The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543

A detailed analysis of the dominant ionized knot in the halo of the planetary nebula NGC 6543 is presented. Observations were made at high spectral and spatial resolution of the [O iii]λ5007-Å line using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. A 20-element multislit was stepped across the field to give almost complete spatial coverage of the large western knot and surrounding halo. The spectra reveal, for the first time, gas flows around the kinematically inert knot. The gas flows are found to have velocities comparable to the sound speed as gas is photoevaporated off an ionized surface. No evidence is found of fast wind interaction with the knot, and we find it likely that the fast wind is still contained in a pressure-driven bubble in the core of the nebula. This rules out the possibility of the knot having its origin in instabilities at the interface of the fast and asymptotic giant branch (AGB) stellar winds. We suggest that the knot is embedded in the slowly expanding red giant wind, and that its surfaces are being continually photoionized by the central star.