Abundances of C, N and O as probes of mixing in low-mass helium-core burning stars

A large population of helium-core-burning clump stars of the Galactic field, revealed by the Hipparcos orbiting observatory, is an excellent target for the analysis of mixing processes in evolved low-mass metal-abundant stars. In this contribution we overview first result of ¹²C, ¹³C, N and O abundance determinations in our extensive project which we started with the aim at deriving the fundamental parameters and abundances of more than 20 chemical elements in a large sample of Galactic clump stars.