Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...506..405s&link_type=abstract
The Astrophysical Journal, Volume 506, Issue 1, pp. 405-423.
Astronomy and Astrophysics
Astronomy
125
Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Abundances, Stars: Population Ii
Scientific paper
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 deg 3578, and tight upper limits to the ^6Li fraction are obtained for an additional seven stars. Two stars, HD 116064 and BD +26 deg 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 ɛ(Li). Two processes involving high-energy particles (cosmic rays) are considered as origins of the ^6Li: spallation reactions (e.g., O + p --> ^6Li) and alpha-alpha 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 alpha-alpha reactions produced most of the observed ^6Li. Consequences of this conclusion are sketched.
Lambert David L.
Nissen Poul Erik
Smith Verne V.
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