钡星的元素丰度分析

发布时间：2018-04-28 04:40

本文选题：观测 + 恒星大气　；参考：《河北师范大学》2011年硕士论文

【摘要】：钡星是一类特殊的红巨星,最初是由Bidelman和Keenan在1951年观测得到[09],其光谱型为G2—K4,光谱中有非常强的BaⅡ4554A线,另外还有SrⅡ线、CH线、CN线,以及C2线(Burbidge et al.1957)。在随后的观测中,人们发现钡星的光谱特征还表现为其他重元素的增丰,比如：Y、zr、La、Ce、Pr、Nd、Sm等。在之后对钡星的研究中,人们已经得到了很多钡星的演化历史和物理属性,但是还有很多问题没有解决,例如造成钡星重元素超丰的具体过程是什么,主要受哪些因素的影响,钡星的运动学特征等等。以此为切入点,我们开展了对钡星的研究工作。 Lu(1991)[60]搜集整理并列表给出了一个389颗钡星的样本表。并采用Warner et al.(1965)删的方法依据BaⅡ4554 A谱线的强度,给出了每颗样本星的钡强度。具体值从1到5表明Ba强度逐渐增大,并定义Ba≥2的样本为强钡星,Ba2的样本为弱钡星。另一方面,McClure(1980)[56]发现绝大部分钡星(甚至可能是全部)都显示视向速度的变化,表明它们有伴星的存在。之后的一些工作测得了大样本钡星的双星轨道参数(Carquillat et al.1998[20], Udry et al.1998a[72],1998b[73], Jorissen et al.1998)。虽然有了这些前期工作,但由于观测限制,对于钡星重元素的直接观测分析还较少,而重元素丰度的分析是研究钡星重元素超丰起源的重要而直接的方法。因而我们建立的研究课题是观测获得大样本钡星的高分辨率高信噪比光谱,进而获得其重元素丰度。如果可能,并将详细比较分析强、弱钡星的特征,并探讨其原因。我们利用中国科学院国家天文台兴隆观测站的2.16米天文望远镜进行了光谱观测,并获得了57颗钡星的高分辨率、高信噪比光栅光谱。国家天文台梁艳春研究员和刘国卿博士已经分别处理和分析了其中的4颗和8颗样本(Liang et al.2003[47], Liu et al.)。本文共处理和分析了其余的45颗样本星。在处理光谱方面,我们用标准的MIDAS软件包得到一维光谱并测量得到每颗目标源的视向速度和元素的等值宽度,然后用前人提出的经验方法迭代计算并得到可靠的大气参数(有效温度(Teff)、表面重力(1ogg)、金属丰度[Fe/H]和微观湍流速度((?))),然后将大气参数及谱线的等值宽度输入所采用的大气模型中,从而得出了17种元素的丰度。我们发现45颗样本星里,除了HD 26是晕星,其它44颗都是盘星。它们的O,Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni等α、Na、Al及铁族元素的丰度与太阳值类似,Y、Zr、Ba、La、Eu等中子俘获元素表现出明显增丰。例如[Ba/Fe], [La/Fe], [Eu/Fe]的中值分别是0.53,0.43,0.39。强钡星的Y、Zr元素表现出第一个峰值,Ba、La、Eu等元素表现出第二个峰值,且比第一个峰值更高。而弱钡星的Y、Zr元素看不出明显增丰,甚至比太阳值还要低,Ba、La、Eu等元素依然能看出明显的增丰。不过,应该提到的是我们采用的是YⅠ、ZrⅠ线来计算得到Y、Zr元素的丰度。有研究表明,如果采用YⅡ、ZrⅡ线的话,丰度值会略有提高(0.1-0.3dex)。然后,我们将样本扩大,增加了Liang et al. (2003), Allen Barbuy (2006a), Smiljanic et al. (2007), Liu et al. (2009), Zacs(1994)工作的共69颗样本星。这样我们采用扩大后的样本(114颗样本星)来进一步分析钡星的特征,特别是比较了强、弱钡星的丰度特征,探讨了可能影响其差别的主要参数,包括金属丰度,双星轨道周期及中子辐照量。我们基于高质量光谱观测获得的样本星的[Ba/Fe]值对钡星进行了重新分类,我们把[Ba/Fe]≥0.69的钡星划分为强钡星,把[Ba/Fe]0.69的钡星划分为弱钡星。因为之前的工作中绝大部分是强钡星,而我们的45颗样本星里很多是弱钡星,这使得我们能够对强、弱钡星的比较更加细致深入。我们发现对于强钡星,随着金属丰度的增大,钡元素丰度降低,对于弱钡星没有明显趋势。这可能意味着Ba超丰较强的那些星相比Ba超丰较弱的那些星属于更老一些的盘族星。不过在较重(hs：Ba和La)与较轻(ls：Y和Zr)元素丰度比率[hs/ls]与[Fe/H]的关系中,却没有看到强、弱钡星的明显差别。我们计算得到样本星的空间速度U、V、W,证明这45颗样本星里除了HD 26是晕星,其它的都是盘星。强、弱钡星的空间速度U、V、W没有明显区别。通过利用星风吸积模型拟合(Liang et al.2000, Zhang et al.1999),我们发现星风吸积模型能更好的解释钡星的重元素超丰：钡星的重元素超丰是由于吸积了其伴星所抛射的重元素物质造成的,而这颗伴星当时是一颗AGB星,现在已经演化为一颗白矮星。然后,我们进一步探讨了另外两个参数对强弱钡星的影响,即双星轨道周期P和其伴星在AGB阶段发生中子俘获过程时的中子辐照量。通过分析,我们发现轨道周期对于造成钡星的重元素超丰有重要影响。一般来说,更短的轨道周期更有利于造成钡星的超丰。而更强的中子辐照量会使得钡星有更高的重元素超丰。不过,整体还是多个参量耦合在一起的复杂的过程。
[Abstract]:Barium star is a special kind of red giant star, which was first observed by Bidelman and Keenan in 1951, and its spectral type is G2 - K4. There are very strong Ba II 4554A lines in the spectrum. In addition, there are Sr II lines, CH lines, CN lines, and C2 lines (Burbidge). In the subsequent observation, the spectral characteristics of barium stars are also found to be other heavy elements. Zeng Feng, such as: Y, Zr, La, Ce, Pr, Nd, Sm and so on.
In the later study of barium stars, many barium stars have been obtained the evolution history and physical properties, but there are many problems that have not been solved, for example, what is the specific process of barium star heavy elements, which is mainly influenced by the factors, the kinematic characteristics of barium stars and so on. Research work.
Lu (1991) [60] collects and lists a sample table of 389 barium stars. Using the method of Warner et al. (1965) deletion, the barium strength of each sample star is given according to the intensity of Ba II 4554 A spectrum. From 1 to 5, the strength of Ba is increased gradually, and the sample of Ba > 2 is a strong barium star, and the sample of Ba2 is a weak barium star.
On the other hand, McClure (1980) [56] found that the vast majority of barium stars (or even all) showed changes in the apparent velocity, indicating the presence of the companion stars. Some of the subsequent work measured the double star orbital parameters of the large sample barium stars (Carquillat et al.1998[20], Udry et al.1998a[72], 1998b[73], Jorissen et al.1998).
In spite of these previous work, the observation and analysis of the barium star heavy elements are less and less due to the observation restrictions, and the analysis of the abundance of heavy elements is an important and direct method to study the super abundant origin of barium stars. Therefore, the study of the high resolution and high signal to noise ratio spectra of large sample barium stars is observed. The heavy element abundance can be obtained. If possible, the characteristics of strong and weak barium stars will be compared and analyzed in detail.
