Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...19713101g&link_type=abstract
American Astronomical Society, 197th AAS Meeting, #131.01; Bulletin of the American Astronomical Society, Vol. 33, p.715
Astronomy and Astrophysics
Astronomy
Scientific paper
We present spatially-resolved long-slit measurements of O II recombination lines and [O III] forbidden lines in the Ring Nebula NGC 6720. We compare the abundances derived from O II and [O III]. We find that the O II emission and the [O III] emission are formed in physically distinct regions: while the [O III] emission generally follows that of Hβ , the O II emission peaks closer to the central star. The O+2 abundance derived from O II is as much as eight times larger than that derived from [O III] in the nebula interior, but is less than a factor two larger in the bright PN shell. These results are not consistent with a model of pure radiative recombination plus temperature fluctuations to explain the discrepant abundances from O II and [O III]. We also present results from a larger sample of planetary nebulae. We find some intriguing correlations. The discrepancy between O II-derived abundances and [O III]-derived abundances is anticorrelated with nebular surface brightness and diameter; larger, low surface brightness PNe have the largest abundance discrepancies, while compact PNe show little or no discrepancy. This suggests a mechanism that is correlated with the evolutionary state of the nebula. We see no correlation with central star temperature or luminosity, nor with nebular ionization.
Dinerstein Harriet L.
Garnett Don R.
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