Discovery of a super-Li rich turn-off star in the metal poor globular
  cluster NGC 6397
  We report on the discovery of a super-Li rich turn-off star in the old (12
Gyr), metal poor ([Fe/H]=-2.1 dex) globular cluster (GC) NGC 6397, based on
high-resolution MIKE/Magellan spectra. This star shows an unusually high
lithium 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 above
the canonical Li-plateau by a factor of 100. This is the highest Li enhancement
found in a Galactic GC dwarf star to date. We discuss several enhancement
mechanisms, but none can unambiguously explain such a high overabundance. The
spectrum of the star shows a possible indication of binarity, but its line
strengths and chemical element abundance ratios are fully compatible with other
turn-off stars in this GC, seemingly ruling out mass transfer from an AGB
companion as origin of the high A(Li). A possible cause is an interaction with
a red giant that has undergone cool bottom processing.
