NGC 6543. I. Understanding the Anatomy of the Cat's Eye

Abstract

Hubble Space Telescope images of NGC 6543 taken in 1994.7 through a variety of narrowband filters yield a very detailed structure in emission lines of low and moderate ionization. On the whole, the core of NGC 6543 is optically thin to ionizing radiation. As expected, the general ionization state of the nebula decreases with radius; however, some of the fluctuations are unexpectedly large in scale and impressive in their complex geometries. Other sinewy or arclike features near the edge of the core, known as the ``caps,'' ``ansae,'' and ``jets,'' are extremely low in ionization. The images show that they are made up of closely packed complexes of very dense knots whose recombination times are <~10 yr. Furthermore, we find thin and perfectly radial features that we interpret as ionization shadows behind many of the dense knots. Image ratios show no detectable microscopic or macroscopic changes in electron temperature T_e seen in the [O III] lines even though the densities probably range between 10³ and 10⁵ cm^-3 in various regions. Finally, no internal variations of extinction or the He⁺/H⁺ ratios are found within the core.

Based on observations made with the NASA/ESA Hubble Space Telescope, some of which were obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.