Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979a%26a....75..326t&link_type=abstract
Astronomy and Astrophysics, vol. 75, no. 3, June 1979, p. 326-339.
Astronomy and Astrophysics
Astrophysics
30
Astronomical Models, Cosmic Dust, H Ii Regions, Infrared Radiation, Infrared Spectra, Interstellar Matter, Absorption Cross Sections, Absorptivity, Graphite, Interstellar Extinction, Ionized Gases, Mathematical Models, Near Infrared Radiation, O Stars, Silicates, Stellar Luminosity, Temperature Distribution
Scientific paper
A numerical model for analyzing infrared emission from dust in compact H II regions is presented. The dust is assumed to consist of graphite, silicate and ice particles, the relative abundance and size of which are determined by fitting observed interstellar extinction and albedo curves. The combined ionization equilibrium of hydrogen and helium is solved for a spherical H II region ionized by a central star and surrounded by a dense neutral shell. The heat balance is solved to obtain the temperature of individual dust particles, and the infrared spectrum is calculated by integrating the dust emission over the H II region and the dense neutral shell. A model for W3A/IRS1 incorporating a central cavity, devoid of gas and dust, with a radius of about 2/3 that of the H II region is constructed. Theoretical spectra are compared with the observed near-infrared spectrum of W3A/IRS1; results suggest that dust in the H II region is strongly depleted. The spectrum is broader than a black-body spectrum as a result of the coexistence of particles of different materials and gradients in the dust temperature distribution. The central exciting star, a hot O star, contributes only about 30% of the total infrared luminosity of W3. The nearby infrared source W3/IRS5 apparently emits the remaining 70%.
de Jong Teije
Tielens Alexander G. G. M.
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