Beryllium in disk and halo stars: Evidence for a beryllium dispersion in old stars

The study of Be in stars of differing metal content can elucidate the formation mechanisms and the Galactic chemical evolution of the light element, Be. We have obtained high-resolution, high signal-to-noise ratio (S/N) spectra of the resonance lines of Be II in eight stars with the High Dispersion Spectrograph (HDS) on the 8.2 m Subaru Telescope on Mauna Kea. Abundances of Be have been determined through spectrum synthesis. The stars with [Fe/H] values greater than -1.1 conform to the published general trend of Be versus Fe. We have confirmed the high Be abundance in HD 94028 and have found a similarly high Be abundance in another star, HD 132475, at the same metallicity: [Fe/H] = -1.5. These two stars are 0.5-0.6 dex higher in Be than the Be-Fe trend. While that general trend contains the evidence for a Galaxy-wide enrichment in Be and Fe, the higher than predicted Be abundances in those two stars shows that there are also local Be enrichments. Possible enrichment mechanisms include hypernovae and multiple supernova explosions contained in a superbubble. One of our stars, G64-37, has a very low metallicity of [Fe/H] = -3.2; we have determined its Be abundance to look for evidence of a Be plateau. Its Be abundance appears to extend the Be-Fe trend to lower Fe abundances without any evidence for a plateau, as had been indicated by a high Be abundance in another very metal-poor star, G64-12. Although these two stars have similar Be abundances within the errors, it could be that their different Be values indicate a Be dispersion even at the lowest metallicities.