BORON IN LITHIUM-DEFICIENT AND BERYLLIUM-DEFICIENT F-STARS

The Goddard High Resolution Spectrograph (GHRS) has been used with the Hubble Space Telescope (HST) to observe the B I region at 2497 Angstr om in nine F and G dwarfs of approximately solar metallicity. The star s were selected because they have a variety of Li and Be deficiencies. Most of the nine stars were newly observed at high spectral resolutio n and high signal-to-noise ratios at the Keck I 10 m telescope, the Ca nada-France-Hawaii 3.6 m telescope, and the University of Hawaii 2.2 m telescope at 3131 Angstrom for Be II and 6708 Angstrom for Li I. With spectrum synthesis we have determined the abundances of B in our nine program stars and in five other stars from the HST archive. The stell ar parameters we have used have been determined in a self-consistent w ay for the program stars and the archive stars. Spectrum synthesis has also been used to determine the Li and Be abundances or upper limits. Corrections to the B and Li abundances due to non-LTE effects have be en applied. The stars originate from the region on the ZAMS of the Li (and Be) dip. In spite of large deficiencies in Li and Be, we find a s triking uniformity in the B abundances, i.e., there is no B dip. In al l cases the Li deficiency is greater than the Be deficiency. For the c oolest and most evolved star in our sample, zeta Her A, the B abundanc e is 0.6 dex lower than the mean for the other stars. This star also h as the largest Be deficiency (more than a factor of 80) and the larges t Li deficiency (more than a factor of 600). These data, together with other studies of the Li dip, argue strongly against diffusion and mas s loss and in favor of slow mixing as the cause of the Li and Be dip a nd the absence of a B dip. Six stars with [Fe/H] from -0.75 to +0.15 h ave Be abundances ranging from the maximum of the sample to a factor o f 4 below the maximum, yet these stars have a B/Be ratio that is const ant to within +/-0.10 dex and that is close to the predictions of Gala ctic cosmic-ray spallation of 10-15. The Be range for four stars with solar metallicity is still a factor of 2, and yet the B/Be ratio is co nstant to within +/-0.03 dex. These results imply that the Galactic co smic-ray production of B and Be is not uniform relative to the product ion of elements such as Fe by stellar nucleosynthesis.