Spectrophotometry of 17 comets. I - The emission features

Abstract

112 sets of image dissector scanner data were obtained at Lick Observatory from 17 comets during a 2.5-yr period, 1980 - 1982. Results obtained include column densities for CN, C<SUB>3</SUB>, CH, C<SUB>2</SUB>, and [O I], new Haser parent scale lengths for CN, C<SUB>3</SUB>, and C<SUB>2</SUB>, and a large body of data on the composition of cometary comae as a function of heliocentric distance. Particularly notable is the well-defined C<SUB>2</SUB> to CN ratio, which decreases roughly as r<SUP>-1.4</SUP> out to r ≅ 1.8 AU and then falls precipitously. Although there is considerable chemical uniformity in most comets studied, two (P/Borrelly and P/Swift-Gehrels) appear significantly deficient in both C<SUB>2</SUB> and C<SUB>3</SUB>. The apparent systematics within the crude Haser paradigm offer suggestions for more realistic chemical modelling studies.