On the particle-size distribution function of cometary dust

The characterization of the particle size distribution in cometary tails is considered. The particle-size related distribution function of the acceleration exerted on the cometary particle by solar radiation pressure used by Finson and Probstein (1968) is introduced, and distribution functions observed for the comets Arend-Roland 1957 III, Bennett 1970 II and Seki-Lines 1962 III are illustrated. It is pointed out that although the distribution functions have features in common, the rate of decrease of the distribution towards zero acceleration (large particles) is not well determined. An approximation for the size distribution in this range obtained from a photometric study of anomalous cometary tails is presented, and used to formulate an a priori distribution law which can be used to approximate all types of expected distributions by varying three key parameters.