Sofia Feltzing

Abundances of O, Fe, Al, Mg, Na and Li determined from high-resolutionand high signal-to-noise spectra of 21 red giant branch (RGB) stars inthe globular cluster NGC 6752 are presented. We demonstrate that theStrömgren c<SUB>1</SUB> index correlates extremely well with themeasured NH, CH and CN indices and that variations in c<SUB>1</SUB> aredue to differences in UV NH band strengths. As shown by Grundahl et al.(cite{grundahl02}), the RGB stars in all 20 globular clusters surveyedpossess large star-to-star variations in their c<SUB>1</SUB> index,which we interpret as significant inhomogeneities in N abundances. Thewell known relations among O and Na and Mg and Al as well as with CN,CH, and NH are also present in these stars, some of which are fainterthan the RGB bump. We find that the Li (6708 Å) equivalent widthbecomes too small to be measured as the luminosity of the stars increaseabove the luminosity of the RGB bump. Taken together, these data enforcethe results of Gratton et al. (cite{gratton01}) for turnoff andsub-giant branch stars, and suggest that in this cluster the abundancecorrelations observed among the brighter giants are in place prior toappreciable RGB ascent and likely due to previous generation(s) ofstars, rather than due to mixing in the observed stars. Based onobservations obtained with the ESO Very Large Telescope UVESspectrograph for programme 65.L-0165(A). Based on observations obtainedwith the Danish 1.5 m telescope at the European Southern Observatory, LaSilla, Chile.