Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...221..797h&link_type=abstract
Astrophysical Journal, Part 1, vol. 221, May 1, 1978, p. 797-809. NSF-supported research;
Astronomy and Astrophysics
Astrophysics
44
Absorption Spectra, Astronomical Maps, Infrared Spectra, Nebulae, H Ii Regions, Hydrogen Ions, Interstellar Gas, Mass Ratios, Silicates, Spectral Resolution
Scientific paper
IR maps of the region around W3 IRS1, IRS3, and IRS5 are presented which were made at eight wavelengths between 4.9 and 20 microns using either a prism-array spectrometer system or an interference-filter photometer. The medium-resolution-array spectrometer data are shown to represent accurately the shape of the silicate feature in W3 as determined by comparison with measurements performed at higher spectral resolution. It is found that the 8.0- to 12.7-micron spectra of IRS1 and IRS3 are fitted well by a model having cold silicate absorption overlying an optically thin silicate emission source. The gas-to-silicate-dust mass ratio inside the H II regions is estimated to be at least 30 times greater than the 'normal' interstellar value of 300, and it is suggested that the dust emitting the 5- to 20-micron radiation in IRS1 and IRS3 is well mixed with the ionized gas responsible for radio emission. A best-fit model for IRS1 is proposed in which the 5- to 20-micron radiation originates from silicate grains at a temperature of about 300 K inside the H II region, which is surrounded by a massive shell of cold dust and gas that is heated by both direct stellar photons and mid-IR radiation from the central region.
Briotta D. A.
Gehrz Robert D.
Hackwell John A.
Smith Jeffrey R.
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