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6Li in metal-poor halo stars: real or spurious?

Published online by Cambridge University Press:  09 March 2010

M. Steffen ,
R. Cayrel ,
P. Bonifacio ,
H.-G. Ludwig  and
E. Caffau
M. Steffen
Affiliation:
Astrophysikalisches Institut Potsdam, Potsdam, Germany
R. Cayrel
Affiliation:
GEPI, Observatoire de Paris/Meudon, France
P. Bonifacio
Affiliation:
GEPI, Observatoire de Paris/Meudon, France CIFIST Marie Curie Excellence Team, Observatoire de Paris/Meudon, France INAF, Observatorio Astronomico di Trieste, Trieste, Italy
H.-G. Ludwig
Affiliation:
GEPI, Observatoire de Paris/Meudon, France CIFIST Marie Curie Excellence Team, Observatoire de Paris/Meudon, France
E. Caffau
Affiliation:
GEPI, Observatoire de Paris/Meudon, France
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Abstract

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The presence of convective motions in the atmospheres of metal-poor halo stars leads to systematic asymmetries of the emergent spectral line profiles. Since such line asymmetries are very small, they can be safely ignored for standard spectroscopic abundance analysis. However, when it comes to the determination of the 6Li/7Li isotopic ratio, q(Li)=n(6Li)/n(7Li), the intrinsic asymmetry of the 7Li line must be taken into account, because its signature is essentially indistinguishable from the presence of a weak 6Li blend in the red wing of the 7Li line. In this contribution we quantity the error of the inferred 6Li/7Li isotopic ratio that arises if the convective line asymmetry is ignored in the fitting of the λ6707 Å lithium blend. Our conclusion is that 6Li/7Li ratios derived by Asplund et al. (2006), using symmetric line profiles, must be reduced by typically Δq(Li) ≈ 0.015. This diminishes the number of certain 6Li detections from 9 to 4 stars or less, casting some doubt on the existence of a 6Li plateau.

Keywords

hydrodynamicsconvectionradiative transferline: profilesstars: atmospheresstars: abundancesstars: individual (G020-024, G271-162, HD 74000, HD 84937)
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S265: Chemical Abundances in the Universe: Connecting First Stars to Planets , August 2009 , pp. 23 - 26
Copyright
Copyright © International Astronomical Union 2010

References

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