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IRAS low-resolution spectral observations of the 10 and 18 micron silicate emission featureThe IRAS LRS Atlas contains 8-23 micron spectra of 1816 stars with silicate emission features. In order to study the shapes of the silicate dust features, the 117 stars whose emission features appear to be optically thin and which have the best signal-to-noise ratio at the longest wavelengths were analyzed. Simple spherical dust shell models were calculated in both the optically thin and the slightly optical thick approximations. From the comparison of the predicted spectra of the dust and stellar continuum, the emissivity function Kappa(lambda) was derived. In the different stars, the shape of the 10-micron feature is either narrow or broad and it is peaked either at about 9.7 microns or at 10 microns. Either particle size effects (particles above 0.75 microns in radius) or optical depth effects (central optical depth about 1) could broaden the 10-micron feature. Chemical composition differences no doubt are also important, particularly as regards the position of the peak of the 10-micron feature. The stars with the peak at 10 microns are more closely confined to the Galactic plane than the stars with the peak at 9.7 microns. The shape of the 18-micron feature is essentially the same in all stars, and can be used to extend the interstellar extinction curve past 13 to 22 microns.
Document ID
19910041753
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Simpson, Janet P.
(NASA Ames Research Center Moffett Field; California, University, Berkeley, United States)
Date Acquired
August 14, 2013
Publication Date
February 20, 1991
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 368
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
91A26376
Funding Number(s)
CONTRACT_GRANT: NCC2-548
Distribution Limits
Public
Copyright
Other

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