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Astron. Astrophys. 362, 786-798 (2000)


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Superbubbles and the Galactic evolution of Li, Be and B

E. Parizot

Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland (parizot@cp.dias.ie)

Received 14 February 2000 / Accepted 6 June 2000

Abstract

From a recent re-analysis of the available data, Be and B Galactic evolution appears to show evidence for a two-slope behaviour with respect to O. The inferred Be/O abundance ratio in halo stars is constant at very low metallicity (primary behaviour) and increases proportionally to O/H at high metallicity (secondary behaviour). We show that this can be explained in the framework of one single model, the `superbubble model', in which Li, Be and B are produced by spallation reactions induced by energetic particles accelerated out of a mixture of supernova (SN) ejecta and ambient interstellar medium inside superbubbles (SBs). All the qualitative and quantitative constraints, including the energetics, the value of the transition metallicity and the 6Li/9Be isotopic ratio, are satisfied provided that the energetic particles have a spectrum flattened at low energy (in [FORMULA]) and that the proportion of the SN ejecta inside SBs is of the order of a few percent. This lends support to Bykov's acceleration mechanism inside SBs and to the SB dynamical evolution model of Mac Low & McCray (1988).

Key words: acceleration of particles – nuclear reactions, nucleosynthesis, abundances – ISM: cosmic rays – Galaxy: abundances


© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000

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