Observatoire de Paris Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Transport of chemical elements in stars : Lithium abundance dispersion in metal-poor stars

lundi 15 novembre 2021, par Morgan Deal (Instituto de Astrofísica e Ciências do Espaço (IA))

Jeudi 18 novembre 2021 à 14h00 , Lieu : Amphithéatre Evry Schatzmann batiment 18

The formation and evolution of light elements in the Universe act as important cosmological constraints. The oldest stars of the Galaxy have long been assumed to display in their outer layers the primordial lithium abundance, although all studies of stellar physics proved that this abundance must have decreased with time. The primordial Li abundance deduced from the observations of the Cosmological Background is indeed larger than the maximum one observed in these stars. Recent observations gave evidence of a large Li abundance dispersion in very metal poor stars.

During this presentation, we show that the amount of depletion needed to solve the lithium problem, can be accounted for a large part by the transport processes of chemical elements in stars. We show that stellar models including non-standard transport processes such as the rotation-induced mixing and penetrative convection are able to explain the lithium surface abundances of Population II stars, when using a lithium initial abundance in accordance with the primordial lithium abundance obtained from latest BBN results.

We also address the general question of the lithium abundance dispersion obtained from observations of carbon enhanced metal-poor stars, and how the interplay of atomic diffusion and accretion of matter modifies the element abundances in these metal-poor stars. In particular, we focus on the hydrodynamic processes that could take place after accretion. We show that the observations of lithium dispersion, associated with carbon enrichment, are well accounted for in terms of accretion onto the metal-poor stars, with accreted masses smaller than a few Jupiter masses, when using a primordial initial lithium abundance.