The chemical composition of red giants - the first dredge-up phase

The first dredge-up changes the red giant atmosphere abundances of Li, Be and B and the participants in the CNO-cycle. Theoretical predictions are reviewed and compared with the observed abundance changes. For the G and K giants (M < or approximately equal to 3 solar masses), the observed and predicted abundance changes are in fair agreement. The 13C-rich giants appear during the main sequence phase to have experienced a slow mixing within the radiative zone outside the core. The supergiants including Cepheids show an O deficiency that is not predicted by standard theory. The speculation is offered that the ON-cycle processed material is transported out by rotationally induced meridional currents or by convention cells to layers that during the red giant phase fall within the deep convective envelope. Several classes of peculiar low luminosity red giants are briefly discussed. (Auth.)