The optical spectrum of NGC 7009 - II. A high-excitation bright ring region on the minor axis

Details The optical spectrum of NGC 7009 - II. A high-excitation bright ring region on the minor axis The optical spectrum of NGC 7009 - II. A high-excitation bright ring region on the minor axis

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.273..973h&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 273, Issue 4, pp. 973-991.

Astronomy and Astrophysics

Astronomy

29

Ism: Abundances, Planetary Nebulae: General, Planetary Nebulae: Individual: Ngc 7009

Scientific paper

Observational data obtained for a small high-excitation region of the north bright ring along the minor axis of NGC 7009 for the region of 3650 to 10050 A 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 two regions: (a) a dominant optically thin, high-temperature, low-density (stratum) region; and (b) a region of relatively small size, low temperature and high density. The chemical composition resembles that found in the bright ring at the end of the major axis, but the intricate and largely unknown structure of this planetary nebula (PN) complicates the analysis considerably. Most of the differences arise from inherent uncertainties in the observational data, nebular structural irregularities, the model and atomic parameters as reported in the preceding paper (Paper I).Some elements (e.g. N) may be more abundant in the knot at the edge of the major axis. Analyses of the low- and high-excitation collisional line features at the bright ring are important in the interpretation of the nebular geometry: the bright ring (or rim) appearance 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 OII, NII, etc., interpreted as recombination 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.

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