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题名:
演化星族合成的应用
其他题名: Applications of Evolutionary Population Synthesis
作者: 李忠木
学位类别: 博士
学位专业: 天体物理
学位授予日期: 2008-01-29
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: 韩占文
学科分类: 天文学
关键词: 演化星族合成 ; 应用 ; 星系 ; 星团 ; 简单星族 ; 复合星族 ; 单星族 ; 双星族
中文摘要: 随着恒星、宇宙学研究的逐渐成熟,星系的形成和演化成了目前天文和天体物理研究中的最大挑战。它不仅能增加我们对星系的理解,也是将恒星的研究和宇宙学的研究结合起来的重要纽带。由于星系的绝大部分可见物质都集中于恒星中,星系中恒星的演化决定了星系演化中的许多观测特性。研究星系中的恒星演化特征可以间接地研究星系的形成和演化。所以确定星系中的恒星成分成了天体物理中很重要的一部分工作。演化星族合成方法正是确定星系中恒星成分的一种有效方法。本文对演化星族合成方法应用中的几个关键问题进行了研究,给出了一些新的结果。 首先,基于用光谱方法难以确定遥远(红移大于0.3)星系和星团星族参数的困难,我们深入分析了利用颜色(它比光谱更容易获得,特别是对遥远天体而言)研究天体星族参数的可能性。结果显示利用颜色可以确定星族参数,我们给出了确定星族参数最好的颜色对以及应用不同颜色对时所得结果的可能误差。这使我们能够通过测光数据确定遥远星系和星团的星族参数,从而更好地进行星系的形成和演化等研究。 其次,由于大部分星系中(包括早型星系)存在近期(1 Gyr内)的恒星形成,这些年轻的恒星会对星系的星族年龄和金属丰度确定造成影响(用颜色方法确定星族参数时会使得到的年龄偏小、金属丰度偏大)。我们对此进行了深入分析,提出了一种能改正这种影响的统计性方法。这样我们就可以通过颜色获得大样本星系的平均星族年龄和金属丰度以及它们的分布。我们还发现星系中年轻星族的存在很可能会影响到星系的一些基本关系,如基本平面和Kormendy关系。当考虑了年轻星族的影响后,星系基本关系的弥散可能会变小,同时测得的星系距离会比用以前的关系测得的值小。 再次,因为有50%以上的恒星处于双星系统中但直接用恒星演化程序计算由大量(百万量级)恒星组成的双星族演化非常困难,我们建立了一个用于快速模拟单星族和双星族的星族等龄分布数据库,计算了单星族和双星族的谱指数、各种颜色等。它使人们能够方便快捷地在星族合成研究和星系形成演化研究中考虑双星演化的影响。这对那些和双星演化有关的特殊现象(如蓝离散星和椭圆星系的紫外反转等)的研究极有意义。 另外,我们详细分析了双星相互作用对星族合成结果和星族研究结果(星族年龄和金属丰度)造成的影响。结果发现双星作用会使星族的颜色变蓝、Hbeta谱指数变大、金属线谱指数变小。当我们用单星族来拟合星系或星团的星族参数时,用谱指数方法得到的年龄会比真实值明显偏小、用颜色方法得到的金属丰度会比真实值明显偏小。我们还发现用双星族模型得到的星族年龄和用单星族模型得到的结果之间存在很好的相关关系,通过单星族模型得到的结果我们就可以估算出用双星族模型得到的结果,这对一些和星族参数绝对量有关的研究很有帮助。另外,我们的结果也显示出尽管用单星族模型和双星族模型得到的星族参数绝对值是不同的,但是用两类模型得到的大部分相对研究结果很类似。 工作中我们还率先使用双星族模型对80多个椭圆星系的星族参数进行了研究,并对一个星系的等级并合形成模型进行了验证。我们的结果基本支持此模型但也显示出了一些矛盾,这些结果对星系的形成和演化研究都很有意义。 总体上,我们的工作主要解决了以前难以对遥远星系和星团进行星族研究、难以用双星族模型进行大规模的星族研究、不清楚双星相互作用对星族研究结果的具体影响等困难,促进了演化星族合成方法在实际天文和天体物理研究中的应用。
英文摘要: The formation and evolution of galaxies has been the biggest challenge in astronomy and astrophysics. It can help us not only to understand the histories of galaxies but also to join the studies of stars and cosmology. Because most of observable mass of galaxies is contained in stars, the evolution of stars determines many integrated peculiarities of galaxies, e.g., luminosity, colours, and spectra. Therefore, one can investigate the formation and evolution of galaxies via studying the stellar contents of galaxies. The determination of stellar contents of galaxies has been a very important part of the studies of astronomy and astrophysics. Evolutionary population synthesis is just a powerful technique for the determination. The thesis investigate on a few key problems in the applications of evolutionary population synthesis technique. Some useful results are shown by our works. First, we investigate the ability of colours for determining the age and metallicity (hereafter stellar-population parameters) of stellar populations. The motivation is that it is difficult to measure the above parameters of distant (redshift > 0.3) galaxies via spectra-like methods, as these is no available spectra. However, colours are usually available for these galaxies. Our results show that colours can be used to determine stellar-population parameters. The best colour pairs for measuring stellar age and metallicity are shown, with possible result uncertainties. The results can help us to explore the stellar populations of distant galaxies, and then to give further investigations to the formation and evolution of galaxies. Second, because some observations showed that most galaxies including early-type ones have recent (within about 1 Gyr) star formations, and young populations can obviously affect the determination of stellar-population parameters, we investigate how young populations affect the determination of the ages and metallicities of populations. A statistical method for correcting the effects of young populations is brought forward by the work. Using this technique, we will be able to obtain the distributions and averages of the stellar-population parameters of a sample of galaxies. We also analyze the effects of young populations on the fundamental plane and Kormendy relation of galaxies. It shows that the scatter of the fundamental relations may be smaller when taking the effects of young populations into account, and we will measure less distances for galaxies after correcting for the effects of young populations. Third, because it is difficult to calculate the isochrones of binary stellar populations via stellar evolution code directly, we build a statistical isochrone database for conveniently and quickly modeling both single-star and binary-star populations. Then we calculate the spectral energy distributions, Lick indices, and colours of both single-star stellar populations and binary-star stellar populations. This makes it possible to conveniently take binary interactions into account when studying the formation and evolution of galaxies. Fourth, we investigate the effects of binary interactions on stellar population synthesis studies. The results show that binary interactions make the colours of populations bluer, Hbeta index larger, and metal line indices smaller. Using a Lick index method to determine stellar age and metallicity, we will obtain obviously less ages compared to the real values of populations. When taking a colour method to measure stellar-population parameters, we will get obviously less stellar metallicities. We also find that the real ages of populations are related to the values fitted via single stellar populations. Thus one can calculate the stellar ages fitted via binary-star stellar populations from the ages and metallicities fitted via single-star stellar populations. It is also shown that the relative results obtained by both single-star and binary-star stellar populations are similar. Fifth, we determine the stellar ages and metallicities of about 80 elliptical galaxies and test a new model for the formation of elliptical galaxies. Our results show some supports to the model, while show an opposition. The result is actually important for galaxy formation investigations. As a whole, the thesis solved some key problems on the applications of evolutionary population synthesis. It makes evolutionary population synthesis technique more powerful and useful in astrophysics studies.
语种: 中文
总页数: 159
内容类型: 学位论文
URI标识: http://ir.ynao.ac.cn/handle/114a53/4654
Appears in Collections:大样本恒星演化研究组_学位论文

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