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We present chemical abundances in three red giants and two turn-off stars inthe metal poor Galactic globular cluster (GC) NGC 6397 based on spectroscopyobtained with the MIKE high resolution spectrograph on the Magellan 6.5-m Claytelescope. Our results are based on a line-by-line differential abundanceanalysis relative to the well-studied red giant Arcturus and the Galactic halofield star Hip 66815. At a mean of -2.10 +/- 0.02 (stat.) +/- 0.07 (sys.) thedifferential iron abundance is in good agreement with other studies in theliterature based on gf-values. As in previous, differential works we find adistinct departure from ionization equilibrium in that the abundances of Fe Iand Fe II differ by ~0.1 dex, with opposite sign for the RGB and TO stars. Thealpha-element ratios are enhanced to 0.4 (RGB) and 0.3 dex (TO), respectively,and we also confirm strong variations in the O, Na, and Al/Fe abundance ratios.Accordingly, the light-element abundance patterns in one of the red giants canbe attributed to pollution by an early generation of massive SNe II. TO and RGBabundances are not significantly different, with the possible exception of Mgand Ti, which is, however, amplified by the patterns in one TO star,additionally belonging to this early generation of GC stars. We discussinterrelations of these light elements as a function of the GC metallicity.

A differential chemical element analysis of the metal poor Globular Cluster NGC 6397