Standard cosmic ray energetics and light element production

The recent observations of an approximately linear relationship between bot h Be and B and iron in metal-poor stars has led to a reassessment of the or igin of the light elements in the early Galaxy. In addition to standard sec ondary production of BeB, it is necessary to introduce a production mechani sm which is independent of the interstellar metallicity (primary). and in w hich freshly synthesized C, O and He are accelerated by supernova shock wav es. Primary mechanisms are expected to he dominant at low metallicity. At m etallicities higher than [O/H] greater than or similar to -1.75, some exist ing data indicate that secondary production is dominant. In this paper, we focus on the secondary process, related to the standard Galactic cosmic ray s, and we examine the cosmic ray energy requirements for both present and p ast epochs. We find the power input to maintain the present-day Galactic co smic ray flux is about 1.5 10(41) erg/s = 5 10(50) erg/century; this estima te includes energy losses from both the escape of high-energy particle and ionization losses from low-energy particles. This implies that, if supernov ae are the sites of cosmic ray acceleration, the fraction of explosion ener gy going to accelerated particles is about similar to 30%. a value which we obtain consistently both from considering the present cosmic ray flux and confinement and from tile present Be-9 and Li-6 abundances. Using the abund ances of Be-9 (and Li-6) in metal-poor halo stars, we extend the analysis t o show the effect of the interstellar gas mass on the standard Galactic cos mic ray energetic constraints on models of Li: Be, and B evolution. The eff iciency of the beryllium production per erg may he enhanced in the past by a factor of about 10; thus the energetic requirement by itself cannot be us ed to rule out a secondary origin of light elements. Only a clear and indis putable observational determination of the O-Fe relation in the halo will d iscriminate between the two processes.