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Proving that ICFs overestimate the nitrogen abundances of FLIERs

Published online by Cambridge University Press:  15 December 2006

Denise R. Gonçalves ,
Barbara Ercolano ,
A. Carnero ,
A. Mampaso ,
R. L. M. Corradi  and
M. J. Barlow
Denise R. Gonçalves
Affiliation:
IAG – Universidade de São Paulo, Brazil; Email: denise@astro.iag.usp.br
Barbara Ercolano
Affiliation:
Department of Physics and Astronomy, University College London, UK
A. Carnero
Affiliation:
Department of Physics and Astronomy, University College London, UK
A. Mampaso
Affiliation:
Instituto de Astrofísica de Canarias, Spain
R. L. M. Corradi
Affiliation:
Instituto de Astrofísica de Canarias, Spain Isaac Newton Group of Telescopes, Spain
M. J. Barlow
Affiliation:
Department of Physics and Astronomy, University College London, UK
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Abstract

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We have recently (Gonçalves et al. 2006) shown that previously reported enhanced N abundances in fast, low-ionization emission regions (FLIERs) of PNe, particularly in NGC 7009, may be due to ionization effects. We reached this conclusion through the 3D MOCASSIN photoionization modeling of the bright inner rim of NGC 7009 and its pair of FLIERs, assuming homogeneous elemental abundances throughout the nebula, for N as well as other elements. The (N$^+$/N)/(O$^+$/O) ratio predicted by our models is 0.60 for the rim and 0.72 for the knots, clearly in disagreement with the N$^+$/N=O$^+$/O assumption of the ionization correction factors (ICF) method. Therefore the ICFs are underestimated in both components, rim and knots, but more so in the knots. This effect is partly responsible for the apparent N overabundance claimed for FLIERs.

Based on the above results we are also investigating what would be the effect of the N/O ICF overestimation on the definition of Type I PNe which do not have FLIERs-like structures.

Keywords

ISM: abundances – planetary nebulae: individual (NGC 7009) – jets and outflows
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S234: Planetary Nebulae in our Galaxy and Beyond , April 2006 , pp. 405 - 406
Copyright
© 2006 International Astronomical Union