How many low-mass stars do destroy (3) He?

Abstract

We recall the current status of the long-standing (3) He 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 (12) C/(13) C 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 (3) He at this evolutionary phase. The high number we get satisfies the galactic requirements for the evolution of the (3) He abundance.