CNO abundance pattern in the red clump stars of the Milky Way

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.