ANALYSIS OF HYDROGEN LYMAN-ALPHA OBSERVATIONS OF THE COMA OF COMET P HALLEY NEAR PERIHELION/

The Pioneer Venus Orbiter Ultraviolet Spectrometer measurements of the Lyman-alpha intensity of atomic hydrogen excited by solar resonance s cattering in the coma of Comet P/Halley acquired from December 28, 198 5, to January 6, 1986, and from January 31, 1986, to March 6, 1986, ar e simulated with the Monte Carlo Particle Trajectory Model corrected f or optical depth effects. Spatially detailed comparisons between data and model show excellent agreement and are used to infer that the high est cometary activity may not be at perihelion, but about 2 1/2 weeks before. An improved set of H2O production rates is presented for the p eriod of time that the spectrometer was observing and is found to be c onsistent with the rates from other types of measurements. The apparen t discrepancy between Stewart (1987, Astron. Astrophys. 187, 369-374) in early March and International Ultraviolet Explorer OH derived rates is resolved. The problem with the conversion of 18-cm OH radio bright nesses to H2O production rates is also discussed. (C) 1995 Academic Pr ess, Inc.