The dust grains in the coma of Comet West

Abstract

The observed variation of reddening as function of the heliocentric distance and the spatial variation of reddening within the coma of Comet West in the visual wavelength range have been considered to infer the properties of the cometary dust grains. The relevant model incorporates the variation in the size distribution function as well as the composition of the spherical grains. The real part of the complex index of refraction (m = m' - im'') is chosen such that m' = 1.6. The imaginary part is required to vary from m'' = 0.2 to 0.05 over the wavelength range 0.4 to 0.7 Mm. This choice of refractive index corresponds to dirty silicate grains. As a by-product, the model also satisfies the observed polarization and albedo for the Comet West.