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L. Kolokolova, B.\AA.S. Gustafson, J. Thomas-Osip, J. Loesel (UF)
Microwave analog experiments allow us to study particles of almost any combination of composition, size and shape. We have taken advantage of this ability and the broadband nature of the University of Florida microwave facility to obtain the intensity, polarization, color, and polarimetric color for a range of particle types. Here we present results for aggregates as the most probable type of cometary grains. These may be particles of size close to the wavelength of visible light aggregated to form structures very large compared to the wavelength. These circumstances make a theoretical study of the light scattered by cometary dust exceedingly difficult and, at least in part, beyond the capability of common numerical techniques. We selected aggregates made of polystyrene, nylon and a mixture of expanded plastic and iron oxide. These materials are, with their refractive indices near 1.6-0.03i, 1.74-0.005i, and 1.7 - 0.2i, microwave analogues to silicates and organic materials expected in cometary dust. The angular dependencies of intensity and polarization were obtained in the scattering angle range [0,165o], and in the wavelength intervals [2.7-3] and [3.5-4] mm, to simulate cometary continuum filters at 0.442 and 0.642 \mu m. The study of light scattering properties of a range of aggregate types and the comparison of laboratory data with data of photometric and polarimetric observations of comets allow us not only to estimate the size and structure of cometary grains but also to study their evolution with distance from the nucleus.
The author(s) of this abstract have provided an email address for comments about the abstract: ludmilla@astro.ufl.edu