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D.C. Knauth (U. Toledo), S.R. Federman (U. Toledo), D.L. Lambert (U. Texas), P. Crane (Dartmouth and NASA)
As part of a study on the variation in the 7Li/6Li ratio, high signal to noise, high resolution spectroscopy of Li~{\small I} (\lambda6708) and K~{\small I} (\lambda4044) were obtained toward \zeta and o Per. The lithium isotope shift is approximately the same as its fine structure splitting (~~0.158~Å), resulting in a blend of the 7Li and 6Li lines. Use of the K~{\small I} line as a velocity template allowed for a straightforward determination of the lithium isotope ratio. The K~{\small I} line at \lambda4044 is a suitable template because it is of comparable strength to the Li~{\small I} lines.
Our high resolution observations show remarkably disparate isotope ratios: 7Li/6Li = 10.6 ± 2.9 toward \zeta Per and 3.6 ± 0.6 and 1.7~±~0.3 toward o Per. While the results for \zeta Per are consistent with the meteoritic value, the ratios for o Per's clouds suggest recent Galactic cosmic ray spallation. This is the first unambiguous evidence for an interstellar 7Li/6Li ratio that differs dramatically from the Solar System value. The low ratios indicate a higher flux of cosmic rays toward o~Per than toward \zeta~Per. A higher flux of cosmic rays toward o~Per was suggested earlier in a study of OH and HD chemistry (Federman, Weber, & Lambert 1996, ApJ, 463,181).
The total lithium abundance and the K/Li ratio are useful in placing the 7Li/6Li ratio into context. We obtained total Li abundances of (12.2~±~2.2)~\times~10-10 toward \zeta Per~and (9.8~±~3.5)~\times~10-10 toward o~Per. The columns of K~{\small I} and Li~{\small I} yielded K/Li ratios that revealed no discernable trend. Since a Li isotope ratio ~~2 toward o~Per suggests newly processed lithium, the comparable total Li abundances and K/Li ratios are unexpected.
The author(s) of this abstract have provided an email address for comments about the abstract: dknauth@astro1.panet.utoledo.edu