7Li/6Li Ratio in Distant Interstellar Media and Primordial 7Li-Implementation in Big-Bang Cosmology and Galactic Chemical Evolution-

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Big Bang Nucleosynthesis, Interstellar Medium And Nebulae In External Galaxies, Galactic Center, Bar, Circumnuclear Matter, And Bulge

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We have detected the isotopic abundance ratio of 7Li/6Li in the interstellar media (ISMs) along the line of sight to HD169454 and HD250290 using High Dispersion Spectrograph equipped with the Subaru Telescope. We also observed ζ Oph for the comparison purpose with the previous data. The first background star HD169454 is at the distance 1.7 kpc inward from the solar sysytem in the Galactic plane, and the absorbing clouds are estimated to locate at 0.125 kpc<=d<=0.7 kpc and/or 1 kpc<=d<=1.7 kpc. If the observed 7Li/6Li ratio is for the gas cloud at the larger distance 1 kpc<=d<=1.7 kpc, this could be the first observation of the ISM 7Li/6Li ratio beyond the solar neighborhood. As for the second background star HD250290, the distance from the solar system is uncertain, 2.2+/-0.2 kpc or 0.439-0.147+0.446 kpc. The observed abundance ratios turn out to be 7Li/6Li = 8.1-1.8+3.6, and 6.3-1.7+3.0 for HD169454 and HD250290, respectively. These values are in reasonable agreement with those observed previously in the ISMs of solar neighborhood within +/-1σ error bars and also consistent with our measurement of 7Li/6Li = 7.1-1.6+2.9 for nearby cloud along the line of sight to ζ Oph. This suggests a piece of evidence for homogeneous mixing and instantaneous recycling of gas component in the Galactic disk. We cannot claim a slope of the 7Li/6Li ratio within +/-1σ error bars as a function of Galactocentric distance RG. Decomposing the observed ISM 7Li/6Li ratio into several possible source of 7Li, we discuss three different contributions to the 7Li from the Galactic cosmic-ray interactions, the stellar nucleosynthesis, and the Big-Bang nucleosynthesis.

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