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Lithium observations in 47 Tucanae *
Received 3 October 1996 / Accepted 21 November 1996
We present high resolution observations
For the third turnoff star only an upper limit could be derived: [Li] 2.19. This upper limit may suggest the presence of some dispersion on the plateau stars of 47 Tuc as it is observed in field stars of similar metallicity.
When compared with field dwarfs of [Fe/H] -0.7 the Li content of 47 Tuc turnoff stars is among the highest observed. Considering the extreme age of 47 Tuc this suggests that no significant depletion affected these stars and it implies a mild Li Galactic enrichment between the epoch of Pop II formation and the formation of 47 Tuc stars with metallicities up to . Spallation reactions, as deduced from Be observations, can account for such an increase.
The remaining two stars are evolved, and only upper limits could be placed at [Li] 0.7 and -0.7. These very low values imply some extra depletion mechanism in addition to dilution as it is observed in evolved field stars by Pilachowki et al (1993) and in NGC 6397 by Pasquini and Molaro (1996).
Key words: stars: abundances stars: Population II globular clusters: individual: 47 Tuc Galaxy: halo cosmology: observations
Send offprint requests to: Luca Pasquini
Online publication: June 30, 1998