Beryllium in the Hyades F and G Dwarfs from Keck HIRES Spectra

Beryllium is not destroyed as easily as Li, so the abundances of Li and Betogether can tell us more about the internal physical processes in stars thaneither element can alone. We have obtained high-resolution (45,000) and highsignal-to-noise (typically 90 per pixel) spectra of the Be II resonance linesin 34 Hyades F and G dwarfs with the Keck I telescope and HIRES. The Beabundances have been derived with the spectrum synthesis method. We find thatBe is depleted in the Li gap in the F stars reaching down to values of A(Be) =0.60, or a factor of nearly seven below the meteoritic Be abundance. There islittle or no depletion of Be in stars cooler than 6000 K, in spite of the largedepletions (0.5 - 2.5 dex) in Li. The mean value of A(Be) for the ten cooleststars is 1.33 +/- 0.06, not far from the meteoritic value of 1.42. The patternin the Be abundances - a Be dip in the F stars and undepleted Be in the coolstars - is well matched by the predictions of slow mixing due to stellarrotation (e.g. Deliyannis and Pinsonneault). The depletions of Li and Beprobably occur simultaneously. The Li and Be abundances are correlated forstars in the temperature range of 5850 - 6680 K, similar to results fromearlier work on Li and Be in F and G field stars. The Hyades G dwarfs have moreBe than the sun; their initial Be may have been larger or they may not be oldenough to have depleted Be. For those Hyades stars which appear to have littleor no depletion of Li or Be, the Li/Be ratio is found to be 75 +/- 30.(abridged)Comment: 14 pages, 2 one-page tables, 13 figures, To be published in Ap