【摘要】 Li元素是性质非常活跃且易发生核反应的轻核元素。其精确的丰度可以检验宇宙大爆炸学说。Li元素在宇宙早期化学演化、元素核合成理论和恒星的结构与演化研究中都有着非常重要的地位。近几年来,人们逐渐认识到在局部热动平衡(LTE)的假设下不能准确得到Li丰度,特别在冷的矮星中非局部热动平衡(non-LTE)效应的影响不容忽视。随着理论的发展,人们对原子参数有了更深入的了解,对non-LTE效应的研究也更趋成熟。确定元素丰度时考虑non-LTE影响已成为主要趋势。该文分析了影响Li元素non-LTE效应的各种机制,介绍了确定Li元素non-LTE效应的重要参数及Li原子模型的发展历程,最后对Li在各类恒星中的non-LTE效应进行了综合分析。更多还原

【Abstract】 Lithium is a special chemical element which is very active and easy to take nuclear reaction.The precision of lithium abundance in stellar atmosphere influences the component elements in Big Bang nucleosynthesis directly.Lithium plays an important role in early universe chemical evolution,theory of nucleosynthesis and stellar structure and evolution.Recently,it has been found that the abundance of lithium can not be determined precisely under the condition of local thermodynamic equilibrium.Especially in cool dwarf stars,the effects of non-Local ther- modynamic equilibrium(non-LTE)can not be ignored.With the development of the theory,the study of the influence of non-LTE is more mature.Now,it has been one of the important trends to be considered. We reveiw the main mechanisms which influence the non-LTE corrections for lithium,such as the resonance line scattering and photon loss,photon suction,ultraviolet overionization,in- flared overrecombination,bound-bound pumping and inelastic collision with H and H~-.The development history of the lithium atomic models is summarized,and the atomic model from Carlsson is discussed in detail. The non-LTE corrections for lithium vary in sign and size when spanning a large range of stellar parameters.Thus,the non-LTE effects for lithium in the sun,disk and halo stars are dis- cussed.It is found that the non-LTE corrections are large for lithium-rich stars and lithium-poor cool stars,with opposite sense between these two categories. Even now,it is still uncertain for the lithium abundance in lithium plateau stars.The debate focuses on the following two questions:Firstly,whether the lithium abundance for these stars depends on effective temperatures and metal abundances? Secondly,whether the lithium abundance in these stars can represent the initial lithium abundance? Although the influence due to the charge reactions is considered in recent lithium atomic models,it still needs more work to check this effect on large samples of halo and disk stars.更多还原