  Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster
were discovered by Boesgaard & Tripicco. Boesgaard & King discovered
corresponding, but smaller, deficiencies in Be in the same narrow temperature
region in the Hyades. With the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope we investigate B abundances in the Hyades F stars to
look for a potential B dip using the B I resonance line at 2496.8 A. The light
elements, Li, Be, and B, are destroyed inside stars at increasingly hotter
temperatures: 2.5, 3.5, and 5x10^6 K respectively. Consequently, these elements
survive to increasingly greater depths in a star and their surface abundances
indicate the depth and thoroughness of mixing in the star. We have
(re)determined Li abundances/upper limits for 79 Hyades dwarfs, Be for 43
stars, and B in five stars. We find evidence for a small drop in the B
abundance across the Li-Be dip. The B abundances for the four stars in the
temperature range 6100-6730 K fit the B-Be correlation found previously by
Boesgaard et al. Models of rotational mixing produce good agreement with the
relative depletions of Be and B in the dip region. We have compared our nLTE B
abundances for the three high B stars on either side of the Li-Be dip with
those found by Duncan et al. for the two Hyades giants. This confirms the
factor of ~10 decline in the B abundance in the Hyades giants as predicted by
dilution due to the deepening of the surface convection zone.

Solar and Stellar Astrophysics