Lithium Isotope Ratios for Interstellar Clouds toward ζ and o Persei

Details Lithium Isotope Ratios for Interstellar Clouds toward ζ and o Persei Lithium Isotope Ratios for Interstellar Clouds toward ζ and o Persei

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...196.4006k&link_type=abstract

American Astronomical Society, 196th AAS Meeting, #40.06; Bulletin of the American Astronomical Society, Vol. 32, p.738

Astronomy and Astrophysics

Astronomy

Scientific paper

As part of a study on the variation in the 7Li/6Li ratio, high signal to noise, high resolution spectroscopy of Li I (λ 6708) and K I (λ 4044) were obtained toward ζ and o Per. The lithium isotope shift is approximately 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 a velocity template allowed for a straightforward determination of the lithium isotope ratio. The K I line at λ 4044 is a suitable template because it is of comparable strength to the Li I lines. Our high resolution observations show remarkably disparate isotope ratios: 7Li/6Li = 10.6 +/- 2.9 toward ζ Per and 3.6 +/- 0.6 and 1.7 +/- 0.3 toward o Per. While the results for ζ 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 ζ 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) x 10-10 toward ζ Per and (9.8 +/- 3.5) x 10-10 toward o Per. The columns 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, the comparable total Li abundances and K/Li ratios are unexpected.

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