Millimeter-wavelength spectroscopy of CO, HCN, H2CO, and CH3OH in C/1996 B2 (Hyakutake)

Millimeter-wavelength spectra were obtained of CO, HCN, H2CO, and CH3OH in comet C/1996 B2 (Hyakutake) with the NRAO 12m telescope on Mar 21, 1996 UT. The emission of CO, H2CO, and HCN was mapped in the coma when the comet was ∼0.16 AU from the Earth, providing a detailed look at the behavior of these species in the inner coma. The mapping data reveal that line profiles, velocity offsets and spatial profiles are not alike for all four molecules. Each coma species shows properties of its own as if they were not determined by their interaction with the water molecules. This preliminary report shows that excitation conditions are the most important factor in shaping the observed lines. Also presented are production rates for these species near perigee.