[Previous] | [Session 31P] | [Next]
F. Peter Schloerb, Amy J. Lovell (FCRAO/Univ. of Mass.)
Millimeter-wave spectral line maps of the molecular emission from comets provide significant constraints on the behavior of outgassing from the comet nucleus and expansion of gases in the coma. We have developed a simple model of gas outflow in the coma for comparison to observations of C/1996 B2 Hyakutake and C/1995 O1 Hale-Bopp which were made with the FCRAO 14m telescope and its focal plane array receiver (Lovell {\it et al.}, this conference). We find that the observations of the brightness distribution and line profile of HCN in comet Hyakutake are typically inconsistent with either spherically-symmetric or preferentially sunward emission. In order to reproduce the observed line shapes and map morphologies, our model suggests that approximately half of the HCN emission originates in small asymmetric "jet" features. Modelling results from comet Hale-Bopp also suggest that the asymmetric velocity structure in the observed lines requires spatial asymmetry in the emission, though generally on scales below the spatial resolution of the data. Our model also employs a simple excitation model to estimate the gas production rates of the comets. The derived production rates generally follow the expected trend with heliocentric distance; however, the data for comet Hyakutake are consistent with the observed visual brightening in the comet a few days prior to its perigee.