A search for millimeter-wave emission from HCN, CO, and CH 3CN in Comet Bradfield (1978c)

Abstract

Millimeter wavelength emission from the “parent” molecules HCN, CO, and CH 3CN, the latter in both its ground and ν 8 = 1 excited vibrational states, was sought from Comet Bradfield (1978c) during March 1978 after comet perihelion, when the heliocentric distance was between 0.45 and 0.55 AU. No lines were detected, and upper limits on the molecular column densities (averaged over the antenna beam) and production rates, Q are estimated. The upper limits on Q for HCN, CH 3CN ( ν 8 = 0), and CH 3CN ( ν 8 = 1) are less than the production rates inferred from the millimeter-wave detection of these species in Comet Kohoutek (1973f). The CO upper limit on Q is comparable to that inferred from a detection of Comet West (1975n) in the rocket uv. It seems likely that the total gas production rate of Comet Bradfield (1978c) was relatively low.