Properties and Evolution of Dust in Comet Tabur (C/1996 Q1) from the Color Maps

Abstract

Spectrophotometric CCD (charge-coupled detector) observations of Comet Tabur (C/1996 Q1) allowed us to accomplish a detailed multi-color photometry of cometary continuum in the near-nucleus region and to obtain the change of spectral properties of the cometary dust with the distance from the nucleus. The technique suggested by L. Kolokolova, K. Jockers, G. Chernova, and N. Kiselev (1997, Icarus 126, 351–361) and further developed in this paper was used to reveal quantitative characteristics of the dust from the data. The size distribution, optical properties of the dust material, and their change with cometocentric distance were obtained. We have found that in the near-nucleus region the dust of Comet Tabur can be described by a power-law size distribution with the power around 2.75–2.95, the lower limit of particle radii ≈0.04–0.14 μm, and the upper limit of the order of several centimeters. The color trends showed that particles became a bit smaller with the distance from the nucleus, but the power of their size distribution remains the same. The change of their size is accompanied by a change in their composition, that could be presented as evaporation of icy or organic grains in a mixture of grains of various composition, or as sublimation of icy mantles from silicate cores or organic mantles from silicate–carbon cores. An ejection in the Sun direction of smaller and of different composition particles was seen from the color scans. These particles had a short lifetime and showed light-scattering properties that are typical for either very transparent particles (perhaps, ice) or particles with the refractive index higher (such as dark organics) than the one for the surrounding coma. The ejection was more pronounced on September 13 than on September 16.