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题名:
演化星族合成在星团及星系中的应用
其他题名: The application of evolutionary population synthesis in star clusters and galaxies
作者: 张余
学位类别: 博士
学位专业: 天体物理
学位授予日期: 2012-05-25
授予单位: 中国科学院研究生院(云南天文台)
授予地点: 北京
导师: 张奉辉
学科分类: 天文学
关键词: 演化星族合成 ; 星族参数 ; 球状星团 ; 星系
中文摘要: 星系形成演化是当今天体物理中研究的热门课题。随着望远镜深度和精度的提高,我们可以得到星系的高分辨,多波段的测光和分光数据,尤其是大口径地面望远镜和高空间分辨率空间望远镜的投入使用,我们可以得到高红移星系的测光和分光数据,利用这些数据,我们在很大程度上可以研究星系的很多特性。而演化星族合成是研究星系的一种有效方法,它是建立在我们对恒星性质(演化、分光、测光)了解的基础之上,借助一些假设(初始质量分布IMF、恒星形成率SFR、增丰史),来确定星团星系积分特性(光度、颜色、光谱)的一种方法。通过与观测得到的颜色光谱进行比较,我们可以研究星团、星系内部的恒星组成成分,星系红移、质量、年龄、红化、SFR等参数,进而研究星团、星系的结构和演化。 按照所采用数据的不同,利用演化星族合成研究星团星系主要有三种方法:(i)星等/颜色,(ii)光谱拟合,以及(iii)光谱吸收特征指数(Lick特征谱指数)。随着观测数据的增多,演化星族合成在星团星系中的应用也越来越广泛,而在对它们进行研究时主要用到的方法就是以上的三种方法,如果在观测数据不受限制的条件下,选取哪种方法更合理?更可靠呢?从这点出发,我们首先是对这三种方法进行了检验,目的是给出三种方法的适用范围,方便人们根据研究对象而选取合理的研究方法。利用银河系内40 个球状星团作为检验样本,将三种方法得到的年龄和金属丰度结果与其它方法得到的结果进行对比,得到了这三种方法在参数确定上的精确度。我们得到这样的结论:(i)对于金属丰度来说,Lick谱指数方法适合用于金属丰度处于−1.5 ≤[Fe/H]≤ −0.7 范围的星族系统的金属丰度的研究;光谱拟合方法适合用于金属丰度处于−2.3 ≤[Fe/H]≤ −1.5范围的星族系统的金属丰度的研究;(ii)对于年龄来说,这三种方法得到的结果与CMD得到的结果有很大的差异,这三种方法得到的年龄要比CMD的结果偏小(平均小2Gyr)。同时我们还利用不同的演化星族合成模型证明了上述结论不依赖于演化星族合成模型。 其次,在我们的工作中,不论采用哪种方法,发现球状星团的年龄确定都存在一些困难,由于在对球状星团进行研究时我们采用了简单星族模型,而由对球状星团的观测可以发现,球状星团内部有很多特殊星的存在,比如,水平分支星、蓝离散星、以及双星,而现在很多演化星族合成模型都是简单星族,都不能全面的把这些特殊星考虑到模型中,所以模型与真实的球状星团存在一些差异。我们结合哈勃望远镜对球状星团所观测的空间高分辨颜色星等图,将球状星图内的水平分支星和蓝离散星扣除后再利用简单星族模型研究它们的年龄。我们发现水平分支星和蓝离散星的存在会使球状星团的年龄变小,所以在对含有这两类恒星的星族系统进行研究时一定不要忽略它们的贡献。由于双星是普遍存在的,所以我们也研究可双星对球状星团的年龄影响,发现双星的存在也会使得球状星团年龄变小。在我们工作中我们给出了这三类星对年龄的具体影响。 后,人们研究星系的恒星质量、平均年龄、金属丰度以及内部恒星形成历史时,普遍采用的方法就是将星系的观测特性与演化星族合成模型进行拟合,所以这里演化星族合成模型起了重要的作用。现在大家普遍采用的还是简单单星族合成模型,而双星相互作用会对星族年龄约1Gyr星族的紫外波段有着重要的贡献,如果利用演化星族合成模型对中等年龄的星族系统进行研究时,未考虑双星相互作用则会对星系的很多参数带来影响。从这点出发,我们工作中利用演化星族合成对星系的研究主要就是有关双星相互作用对红移z ∼ 2.0处星系的颜色/星等的影响。我们利用蒙特卡洛模拟方法结合Yunnan-ssp和Yunnan-bsp演化星族合成模型,模拟产生不同红移处不同类型的星系样本,利用星系内部的恒星形成持续时标不同,我们将这些星系样本分为两类,A子类为恒星形成短持续时标的星系,B子类为恒星形成长持续时标的星系,通过比较它们的颜色星等以及颜色颜色随红移的变化关系,研究双星相互作用对红移z = 2处星系颜色/星等的影响,我们发现双星相互作用对A子类样本星系在红移z = 2处的具有明显影响,双星相互作用会使g 波段星等变蓝约1.5mag,g − r变蓝大约1.0mag,而u − g则变红约1.5mag。
英文摘要: Understanding the formation and evolution of galaxies is one of the most importantquestions in cosmology. With increases in telescope size and proved instruments, we can obtain multiband photometric and high-resolution spectroscopic data of extragalactic data. It is possible to take advantage of these data to study the properties of galaxies to an ever greater extent. Evolutionary population synthesis (EPS) is one of the methods used to study the properties of galaxies. People can build the EPS models based on the stellar evolution theory, stellar spectral library and the assumption of stellar initial mass function. The stellar masses, mean ages, metallicites and star formation histories of galaxies can be obtained via fitting the observations of galaxies to the EPS models. We can also use EPS to study the structure and evolution of galaxies. Based on the EPS models, there have three very common methods used in the galaxy studies, namely color, Lick-index and spectrum-fitting methods. It is very important to test and estimate the reliability