⁶Li/⁷Li isotopic ratio in the most metal-poor binary CS22876-032

We present high-resolution and high-quality UVES spectroscopic data of the most metal-poor binary CS 22876-032 ([Fe/H] ∼ -3.7 dex) in the Li I λ 670.8 nm doublet spectral region to investigate the ⁶Li/⁷Li isotopic ratio. We add together all 28 spectra corrected for radial velocity and normalized. We create a grid of 3D-NLTE synthetic spectra, to take into account the line profile asymmetries induced by stellar convection, and perform Monte Carlo simulations to evaluate the error of the Li line profile fitting. Individual fits to the observed Li profile of the primary star show that the veiling factor does not affect the derivation of the ⁶Li/⁷Li isotopic ratio and only modifies the Li abundance, A(Li), by about 0.10 dex. The preliminary analysis of spectra at the velocity reference frame of the primary star of this binary system provides A(Li) = 2.14±0.01 dex and ⁶Li/⁷Li = 0.05±0.04 at 68% confidence level. This is therefore consistent with no detection of ⁶Li and may provide an upper-limit to the isotopic ratio of ⁶Li/⁷Li < 0.09 ratio at this very low metallicity. In addition, we improve the determination of the Li abundance of A(Li) = 1.60±0.05 dex in the secondary star in this system, which is about 0.5 dex lower than the Li abundance of the primary star. These preliminary results does not solve nor aggravate the cosmological ⁷Li problem but does not support either the need for non-standard ⁶Li production in the early Universe.