AGB Stars and the Observed Abundance of Neon in Planetary Nebulae

Abstract

Asymptotic giant branch stars are expected to produce ²²Ne through the combined H and He burning that operates during their thermally pulsing evolution. However, observationally there is a fairly tight correlation between the O and Ne abundances as measured in planetary nebulae in various populations. In this paper we use recent detailed stellar evolutionary calculations for compositions appropriate to the Galaxy and the Large Magellanic Cloud, in an attempt to determine if the models are consistent with the observed abundances. We show that there is only a narrow range in stellar mass, about 2 to 4 M_o (lower for lower [Fe/H]) where ²²Ne is produced in sufficient quantities to affect the total observed elemental neon abundance, which is mostly ²⁰Ne. The models appear to be consistent with the observations, but a more thorough analysis is required.