  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 (2 sigma criterion), or from 5 to 2 (3
sigma 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 A 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.
