Molecular Line Imaging of Comet Hale-Bopp

J. E. Dickens, A. J. Lovell, C. H. De Vries, W. M. Irvine, F. P. Schloerb, M. C. Senay (FCRAO U. Massachusetts-Amherst)

We present images of comet C/1995 O1 Hale-Bopp in the millimeter-wave emission of the neutral gases HCN and CS. The data were obtained between October, 1996, and June, 1997, using the 15-element QUARRY focal plane array on the Five College Radio Astronomy Observatory (FCRAO) 14-m telescope. This observing campaign represents the first long-term cometary molecular mapping program, and concentrates on the HCN J=1-0 rotational transition, along with CS J=2-1 during the months surrounding the comet's perihelion passage. Significant, time-variable asymmetries are visible in the maps, and when both HCN and CS were mapped close in time to one another, asymmetries and elongations are correlated in the two molecular line images. Preliminary modelling suggests the observed asymmetries can be accounted for by anisotropic emission of gas from the nucleus, with perhaps 25-50% of the emission occuring in ``jets.''