UMN-TH-1924/00

TPI-MINN-00/48

CERN-TH/2000-288

astro-ph/0010121

October 2000

The recent observations of an approximately linear relationship between both Be and B and iron in metal poor stars has led to a reassessment of the origin of the light elements in the early Galaxy .
In addition to standard secondary production of BeB , it is necessary to introduce a production mechanism which is independent of the interstellar metallicity ( primary ) , and in which freshly synthesized C , O and He are accelerated by supernova shock waves .
Primary mechanisms are expected to be dominant at low metallicity .
At metallicities higher than O/H \gtrsim - 1.75 , existing data might indicate that secondary production is dominant .
In this paper , we focus on the secondary process , related to the standard galactic cosmic rays , and we examine the cosmic ray energy requirements for both present and past epochs .
We find the power input to maintain the present-day Galactic cosmic ray flux is about 1.5 \times 10 ^ { 41 } { erg / s } = 5 \times 10 ^ { 50 } { erg / century } ; this estimate includes energy losses from both the escape of high-energy particle and ionization losses from low-energy particles .
This implies that , if supernovae are the sites of cosmic ray acceleration , the fraction of explosion energy going to accelerated particles is about \sim 30 \% , a value which we obtain consistently both from considering the present cosmic ray flux and confinement and from the present ^ { 9 } { Be } and ^ { 6 } { Li } abundances .

Using the abundances of ^ { 9 } { Be } ( and ^ { 6 } { Li } ) in metal-poor halo stars , we extend the analysis to show the effect of the interstellar gas mass on the standard galactic cosmic ray energetic constraints on models of Li , Be , and B evolution .
The efficiency of the beryllium production per erg may be enhanced in the past by a factor of about 10 ; thus the energetic requirement by itself can not be used to rule out a secondary origin of light elements .
Only a clear and undisputable observational determination of the O-Fe relation in the halo will discriminate between the two processes .