The Lithium test for multiple populations in Globular Clusters: Lithium in NGC 2808. (arXiv:1901.01273v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+DAntona_F/0/1/0/all/0/1">Francesca D'Antona</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ventura_P/0/1/0/all/0/1">Paolo Ventura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marino_A/0/1/0/all/0/1">Anna Fabiola Marino</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milone_A/0/1/0/all/0/1">Antonino P. Milone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tailo_M/0/1/0/all/0/1">Marco Tailo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Criscienzo_M/0/1/0/all/0/1">Marcella Di Criscienzo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vesperini_E/0/1/0/all/0/1">Enrico Vesperini</a>
In the globular cluster NGC2808, a quasi-standard initial lithium abundance
is derived for a red giant belonging to the `extreme’ population, characterized
by a large helium overabundance, and by abundances of proton capture elements
typical of nuclear processing in gas at very high temperatures, where the
initial lithium has been fully destroyed. The observations of lithium in such
extreme cluster stars are important to test different models for the formation
of multiple populations in old Globular Clusters. In the asymptotic giant
branch (AGB) scenario, fresh lithium is synthetized during the initial phases
of hot bottom burning which, afterwards, synthetize the other p-capture
elements. We model the abundance of lithium in the ejecta of superAGB models,
finding values consistent or larger than observed in the `extreme’ giant; these
same models describe correctly the magnesium depletion and silicon enrichment
of the extreme population of NGC 2808, so the overall agreement provides
further support to the AGB scenario. In the models involving massive or
supermassive stars, the Lithium observed requires a mixture of the lithium-free
ejecta of the polluting population with more than 40% of standard-lithium
pristine gas. The extended chemical anomalies of NGC 2808 stars are then to be
all explained within at most 60% of the possible dilution range, the initial
helium mass fraction in the ejecta should be Y >= 0.5, to account for the Ye
0.38-0.40 of the extreme population, and further observations of p-process
elements are needed to check the model.
In the globular cluster NGC2808, a quasi-standard initial lithium abundance
is derived for a red giant belonging to the `extreme’ population, characterized
by a large helium overabundance, and by abundances of proton capture elements
typical of nuclear processing in gas at very high temperatures, where the
initial lithium has been fully destroyed. The observations of lithium in such
extreme cluster stars are important to test different models for the formation
of multiple populations in old Globular Clusters. In the asymptotic giant
branch (AGB) scenario, fresh lithium is synthetized during the initial phases
of hot bottom burning which, afterwards, synthetize the other p-capture
elements. We model the abundance of lithium in the ejecta of superAGB models,
finding values consistent or larger than observed in the `extreme’ giant; these
same models describe correctly the magnesium depletion and silicon enrichment
of the extreme population of NGC 2808, so the overall agreement provides
further support to the AGB scenario. In the models involving massive or
supermassive stars, the Lithium observed requires a mixture of the lithium-free
ejecta of the polluting population with more than 40% of standard-lithium
pristine gas. The extended chemical anomalies of NGC 2808 stars are then to be
all explained within at most 60% of the possible dilution range, the initial
helium mass fraction in the ejecta should be Y >= 0.5, to account for the Ye
0.38-0.40 of the extreme population, and further observations of p-process
elements are needed to check the model.
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