Properties and evolution of dust in Comet Tabur (C/1996 Q1) from the colormaps

Spectrophotometric CCD (charge-coupled detector) observations of Comet Tabu r (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 wa s used to reveal quantitative characteristics of the dust from the data. Th e size distribution, optical properties of the dust material, and their cha nge with cometocentric distance were obtained. We have found that in the ne ar-nucleus region the dust of Comet Tabur can be described by a power-law s ize distribution with the power around 2.75-2.95, the lower limit of partic le radii approximate to4.04 + 0.14 mum, and the upper limit of the order of several centimeters. The color trends showed that particles became a bit s maller with the distance from the nucleus, but the power of their size dist ribution remains the same. The change of their size is accompanied by a cha nge in their composition, that could be presented as evaporation of icy or organic grains in a mixture of grains of various composition, or as sublima tion of icy mantles from silicate cores or organic mantles from silicate-ca rbon cores. An ejection in the Sun direction of smaller and of different co mposition particles was seen from the color scans. These particles had a sh ort lifetime and showed light-scattering properties that are typical for ei ther very transparent particles (perhaps, ice) or particles with the refrac tive 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 . (C) 2001 Academic Press.