18-cm wavelength radio monitoring of the OH radical in comet P/Halley 1982i

Abstract

The 1667 MHz and 1665 MHz transitions of the OH radical were detected and monitored nearly daily in comet Halley 1982i with the Nan9ay radio telescope. The observations cover the period July 1985 to July 1986 and provide a unique test for the excitation mechanisms of the OH molecule and the kinematic models ofthe OH coma. The heliocentric velocity range was fully observed between - 26.8 and 26.8 km s - 1 and 6 line reversals were covered. The OH-parent production rate of P/Halley was measured between 3.4 AU (pre-perihelion) and 2.8 AU from the Sun (post-perihelion). We find new effects like significant short- term variations of the OH-parent production rate in a few days, large variations of the half power profile width and anomalous line shapes.