Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000esasp.456..343h&link_type=abstract
ISO beyond the peaks: The 2nd ISO workshop on analytical spectroscopy. Eds. A. Salama, M.F.Kessler, K. Leech & B. Schulz. ESA-SP
Astronomy and Astrophysics
Astronomy
7
Ir Spectra, Artifacts, Crystalline Silicates, Amorphous Features, Sic, Dust Size
Scientific paper
Infrared (IR) spectra of powder dispersions are prone to artifacts. Understanding the conditions under which artifacts are produced in laboratory spectra, allows intrisic features in IR spectra of dust in astronomical enviroments to be distinguished. The types of problems that can occur are illustrated by examples of SiC, SiO2 (quartz), and two chain silicates. Position, width, maximum absorbance, as well as relative intensity are all altered by sampling conditions (film thickness, i.e. path length, and the percentage of the total area that the sample effectively covers) but to degrees dependent on the strength of the band. As thickness increases above <= 0.1 μm, strong bands, e.g. Si-O stretching in the 10 μm region, become increasingly rounded and flat-topped, due to light leakage around the particles. The absorbance depends on the amount of sample coverage. The observed smooth, near featureless, 10 μm profiles of astronomical dusts could thus be produced by sub-micron-sized crystalline silicates (see also teHOFM_bowey11;b). The 10 μm region is expected to be problematic for species indentification when the dust cloud is dense or has large grains. Care must be taken in interpreting this region and the intense peaks near 20-25 μm. Due to the large variation of extinction coefficients among the various IR peaks in silicates, for a dust or dispersion, particles creating optically thin spectra in the mid-IR are not the same particles that create the far-IR patterns.
Bowey Janet E.
Hofmeister Anne. M.
Keppel E.
Speck Angela Karen
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