解决G矮星问题的银河系化学演化三成分模型

Solving the G-dwarf Problem with a Three-Component Model of the Chemical Evolution of the Galaxy

为解释著名的G矮星问题，提出银河系化学演化的三成分模型，即由银晕、厚盘和薄盘所构成的演化模型．相邻演化阶段间隔着一个快速坍缩过程．对不同星族成分的演化过程分别进行模拟，并在总体上得到一个太阳附近区域的G矮星丰度分布函数．检验了三种不同的模型：初始富化模型、比例生成模型和坍缩模型．利用最小二乘拟合得到最佳模型的参数．结果表明，太阳附近区域的化学演化受物质交换的影响较小，至少在银河系演化的晚期，可将太阳附近区域看作封闭系统．同时，单位质量中新合成的重元素比例对三种恒星成分可分别近似为常数，其差别则说明不同星族恒星的初始质量函数存在着显著差异．

A three-component chemical evolution model of the Galaxy is presented, which casts a new light on the G-dwarf problem. The model is based on a scenario of the Gaiaxy consisting of three major evoluti0nary phases: halo, thick disk and thin disk, separated by two short interludes of rapid collapse. The evolution of different stellar populations are treated separately, the combination of which yields an overall metallicity distribution function for the solar neighbourhood. We tested three different models using the same set of basic equations: the 'prompt initial enrichment' (PIE) model, the 'proportional yield'(PPY) model and the 'collapse' (CLP) model. Best-fit parameters are derived. The results show that the different populations have remarkably different IMFs, while mass exchange has only minimally affected the chemical evolution in the solar vicinity, so that the latter can be regarded as a closed system, at least in the late stage of Galactic evolution.