Journal Article

The 10-μm profile of molecular-cloud and diffuse ISM silicate dust

J. E. Bowey, A. J. Adamson and D. C. B. Whittet

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 298, issue 1, pages 131-138
Published in print July 1998 | ISSN: 0035-8711
Published online July 1998 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1998.01640.x
The 10-μm profile of molecular-cloud and diffuse ISM silicate dust

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Abstract

High signal-to-noise ratio spectra are presented of the 10-μm silicate absorption feature in lines of sight towards Elias 16 and 18 in the Taurus dark cloud, and towards the heavily reddened supergiant Cyg OB2 no. 12. The observations are fitted with laboratory and astronomical spectra to produce intrinsic absorption profiles. These features, which represent molecular-cloud and diffuse ISM dust respectively, are better fitted with emissivity spectra of the Trapezium and μ Cephei than they are with those of laboratory, terrestrial, or other observations of circumstellar silicates. The difference in width between the silicate band in the two environments can be almost entirely ascribed to a broad excess absorption in the long-wavelength wing of the profiles, which is much stronger in the molecular-cloud lines of sight, and possibly reflects grain growth in the denser environment. Limits are placed on the strength of fine spectral structure; if there is a crystalline silicate component in these spectra, it is most likely to be serpentine. Column-density upper limits for methanol and the photolysis product hexamethylenetetramine (HMT) are less than a few per cent of those of water ice and silicates.

Keywords: ISM: clouds; dust; extinction; ISM: molecules; infrared: ISM: lines and bands

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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