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Astron. Astrophys. 336, 915-919 (1998)

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How many low-mass stars do destroy 3He?

C. Charbonnel and J.D. do Nascimento Jr

Laboratoire d'Astrophysique de Toulouse, UMR 5572 CNRS, 16 Avenue E. Belin, F-31400 Toulouse, France

Received 1 April 1998 / Accepted 18 May 1998


We recall the current status of the long-standing 3He problem, and its possible connection with chemical anomalies on the red giant branch. In this context, we collect in the literature all the available observations of the carbon isotopic ratio in field and cluster giant stars. Using the HIPPARCOS parallaxes, we get constraints on the evolutionary status of the field stars of the sample. This allows us to identify the stars that have passed the luminosity function bump and present 12C/13C ratios in disagreement with the standard predictions of stellar evolutionary models. We determine statistically what fraction of low mass stars experience an extra-mixing process on the red giant branch, and are then expected to destroy their 3He at this evolutionary phase. The high number we get satisfies the galactic requirements for the evolution of the 3He abundance.

Key words: nuclear reactions, nucleosynthesis, abundances – stars: abundances – stars: interiors – stars: rotation

Send offprint requests to: Corinne.Charbonnel@obs-mip.fr

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© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998