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Graphite Grains and Graphite-Core-Ice-Mantle Grains

Published online by Cambridge University Press:  08 February 2017

N. C. Wickramasinghe
N. C. Wickramasinghe*
Affiliation:
California Institute of Technology, Pasadena, California

Extract

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Among the First Requirements for a Grain Model is that it should explain the observed interstellar extinction law or laws as they are now understood; a desirable feature of such a model is that as few ad hoc assumptions be made as possible.

A criticism of the classical ice grain theory is that a very narrow range of grain sizes (or a size distribution with a size parameter specified to within a few percent) must be postulated in order to obtain a fit with the mean extinction law. (See refs. 1 and 2.) While it is true that regional variations in the extinction law have recently been detected (refs. 3 and 4), the best available evidence indicates that the extinction law is quite uniform when averaged over individual large regions which are widely distributed in the galaxy. (See ref. 5 and paper by Nandy in the present compilation.) The restriction of particle size to a radius within a few percent of an arbitrarily specified value (r ≈ 3 X 10-5 cm) demanded on the basis of pure ice absorption is therefore considered quite unsatis-factory, particularly in view of the fact that no characteristic size parameter emerges from the Oort-van de Hulst theory for the formation and destruction of grains. (See ref. 6.)

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 7: Proper Motions , August 1965 , pp. 167 - 184
Copyright
Copyright © Kluwer Academic Publishers 1965

References

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