Testing Spallation Processes with Beryllium and Boron

The nucleosynthesis of Be and B by spallation processes provides uniqueinsight into the origin of cosmic rays. Namely, different spallation schemespredict sharply different trends for the growth of LiBeB abundances withrespect to oxygen. ``Primary'' mechanisms predict BeB $\propto$ O, and are wellmotivated by the data if O/Fe is constant at low metallicity. In contrast,``secondary'' mechanisms predict BeB $\propto$ O$^2$ and are consistent withthe data if O/Fe increases towards low metallicity as some recent data suggest.Clearly, any primary mechanism, if operative, will dominate early in thehistory of the Galaxy. In this paper, we fit the BeB data to a two-componentscheme which includes both primary and secondary trends. In this way, the datacan be used to probe the period in which primary mechanisms are effective. Weanalyze the data using consistent stellar atmospheric parameters based onBalmer line data and the continuum infrared flux. Results depend sensitively onPop II O abundances and, unfortunately, on the choice of stellar parameters.When using recent results which show O/Fe increasing toward lower metallicity,a two-component Be-O fits indicates that primary and secondary componentscontribute equally at [O/H]$_{eq}$ = -1.8 for Balmer line data; and[O/H]$_{eq}$ = -1.4 to -1.8 for IRFM. We apply these constraints to recentmodels for LiBeB origin. The Balmer line data does not show any evidence forprimary production. On the other hand, the IRFM data does indicate a preferencefor a two-component model, such as a combination of standard GCR andmetal-enriched particles accelerated in superbubbles. These conclusions rely ona detailed understanding of the abundance data including systematic effectswhich may alter the derived O-Fe and BeB-Fe relations.Comment: 40 pages including 11 ps figures. Written in AASTe