贫金属星元素丰度主要r-与弱r-过程比例研究

发布时间：2018-01-16 06:10

本文关键词：贫金属星元素丰度主要r-与弱r-过程比例研究　出处：《河北师范大学》2011年硕士论文　论文类型：学位论文

【摘要】：贫金属恒星被誉为核合成和星系化学演化历史的“化石”。研究其元素丰度,对检验核合成理论和探索恒星形成具有十分重要的意义。s-过程已经为人所知:发生在中低质量AGB星,而需要高中子密度环境的r-过程的本质依旧神秘。关于r-过程核合成场所的理论研究刚刚起步,贫金属星不同核合成过程对中子俘获元素丰度的贡献比例仍不清楚。本文以元素核合成基本理论为基础,用参数化的方法研究了r-过程超丰贫金属星主要r-过程和弱r-过程所占的比例,得到轻元素、铁族元素、轻中子俘获元素和从Ba到Pb的重中子俘获元素的主要r-过程比例随着[Eu/Fe]的分布情况。经过比较发现各元素比例基本上是合理有效的,表明r-过程增丰贫金属星至少有两种不同的核合成过程:主要r-过程和弱r-过程共同贡献中子俘获元素的丰度。主要r-过程主要产生重中子俘获元素,对于轻中子俘获元素丰度的贡献则是弱r-过程占有绝对优势。研究还发现各贫金属星样品星各元素的比例系数明显不相等,这说明各核合成过程对中子俘获元素丰度的贡献比例随原子序数的不同而不同,表明这些元素核合成过程可能产生于几个不同的场所。对早期银河系化学演化研究及轻元素,重中子俘获元素的r-过程模型研究可以看出,s-过程和r-过程都可以分为两个分量,从而分解出两种不同核合成过程的贡献比例并计算其元素丰度。这样就能把核合成过程都能量化到每一个分量系数里,就可以从整体上衡量恒星核合成过程的主要组成,从而知道恒星形成的天体物理环境及场所。虽然这种计算模型还存在不足之处,但是可以肯定,对观测元素很全的r-过程超丰贫金属星来说,这个方法不失为一种行之有效的途径。
[Abstract]:The metal-poor stars are known as "fossils" in the history of nuclear synthesis and galaxy chemical evolution. It is of great significance to test the nuclear synthesis theory and to explore the star formation. S- process is well known: it occurs in low and low mass AGB stars. However, the nature of r-process, which needs high-school sub-density environment, is still mysterious. The theoretical research on r-process nuclear synthesis site is just beginning. The contribution of different nucleation processes to the abundance of neutron capture elements is still unclear. Based on the basic theory of element nucleus synthesis, the proportion of main r-process and weak r-process in r-process superabundant and poor metal stars is studied by parameterization method. The light elements and iron group elements are obtained. The major r-process ratios of light neutron capture elements and heavy neutron capture elements from Ba to Pb are as follows [After comparison, it was found that the proportion of each element was basically reasonable and effective. It is shown that there are at least two different nuclear synthesis processes in the r-process: the main r-process and the weak-r-process contribute to the abundance of neutron capture elements, and the main r-process mainly produces heavy neutron trapping elements. The contribution to the abundance of light neutron capture elements is dominated by the weak r-process. It is also found that the proportion coefficients of the elements in the sample stars of the poor metal stars are obviously not equal. This indicates that the contribution of each nuclear synthesis process to the abundance of neutron capture elements varies with the atomic number, indicating that the nuclear synthesis process of these elements may occur in several different sites. For the study of chemical evolution of the early Milky way galaxy and the study of light elements, the r-process model of heavy neutron capture elements can be found that both the S-process and the r-process can be divided into two components. Thus, the contribution ratio of two different nuclear synthesis processes is decomposed and the element abundance is calculated, so that the nuclear synthesis process can be quantified into each component coefficient. The main components of the process of star nucleation can be measured as a whole, and the astrophysical environment and location of star formation can be known. Although this computational model has some shortcomings, it can be confirmed. This method is an effective method for the observation of very complete elements in the r-process superrich and poor metal stars.
【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：P145.3

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