Ion composition and solar wind interaction: Observations of comet C/1995 O1 (Hale-Bopp)

The extraordinary brightness of comet Hale-Bopp (C/1995 O1) offered the rar e opportunity to investigate its ion tail by observations over a wide range of wavelengths. For the first time, ion emission lines could be detected i n the radio domain, originating from H3O+, HCO+ and CO+ ions. Observations in the extreme ultraviolet range showed O+ emissions. Optical imaging obser vations show a spectacular detail of structures in the ion tail. The combin ed measurements of the ion spatial distribution and dynamic provide a wealt h of information which needs to be understood in terms of models of the com et-solar wind interaction and ion-neutral molecule reactions in the coma.