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There are nine metal-deficient stars that have Li abundances well below theLi plateau that is defined by over 100 unevolved stars with temperatures above5800 K and values of [Fe/H] $<$ $-$1.0. Abundances of Be have been determinedfor most of these ultra-Li-deficient stars in order to investigate the cause ofthe Li deficiencies. High-resolution and high signal-to-noise spectra have beenobtained in the Be II spectral region near 3130 \AA for six ultra-Li-deficientstars with the Keck I telescope and its new uv-sensitive CCD on the upgradedHIRES. The spectrum synthesis technique has been used to determine Beabundances. All six stars are found to have Be deficiencies also. Two havemeasurable - but reduced - Be and four have only upper limits on Be. Theseresults are consistent with the idea that these Li- and Be-deficient stars areanalogous to blue stragglers. The stars have undergone mass transfer events (ormergers) which destroy or dilute both Li and Be. The findings cannot be matchedby the models that predict that the deficiencies are due to extra-mixing in asubset of halo stars that were initially rapid rotators, with the possibleexception of one star, G 139-8. Because the ultra-Li-deficient stars are alsoBe-deficient, they appear to be genuine outliers in population of halo starsused to determine the value of primordial Li; they no longer have the Li intheir atmospheres that was produced in the Big Bang.

Beryllium in Ultra-Lithium-Deficient Halo Stars - The Blue Straggler Connection