THE NEW DETECTIONS OF7Li/6Li ISOTOPIC RATIO IN THE INTERSTELLAR MEDIA

We have determined the isotopic abundance ratio of 7Li/6Li in the interstellar media (ISMs) along lines of sight to HD169454 and HD250290 using the High-Dispersion Spectrograph on the Subaru Telescope. We also observed ζ Oph for comparison with previous data. The observed abundance ratios were 7Li/6Li = 8.1+3.6 –1.8 and 6.3+3.0 –1.7 for HD169454 and HD250290, respectively. These values are in reasonable agreement with those observed previously in the solar neighborhood ISMs within ±2σ error bars and are also consistent with our measurement of 7Li/6Li = 7.1+2.9 –1.6 for a cloud along the line of sight to ζ Oph. This is good evidence for homogeneous mixing and instantaneous recycling of the gas component in the Galactic disk. We also discuss several source compositions of 7Li, Galactic cosmic-ray interactions, stellar nucleosynthesis, and big bang nucleosynthesis.