Water Production Rates in Comet P/Halley from IUE Observations of HI Lyman-β

Abstract

During the 1985-1986 apparition of Comet P/Halley, the International Ultraviolet Explorer (IUE) satellite observed the comet using both the long-wavelength and short-wavelength spectrographs. The combination of a spherical radiative transfer model and the hybrid gas-dynamic/Monte Carlo model for hydrogen coma, which had been used to analyze H Lyman-α IUE observations of Comet P/Giacobini-Zinner, has been applied to a large body of H observations of Comet Halley taken with the short wavelength spectrograph. The data include nucleus-centered large aperture observations as well as a few serendipitous offset observations. The inferred water production rates from the nucleus-centered observations are compared herein with a self-consistent analysis already performed for the IUE observations of OH. The agreement is quite good despite the high degree of optical depth in the coma during its most active periods. The results imply that, in order to bring the H and OH observations into agreement at all heliocentric distances, a model for OH which accounts for the variation of the outflow speed of the coma with heliocentric distance is required.