Introduction

In several elliptical PNe, a number of structures have been observed which are called : rims, shells, caps, ansae, knots, etc. in addition to the haloes. Some are macrostructures (rims, shells, haloes) constituting in a sense the bulk of the nebula itself. They can either be homogeneous or contain themselves smaller structures. Others are microstructures, and some of them qualify as FLIERs (see below).

Balick et al. (1993; hereafter paper I) explored the spectra of microstructures in three elliptical PNe : NGC 3242, 7662, and IC 2149. They found that NGC 3242 and 7662 contain pairs of low ionization knots moving at supersonic velocity relative to the ambient gas. They have been named FLIERs (fast low ionization emitting regions). Various interpretations were discussed, but a convincing explanation was not found.

Here we present a preliminary study of microstructures in three more elliptical PNe : NGC 6543, 6826 and 7009.

Observations

The observations were performed using the Palomar 5-m telescope and double spectrograph at dispersions of 2.1 Å/pixel in the blue (3400-5150 Å) and 3.1 Å/pixel in the red (5150-7600 Å). The effective resolution corresponds to about 300 km s−1. Along the slit each pixel is 0″.58 for the red and 0″.78 for the blue. Typical seeing was about 1.5 arcsec.