Planetary nebula haloes: Pt. 2

New spectra and images of the large halo around the 'triple-shell' planetary nebula NGC 7662 are presented. The halo's electron temperature, Tc(O2-) = 17500 K, is 4400 K higher than the value for the bright core, and apparent O/H and Ne/H ratios are almost a factor 2 lower in the halo. The ionized halo mass is ≤0.19 the solar mass. Combined spectroscopic results for the haloes of NGC 6543, NGC 6826 and NGC 7662 are interpreted in terms of shocked filamentary regions, with the energy input coming from the hot, fast central star winds of these objects. For NGC 6543 only 3 per cent of the mechanical luminosity of the winds needs to be converted to provide the excess heating observed. It is shown that the halo emission is not due to a rapid drop in the central stars' luminosity. (author)