We used the 2.16 meter telescope of the 2.16 meter telescope at the National Astronomical Observatory of the National Astronomical Observatory of the Chinese Academy of Sciences. We obtained the high resolution and high signal to noise ratio raster spectra of 57 barium stars. The National Observatory Liang Yanchun and Dr. Liu Guoqing have processed and analyzed 4 and 8 samples (Liang et al.2003[47], L). IU et al.). This paper deals with and analyzes the remaining 45 sample stars. In the spectrum of processing, we use the standard MIDAS package to obtain the one-dimensional spectrum and measure the apparent velocity of each target source and the equivalent width of the element. Then the reliable atmospheric parameters (effective temperature (Tef) are calculated and obtained by the previous empirical methods. F), the surface gravity (1ogg), the metallicity [Fe/H] and the microscopic turbulence velocity ((?))), and then input the equivalent width of the atmospheric parameters and the spectral lines into the atmospheric model adopted, thus obtaining the abundance of the 17 elements.
We found that in 45 sample stars, except that HD 26 is a halo star, the other 44 are disc stars. Their O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, and so on are similar to the sun value. 9. strong barium star Y, Zr element shows the first peak, Ba, La, Eu and other elements show second peaks, and higher than the first peak. And the weak barium star Y, Zr element can not see obvious increase, even lower than the sun value, Ba, La, Eu and other elements can still see obvious enhancement. However, it should be mentioned that we used Y I, Zr I line The abundance of Y and Zr elements is calculated. Studies show that if the Y II and Zr II lines are used, the abundance will increase slightly (0.1-0.3dex).
Then, we expand the sample, add the Liang et al. (2003), Allen Barbuy (2006a), Smiljanic et al. (2007), Liu et al. (2009), and 69 sample stars working (1994). So we use an expanded sample (114 sample stars) to further analyze the characteristics of the barium star, especially the comparison of the strong, weak barium star abundances. The main parameters that may affect the difference are discussed, including metallicity, double orbit period and neutron exposure.
We reclassified barium stars based on the [Ba/Fe] values of the sample stars obtained by high mass spectroscopic observations. We divide the barium stars of [Ba/Fe] > 0.69 into strong barium stars and divide the barium star of [Ba/Fe]0.69 into weak barium stars.
Because most of the previous work is strong barium, and many of our 45 sample stars are weak barium stars, which makes it possible for us to compare the strong, weak barium stars more carefully. We found that for strong barium stars, as the abundance of metal increases, the abundance of barium decreases, and there is no obvious trend to the weak barium star. This may mean Ba super. Those stars in the stronger and stronger than those with the Ba superabundance are older, but in the relation of heavier (hs:Ba and La) to the lighter (ls:Y and Zr) element abundances [hs/ls] and [Fe/H], there is no obvious difference between strong and weak barium stars.
We calculate the space velocity of the sample star U, V, W, which proves that the 45 star sample stars except HD 26 are halo stars, the other are all disc stars. Strong, weak barium star space velocity U, V, W has no obvious difference.
By using the Liang et al.2000 model (Zhang et al.1999), we found that the stellar wind accretion model can better explain the heavy element super abundance of barium Star: the barium star's heavy element overabundance is caused by the heavy element material that accretion of its companion star, and the companion star was a AGB star at the time, and now it has evolved into one. A white dwarf.
Then, we further discuss the effect of the other two parameters on the barium star, that is, the double star orbit period P and the neutron irradiation amount of its companion star during the neutron capture process at the AGB stage. By analysis, we find that the orbit period has an important effect on the heavy element of the barium star. Generally, the shorter orbit period is more favorable. The barium star is caused by the super abundance of the barium star, and the stronger neutron radiation will make the barium star have a higher weight of heavy elements. However, the whole process is a complex process coupled with a number of parameters.

【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】：P144

【共引文献】