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In the globular cluster NGC2808, a quasi-standard initial lithium abundanceis derived for a red giant belonging to the `extreme' population, characterizedby a large helium overabundance, and by abundances of proton capture elementstypical of nuclear processing in gas at very high temperatures, where theinitial lithium has been fully destroyed. The observations of lithium in suchextreme cluster stars are important to test different models for the formationof multiple populations in old Globular Clusters. In the asymptotic giantbranch (AGB) scenario, fresh lithium is synthetized during the initial phasesof hot bottom burning which, afterwards, synthetize the other p-captureelements. We model the abundance of lithium in the ejecta of superAGB models,finding values consistent or larger than observed in the `extreme' giant; thesesame models describe correctly the magnesium depletion and silicon enrichmentof the extreme population of NGC 2808, so the overall agreement providesfurther support to the AGB scenario. In the models involving massive orsupermassive stars, the Lithium observed requires a mixture of the lithium-freeejecta of the polluting population with more than 40% of standard-lithiumpristine gas. The extended chemical anomalies of NGC 2808 stars are then to beall explained within at most 60% of the possible dilution range, the initialhelium mass fraction in the ejecta should be Y >= 0.5, to account for the Ye0.38-0.40 of the extreme population, and further observations of p-processelements are needed to check the model.

The Lithium test for multiple populations in Globular Clusters: Lithium in NGC 2808