Analysis of coma dust optical properties in Comet C/1995 O1 (Hale-Bopp) II. Effects of polarization

Efforts to apply a single-scattering polarized radiative transfer code to i nterpret photopolarimetric measurements of coma dust optical properties in Comet Hale-Bopp corroborate previous photometrically derived conclusions co ncerning the predominance of small sized particles in Hale-Bopp's coma. Cal culations of the degree of linear polarization (DP) as a function of observ ation phase angle (alpha) produced by prolate spheroidal crystalline olivin e particles with effective radii (a = 0.216 mum) are compatible with the co met's measured polarization in standard filters at lambda = 0.4845 and 0.68 4 mum. Our rudimentary "trade-off" studies highlight the extreme sensitivit y of DP to dust particle size and shape. A combination of viewing geometry effects in association with enhanced multiple scattering might provide a qu antitative explanation of the negative polarization for 0 degrees less than or equal to alpha less than or equal to 20 degrees seen in Hale-Bopp and o ther comets. (C) 2001 Academic Press.