Light element ( ^ { 6 } Li , ^ { 7 } Li and ^ { 9 } Be ) depletion isochrones for halo stars have been calculated with standard stellar evolution models .
These models include the latest available opacities and are computed through the sub-giant branch .
If ^ { 6 } Li is not produced in appreciable amounts by stellar flares , then the detection of ^ { 6 } Li in HD 84937 by Smith , Lambert & Nissen ( 1993 ) is compatible with standard stellar evolution and standard big bang nucleosynthesis only if HD 84937 is a sub-giant .
The present parallax is inconsistent with HD 84937 being a sub-giant star at the 2.5 \sigma level .
The most metal poor star with a measured ^ { 9 } Be abundance is HD 140283 , which is a relatively cool sub-giant .
Standard stellar evolution predicts that ^ { 9 } Be will have been depleted in this star by \sim 0.3 dex ( for T _ { eff } = 5640 K ) .
Revising the abundance upward changes the oxygen-beryllium relation , suggesting incompatibility with standard comic ray production models , and hence , standard big bang nucleosynthesis .
However , an increase in the derived temperature of HD 140283 to 5740 K would result in little depletion of ^ { 9 } Be and agreement with standard big bang nucleosynthesis .