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Convection and 6Li in the atmospheres of metal-poor halo stars

Published online by Cambridge University Press:  23 April 2010

Matthias Steffen ,
R. Cayrel ,
P. Bonifacio ,
H.-G. Ludwig  and
E. Caffau
Matthias Steffen
Affiliation:
Astrophysiklaisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany email: [email protected]
R. Cayrel
Affiliation:
GEPI – Observatoire de Paris, Paris, France
P. Bonifacio
Affiliation:
GEPI – Observatoire de Paris, Paris, France
H.-G. Ludwig
Affiliation:
ZAH-Landessternwarte, Königstuhl 12, D-69117 Heidelberg, Germany
E. Caffau
Affiliation:
GEPI – Observatoire de Paris, Paris, France
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Abstract

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Based on 3D hydrodynamical model atmospheres computed with the CO5BOLD code and 3D non-LTE (NLTE) line formation calculations, we study the effect of the convection-induced line asymmetry on the derived 6Li abundance for a range in effective temperature, gravity, and metallicity covering the stars of the Asplund et al. (2006) sample. When the asymmetry effect is taken into account for this sample of stars, the resulting 6Li/7Li ratios are reduced by about 1.5% on average with respect to the isotopic ratios determined by Asplund et al. (2006). This purely theoretical correction diminishes the number of significant 6Li detections from 9 to 4 (2σ criterion), or from 5 to 2 (3σ criterion). In view of this result the existence of a 6Li plateau appears questionable. A careful reanalysis of individual objects by fitting the observed lithium 6707 Å doublet both with 3D NLTE and 1D LTE synthetic line profiles confirms that the inferred 6Li abundance is systematically lower when using 3D NLTE instead of 1D LTE line fitting. Nevertheless, halo stars with unquestionable 6Li detection do exist even if analyzed in 3D-NLTE, the most prominent example being HD 84937.

Keywords

stars: abundancesatmospheres – hydrodynamics – convectionradiative transfer – line: formationprofiles – stars: individual (G271-162, HD 74000, HD 84937)
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S268: Light Elements in the Universe , November 2009 , pp. 215 - 220
Copyright
Copyright © International Astronomical Union 2010

References

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