[Previous] | [Session 17] | [Next]
F.P. Schloerb, A.J Lovell, C.H. DeVries, A Chander (FCRAO)
Observations of the 18-cm OH transitions in comets provide a means to measure gas production, kinematics, and OH excitation in comets. We present the results of modelling of observations of the radio OH emission from Comet Hale-Bopp, obtained with the NRAO 43m antenna located in Greenbank, W.V. The radio emission from Comet Hale-Bopp was monitored during August 1996 - September 1997. The strength of the signal was sufficient to enable mapping observations of the coma, which is extended even in the 18 arcmin telescope beam. In this paper, we present the results of fitting models of gas outflow to the radio spectral line maps. The model parameters include the parent outflow velocity, a day-night asymmetry in the gas production from the nucleus, and collisional quenching of the radio emission in the inner coma. We find, in the case of the March 1997 maps, that the models require: (1) a significant day-night asymmetry to explain the line shapes; and (2) quenching of the radio emission in the inner 400,000 km of the coma to explain the observed radial fall-off in the maps. The very large scale of the collisionally quenched region appears to be consistent with the very high gas production of Comet Hale-Bopp.