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On the Origin of the 10 Micron Depressions in the Spectra of Compact Infrared Sources

Kwan, John and Scoville, Nick (1976) On the Origin of the 10 Micron Depressions in the Spectra of Compact Infrared Sources. Astrophysical Journal, 209 . pp. 102-107. ISSN 0004-637X. doi:10.1086/154696.

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The 10 µ depression observed in the spectrum of a compact infrared object is usually ascribed to absorption by intervening cold silicate grains, and the underlying source spectrum is taken to be either a blackbody or a blackbody with superposed excess 10 µ emission. We question this assumption of the underlying source spectrum for optically thick compact sources. We find, upon modeling both the objects BN and W3 IRS5, that the source actually emits less at the 10 µ resonance than outside the resonance, so that a depression at 10 µ already exists in the source spectrum. This difference in emission arises because, due to the higher opacity in the resonance, the observed 10 µ radiation is produced further out in the source than is the radiation just outside the resonance. And the lower dust temperature further out gives rise to a weaker emission at 10 µ than in the continuum. An observed 10 µ depression can be largely due to this effect, and little or no intervening extinction is required. This explanation of the 10 µ depression leads to a correlation such that the magnitude of depression will increase with decreasing color temperature of the source. It also predicts no depression at 20 µ for sources with color temperatures greater than 200 K. Observations at 20 µ would then be able to decide on the validity of this explanation.

Item Type:Article
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Scoville, Nick0000-0002-0438-3323
Additional Information:© 1976. The American Astronomical Society. Received 1975 December 29; revised 1976 March 12. We thank Dr. R. Knacke and an unknown referee for helpful comments.
Subject Keywords:infrared: sources — opacities
Record Number:CaltechAUTHORS:20190403-153007836
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94423
Deposited By: George Porter
Deposited On:05 Apr 2019 19:37
Last Modified:16 Nov 2021 17:05

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