Origin and Evolution of the Light Nuclides |
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Authors: | N Prantzos |
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Institution: | (1) Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France |
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Abstract: | After a short historical (and highly subjective) introduction to the field, I discuss our current understanding of the origin
and evolution of the light nuclides D, 3He, 4He, 6Li, 7Li, 9Be, 10B and 11B. Despite considerable observational and theoretical progress, important uncertainties still persist for each and every one
of those nuclides. The present-day abundance of D in the local interstellar medium is currently uncertain, making it difficult
to infer the recent chemical evolution of the solar neighborhood. To account for the observed quasi-constancy of 3He abundance from the Big Bang to our days, the stellar production of that nuclide must be negligible; however, the scarce observations of its abundance in planetary nebulae seem to contradict this idea. The observed
Be and B evolution as primaries suggests that the source composition of cosmic rays has remained ∼constant since the early
days of the Galaxy, a suggestion with far reaching implications for the origin of cosmic rays; however, the main idea proposed
to account for that constancy, namely that superbubbles are at the source of cosmic rays, encounters some serious difficulties.
The best explanation for the mismatch between primordial Li and the observed “Spite-plateau” in halo stars appears to be depletion
of Li in stellar envelopes, by some yet poorly understood mechanism. But this explanation impacts on the level of the recently
discovered early “6Li plateau”, which (if confirmed), seriously challenges current ideas of cosmic ray nucleosynthesis. |
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Keywords: | Light elements Chemical evolution Early Galaxy Metal-poor stars Cosmic rays |
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