1998ApJ...506..405S

High-resolution echelle spectra of the 6707.8 Å Li I absorption line in spectra of metal-poor halo dwarfs and subgiants are analyzed for the isotopic fractions of ⁶Li and ⁷Li. Positive detections of ⁶Li are reported for two stars, HD 84937 and BD +26° 3578, and tight upper limits to the ⁶Li fraction are obtained for an additional seven stars. Two stars, HD 116064 and BD +26° 2606, were found to be double-lined spectroscopic binaries and were rejected from the analysis. Elemental Li abundances were also derived for the nine program stars: the Li abundance is identical across the sample (excluding the spectroscopic binaries) to within ±0.04 dex in log ε(Li). Two processes involving high-energy particles (cosmic rays) are considered as origins of the ⁶Li: spallation reactions (e.g., O + p ⟶ ⁶Li) and α-α fusion reactions. The contribution of spallation reactions may be assessed empirically using the published Be and B abundances. The observed ⁶Li/Be ratio is significantly in excess of that expected from spallation. In view of the fact that the surface ⁶Li abundance has almost certainly been somewhat depleted by exposure to warm protons, the conclusion is that α-α reactions produced most of the observed ⁶Li. Consequences of this conclusion are sketched.