IUE observations of the UV spectrum of comet Bradfield

Abstract

Comet Bradfield (1979l), discovered shortly after perihelion, on Christmas day 1979, is characterized by a retrograde orbit of period ≈250yr. This orbit was very favourable for observation by the IUE satellite¹, and the first observations, the preliminary results of which are reported here, were made on 10 and 11 January 1980. Previously, comprehensive vacuum UV cometary spectra were available only for Comet West (1976VI) from rocket observations^2,3 and Comet Seargent (1978m) obtained with IUE⁴, hence three comets have now been observed in the wavelength region where most of the major constituents are detectable spectroscopically. The UV spectra of these comets are remarkably similar, despite large differences between them in the gas-to-dust ratio and the different heliocentric distances at which the observations were made, and although the statistical basis is still very small, the implication for cosmogony is that nearly all comets have the same primary composition and origin.