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Dispersion of Polarization in Reflection Nebulae

Published online by Cambridge University Press:  08 February 2017

Thomas Gehrels
Thomas Gehrels*
Affiliation:
University of Arizona, Tucson, Arizona

Extract

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A Few Observations Were Made in NGC 7023 with filters at 0.36, 0.56, and 0.74 μ The wavelength dependence of polarization fitted with a straight line shows an appreciable rise with longer wavelengths. (See refs. 1 and 2.) The observations at the three filters were compared with Mie calculations obtained from Dr. B. M. Herman and General S. R. Browning of the University of Arizona for various refractive indices and particle sizes. Only single particle sizes have been considered, and therefore the results are preliminary. The present work represents a first reconnaissance to learn the techniques and some of the geometrical conditions.

A firm conclusion, however, is reached in ruling out purely graphitic and purely metallic interstellar grains. The reasoning is as follows: The polarizations in various reflection nebulae (observed by Elvius and Hall) are “positive” and strong, and the color dependence is strong, with a fairly steep rise toward longer wavelengths; this behavior occurs for scattering angles from 20° to 70°. Such behavior is found in the Mie calculations at 2<a/λ ≅ 1.5. (See ref. 3.)

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 7: Proper Motions , August 1965 , pp. 105 - 109
Copyright
Copyright © Kluwer Academic Publishers 1965

References

1. Thomas, Gehrels; and Teska, Thomas M.: The Wavelength Dependence of Polarization. Appl. Opt., vol. 2, 1963, p. 67.Google Scholar
2. Gehrels, T.: Measurements of the Wavelength Dependence of Polarization. Lowell Obs. Bull., vol. 4, 1960, p. 300.Google Scholar
3. Van De Hulst, H. C.: Light Scattering by Small Particles.” John Wiley & Sons, Inc., 1957, pp. 152–153.Google Scholar
4. Gehrels, T.: The Wavelength Dependence of Polarization II Interstellar Polarization. Astron. J., vol. 65, 1960, p. 472.Google Scholar