An analysis of the infrared continuum of comets

Observations of infrared cometary continua which depend on thermal emission from grains are a powerful supplement to deductions concerning the nature of grains from light scattering in the visible. For grains of dirty ice, iron, quartz, and graphite, the absorption cross-section, angular scattering cross-sections, and thermal emission have been calculated. From these the grain temperature as a function of heliocentric distance has been obtained. This determines a theoretical cometary flux distribution which may then be compared with observed data. The analysis is applied to the infrared observations of Comet Ikeya-Seki 1965f of Becklin and Westphal. Reliable evaluations of grain properties do not appear possible from existing measurements