Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...261..567o&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 261, no. 2, p. 567-578.
Astronomy and Astrophysics
Astrophysics
249
Interstellar Matter, Silicates, Stellar Envelopes, Astronomical Models, Iron, Magnetite, Opacity, Silicon Carbides
Scientific paper
Observational determinations of opacities of circumstellar silicates, relative to the peak value near 10 microns, are used to estimate the optical constants n and k, the real and imaginary parts of the index of refraction. Circumstellar dust is modified by processing within the interstellar medium. This leads to higher band strengths and a somewhat larger ratio of the opacities at the 18 and 10-micron peaks, compared with circumstellar silicates. By using an effective-medium theory, we calculate the effects of small spherical inclusions of various materials (various oxides, sulfides, carbides, amorphous carbon, and metallic iron) upon silicate opacities. Some of these can increase the absorption coefficient k in the 2-8 micron region appreciably, as is needed to reconcile laboratory silicate opacities with observations of both the interstellar medium and envelopes around late-type stars. We give tables of two sets of optical constants for warm oxygen-deficient and cool oxygen-rich silicates, representative for circumstellar and interstellar silicates. The required opacity in the 2-8 micron region is provided by iron and magnetite.
Henning Th
Mathis John S.
Ossenkopf Volker
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