  Beryllium is not destroyed as easily as Li, so the abundances of Li and Be
together can tell us more about the internal physical processes in stars than
either element can alone. We have obtained high-resolution (45,000) and high
signal-to-noise (typically 90 per pixel) spectra of the Be II resonance lines
in 34 Hyades F and G dwarfs with the Keck I telescope and HIRES. The Be
abundances have been derived with the spectrum synthesis method. We find that
Be 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 is
little or no depletion of Be in stars cooler than 6000 K, in spite of the large
depletions (0.5 - 2.5 dex) in Li. The mean value of A(Be) for the ten coolest
stars is 1.33 +/- 0.06, not far from the meteoritic value of 1.42. The pattern
in the Be abundances - a Be dip in the F stars and undepleted Be in the cool
stars - is well matched by the predictions of slow mixing due to stellar
rotation (e.g. Deliyannis and Pinsonneault). The depletions of Li and Be
probably occur simultaneously. The Li and Be abundances are correlated for
stars in the temperature range of 5850 - 6680 K, similar to results from
earlier work on Li and Be in F and G field stars. The Hyades G dwarfs have more
Be than the sun; their initial Be may have been larger or they may not be old
enough to have depleted Be. For those Hyades stars which appear to have little
or no depletion of Li or Be, the Li/Be ratio is found to be 75 +/- 30.
(abridged)
