Giants reveal what dwarfs conceal: Li abundance in lower RGB stars as diagnostic of the primordial Li
Giants reveal what dwarfs conceal: Li abundance in lower RGB stars as diagnostic of the primordial Li
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巨星揭示了矮星所隐藏的东西：较低RGB恒星中的Li丰度可以作为原始Li的诊断
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发表时间：
2011
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通讯作者：
France.
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作者：
A. Mucciarelli;M. Salaris;P. T. U. O. Bologna;Italy.;A. R. Institute;Liverpool John Moores University;UK.;G. D. Paris;Cnrs;U. Diderot;France.
从第II族矮星和由WMAP/BBNS得到的宇宙Li丰度之间的差异仍然远未得到解决，我们研究了利用第II族低RGB星的Li丰度作为宇宙Li的经验诊断的替代途径。理论和观测都表明，与矮星相比，红巨星表面A(Li)在第一次挖掘完成后和RGB凸起之前，对原子扩散效率的敏感性要低得多。在不同物理假设下计算的标准恒星模型表明，原子扩散对确定A(Li)0的影响为0.07dex(远小于MS星的情况)，其他参数(过冲、年龄、初始Y、混合长度)的合理变化基本不影响A(Li)0。在金属丰度范围[Fe/H]=-3.4/-1.4Dex范围内，我们测量了17颗晕低RGB星的表面Li含量。然后，在适当的恒星模型中，通过考虑初始和挖掘后A(LI)之间的差异，可以推断出初始LI。它主要依赖于所用的T(Ef)标度，对原子扩散的效率只有微弱的敏感性，只要忽略与原子扩散竞争的过程所造成的Li破坏。最终的A(Li)0的范围相对较窄(2.28/2.46Dex)，比WMAP/BBNS的预测低0.3-0.4Dex。GCS NGC6397、NGC6752和M4的分析证实了A(Li)0的这些值。我们的结果提供了与大爆炸值差异的独立定量估计，并为解决这种差异而调用的物理过程设置了非常稳健的约束。
The discrepancy between cosmological Li abundance inferred from Population II dwarf stars and that derived from WMAP/BBNS is still far from being solved.We investigated, as an alternative route, the use of Li abundances in Population II lower RGB stars as empirical diagnostic of the cosmological Li. Both theory and observations suggest that the surface A(Li) in red giants after the completion of the first dredge-up and before the RGB bump, are significantly less sensitive to the efficiency of atomic diffusion, compared with dwarf stars. Standard stellar models computed under different physical assumptions show that the inclusion of the atomic diffusion has an impact of 0.07dex in the determination of A(Li)0 (much smaller than the case of MS stars) and it is basically unaffected by reasonable variations of other parameters (overshooting, age,initial Y, mixing length). We have determined the surface Li content of 17 Halo lower RGB stars,in the metallicity range [Fe/H]=-3.4 /-1.4 dex. The initial Li has then been inferred by accounting for the difference between initial and post-dredge up A(Li) in the appropriate stellar models. It depends mainly on the used T(eff) scale and is only weakly sensitive to the efficiency of atomic diffusion,so long as one neglects Li destruction caused by the process competing with atomic diffusion. Final A(Li)0 span a relatively narrow range (2.28 /2.46 dex), and is 0.3-0.4 dex lower the WMAP/BBNS predictions. These values of A(Li)0 are corroborated by the analysis of the GCs NGC6397, NGC6752 and M4. Our result provides an independent quantitative estimate of the difference with the Big Bang value and sets a very robust constraint for the physical processes invoked to resolve this discrepancy.