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[31.02] Interferometric imaging of molecular lines in comet Hale-Bopp

D. Bockel\'ee-Morvan (Observatoire de Paris), J Wink (IRAM), D. Despois (Observatoire de Bordeaux), N. Biver (IfA, University of Hawaii), P. Colom, J. Crovisier, E. G\'erard, E. Lellouch (Observatoire de Paris), L. Jorda (MPI fur Aeronomie, Katlenburg-Lindau)

Comet Hale-Bopp has been observed in October and March 1997 at the IRAM Plateau de Bure Interferometer. Millimetre lines of 8 molecules (HCN, HNC, CO, H₂CO, H₂S, SO, CS and CH₃OH) have been mapped with spatial resolutions of 1 to 3 arcsec. Both spectra and maps present temporal modulations linked to the nucleus rotation period of 11.3 hours, showing the presence of rotating molecular structures in the coma. The rotating CO jet remains equally active during both day and night, indicating CO production from below the surface. The analysis of the radial distribution of the molecules shows that some species are not directly released from the nucleus. Best evidences are for H₂CO et SO. The comparaison between HCN and HNC maps shows that these two species have similar photodissociation lifetimes. Evidences that HNC is produced in the coma are seen, supporting its formation in the coma by chemical reactions, as proposed for explaining the heliocentric variation of its abundance. Simultaneous maps of several lines of CH₃OH at 241 GHz allow us to study the evolution of the rotation temperature with distance to nucleus. The coldest temperatures found in the outer coma agree with excitation model.