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Centro de Astrofísica da Universidade do Porto

The carbon abundance problem in planetary nebulae

C. Rola, G. Stasińska

Abstract
We have reexamined the problem of the discrepancy between carbon abundances in planetary nebulae derived from the CII lambda(4267) and CIII) lambda(1909) line intensities. To this end, we have compiled the published optical and ultraviolet data allowing to compute C/O in planetary nebulae, and constructed diagrams providing a synthetic view of the problem. We have performed Monte-Carlo simulations to study the effect of observational errors in the measurement of line intensities, and have found that C/O abundance ratios derived from the CII lambda(4267) lines are strongly biased towards too large values, which explains a large part of the trend seen in the observational diagrams. Taking into account the observational errors, we discuss some other explanations which have been proposed to resolve the discrepancy, such as temperature fluctuations. Adopting the C/O values from the CIII) lambda(1909) lines, we find that carbon-rich objects represent less than one half of the total number of planetary nebulae. This is significantly less than the proportions quoted in previous studies. The percentage of carbon-rich objects among Type I and Non Type I Galactic planetary nebulae are similar, contrary to what is found in the Magellanic Clouds.

Astronomy and Astrophysics
Volume 282, Page 199
February 1994

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