Boron in Halo Giants : a Solution to the D+3HE Crisis in Big Bang Nucleosynthesis?

Details Boron in Halo Giants : a Solution to the D+3HE Crisis in Big Bang Nucleosynthesis? Boron in Halo Giants : a Solution to the D+3HE Crisis in Big Bang Nucleosynthesis?

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6599d&link_type=abstract

HST Proposal ID #6599

Physics

Hst Proposal Id #6599 Stellar Populations

Scientific paper

We propose to make Boron observations which can definitivelydistinguish between mass loss and mixing as the cause of thelow ^12C/^13C ratios seen in evolved halo stars. This can helpsolve a long-standing problem which signals a fundamentalfailure of standard stellar evolution theory. As standardmodels evolve off the main sequence and their convection zonesdeepen, CN-synthesized ^13C is dredged up, lowering the^12C/^13C ratio from ~ 90 to about 50, in agreement withobservation. However, the observed C ratio in more evolvedstars declines precipitously, sharply contradicting themodels, and reaches the CN-cycle equilibrium value of 3 -- 4.Two proposed mechanisms remain viable to explain this: giantbranch mass loss and mixing. Boron abundances will remainconstant in the case of mass loss, but will decline belowtheir maximal dilution value in the case of mixing. Thisallows the proposed observations to clearly discriminatebetween the models, possibly with important implications forcosmology. If mixing is correct, then the ^3He (includingprimordial ^3He) is destroyed, moving the heretofore stringentD+^3He constraint of big bang nucleosynthesis (BBN) to lowerOmega_b. This could help resolve the current crisis in BBN,caused by increasingly precise observations of light elementabundances which do not agree with theoretical predictions.Furthermore, mixing of freshly synthesized ^4He could lowerglobular cluster age estimates.

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