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arXiv 0707.4598astro-ph
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爆炸为Ia型超新星的中等质量密近双星的比例

On the fraction of intermediate-mass close binaries that explode as type-Ia supernovae

Dan Maoz

摘要:

Ia型超新星(SNe-Ia)被认为是由白矮星(WD)的热核失控造成的,这些白矮星接近于克拉塞卡极限,要么是通过伴星的吸积,要么是与另一颗WD合并。我汇编观测估计的分数η的中等质量的恒星,最终爆炸为SNe-Ia,补充他们与几个新的估计,并比较它们自洽。这些估计是基于五种不同的方法,每一种方法都利用了一些与SN-Ia速率相关的观测数据,并结合了关于IMF的假设:恒星形成星系中SN-Ia与核心坍缩速率的比率;每单位恒星形成速率的SN-Ia速率;每单位恒星质量的SN-Ia速率;星系团中铁与恒星质量的比率;以及星系团中的丰度比率。这五种方法表明,在初始质量为3- 8M_sun的所有恒星中,约有2-40%的恒星(通常认为的SN-Ia祖先)爆炸为SNe-Ia。对于一系列合理的IMF,eta~15%的分数与所有五种方法一致。再考虑到这类恒星的双星比例、质量比分布、分离分布和双重性(每个双星只能产生一次超新星-Ia爆炸),这意味着几乎每个中等质量的近距离双星最终都是超新星-Ia,或者可能比祖先系统更多的超新星-Ia。理论上预期的分数一般要低一到两个数量级。问题可以解决:如果所有的观测估计都是错误的;或者是一个“中等偏重”的IMF;或者是某种机制,大大提高了向SN-Ia爆炸的双星演化的效率;或者是SNe-Ia的非双星起源。

英文摘要:

Type-Ia supernovae (SNe-Ia) are thought to result from a thermonuclear runaway in white dwarfs (WDs) that approach the Chandrasekhar limit, either through accretion from a companion or a merger with another WD. I compile observational estimates of the fraction eta of intermediate-mass stars that eventually explode as SNe-Ia, supplement them with several new estimates, and compare them self-consistently. The estimates are based on five different methods, each utilising some observable related to the SN-Ia rate, combined with assumptions regarding the IMF: the ratio of SN-Ia to core-collapse rates in star-forming galaxies; the SN-Ia rate per unit star-formation rate; the SN-Ia rate per unit stellar mass; the iron to stellar mass ratio in galaxy clusters; and the abundance ratios in galaxy clusters. The five methods indicate that a fraction in the range eta~2-40% of all stars with initial masses of 3-8 M_sun (the generally assumed SN-Ia progenitors) explode as SNe-Ia. A fraction of eta~15% is consistent with all five methods for a range of plausible IMFs. Considering also the binarity fraction among such stars, the mass ratio distribution, the separation distribution, and duplicity (every binary can produce only one SN-Ia explosion), this implies that nearly every intermediate mass close binary ends up as a SN-Ia, or possibly more SNe-Ia than progenitor systems. Theoretically expected fractions are generally one to two orders of magnitude lower. The problem could be solved: if all the observational estimates are in error; or with a ``middle-heavy'' IMF; or by some mechanism that strongly enhances the efficiency of binary evolution toward SN-Ia explosion; or by a non-binary origin for SNe-Ia.

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