Beryllium in the Ultra-Lithium-deficient, Metal-Poor Halo Dwarf G186-26

The vast majority of low-metal halo dwarfs show a similar amount of Li; this has been attributed to the Li that was produced in the big bang. However, there are nine known halo stars with T > 5900 K and [Fe/H] < -1.0 that are ultra-Li-deficient. We have looked for Be in the very low metallicity star G186-26, at [Fe/H] = -2.71, which is one of the ultra-Li-deficient stars. This star is also ultra-Bedeficient. Relative to Be in the Li-normal stars at [Fe/H] = -2.7, G186-26 is down in Be by more than 0.8 dex. Of two potential causes for the Li deficiency-mass transfer in a pre-blue straggler or extra rotationally induced mixing in a star that was initially a very rapid rotator-the absence of Be favors the blue straggler hypothesis, but the rotation model cannot be ruled out completely.