Comets Okazaki-Levy-Rudenko (1989 XIX) and Levy (1990 XX): Polarimetry and Stellar Occultations

Abstract

The results of polarimetric observations of comets Okazaki-Levy-Rudenko 1989 XIX and Levy 1990 XX and two stellar occultations by the latter comet are presented. Wavelength, phase angle, and aperture dependences of polarization are discussed. During the outburst activity of comet Levy variations of the polarization parameters were registered. From a stellar occultation by comet Levy the optical thickness of the coma is found to be τ = 0.40 ± 0.06 at a distance of 3500 km from the nucleus on the sunward side. The measured light flux, negative polarization, and high optical thickness in the observed regions of coma assume the presence in the coma of either a large number of Rayleigh particles with addition of some large ones, or a large number of absorbing fluffy grains on which multiple reflections of light are possible, or their mixture. Analysis of the polarimetric observations of occulted stars by the comet indicates the presence of oriented nonspherical particles in the coma. The observations of stellar occultations are seen to be useful probes of oriented and Rayleigh particles.