Lithium abundances in metal-poor stars

Abstract

Aims. Lithium abundances for 19 metal-poor stars are determined using high-resolution spectroscopy. The abundances of stars on the lithium plateau are discussed. Methods. All abundance results are derived from NLTE statistical equilibrium calculations and spectrum synthesis methods.Results. In agreement with previous analyses it is found that excitation and de-excitation due to hydrogen collisions are negligible for the lithium line formation process, while charge transfer reactions are an important source of thermalization. However, the resulting NLTE effects on the determination of lithium abundances for metal-poor stars are negligible (<0.06 dex). Conclusions. The mean lithium abundance for stars on the lithium plateau determined from NLTE analyses is A(Li) ∼ 2.26, while it is 2.21 dex when charge transfer reactions are included. The latter result enhances the discrepancy between the observed lithium abundances and the primordial lithium abundance as inferred by the WMAP analysis of the cosmic microwave background. This discrepancy may be explained by metal diffusion.

SYSTEMATIC NON-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. II. ABUNDANCE PATTERNS FROM Li TO Eu*

“…The Li I asymmetric profile shape (see Figure 3 for HD 134169) is mainly caused by the two doublet structure components, Li I λ6707.76 and Li I λ6707.91. They were treated, using atomic data from Shi et al (2007) with all the HFS components included. Taking all the blended lines in the asymmetric core region into account produces no more than 0.005 dex change in the derived Li abundance, as shown by our test calculations for all the stars with [Fe/H] > −0.2 in our sample.…”

Effect of exotic long-lived sub-strongly interacting massive particles in big bang nucleosynthesis and a new solution to the Li problem

“…At T 9 ∼ 1 the 4 He synthesis occurs as in SBBN, and about one third of X 0 particles are captured by 4 He nuclei. 4 He X nuclei produced in this epoch react with normal nuclei, and affect abundances of 7 Li [by 4 He X (t, 7 Li)X], 6 Li X [by 4 He X (d, γ) 6 Li X ], and 8 Be X [by 4 He X (α, γ) 8 Be X ]. Note that 6 Li X nuclei produced at T 9 ∼ 1 experience a strong destruction process, i.e., 6 Li(p, 3 Heα)X.…”

“…The boxes represent the adopted abundance constraints from Refs. [39,40] for 4 He, [41] for D, [42] for 3 He, [4] for 7 Li, and [2] for 6 Li, respectively. The vertical stripe corresponds to the 2 σ Ω B h 2 limits provided by WMAP [9].…”

“…Primordial lithium abundances are inferred from measurements in metal-poor halo stars (MPHSs). Observed abundances are roughly constant as a function of metallicity [3,4,1,2,[5][6][7] at 7 Li/H= (1 − 2) × 10 −10 . The theoretical prediction of the SBBN model is, however, a factor of 2-4 higher, e.g., 7 Li/H=(5.24 +0.71 −0.67 ) × 10 −10 [8], when its parameter, the baryon-to-photon ratio η, determined from the observation with Wilkinson Microwave Anisotropy Probe (WMAP) of the cosmic microwave background (CMB) radiation [9] is used.…”

Observational signatures for depletion in the Spite plateau: solving the cosmological Li discrepancy?

“…Due to its cosmological significance, there have been many studies devoted to Li in metal-poor field stars (e.g. Meléndez & Ramírez 2004;Boesgaard et al 2005;Charbonnel & Primas 2005;Nissen et al 2005;Asplund et al 2006;Bonifacio et al 2007;Shi et al 2007;Hosford et al 2009;Aoki et al 2009), with observed Li abundances at the lowest [Fe/H] from as low as A Li = 1.94 to as high as A Li = 2.37.…”