贫金属星钡元素的奇偶同位素丰度比测定和Ba星大气参数的确定

发布时间：2018-05-17 04:01

本文选题：恒星 + 大气参数　；参考：《河北师范大学》2015年硕士论文

【摘要】：本文分为两大部分:第一部分测定了一颗r/s星HE0338-3945和r-II星CS31082-001的钡元素的奇偶同位素丰度比,从同位素的角度研究了贫金属情况下r-和s-过程的中子俘获核合成情况和发生场所,以及相关恒星的形成机制问题。对元素同位素丰度的测量可以给恒星演化模型提供相较于元素丰度更加严格的观测约束,进而为精确了解恒星内部核合成及演化过程提供了保障。光谱取自高分辨率、高信噪比的UVES光谱。采用Mashonkina等人(2006)的方法,首先利用受超精细结构效应影响较小的次级线λ5853和λ6496确定Ba元素的丰度,然后考虑到共振线λ4554受到强烈的超精细结构(HFS)影响,通过改变Ba元素的奇偶同位素丰度比例,采用光谱综合的方法来拟合谱线λ4554的轮廓,并通过卡方检验的方法获取最佳偶奇比值。原因在于对于分裂后的谱线λ4554的吸收轮廓,尽管偶同位素谱线的吸收仍旧位于线心位置,但是奇同位素谱线的吸收则主要处于线翼位置并且具有不对称性,所以拟合非对称性的谱线轮廓即可测得元素奇偶同位素丰度比。通过元素的奇偶同位素丰度比oddf可以得到r-和s-过程对Ba元素的相对贡献,进而研究该星的重元素形成机制。研究发现,不同于纯r-过程丰度模式,对应于太阳纯s-过程的oddf比例并不适合于贫金属星,其与恒星的金属丰度和质量有很强的依赖关系。第二部分确定了22课钡星的大气参数。我们基于高信噪比、高分辨率的ELODLE光谱,通过光谱综合的方法来确定该22颗钡星的恒星大气参数。利用Alonso等人(1999)给出颜色与有效温度的关系来确定恒星的有效温度;采用三角视差法确定恒星的表面重力,该方法主要基于表面重力与有效温度的关系,同时利用Fe I、Fe II线的电离平衡方法进行了验证。利用测定的Fe线的等值宽度,初步计算出各谱线对应的[Fe/H]及平均值,最后通过迭代的方法进行验证。
[Abstract]:This paper is divided into two parts: in the first part, the parity isotope abundance ratio of barium element in HE0338-3945 and r-II star CS31082-001 is measured, and the neutron capture nuclear synthesis of r- and s- processes in the case of poor metal is studied from the perspective of isotopes. And related star formation mechanisms. The measurement of the isotopic abundance of elements can provide a more strict observation constraint than the element abundance in the stellar evolution model, and thus provide a guarantee for the accurate understanding of the nuclear synthesis and evolution process in the stellar interior. The spectrum is taken from the UVES spectrum with high resolution and high signal-to-noise ratio. Using the method of Mashonkina et al. 2006, the abundance of Ba elements is determined by using the secondary lines 位 5853 and 位 6496, which are less affected by hyperfine structure effect, and then considering that the resonance line 位 4554 is strongly influenced by hyperfine structure. By changing the parity isotope abundance ratio of Ba elements, the spectral synthesis method is used to fit the profile of spectral line 位 4554, and the best even and odd ratio is obtained by chi-square test. The reason is that for the absorption profile of the split spectral line 位 4554, although the absorption of even isotope lines is still located at the center of the line, the absorption of odd isotope lines is mainly located at the line wing and has asymmetry. So fitting the asymmetrical line profile can measure the abundance ratio of even and odd isotopes of elements. The relative contribution of r- and s- processes to Ba elements can be obtained by the parity isotope abundance ratio (oddf) of elements, and the formation mechanism of heavy elements of the star can be studied. It is found that, unlike the pure r-process abundance model, the oddf ratio corresponding to the solar pure S-process is not suitable for the metal-poor stars, and it is strongly dependent on the metal abundance and mass of the stars. In the second part, the atmospheric parameters of 22 class barium stars are determined. Based on the high signal-to-noise ratio (SNR) and high resolution ELODLE spectra, the atmospheric parameters of the 22 barium stars are determined by spectral synthesis method. The relationship between color and effective temperature is given to determine the effective temperature of stars, and the triangular parallax method is used to determine the surface gravity of stars, which is mainly based on the relationship between surface gravity and effective temperature. At the same time, the ionization equilibrium method of Fe Ion Fe II line was used to verify the results. Using the measured equivalent width of Fe lines, the corresponding [Fe/H] and average values of each spectral line are calculated and verified by iterative method.
【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P148

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