The optical spectrum of NGC 7009 - I. A low-excitation bright ring region on the major axis

Details The optical spectrum of NGC 7009 - I. A low-excitation bright ring region on the major axis The optical spectrum of NGC 7009 - I. A low-excitation bright ring region on the major axis

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.273..958h&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 273, Issue 4, pp. 958-972.

Astronomy and Astrophysics

Astronomy

29

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

Scientific paper

Recent observations suggest that NGC 7009 has a very complicated structure. Detailed high-spectral-resolution observations of the spectrum of NGC 7009 have been made for two regions in the bright ring on the major and minor axes, for the wavelength region 3650 to 10050 A, using the Hamilton echelle spectrograph of the Lick Observatory. In this article we present only the results for the major axis. We have analysed the nebular spectra with aid of theoretical photoionization models and come to the following conclusions: (i) it appears that such a photoionization model can fit the emission reasonably well in the bright ring; (ii) it is unlikely that the knots lie along an axis that is highly inclined with respect to the observer, an idea which was introduced from kinematical studies, wherein the knots are considered as a by-product of highly collimated outflows. NGC 7009 is oxygen-rich because the O/C ratio exceeds 1. The relative abundances of C, O and K appear to be smaller than in the Sun; abundances of other `metals' seem to be comparable with the solar values. With the help of the model, a comparison of the Hamilton data with the previous image-tube scanner (ITS) data suggests that a variation in nitrogen abundance may exist in NGC 7009, a result in harmony with that obtained by previous workers.

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