Interstellar Extinction Law Research Articles

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.)

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