THE OPTICAL-SPECTRUM OF NGC-7009 .2. A HIGH-EXCITATION BRIGHT RING REGION ON THE MINOR AXIS

Observational data obtained for a small high-excitation region of the north bright ring along the minor axis of NGC 7009 for the region 3650 to 10 050 Angstrom have been analysed. From various collisional lines , plasma diagnostics and chemical abundances are found for this region . Our analysis shows that emission from the bright ring (or rim) along the minor axis appears to be the combination of contributions from tw o regions: (a) a dominant optically thin, high-temperature, low-densit y (stratum) region; and (b) a region of relatively small size, low tem perature and high density. The chemical composition resembles that fou nd in the bright ring at the end of the major axis, but the intricate and largely unknown structure of this planetary nebula (PN) complicate s the analysis considerably. Most of the differences arise from inhere nt uncertainties in the observational data, nebular structural irregul arities, the model and atomic parameters as reported in the preceding paper (Paper I). Some elements (e.g. N) may be more abundant in the kn ot at the edge of the major axis. Analyses of the low- and high-excita tion collisional line features at the bright ring are important in the interpretation of the nebular geometry: the bright ring (or rim) appe arance in the low-excitation-line monochromatic images is possibly the projected effect of a high-density (low-excitation) equatorial ring, which is embedded in a low-density (high-excitation) shell. We compare results from permitted lines of O II, N II, etc., interpreted as reco mbination features for regions in the ring at the end of the major and minor axes. High-spatial-resolution monochromatic imaging of NGC 7009 is urgently needed.