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题名	Ia型超新星前身星的质量积累效率研究
作者	马鑫
学位类别	硕士
答辩日期	2013-12
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
关键词	吸积 新星 演化 超新星 白矮星 星风
其他题名	The mass accreting efficiency for the progenitors of type Ia supernovae
学位专业	天体物理
中文摘要	Ia型超新星具有可校准的光度。上世纪末，人们通过Ia型超新星测距发现宇宙在加速膨胀，揭示了暗能量的存在，开创了宇宙学研究的全新局面。这一结果也因此获得了2011年诺贝尔物理学奖。但是Ia型超新星是怎么来的，即Ia型超新星的前身星模型，人们还不是很清楚。单简并模型在本世纪初的几十年里一直占主导地位，现在也被认为是Ia型超新星前身星的一个主要模型。但是人们对于单简并模型的核心物理过程——碳氧白矮星吸积并增长质量，并没有很好的理解。本论文首先详细介绍了Ia型超新星的研究进展，包括观测进展、爆炸模型和前身星模型，然后对白矮星吸积模型的研究现状和存在的问题进行了阐述。最后介绍了我在白矮星吸积方面的工作，以及工作展望。基于稳态模型的研究表明，白矮星吸积物质时所表现出来的性质和白矮星的吸积速率息息相关。我们通过最新的恒星演化程序MESA，从更真实的白矮星模型研究了白矮星吸积物质时的性质。我们假设被吸积物质的化学丰度和太阳的化学丰度类似，白矮星的质量从0.5到1.378个太阳质量，吸积率从10^(-8)太阳质量每年 到 10^(-5)太阳质量每年。我们的模型得到了和稳态模型类似的结果：当吸积率较高的时候白矮星会膨胀成红巨星，当吸积率较低的时候白矮星表面会发生氢闪耀，只有在一个很窄的吸积率范围内白矮星才能稳定吸积质量。爱丁顿光度是一个天体表面的引力与其辐射压力达到平衡时的光度，当恒星表面的光度超过爱丁顿光度的时候，会触发超爱丁顿星风。人们在研究吸积天体的爱丁顿星风的触发条件时，一般都只考虑了吸积光度。但是，如果白矮星吸积物质发生稳定的氢壳层燃烧，这个燃烧壳层在白矮星的光球层下面，核反应产生的光度也应该用来抵抗引力。我们研究发现，如果我们计算爱丁顿星风的触发条件时把核反应的光度也考虑进去，那么就会得到一个比前人结果低得多的爱丁顿吸积率，从而更容易产生超爱丁顿星风。这个超爱丁顿星风可以在高吸积率的时候阻止白矮星包层的膨胀。此前的红巨星区域被新的超爱丁顿星风区域所代替。在这种超爱丁顿星风模型下，氢壳层底部的物质会以爱丁顿临界吸积速率燃烧转变成氦。如果氦在积累一定的程度后，也发生燃烧（安静的或爆发式的）进而转变成碳和氧，那么碳氧白矮星的质量将会有效增长。最终可能会达到钱德拉塞卡质量极限而发生Ia型超新星爆炸。因此，超爱丁顿星风模型可以替代Hachisu等人1996年提出的光学厚星风模型。两者产生Ia型超新星的条件和性质是类似的，但是由于超爱丁顿星风在低金属丰度条件下同样可以触发，因此，该模型可以解释光学厚星风无法解释的高红移处的Ia型超新星。
英文摘要	Type Ia supernovae (SNe Ia) are "standardizable candles". At the end of the last century, researchers discovered the accelerated expansion of the universe by means of luminosity distance measurements via SNe Ia, from which the existence of dark energy was derived, which in turn ushered in a new age for cosmology. This work consequently won the 2011 Nobel Prize. However, the origin of SNe Ia, namely the identity of their progenitor systems, remains unknown. The single degenerate (SD) model has been dominant over the past few decades, and is still currently considered one of the most probable candidates for SN Ia progenitors, yet the process of accretion onto a carbon-oxygen white dwarf (CO WD), which is vital to the SD scenario, is not well understood. This work summarizes previous research on SNe Ia in detail, including observational progress, detonation models, and progenitor models, before proceeding to explain the current status and outstanding problems regarding CO WD accretion models. At the end, the author’s work concerning CO WD accretion, as well as its implications for future research, will be introduced.According to research based on steady-state models, accreting WD properties are a direct indicator of their accretion rates. Using MESA, the most advanced stellar evolution code to date, we studied the properties of accreting WDs with an authentic WD model. We assume the accreted material is of a similar chemical composition to solar material. Our study focuses on WD masses ranging from 0.5 to 1.378Msun, and on accretion rates ranging from 10^(-8) to 10^(-5)Msun/yr. Our model yields results similar to the steady-state model: when the accretion rate is too high, the WD will expand into a red giant, while when it is too low, H flashes will occur on the surface of the WD, thereby leaving only a very narrow accretion rate window to allow stable accretion.The Eddington luminosity (EL) is the luminosity at which the photon pressure at the surface of a celestial body is in equilibrium with its gravity. When the luminosity of a star exceeds its EL, it will trigger a phenomenon known as the Super-Eddington Wind (SEW). Previous research on the criteria for SEW focused exclusively on the accretion luminosity. However, if the matter accreted onto the COWD undergoes stable H shell burning, and this H shell is located beneath the WD’s photosphere, the luminosity which arises from this burning can also be used to counter gravity. We found that the SEW is triggered at much lower accretion rates,than previously thought, when the contribution of nuclear burning to the total luminosity is included. In this model, the H inthe accreted material is burnt into He at a rate around $\dot{M}_{\rm Edd}$. If the underlying He is further burnt into C and O, the WD mass then increases and possibly reaches the Chandrasekhar limit and produce a SN Ia. Thus presenting an alternative to the optically thick wind proposed by Hachisu et al. Furthermore, the SEW works in low-metallicity environments. Therefore, our model may explain SNe Ia observed at high redshifts which the optically thick wind cannot explain.
语种	中文
学科主题	天文学
页码	64
内容类型	学位论文
源URL	[http://ir.ynao.ac.cn/handle/114a53/4674]
专题	云南天文台_大样本恒星演化研究组
推荐引用方式 GB/T 7714	马鑫. Ia型超新星前身星的质量积累效率研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2013.

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