Abstract
We present the results of a study aimed at determining the 12C/13C ratio in two samples of planetary nebulae (PNe) by means of mm-wave observations of 12CO and 13CO. The first group includes six PNe which have been observed in the 3He+ hyperfine transition; the other group consists of 23 nebulae with rich molecular envelopes. We have determined the isotopic ratio in 14 objects and the results indicate a range of values between 9 and 23. In particular, three PNe have ratios well below the value predicted by standard evolutionary models (≳ 20), indicating that some extra-mixing process has occurred in these stars. We briefly discuss the implications of our results for standard and nonstandard stellar nucleosynthesis.
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Palla, F., Galli, D., Bachiller, R. et al. Measurements of the 12C/13C Ratio in Planetary Nebulae and Implications for Stellar Evolution. Space Science Reviews 84, 177–183 (1998). https://doi.org/10.1023/A:1005019302051
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DOI: https://doi.org/10.1023/A:1005019302051