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D.C. Knauth, S.R. Federman (U. Toledo)
Models of Big Bang Nucleosynthesis account for approximately 10% of the current 7Li abundance. Another production route is through Galactic cosmic ray (GCR) spallation reactions. GCR spallation accounts for the current abundance of 6Li but only 10 - 25% of the 7Li abundance. Stellar sources dominate 7Li production in the Galaxy, although their exact nature is unclear. Through studies of the interstellar 7Li/6Li ratio, information about pathways for Li production is revealed.
Previous studies of the interstellar 7Li/6Li ratio show variations in its value. Ultra-high-resolution (R ~ 360,000), high signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2 Associations were obtained to probe these variations. The observations confirm earlier findings of a low 7Li/6Li ratio of about 2 toward o~Per, the value predicted from models of GCR spallation reactions. Other observations of nearby stars yield isotopic ratios closer to the Solar System value (7Li/6Li = 12.3). My results suggest that the 7Li/6Li ratio has not changed significantly during the last 4.5 billion years and that a ratio ~ 12 represents most gas in the solar neighborhood.
In attempt to explain the low ratio toward o~Per, the role of stellar flares from young stars in IC~348 was investigated, but the amount of 6Li created in stellar flares is negligible. In addition, fractionation cannot account for the low 7Li/6Li ratio as the abundance of LiH is too low. The likely scenario is that the initial Li was destroyed by a supernova explosion and then resynthesized during enhanced GCR spallation reactions.
Another interesting result is that there appears to be a constant stellar contribution to 7Li in the solar neighborhood, suggesting that one or two processes dominate 7Li production in the Galaxy. Further studies of stellar and interstellar Li, as well as s-process and r-process elements, are necessary to determine the stellar source(s) of 7Li. Crucial to our understanding of Li evolution are observations of the other light nuclei, 9Be, 10B, and 11B.
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The author(s) of this abstract have provided an email address for comments about the abstract: dknauth@pha.jhu.edu