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; thishas been attributed to the Li that was produced in the Big Bang. However, thereare nine known halo stars with T $>$ 5900 K and [Fe/H] $<$ $-$1.0 that areultra-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. Thisstar is also ultra-Be deficient. Relative to Be in the Li-normal stars at[Fe/H] = $-$2.7, G 182-26 is down in Be by more than 0.8 dex. Of two potentialcauses for the Li-deficiency -- mass-transfer in a pre-blue straggler or extrarotationally-induced mixing in a star that was initially a very rapid rotator-- the absence of Be favors the blue-straggler hypothesis, but the rotationmodel cannot be ruled-out completely.Comment: Accepted for Ap.J. Letters 10 pages, 4 figure