A uniform analysis of boron in F and G disk dwarfs from Hubble Space Telescope archival spectra

The boron abundance is derived for 14 near-solar metallicity F and G dwarfs from the archived data set of spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph in the region of the B I resonance line near 2497 Angstrom. These abundances are derived in a uniform way with respect to recent work on solar boron. The synthetic spectra of the B I region were calculated by means of an improved linelist to fit the spectra of the stars spanning a range in T-eff between 5650 and 6700 K and metallicity between [Fe/H] = -0.75 and +0.15. The synthetic spectra were computed considering all major sources of metal opacities and, in particular, an updated lower value of Mg I b-f opacity at 2500 Angstrom was used in the calculations. Adopting Li and Be abundances from the literature, significant B depletions (similar to 0.3-0.5 dex) are found only for the two stars with the most extreme Li depletions (greater than or equal to 2.5 dex) and Be depletions (greater than or equal to 1.5 dex), although the trend of B versus Be indicates that mild B depletions may exist in many of the stars. These results are in concordance with the Boesgaard et al. conclusion that a slow mixing in the outer envelope is responsible for depletions of Li, Be, and B. Stars with less severe Li and Be depletions exhibit roughly solar [B/Fe] ratios. A comparison of the boron abundances from the disk stars (with undepleted boron) with metal-poor halo dwarfs reveals that B is linearly related to Fe over the entire range of metallicities from [Fe/H] similar to -2.5 to 0.1. The B/Be ratio found for stars with near-solar metallicities and no Li depletion is B/Be = 27 +/- 5, equal to the solar ratio (B/Be = 23).