A Critique of the Spite Plateau, and the Astration of Primordial Lithium

Abstract

We investigate the distribution of the lithium abundances, A(Li), of metal-poor dwarf and subgiant stars within the limits 5500 K< eff < 6700 K, –6.0 < [Fe/H] < –1.5, and log >∼3.5 (a superset of parameters first adopted by Spite and Spite), usingliterature data for some 200 stars.We address the problem of the several methods that yield eff differences up to 350 K, and henceuncertainties of 0.3 dex in [Fe/H] and A(Li), by anchoring eff to the Infrared Flux Method.We seek to understand the behaviourof A(Li) as a function of [Fe/H] – small dispersion at highest [Fe/H], “meltdown” at intermediate values (i.e. large spread in Libelow the Spite Plateau), and extreme variations at lowest [Fe/H]. Decreasing A(Li) is accompanied by increasing dispersion.Insofar as [Fe/H] increases as the universe ages, the behavior of A(Li) reflects chaotic star formation involving destruction ofprimordial Li, which settles to the classic Spite Plateau, with A(Li) ∼ 2.3, by the time the Galactic halo reaches [Fe/H] ∼ –3.0.We consider three phases: (1) first star formation in C-rich environments ([C/Fe] > 2.3), with depleted Li; (2) silicates-dominatedstar formation and destruction of primordial Li during pre-main-sequence evolution; and (3) materials from these two phasesco-existing and coalescing to form C-rich stars with A(Li) below the Spite Plateau, leading to a toy model with the potential toexplain the “meltdown”. We comment on the results of Mucciarelli et al. on the Lower RGB, and the suggestion of Aguado etal. favouring a lower primordial lithium abundance than generally accepted.