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 \pm 0.06 \pm 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 .