LiBeB Evolution: Three Models
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We consider the three principal LiBeB evolutionary models, CRI in which the cosmic-ray source at all epochs of Galactic evolution is the average ISM, CRI+LECR in which metal enriched low energy cosmic rays (LECRs) are superimposed onto the CRI cosmic rays, and CRS in which the cosmic-ray source, accelerated in superbubbles, is constant, independent of the ISM metallicity. By considering the evolutionary trend of log(Be/H) vs. both [Fe/H] and [O/H], we demonstrate that the CRI model is energetically untenable. We present evolutionary trends for B-11/B-10 and B/Be which, combined with future precision measurements, could distinguish between the CRS and CRI+LECR models. We show that delayed LiBeB synthesis in the CRS model, due to the transport of the cosmic rays, could explain why log(Be/H) is steeper vs. [O/H] than vs. [Fe/H]. We also show that delayed deposition of Fe into star forming regions, due to its incorporation into high velocity dust, could provide an explanation for the possible rise of [O/Fe] with decreasing [Fe/H]. Observations of refractory and volatile alpha-elements could test this scenario. There seems to be a need for pregalactic or extragalactic Li-6 sources.
latex 10 pages, 7 double panel figures, uses newpasp.sty To appear in The Light Elements and Their Evolution, IAU Symp. 198, L. da Silva, M. Spite and R. de Medeiros, eds., ASP
latex 10 pages, 7 double panel figures, uses newpasp.sty To appear in The Light Elements and Their Evolution, IAU Symp. 198, L. da Silva, M. Spite and R. de Medeiros, eds., ASP