Recent determinations of the abundance of the light-element Li in very metal-poor stars show that its intrinsic dispersion is essentially zero and that the random error in the estimated mean Li abundance is negligible. However, a decreasing trend in the Li abundance toward lower metallicity indicates that the primordial abundance of Li can be inferred only after allowing for nucleosynthesis processes that must have been in operation in the early history of the Galaxy. We show that the observed Li versus Fe trend provides a strong discriminant between alternative models for Galactic chemical evolution of the light elements at early epochs. We critically assess current systematic uncertainties and determine the primordial Li abundance within new, much tighter limits: (Li/H)p = 1.23+0.68-0.32 × 10-10. We show that the Li constraint on ΩB is now limited as much by uncertainties in the nuclear cross sections used in big bang nucleosynthesis (BBN) calculations as by the observed abundance itself. A clearer understanding of systematics allows us to sharpen the comparison with 4He and deuterium and the resulting test of BBN.
Bibliographical noteFunding Information:
The authors gratefully acknowledge discussions with C. P. Deliyannis, M. Pinsonneault, and J. A. Thorburn on issues of stellar depletion. S. G. R. thanks the Institute of Astronomy of the University of Cambridge for provision of facilities following the closure of the Royal Greenwich Observatory. The work of K. A. O. was supported in part by DoE grant DE-FG02-94ER-40823 at the University of Minnesota. T. C. B. acknowledges support from grant AST 95-29454 from the National Science Foundation.
- Cosmology: theory
- Galaxy: halo
- Nuclear reactions, nucleosynthesis, abundances
- Stars: Population II