Imaging of H₂O⁺ in the coma of comet Halley

Previous investigations applying the "ring masking" technique to CCD images obtained at the South African Observatory in the period 13-18 March 1986, led to the detection of CN, C₂, C₃ and ([OI] + NH₂) jet features in the coma of comet Halley (Cosmovici et al., Nature 332, 705-709, 1988). In complement to these results we report here the detection of new features in water ion emission at 6193 Å which may be used as a tracer for the time-dependent anisotropic emission profile of the water vapour from the cometary nucleus. South Africa images, as well as Catalina Observatory data with identical filters on 20 January and 7, 8 and 24 March 1986, are utilized in order to exclude instrumental errors. Because of the narrow bandwidth of the filter (6192±44 Å) other significant molecular contaminations are considerably reduced. The observed peculiar H₂O features can be explained by the stronger H₂O⁺/dust contrast in the ion tail or by a possible mechanism of negative charging of the dust in the cometary coma.