TY - JOUR
T1 - Implications of a high population II B/Be ratio
AU - Fields, Brian D.
AU - Olive, Keith A.
AU - Schramm, David N.
N1 - Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 1995/2/1
Y1 - 1995/2/1
N2 - The observed boron/beryllium ratio in extreme Population II stars has been interpreted as evidence of Be and B synthesis by early Galactic cosmic rays. However, a recent reanalysis of the boron abundance in the Population II halo star HD 140283 suggests that B/H may be larger than previously reported, by as much as a factor of 4. This would yield a B/Be ratio lying in the range 14 ≲ B/Be ≲ 50. The possibility of a high Population II B/Be ratio stresses the importance of the upper limit to the B/Be ratio arising from cosmic-ray production. It is found that the limit to cosmic-ray-produced B/Be depends upon the assumed cosmic-ray spectrum. For any Population II comic-ray spectrum that is a single power law in either total energy per nucleon or in momentum, the B/Be ratio is constrained to lie in the range 7.6 ≲ B/Be ≲ 14. Thus, if the new B/Be ratio is correct, it requires either a bimodal cosmic-ray flux with a large low-energy component, or, for another B source, possibly the proposed v-process in supernovae, either of which may be helpful in explaining the observed 11B/10B ratio. Finally, it is noted that the boron reanalysis highlights the uncertainty in our knowledge of the B/Be ratio, and the need for additional data on Be and B abundances.
AB - The observed boron/beryllium ratio in extreme Population II stars has been interpreted as evidence of Be and B synthesis by early Galactic cosmic rays. However, a recent reanalysis of the boron abundance in the Population II halo star HD 140283 suggests that B/H may be larger than previously reported, by as much as a factor of 4. This would yield a B/Be ratio lying in the range 14 ≲ B/Be ≲ 50. The possibility of a high Population II B/Be ratio stresses the importance of the upper limit to the B/Be ratio arising from cosmic-ray production. It is found that the limit to cosmic-ray-produced B/Be depends upon the assumed cosmic-ray spectrum. For any Population II comic-ray spectrum that is a single power law in either total energy per nucleon or in momentum, the B/Be ratio is constrained to lie in the range 7.6 ≲ B/Be ≲ 14. Thus, if the new B/Be ratio is correct, it requires either a bimodal cosmic-ray flux with a large low-energy component, or, for another B source, possibly the proposed v-process in supernovae, either of which may be helpful in explaining the observed 11B/10B ratio. Finally, it is noted that the boron reanalysis highlights the uncertainty in our knowledge of the B/Be ratio, and the need for additional data on Be and B abundances.
KW - Cosmic rays
KW - Nuclear reactions, nucleosynthesis, abundances
KW - Stars: Population II
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U2 - 10.1086/175224
DO - 10.1086/175224
M3 - Article
AN - SCOPUS:11944253971
SN - 0004-637X
VL - 439
SP - 854
EP - 859
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -