Mosaicked images and spectra of J = 1 → 0 HCN and HCO⁺ emission from comet Hale-Bopp (1995 O1)

We used the BIMA array to map comet Hale-Bopp (1995 O1) in HCN and HCO⁺ emission at 89 GHz with 10″ angular resolution. The mosaicked images with seven pointing centers were combined with single-dish data to form completely sampled images of a region ∼ 4′ in diameter. The HCN image is roughly compatible with a Haser model in which most of the HCN comes from the nucleus. However, clear deviations from circular symmetry are present, and roughly 20% of the HCN does not appear to come from the nuclear source. Frequently, the HCN has an asymmetric, double-peaked profile. The double peak is expected from the Haser model, and the asymmetry observed on April 3 could come from an increased gas production toward the Sun and facing the observer. The abundance of HCN relative to H₂O is ∼ 0.3%. The HCO⁺, in contrast, is smooth, almost completely resolved in the interferometer observations, and offset toward the ion tail by about 1′. This behavior is compatible with expectations from a simple scaling of previous work.