太阳邻域恒星的元素丰度分析

发布时间：2018-05-31 13:37

本文选题：银河系 + 恒星　；参考：《河北师范大学》2016年硕士论文

【摘要】：太阳邻域的F型和G型矮星被看做是能反映银河系化学演化历史的“活化石”,其化学丰度对我们了解银河系的起源和演化过程有着重要意义。我们的工作就是通过观测这类恒星中各种元素的化学丰度,研究恒星的化学演化,进而探究银河系的结构和化学演化。利用中国科学院国家天文台兴隆观测基地的2.16米望远镜及其附属的光纤摄谱仪(HRS),观测获得了来自Geneva-Copenhagen Survey(GSC)星表的100颗太阳邻域的F型和G型矮星的高分辨率(R≈40000)、高信噪比(S/N≥100)光谱。采用IRAF软件包进行一维光谱的抽取和等值宽度的测量,并利用Kurucz的局部热动平衡大气模型,利用ABUNTEST8程序包分别计算出100颗样本星的Na、Mg、Al、Si、Ca、Ti、Cr、Ni、Fe、Zn、Y、Ba、O等13种元素的化学丰度。结合恒星运动学的星族成分划分标准、恒星年龄、恒星平均轨道半径及离开银道面的距离等相关信息,分析了不同星族成分的元素丰度分布,得到了以下主要结论。(1)薄盘恒星和厚盘恒星的ɑ元素(Mg、Si、Ca、Ti、O)丰度不能完全分开,在我们的样本范围中,既存在运动学属于薄盘,但[α/Fe]属于厚盘的恒星,也存在运动学属于厚盘,但[α/Fe]属于薄盘的恒星。厚盘星的[α/Fe]整体高于薄盘星的[α/Fe],但是在-0.7≤[Fe/H]≤-0.3的范围内存在较为严重的混合。(2)薄盘星和厚盘星的[O/Fe]无明显分离,但厚盘星的O元素丰度平均高于薄盘星,且元素丰度随金属丰度的增加而持续减小,这一现象存在于整个样本范围内,并且在[Fe/H]=-0.3附近存在膝状下降(knee)现象。(3)对于铁族元素(Cr、Ni、Zn),各元素的丰度分布并不完全一致,Cr和Ni的元素丰度整体在零附近。对于这三种元素,样本中的厚盘星的元素丰度没有整体高于薄盘星的趋势,且薄、厚盘的恒星存在明显混合,从元素丰度上很难将二者区分开。(4)对于奇Z元素(Na、Al)来说,我们的结果表明[Na/Fe]基本上与铁族元素的演化趋势一致,整体上与[Fe/H]没有相关性,且厚盘和薄盘恒星的[Na/Fe]也没有明显区分,但对[Fe/H]0的富金属盘星,[Na/Fe]表现出随金属丰度的增加而略微增加的趋势。[Al/Fe]随[Fe/H]的关系和ɑ元素相似,厚盘星的丰度平均高于薄盘恒星。(5)中子俘获元素(Ba、Y)的元素丰度在薄盘和厚盘恒星之间同样存在明显混合,且Ba和Y有着相近的丰度分布,与ɑ元素明显不同的是,其薄盘星的丰度普遍高于厚盘星的丰度,且薄盘星的丰度弥散更大。(6)在太阳附近的内盘,厚盘恒星存在一个负的[ɑ/Fe]径向丰度梯度,而对外盘的厚盘恒星而言,随着Rm的增加,厚盘恒星的[ɑ/Fe]丰度又会微弱增加。而薄盘恒星的[ɑ/Fe]存在一个正的径向丰度梯度。尽管薄盘和厚盘恒星的[ɑ/Fe]没有一个确切的分界,但平均来讲厚盘恒星的[ɑ/Fe]要高于薄盘。(7)薄盘星和厚盘星在Z方向也无法完全分开,样本中的薄盘星主要分布在Zmax≤0.5kpc的范围内,厚盘星则在0kpc≤Zmax≤2kpc的范围内分布的比较均匀。(8)关于恒星年龄和金属丰度,样本中的厚盘星的年龄整体高于薄盘星,且ɑ元素丰度随恒星年龄的增加而增加,所以存在恒星年龄-金属丰度关系。这些结果表明,虽然薄盘星和厚盘星的元素丰度在统计平均的结果上存在差异,但我们无法通过元素丰度把薄盘恒星和厚盘恒星准确的区分开,即使对于ɑ元素也是如此,在[Fe/H]=-0.5附近丰度存在严重混合。因此,对于不同星族元素丰度能否准确区分,以及通过运动学特征划分星族成分的可靠性,仍然需要更多的样本来进行进一步的研究。
[Abstract]:The F and G dwarfs of the solar neighborhood are regarded as "living fossils" that reflect the history of the Milky Way's chemical evolution. Their chemical abundance is of great significance to our understanding of the origin and evolution of the Milky way. Our work is to investigate the chemical evolution of stars by observing the chemical abundance of various elements in these stars. The structure and chemical evolution of the Milky way. Using the 2.16 meter telescope and its attached optical fiber spectrograph (HRS) of the National Astronomical Observatory, the National Astronomical Observatory of the National Astronomical Observatory, the high resolution (R) 40000 and the high signal to noise ratio (S/N > 100) spectrum of 100 F and G dwarfs from the solar neighborhood of the Geneva-Copenhagen Survey (GSC) star are observed. Using the IRAF software package for the extraction of one dimensional spectrum and the measurement of the equivalent width, and using the local thermal equilibrium atmosphere model of Kurucz, the ABUNTEST8 program package is used to calculate the chemical abundances of the 13 elements, such as the Mg, Al, Si, Ca, Ti, Cr, Ni, Fe, Cr, Ni, Fe, Cr, Ni, and star composition of stellar kinematics. Age, the average orbital radius of the star and the distance away from the silver channel, analysis the distribution of the element abundances of different star groups, and get the following main conclusions. (1) the abundance of Mg, Si, Ca, Ti, O in the thin disk star and the thick disk star can not be completely separated. In our sample range, the existing kinematics belongs to the thin disk, but [alpha /F] E] is a thick disk star, and the kinematics belongs to the thick disk, but [alpha /Fe] belongs to the thin disk star. [alpha /Fe] as a whole is higher than that of thin disc [alpha] /Fe], but in -0.7 < < [Fe/H] < -0.3 > there is a more serious mixture. (2) the [O/Fe] of the thin disc star and the thick disc star is not clearly separated, but the abundance of the O element in the thick disk star is higher than that of thin. Disc star, and the element abundance continues to decrease with the increase of metal abundance, this phenomenon exists in the whole sample range, and there is a geniculate descent (knee) phenomenon near [Fe/H]=-0.3. (3) for the iron element (Cr, Ni, Zn), the abundance distribution of each element is not completely consistent, and the element abundances of Cr and Ni are in the vicinity of zero. For these three elements The element abundance of the thick disk stars in the sample has no overall higher than the trend of the thin disc star, and the thin, thick disk stars have a distinct mixture, and it is difficult to separate the two from the element abundance. (4) for the odd Z element (Na, Al), our results show that the [Na/Fe] is basically consistent with the evolution trend of the iron element, and is not related to [Fe/H] as a whole. The [Na/Fe] of the thick disk and thin disk star has no obvious distinction, but for the [Fe/H]0 rich metal disk star, the [Na/Fe] shows a slight increase with the increase of the metallicity, and the.[Al/Fe] is similar to the [Fe/H]. The abundance of the thick disk star is higher than that of the thin disk star. (5) the element abundance of the medium subtrapping element (Ba, Y) is in the thin disk and the thick disk. The same obvious mixture between the stars and Ba and Y has a similar abundance distribution. The abundance of the thin disc stars is generally higher than the abundance of the thick disc stars, and the abundance of the thin disc stars is greater. (6) there is a negative /Fe] radial abundance gradient in the inner disk near the sun, and the thick disk of the outer disk is constant. In the star, with the increase of Rm, the /Fe] abundance of the thick disk star will be slightly increased. The [/Fe]] of the thin disk star has a positive radial abundance gradient. Although there is no exact dividing line between the thin disk and the thick disk star, the /Fe] of the thick disk star is higher than the thin disk. (7) the thin disc star and the thick disk star are not in the direction of Z. The thin disc star in the sample is mainly distributed in the range of Zmax < 0.5kpc, and the thick disc star is more evenly distributed in the range of 0kpc < Zmax < < 2kpc. (8) the age of the star and the abundance of metal, the age of the thick disc star in the sample is higher than that of the thin star, and the abundance of the element increases with the age of the star. Star age metallicity relations. These results show that although the element abundances of thin disc stars and thick disc stars differ in statistical mean results, we can not separate the thin disk stars from the thick disk stars by the abundance of elements, and even for the elements, there is a serious mixture in the abundance near [Fe/H]=-0.5. Therefore, More samples are still needed for further research on whether the abundance of different family elements can be accurately differentiated and the reliability of the star composition is divided by kinematic characteristics.
【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P152;P148

【相似文献】