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Astron. Astrophys. 355, 69-78 (2000)


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Measurements of 12C/13C in planetary nebulae: Implications on stellar and Galactic chemical evolution

F. Palla 1, R. Bachiller 2, L. Stanghellini  *  3,4, M. Tosi 3 and D. Galli 1

1 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
2 Observatorio Astronómico Nacional (IGN), Campus Universitario, Apdo. 1143, 2880 Alcalá de Henares (Madrid), Spain
3 Osservatorio Astronomico di Bologna, Viale Berti Pichat 6/2, 40126 Bologna, Italy
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA

Received 19 April 1999 / Accepted 8 November 1999

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 millimeter wave observations of 12CO and 13CO. The first group includes six PNe which have been observed in the 3He+ hyperfine transition by Balser et al. (1997); the other group consists of 22 nebulae with rich molecular envelopes. We have determined the carbon isotopic ratio in 14 objects, 9 of which are new detections. The results indicate a range of values of 12C/13C between 9 and 23. We estimate the mass of the progenitors of the PNe of our sample and combine this information with the derived 12C/13C  isotopic ratios to test the predictions of stellar nucleosynthesis models.

We find that the majority of PNe have isotopic ratios below the values expected from current standard asymptotic giant branch models in the mass range of interest. We suggest that the progenitors of the PNe must have undergone a non-standard mixing process during their red giant phase and/or asymptotic giant phase, resulting in a significant enhancement of the 13C abundance in the surface layers. Our study confirms a similar behaviour inferred from spectroscopic observations of field population II stars and globular cluster giants, and extends it to the final stages of stellar evolution. Finally, we discuss the implications of our results on models of Galactic chemical evolution of 3He and 12C/13C.

Key words: ISM: planetary nebulae: general – radio lines: ISM – Galaxy: evolution

* Affiliated with the Astrophysics Division, Space Science Department of ESA

Send offprint requests to: F. Palla

Correspondence to: palla@arcetri.astro.it

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000

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