Open AccessThe 10‐μm profile of molecular‐cloud and diffuse ISM silicate dust
Author(s) -
Bowey J. E.,
Adamson A. J.,
Whittet D. C. B.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01640.x
Subject(s) - physics , silicate , spectral line , astrophysics , molecular cloud , absorption spectroscopy , absorption (acoustics) , opacity , line of sight , astronomy , stars , optics
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.