain models used in this study are consistent with observations of isolated interstellar clouds and the diffuse interstellar meduim. We exploited the wealth of published observations of these two H II regions to constrain the free parameters of the infrared emission models. These models represent a comprehensive, multi-wavelength study of each H II region. The contribution of nebular lines to the IR emission observed by IRAS was calculated from radio continuum measurements. Emission lines are found to contribute only a few percent of the total IR emission. Despite their regular appearance, both H II regions have significant deviations from spherical symmetry. In particular, the IR emission for the lambda Orionis H II region requires a nonspherical distribution of dust near the central core. I_ν(60)/I_ν(100) is not representative of a single grain temperature within either H II region. Therefore, a grain component separate from the grains emitting at 100 microns is required to supply the excess 60 microns emission. These emitters could be either small (50 to 200 Angstroms) grains that experience strong temperature fluctuations or "astronomical" iron grains that attain high equilibrium temperatures. In order to match the IRAS observations, the abundance of the grains that produce the 12 and 25 microns emission in the ISM must be reduced inside the ionized regions. This depletion occurs in radiation fields 20 to 36 times the UV component of the diffuse ISRF. The destruction mechanism for the 12 and 25 microns carriers is not well modeled by sublimation or molecular disruption.
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