As a part of a study on the variation in the 7Li/6Li ratio, high signal tonoise, high resolution spectroscopy of Li I (6708 Angstroms) and K I (4044Angstroms) were obtained toward zeta and o Per. The lithium isotope shift isapproximately the same as its fine structure splitting (0.158 Angstroms),resulting in a blend of the 7Li and 6Li lines. Use of the K I line as avelocity template allowed a straightforward determination of the lithiumisotopic ratio. Our high resolution observations show remarkably disparate isotope ratios:7Li/6Li = 1 0.6 +/- 2.9 toward zeta Per and 3.6 +/- 0.6 and 1.7 +/- 0.3 towardo Per. While the results toward zeta Per are consistent with the meteoriticvalue, the ratio toward o Per's clouds suggest recent Galactic cosmic rayspallation. This is the first clear and unambiguous evidence for aninterstellar 7Li/6Li ratio that differs dramatically from the Solar Systemvalue. The low ratio indicates a higher cosmic ray flux toward o Per thantoward zeta Per. A higher flux of cosmic rays toward o Per was suggestedearlier in a study of OH and HD chemistry (Federman, Weber, & Lambert 1996, ApJ463, 181). The total lithium abundances and the K/Li ratio are useful in placing the7Li/6Li ratio into context. We obtained total lithium abundances of (12.2 +/-2.2) x 10^(-10) toward zeta Per and (9.8 +/- 3.5) x 10^(-10) toward o Per. Thecolumns of K I and Li I yielded K/Li ratios that revealed no discernable trend.Since a Li isotope ratio ~2 toward o Per suggests newly processed lithium, thecomparable total Li abundances and K/Li ratios are unexpected.
展开▼
