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Lithium abundances in exoplanet-host stars: modelling

Matthieu Castro
CAUL

Abstract
Exoplanet-host stars (EHS) are known to present surface chemical abundances different from those of stars without any detected planet (NEHS). EHS are, on the average, overmetallic compared to the Sun. The observations also show that, for cool stars, lithium is more depleted in EHS than in NEHS. The overmetallicity of EHS may be studied in the framework of two different scenarii. The first one assumes that the protostellar cloud was originally overmetallic : in this case, the resulting star is overmetallic from the centre to the surface. The second one assumes that the overmetallicity is due to accretion of planetesimals during the formation period of the planetary system : in this case the star is overmetallic only in its outer mixed zone. We have computed main sequence stellar models with various masses, metallicities and accretion rates. The results show different profiles for the lithium destruction according to the scenario. We compare these results to the spectroscopic observations of lithium. Our models show the same increase of lithium depletion towards the coldest stars. Furthermore, this destruction seems not to be linked to the overmetallicity of the EHS, independently of the model. But we show that an increase of the shear instability below the convective zone, triggered by a angular momentum transfer due to the planetary migration, could be the cause of the underabundance of lithium in cold EHS.

2008 March 19, 13:30

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