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| Paper: |
Boron in Lithium- and Beryllium-Deficient F Stars |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
903 |
| Authors: |
Boesgaard, Ann Merchant; Deliyannis, Constantine P.; Stephens, Alex; Lambert, David L. |
| Abstract: |
The Goddard High Resolution Spectrograph (GHRS) has been used with the Hubble Space Telescope (HST) to observe the B 1 region at 2497 AA in nine F and G dwarfs of approximately solar metallicity. The stars were selected because they have a variety of Li and Be deficiencies. Most of the nine stars were newly observed at 3131 AA for Be 2 and 6708 AA for Li 1 at high spectral resolution and high signal-to-noise ratios at the Keck I 10-m telescope, the Canada-France-Hawaii 3.6-m telescope and the University of Hawaii 2.2-m telescope. Spectrum synthesis has been used to determine the Li and Be abundances or upper limits, as well as B abundances in our nine program stars and in five other stars from the HST archive. Corrections to the B and Li abundances due to non-LTE effects have been 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 striking uniformity in the B abundances, i.e. there is no B dip. For the coolest and most evolved star in our sample, zeta Her A, the B abundance is a factor of three lower than the mean for the other stars. This star also has the largest Be deficiency (more than a factor of 60) and the largest Li deficiency (more than a factor of 500). These data, together with other studies of the Li dip, argue strongly against diffusion and mass loss and in favor of slow mixing as the cause of the Li and Be dip and the absence of a B dip. Six stars with [Fe/H] from -0.75 to +0.15 have Be abundances ranging from the maximum of the sample to a factor of four (0.6 dex) below the maximum yet these stars have a B/Be ratio that is constant to within +/-0.10 dex and that is close to the predictions of galactic cosmic ray spallation of 10-15. This indicates that the galactic cosmic ray production of B and Be is not uniform relative to the production of elements such as Fe by nucleosynthesis in stars. |
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