Pre- and postperihelon abundances of gas and dust in comet Halley

Photometrically calibrated spectra of comet P/Halley (1986 III) were recorded between 1985 September 12-1986 June 10 using the Ohio State University Image Dissector Scanner on the Perkins 72 inch telescope at the Lowell Observatory. Column densities of CN, C3, CH, C2, and NH2 were calculated from measured fluxes in these spectra, and molecular scale lengths were deduced from the radial distribution of CN, C3, C2, and NH2. Production rates were computed using the new scale lengths and a Haser model analysis. Continuum emission at 4260 A was used to derive gas-to-dust ratios. The data indicate than comet Halley was approximately 2-5 times more abundant in gas and dust at postperihelion than preperihelion. On 1986 June 8 we observed the onset of a cometary ourburst which appeared very strong in dust production. The gas-to-dust ratios appeared to be subject to changes as a result of short-term outbursts but otherwise did not exhibit any systematic dependence on heliocentric distance. Reflectivity gradients of the continuum were also measured from the spectra. While most of the continua were red, blue continua were also observed which may be correlated with dust outbursts.