ANALYSIS OF HYDROGEN H-ALPHA OBSERVATIONS OF THE COMA OF COMET P/HALLEY

Ground-based Fabry-Perot observations of the hydrogen coma of comet P/Halley in the Ha (6563 angstrom) line were acquired on 10 nights between 1985 mid-December and 1986 mid-January. These observations are analyzed using a Monte Carlo Particle Trajectory Model. Model calculations were undertaken for both the line profile and the two-dimensional Halpha brightness on the sky plane. Model calculations accurately reproduced both the measured line profile and the integrated brightness obtained through the observing aperture. The H2O production rates determined in this manner were compared with revised values derived from [O I] 6300 angstrom observations of comet Halley, also taken with the same instrument. For measurements obtained on the same day, these two H2O production rates are in excellent agreement. This agreement verifies and demonstrates the underlying consistency of the H2O photochemistry and coma outflow dynamics for comet Halley. Comparisons of these H2O production rates were also made with H2O production rates determined by other independent observations of the H and OH comae, where the various measurements sampled different spatial scales and had different aperture locations. Because of the different time delays and spatial averaging introduced by the different spatial scales and aperture locations, the derived H2O production rates will not be identical to the instantaneous H2O production rates at the nucleus. The derived H2O production rates determined on the same day from the different measurements were, nevertheless, in excellent agreement with only small differences that were qualitatively consistent with the expected time delays. Collectively these observations provide a nearly daily time coverage for the H2O production rates from almost 50 days preperihelion to 130 days postperihelion with only one 18 day preperihelion gap.