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. 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. served 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.