The Dust Coma of Comet C/1999 S4 (Linear)

Comet C/1999 S4 (LINEAR) showed a very special behaviour between 28 June and1 July 2000. Optical observations of the dust coma in two distinct continuum bandsrevealed that it changed morphologically as well as in colour. The two-dimensionalcoma morphology indicates a splitting of the nucleus which probably occurred shortlybefore the observations of 28 June 2000. The distribution of the dust particles in sunand tail direction reflected by the slopes of the radial profiles indicate the presence ofa considerable amount of disintegrating dust particles in the sunward hemisphere andan overabundance of dust, reflecting at 440 nm, within the first 18,000 km of the dusttail. The spatial profiles of the (BC–RC) colour index in sun direction are distinctly different on 28 June and 1 July, indicating the production of a large amount of particles observable in blue continuum after 28 June.