The oxygen and neon abundances in planetary nebulae: implications for stellar nucleosynthesis

The oxygen and neon abundances of 171 planetary nebulae located in the Galaxy, the Large and Small Magellanic Clouds and M31 have been calculated, using published spectrophotometric data. The resulting abundances of these two elements exhibit a strong linear relation between them which appears to be universal in the sense that it is independent of the host galaxy. The average Ne/O by mass in planetary nebulae is found to be 0.21. The Ne–O relation closely matches the one observed in extragalactic H II regions which suggests that abundances of these elements in intermediate-mass stars are not altered significantly by nucleosynthesis above or below the levels originally present at the time of their birth. Nevertheless, the Ne–O relation does not rule out ON cycling as a nitrogen production mechanism in progenitors of planetary nebulae.