MODELING OF MIDINFRARED DUST EMISSION FROM P SWIFT-TUTTLE/

Comet P/Swift-Tuttle was observed at 11.7 mu m on 12 nights over the c ourse of three weeks in November 1992 using the UCSD mid-infrared imag ing camera (Fomenkova et nl., 1995). The large number of images obtain ed and the overall high quality of the data permit the continued study of the rich dust structures apparent in this active comet. We present a model to interpret the features observed in these images using oliv ine spheres (MgFeSiO4) as representative dust grains, and illustrate t he validity of the model by applying it to the image taken on UT 9. 1 November. A fully three-dimensional Monte Carlo simulation based on :t he Finson-Probstein model (1968) is performed, and Mie scattering theo ry is used to characterize the properties of the grains. We found that the comet executes simple rotation about an axis whose obliquity is 4 5 +/- 10 degrees. Our best-fit dust grain size distribution in the siz e range from 0.6 to 10.0 mu m is of the form f(a) similar to a(-beta) with beta = 2.5 +/- 0.5, not quite as steep as the distribution (beta = 3.7) measured for comet P/Halley (McDonnell er al., 1991). (C) 1998 Elsevier Science Ltd. All rights reserved.