Observations of unusually small dust grains in the coma of comet Hale-BoppC/1995 O1

We present 1.2-18.3 mum photometry of comet 1995 01 (Hale-Bopp). Our observ ations spanned nearly 4 months pre- and post-perihelion. The dust grain siz e-dependent parameters of superheat, 10 mum silicate excess, and albedo are used to make determinations about the Hale-Bopp coma grain population. The evolution of the coma grain size distribution is tracked by measuring thes e parameters over a range of heliocentric distances. We also observed sever al regions in the Hale-Bopp coma revealing significant gradients in the mea sured color temperature suggesting differences in the dust grain size distr ibution. Finally, we compare the grain size-dependent parameters to those o f 11 other bright comets. The extreme values of these parameters displayed by Hale-Bopp suggest it had a smaller mean dust grain size than those assoc iated with the other comets.