2004AJ....127.2269B

Hubble Space Telescope images of NGC 6543 taken in 1994.7 and 2000.7 reveal a pattern of overall expansion of its core over 6 years. Spatial scale changes of the sharp edges of filamentary structures are consistent with purely radial motions. One prolate ellipsoid, E25, lies along the overall symmetry axis of the core. We find that it expands uniformly with an expansion age of 1300 yr. Around it is an unusual feature that appears like the projection of two bubbles joined at a common waist called E105 along the minor axis of the core. The bubbles, whose outline defines the core of NGC 6543, expands with an expansion age of 1500 yr; however, the growth rate of its waist, E105, is about 70% larger than the bubbles. We show how this can be explained geometrically. Three pairs of sinewy low-ionization features, called caps, ansae, and jets, are seen at or beyond the perimeter of the core. Our studies of these features suggest that their expansion ages are somewhat larger than those of E25 or the bubbles. In addition, we find that the [O III] surface brightness has generally increased by as much as 3% and the [N II] flux has decreased by about 7% or more in 6 yr. Flux changes like these are expected for an expanding nebula whose densities and recombination rates decrease and as dense filaments become more permeable to ionizing radiation. We discuss the potential applicability of the interacting stellar wind (ISW) model to the various components in the core of NGC 6543. ISW is very congruent with the structure and expansion of E25. It may apply also to the E105/bubble complex, although this is far from clear. ISW cannot account for the morphologies or formation of the caps, ansae, and jets.