First Dredge-Up and further Mixing Mechanisms along the Red Giant Branch in Field Stars

In this research we use a large sample of field metal-poor stars ([Fe/H]<-1) in different evolutionary phases to prove observationally that (small mass) subgiants (stars brighter than the first dredge-up and fainter than the RGB bump) have abundances of light elements in agreement with predictions from classical evolutionary models. A further mixing episode occurs just after the RGB bump, in agreement with the predictions by Charbonnel (1994, A&A, 282, 811; 1995, ApJ, 453, L41) The O-Na anti-correlation, typical signature observed amongst globular cluster giants, is not present amongst field stars.