Two distinct halo populations in the solar neighborhood: IV. Lithium abundances

Abstract

Context. A previous study of F and G main-sequence stars in the solar neighborhood has revealed the existence of two distinct halo populations with a clear separation in [α/Fe] for the metallicity range-1.4 < 0.9 and heavy-element mass fractions 0.001 Z < 0.006, the lithium abundance is well fitted by a relation A(Li) = a 0 + a 1 M + a 2 Z + a 3 M Z, where a 0, a 1, a 2, and a 3 are constants. Extrapolating this relation to Z = 0 leads to a lithium abundance close to the primordial value predicted from standard Big Bang nucleosynthesis calculations and the WMAP baryon density. The relation, however, does not apply to stars with metallicities below [Fe/H]-1.5. Conclusions. We suggest that metal-rich halo stars were formed with a lithium abundance close to the primordial value, and that lithium in their atmospheres has been depleted in time with an approximately linear dependence on stellar mass and Z. The lack of a systematic difference in the Li abundances of high-and low-alpha stars indicates that an environmental effect is not important for the destruction of lithium. © 2012 ESO.