of these methods, especially because many extragalactic studies are heavily dependent on them. Galactic globular clusters provide an excellent medium for such test, because they can be considered as simple stellar populations. We present ages and metallicities for 40 globular clusters as determined from these three methods based on the Bruzual & Charlot EPS models. By comparing with the ages obtained from color-magnitude diagrams and metallicities obtained from the spectra of stars, we are able to estimate the ability of these methods to determination parameters. As a result, we find that: (i) for the metallicity, our derived metallicities agree with those derived from the spectra of stars, Lick-index method is suitable to study metallicity for the stellar population systems in the range of −1.5 .[Fe/H]. −0.7 and spectrum-fitting method is suitable to study metallicity for the stellar population systems in the range of −2.3 .[Fe/H]. −1.5; (ii) for the age, these three methods have difficulties in age determination, our derived ages are smaller (about 2.0 Gyr, on average) than the results of CMDs for all these three methods. We use Vazdekis and Maraston models to analyze whether our results are dependent on EPS models, and find that the tendency of these two models is the same as that of Bruzual & Charlot models. Our results are independent of the EPS models. Besides the age-metallicity degeneracy, we examine the possible effects of other factors (horizontal branch morphology, blue straggler stars, binary interactions and α−enhancement) and give quantitative analysis of the influences of these factors on age determinations. People can study the stellar masses, mean ages, metallicites and star formation histories of galaxies via fitting the observations of galaxies to the EPS models, and the EPS models play an important role in such studies. The binary stars can significantly affect the ultraviolet (UV) spectra of intermediate-age (∼ 1.0 Gyr) stellar populations. Binary stars are very common in the Universe, hence binary stars are important for the optical (observed frame) colors for galaxies at z∼ 2.0, when the rest frame UV emission is shifted to optical passbands. We use the Monte Carlo method to simulate the galaxy sample with different redshift and morphology based on two different EPS models (Yunnan-ssp and Yunnan-bsp). We present the magnitudes and colors in observed frame for galaxies with star formation rate described by three forms, and we divide our galaxy sample into two sample to study the influence of binary stars on the magnitudes and colors for galaxies, one is with short star formation time scale, and the other is with long star formation time scale. We find the binary stars can alter the magnitudes and colors for the galaxies with short star formation time scale, binary stars can make the g band bluer about 1.5mag, g − r bluer about 1.0mag, u − g redder about 1.5mag.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ynao.ac.cn/handle/114a53/4669
Appears in Collections:大样本恒星演化研究组_学位论文

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