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Published online by Cambridge University Press: 13 April 2010
Hipparcos orbiting observatory has revealed a large number of helium-core- burning “clump” stars of the Galactic field. These low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the standard stellar theory. In this contribution we overview available results of 12C, 13C, N and O abundances obtained by high-resolution spectra for clump stars and discuss them in the light of current predictions of stellar evolution models.