Evolution of lithium-beryllium-boron and oxygen in the early Galaxy

Oxygen is a much better evolutionary index than iron to describe the histor y of lithium-beryllium-boron (LiBeB) since it is the main producer of these light elements at least in the early Galaxy. The O-Fe relation is crucial to the determination of the exact physical process responsible for the LiBe B production. At low metallicity, if [O/Fe] vs. [Fe/H] is flat, then the pr oduction mode is independent of the interstellar metallicity, BeB is propor tional to oxygen, i.e. is of primary nature. If not, the production mode is a function of the progressive enrichment in O of the interstellar medium, BeB varies rather as the square of O, i.e. is of secondary nature. In the f irst case, fast nuclei enriched into He, C and O injected by supernovae. an d accelerated in surrounding superbubbles would explain the primary trend. In the second case, the main spallative agent would be the standard galacti c cosmic rays. Calculated nucleosynthetic yields of massive stars, estimate s of the energy cost of production of beryllium nuclei, and above all recen t observations reported in this meeting seem to favor the primary mechanism , at least in the early Galaxy. (C) 2001 Elsevier Science BY All rights res erved.