OH radio observations of Comet Halley

Results of OH observations of P/Halley obtained with the NRAO 43 m antenna between July 1985 and May 1986 are presented. Using Radio Model 1986a, the OH production rate derived from these data follows an rh(-2) law for heliocentric distances in the range 0.6 to 2.1 AU. Comparison of radio OH production rates to those estimated by UV techniques continues to show that the radio technique finds systematically lower production rates. Observations of the OH line shape show that the line width increases as the comet approaches perihelion, and that the broader line widths persist after perihelion out to at least rh = 1AU. Modeling of the profiles suggest that this may be accounted for through an increase in the velocity of the OH parent. The mean velocity of the OH emission (after correction for the OH Greenstein effect) is slightly blue shifted compared to the nucleus velocity and suggests that the outgassing from the nucleus is largely directed sunward.