Light from Reflection Nebulae. I. Dielectric Versus Metallic Particles

Abstract

Calculations have been performed for a wide variety of models of reflection nebulae and for a range of nebular grain optical characteristics. Several variations in the theory have been considered, based on pure single scattering and single scattering modified by internal nebular extinction. All the calculations use the scattering by spheres as given by Mie theory. A criterion based on the B - V color difference between the star and the nebula is developed which may be used to exclude either classical dielectric grains (radius 0.3 ) or small (radius 0 Os metallic, graphite, or dielectric grains. For those cases in which the illuminating star is at or near the front surface of the nebula the small metallic and dielectric grains always produce a significantly bluer color of the nebula than do the classical dielectric grains. Furthermore, on the basis of a homogeneous plane-parallel slab geometry for the nebula, the degree of variability of the nebular color is much greater for the classical dielectric grains than for the metallic grains.