Panel a) [C/Fe] and [N/Fe] abundances for NGC 1851 stars. Stellar atmospheres and spectral syntheses were derived by assuming the Alonso et al. (1999) temperature scale. The symbols are the same as in Fig. 7. Abundances and relative uncertainties for stars in M 5 from Cohen et al. (2002) are also shown as crosses for comparison. Panel b) the same as in the left panel, but assuming temperatures and gravities obtained from the isochrones.