New Beryllium results in halo stars from Keck/HIRES spectra

Abstract

Abstract. We have obtained high-resolution, high signal-to-noise Keck spectra to determine Be abundances in over 100 stars in the Galactic halo. The stellar metallicities range from [Fe/H] = −0.50 to −3.50. Using this large sample, we have examined the trends of Be with Fe and Be with O. We find a real dispersion in Be at a given [O/H] that indicates that Be may not be a good cosmochronometer. Our results indicate that the dominant production mechanism for Be changes as the Galaxy ages. In the early eras of the Galaxy, when massive stars become supernovae, Be is produced from the acceleration of energetic CNO atoms which bombard protons in the vicinity of supernovae. Later spallation reactions occur as high energy protons bombard CNO atoms in the interstellar gas. The change occurs near [Fe/H] = −2.2. We have found that Be is deficient in Li-deficient halo stars, which favors the blue straggler analog hypothesis.

New Lithium Measurements in Metal-Poor Stars1

“…As described in detail in §5.1 of Stephens et al (1997), observations of Be in such stars can place constraints on numerous candidate mechanisms responsible for the Li depletion in these objects. The Be abundance derived by Smiljanic et al (2009) places HIP 36491 just above the mean Galactic Be-Fe trend at our metallicity in both their Figure 10 as well as in Figure 2 of the independent study of Boesgaard et al (2010). Any Be depletion in this star is apparently limited to ≤0.1 dex if one compares the abundance to the upper envelope of the Smiljanic et al (2009) and Boesgaard et al (2010) Be-Fe data.…”

“…The Be abundance derived by Smiljanic et al (2009) places HIP 36491 just above the mean Galactic Be-Fe trend at our metallicity in both their Figure 10 as well as in Figure 2 of the independent study of Boesgaard et al (2010). Any Be depletion in this star is apparently limited to ≤0.1 dex if one compares the abundance to the upper envelope of the Smiljanic et al (2009) and Boesgaard et al (2010) Be-Fe data. The inequality of inferred Li and Be depletion, ∼0.4 dex versus ∼0 dex, would seem to exclude diffusion as a causal mechanism.…”