HST STIS OBSERVATIONS OF THE MIXING LAYER IN THE CAT’S EYE NEBULA*

Abstract

Listen

Translate article

ABSTRACT Planetary nebulae (PNe) are expected to have a ∼105 K interface layer between the ≥ 106 K inner hot bubble and the ∼104 K optical nebular shell. The PN structure and evolution, and the X-ray emission, depend critically on the efficiency of the mixing of material at this interface layer. However, neither its location nor its spatial extent have ever been determined. Using high-spatial resolution HST STIS spectroscopic observations of the N v λ λ 1239,1243 lines in the Cat’s Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N v λ1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5 × 10 16 cm and an electron density of ∼200 cm−3 for the mixing layer. With a thermal pressure of ∼2 × 10−8 dyn cm−2, the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543.