Astrophysical 7Li as a product of Big Bang nucleosynthesis and galactic cosmic-ray spallation

Abstract

RECENTLY measured abundances of beryllium1–4 and boron5 in a number of hot population II halo stars are orders of magnitude above the predicted abundances of those elements from standard Big Bang nucleosynthesis6. Be and B do not, however, show a plateau of constant abundance over a wide range of low metallicities and high temperatures, as is the case for 7Li (refs 7–15). The implication is that the 7Li abundance is largely primordial, whereas the Be and B abundances are due to galactic cosmic ray (GCR) spallation reactions16–22 on top of a much smaller Big Bang component23. But GCR spallation should also produce 7Li. As a consistency check on the combination of Big Bang nucleosynthesis and GCR spallation, we use the Be and B data to subtract from the measured 7Li abundance an estimate of the amount generated by GCR spallation21,22 for each star in the sample, and then add to this baseline an estimate of the metallicity-dependent augmentation of 7Li, due to spallation. The slightly reduced primordial 7Li abundance is still consistent with Big Bang nucleosynthesis, and a single GCR spallation model can fit the Be, B and corrected 7Li abundances for all the stars in the sample.