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We report on the discovery of a super-Li rich turn-off star in the old (12Gyr), metal poor ([Fe/H]=-2.1 dex) globular cluster (GC) NGC 6397, based onhigh-resolution MIKE/Magellan spectra. This star shows an unusually highlithium abundance of A(Li)_NLTE = 4.03 +/- 0.06 +/- 0.14 dex (or, 4.21,accounting for possible contamination from a binary companion) that lies abovethe canonical Li-plateau by a factor of 100. This is the highest Li enhancementfound in a Galactic GC dwarf star to date. We discuss several enhancementmechanisms, but none can unambiguously explain such a high overabundance. Thespectrum of the star shows a possible indication of binarity, but its linestrengths and chemical element abundance ratios are fully compatible with otherturn-off stars in this GC, seemingly ruling out mass transfer from an AGBcompanion as origin of the high A(Li). A possible cause is an interaction witha red giant that has undergone cool bottom processing.

Discovery of a super-Li rich turn-off star in the metal poor globular cluster NGC 6397