r-Ⅱ星钡元素的奇同位素比例研究

发布时间：2018-07-12 15:29

本文选题：化学演化 + 大气参数　；参考：《河北师范大学》2017年硕士论文

【摘要】：到目前为止,人们对于r-过程的核合成场所仍不是很明确。研究恒星的核合成历史及其形成机制问题仍是一项很重要的任务。现在的理论研究表明,处于贫金属环境下的重元素的核合成过程主要由r-过程主导。我们在考虑非局部热动平衡情况下分析贫金属环境下钡元素的奇同位素比例,从同位素的角度分析能为理论研究提供更为严格的观测约束。研究r-过程元素增丰的恒星对于更好的了解r-过程元素的本质和起源是至关重要的。由此我们对四颗r-过程元素增丰的金属丰度很贫的巨星进行了钡元素奇同位素丰度比的测定,这四颗来自汉堡巡天的目标源分别为CS29491-069([r/Fe]=+1.1)、HE1219-0312([r/Fe]=+1.5)、HE2252-4225([r/Fe]=+0.80)和HE2327-5642([r/Fe]=+0.99)。我们利用高分辨率高信噪比的光谱,通过拟合受超精细结构影响的钡元素共振谱线4554?的谱线轮廓来测定钡元素的奇同位素比例。测量钡元素奇同位素所占比例时需确保共振谱线4554?的丰度和次级谱线5853?和6496?的丰度一致。在确保丰度值不变时,通过调节宏观湍流速度拟合共振谱线并利用卡方检验得到最佳钡元素奇同位素比例。为了确保测量的一致性,我们利用铁线重新测定了四颗样本星的大气参数:有效温度、表面重力、金属丰度和微观湍流,大气参数的测定均考虑了受非局部热动平衡状态的影响。利用铁线丰度不受激发电势和谱线吸收强度的影响来测定有效温度和微观湍流,表面重力的确定则取自中性铁丰度和一次电离铁丰度的电离平衡。测得四颗样本星CS29491-069、HE1219-0312、HE2252-4225和HE2327-5642钡元素的奇同位素比例分别为0.46±0.08、0.51±0.09、0.48±0.12和0.50±0.13,它们对应着的钡元素均是由纯r-过程主导的。四颗r-II恒星均表现出很高的r-过程贡献比表明在这一类恒星中大部分的重元素均通过r-过程合成。得出的结论和贫金属星基于丰度模式下的结果一致。
[Abstract]:So far, the site of R-process nuclear synthesis is still unclear. It is still an important task to study the nuclear synthesis history and its formation mechanism of stars. Current theoretical studies show that the nucleation process of heavy elements in poor metal environment is dominated by r-process. We analyze the odd isotopic ratios of barium elements under the condition of non-local thermo-dynamic equilibrium. From the point of view of isotopes, we can provide a more strict observation constraint for theoretical research. The study of stars with increasing r-process elements is essential for a better understanding of the nature and origin of r-process elements. Therefore, we have measured the odd isotopic abundance ratios of barium elements in four superstars with poor metal abundance. The target sources of these four species are CS29491-069 ([r / Fe] = 1.1) HE1219-0312 ([r / Fe] = 1.5) HE2252-4225 ([r / Fe] = 0.80) and HE2327-5642 ([r / Fe] = 0.99). By using the high resolution and high signal-to-noise ratio spectra, we fit the resonance lines of barium affected by hyperfine structure 4554? To determine the odd isotopic ratio of barium elements. When measuring the proportion of odd isotopes of barium elements, we should ensure that the resonance spectrum line is 4554? The abundance and secondary line 5853? And 6496? The abundance is consistent. When the abundance value is constant, the optimal ratio of odd barium isotopes is obtained by adjusting the macroscopic turbulence velocity to fit the resonance spectrum line and using chi-square test. To ensure consistency in measurements, we re-measured the atmospheric parameters of four sample stars using iron wires: effective temperature, surface gravity, metal abundance and microscopic turbulence. The measurement of atmospheric parameters takes into account the influence of nonlocal thermodynamic equilibrium state. The effective temperature and micro-turbulence are determined by the iron-wire abundance independent of the excitation potential and the absorption intensity of the spectral line. The determination of surface gravity is based on the ionization equilibrium of the neutral iron abundance and the primary ionization iron abundance. The odd isotopic ratios of four sample stars, CS29491-069, HE1219-0312, HE2252-4225 and HE2327-5642, are 0.46 卤0.080.51 卤0.09U 0.48 卤0.12 and 0.50 卤0.13, respectively. The corresponding barium elements are all dominated by pure r-process. All four r-II stars exhibit a high r-process contribution ratio, indicating that most of the heavy elements in these stars are synthesized by r-process. The results obtained are consistent with the results based on the abundance model of the 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】：2017
【分类号】：P148

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