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题名:
Ia型超新星前身星研究
其他题名: Progenitors of Type Ia Supernovae
作者: 孟祥存
学位类别: 博士
学位专业: 天体物理
学位授予日期: 2008-06-05
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: 双星 ; 密近双星---恒星 ; 演化---超新星 ; 广义---白矮星 ; 金属丰度
中文摘要: 这是一篇关于Ia型超新星前身星研究的博士论文。本文详细介绍了有关Ia型超新星的历史发展及研究现状,特别是详细介绍了Ia型超新星的前身星模型和爆炸模型以及一些相关的观测认证。在这些前身星模型中最流行的是单简并星钱德拉塞卡质量极限模型。在这个模型中,Ia型超新星的前身星是由一颗碳氧白矮星和一颗主序星或者亚巨星(WD+MS)组成的双星系统。碳氧白矮星通过稳定的洛希瓣物质交流从伴星吸积物质从而增加自身质量,当其质量达到钱德拉塞卡质量极限的时候,发生了Ia型超新星爆炸。在这个模型的框架下,并且利用Hachisu et al(1996)的光学厚星风假设,我们全面、系统的研究了这个模型的各种性质,包括前身星系统的参数空间、Ia型超新星的诞生率、爆炸后伴星的性质以及爆炸抛射物对伴星的碰撞等等。经过我们的研究发现:(1)能发生Ia型超新星爆炸的双星系统的参数空间随金属丰度有明显的变化。(2)对于从WD+MS系统得到的Ia型超新星,其延迟时标约为1Gyr。并且随金属丰度的增加,Ia型超新星的爆炸时刻提前、诞生率增加,而且平均亮度增加。(3)从WD+MS系统得到的银河系中Ia型超新星的诞生率约为(0.7-1)×10-3yr-1,尽管比观测小,但仍然可以和观测相比较。(4)爆炸后伴星的各种积分性质,包括质量、半径、表面重力加速度和空间速度等,都与Tycho超新星伴星的性质相符。(5)根据Marietta et al.(2000)和Kasen et al.(2004)的数值模拟结果,我们发现至少有75%的Ia型超新星可以探测到偏振信号。(6)我们的模型可以解释观测上Ia型超新星光极大时刻的色余分布。(7)双星系统的初始周期、伴星的初始质量以及发生物质交换时伴星所处的演化状态对Ia型超新星爆炸抛射物与伴星之间的相互作用有重要影响。在研究Ia型超新星前身形时,碳氧白矮星质量随金属丰度的变化也是一个非常重要的问题,因为若给定零龄主序星的质量后,不同金属丰度环境中形成的碳氧白矮星质量不同,就很有可能会影响双星演化的最终结果。在本文中,我们也研究了恒星在零龄主序时的质量与其演化成白矮星后的质量之间的关系(以下简称初始-终止质量关系)随金属丰度的演化。经过我们研究发现:初始一终止质量关系随金属丰度Z存在明显的演化。当Z=0.04时,对于给定初始质量的恒星,其最终得到的白矮星的质量最小。从Z=0.04开始,无论是增加还是减小金属丰度,其终止质量都将增加。当Z≥0.02且初始质量Mi≤1.0%时,恒星的最终命运可能是变成一颗氦白矮星。因此,在年老的富金属的星团中应该存在大量的氦白矮星,这与观测相符。
英文摘要: This doctorial thesis is on the progenitors of type Ia supernovae (SNe Ia). In the thesis, I reviewed the study of SNe Ia, especially about the progenitor models and explosion models of SNe Ia. Among all the progenitor models, the most widely accepted one is the single degenerate Chandrasekhar model, in which a carbon-oxygen white dwatf (CO WD) accretes hydrogen-rich material from its companions until its mass reaches a mass $\sim 1.378 M_{\odot}$ (close to Chandrasekhar mass), and then explodes as a SN Ia. The companion is probably a main sequence star or a slightly evolved star (WD+MS). In the theoretical framework of optically thick wind suggested by Hachisu et al. (1996, ApJ, 470, L97), we studied the propeties of WD + MS channel comprehensively and systematically, including the parameter space of progenitors for SNe Ia, the evolution of birth rate of SNe Ia with time, the properties of the companion before and after SNe Ia explosion, and the impact between explosion ejecta and the companion. We found that: (1) The parameter space of WD + MS systems for SNe Ia evolves with metallicity. (2) The delayed time of SNe Ia from WD + MS channel is about 1 Gyr. The explosion time of SNe Ia becomes earlier for a high metallicity. The birth rate and the mean luminosity of SNe Ia increase with metallicity. (3) The Galactic birth rate of SNe Ia from WD+MS channel is around (0.7-1.0)$\times10^{\rm -3}{\rm yr^{\rm -1}}$, which is smaller but comparable to that inferred from observations. (4) The properties of the companions after SNe Ia explosion from WD + MS channel, including mass, radius, surface gravity and space velocity, are well consistent with those of Tycho G. (5) Based on the numerical simulation of Marietta et al. (2000, ApJS, 128, 615) and Kasen et al. (2004, ApJ, 610, 876), we studied the the percentage of SNe Ia with polarized spectrum and found that at least 75\% of all SNe Ia can be detected by spectropolarimetric observations. (6) We can reproduce the distribution of color excess of SNe Ia at maximum light. (7) When one studies the interaction between supernova explosion ejecta and companion, the initial orbital period and the initial mass of companion in a WD + MS system as well as the evolutionary phase of companion when mass transfer begins, are very important. When one studies the progenitor models of SNe Ia, the dependence of the mass of CO WD on metallicity (i.e. the dependence of initial-final mass relationship on metallicity) is also very important. We also studied the dependence of initial-final mass relationship on metallicity and found that there is an obvious dependence of initial-final mass relationship on metallicity and the dependence is not monotone. When $Z=0.04$, the final mass of the WD for a given initial mass is at minimum. For higher or lower $Z$, the mass of WD is higher. For $Z\geq0.02$, helium white dwarfs are formed from stars with initial mass less than $1.0M_{\odot}$. This result means that there should be many helium white dwarfs in metal-rich old clusters, which is supported by the observation of NGC6791.
语种: 中文
总页数: 185
内容类型: 学位论文
URI标识: http://ir.ynao.ac.cn/handle/114a53/4656
Appears in Collections:大样本恒星演化研究组_学位论文

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