Fast, low-ionization emission regions and other microstructures in planetary nebulae

Abstract

Planetary nebulae (PNs) have highly articulated structures, called "microstructures", little of which has been explored with spectrophotometry at high spatial resolution. We report spectrophotometric observations of microstructures characterized by both high SNR and high spatial resolution (1."5)along the symmetry axes of NGC 3242, NGC 7662, and IC 2149. Of particular interest in these PNs are pairs of low-ionization and/or high-velocity ansae and jets (fast, low-ionization emission regions (FLIERs) on nearly opposite sides of their respective central stars, or nuclei. We present deep optical spectra of FLIERs in all three PNs and discuss their consequences. The strong low-ionization lines of O°, N⁺, O⁺, and S⁺, substantial space velocities, and temperatures and densities of FLIERs are not well explained either by models of edge-on ionization fronts or by models built on analogies to shock-excited Herbig-Haro objects.