Submillimeter molecular line observations of cometary Levy (1990c)

Abstract

Observations of HCN and H2CO in Comet Levy (1990c) obtained at the Caltech Submillimeter Observatory during August 1990 are presented. The HCN J=3-2 rotational line was measured at high spectral resolution (0.1 km/s) and mapped at 13 points over a region of approximately 1.5 arcmin. Analysis of the line profile and the map suggest only slight deviations from the distribution expected for isotropic outgassing of HCN from the nucleus at a velocity of 0.7 plus or minus 0.1 km/s. Observations of the HCN J=4-3 and H2CO5(sub 15)4(sub 14) transitions were obtained simultaneously on two days following the HCN J=3-2 measurements. These transitions are the first submillimeter spectral lines to be detected in a comet. Five point maps of the emission show good consistency between the J=3-2 and J=4-3 HCN observations for an HCN production rate of 2 x 10(exp 26) and a rotational temperature of approximately 30 K. The map of H2CO emission indicates that it is more extended than the prediction of models in which H2CO originates entirely from the nucleus. H2CO may also originate from an extended source in the coma