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Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in cometC/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bureinterferometer on 11 March, 1997. The observations were conducted in bothsingle-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectralresolution. Images of CO emission with 1.7 to 3" angular resolution wereobtained. The ON-OFF and interferometric spectra show a velocity shift withsinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35h. The peak position of the CO images moves perpendicularly to the spin axisdirection in the plane of the sky. This suggests the presence of a CO jet,which is active night and day at about the same extent, and is spiralling withnucleus rotation. The high quality of the data allows us to constrain thecharacteristics of this CO jet. We have developed a 3-D model to interpret thetemporal evolution of CO spectra and maps. The CO coma is represented as thecombination of an isotropic distribution and a spiralling gas jet, both ofnucleus origin. Spectra and visibilities (the direct output of interferometricdata) analysis shows that the CO jet comprises ~40% the total CO production andis located at a latitude ~20 degrees North on the nucleus surface. Ourinability to reproduce all observational characteristics shows that the realstructure of the CO coma is more complex than assumed, especially in the firstthousand kilometres from the nucleus. The presence of another moving COstructure, faint but compact and possibly created by an outburst, isidentified.

Interferometric imaging of carbon monoxide in comet C/1995 O1 (Hale-Bopp): evidence for a strong rotating jet