The r-Process in Supernova Explosions from the Collapse of O-Ne-Mg Cores
The r-Process in Supernova Explosions from the Collapse of O-Ne-Mg Cores
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DOI：
10.1086/376617
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发表时间：
2003-02
期刊：
影响因子：
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通讯作者：
S. Wanajo;M. Tamamura;N. Itoh;K. Nomoto;Y. Ishimaru;T. Beers;S. Nozawa
中科院分区：
文献类型：
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作者：
S. Wanajo;M. Tamamura;N. Itoh;K. Nomoto;Y. Ishimaru;T. Beers;S. Nozawa
虽然r-过程核的起源仍然是一个长期存在的谜，但最近对银河系晕中极贫金属恒星的光谱研究强烈表明它与核心坍缩超新星有关。在这项研究中，我们研究的r-过程核合成的“提示超新星爆炸”从一个8-10 M的祖星星作为替代方案的“中微子风”机制，这也被认为是一个有前途的网站的r-过程。在目前的模型中，祖先星星在其中心形成了一个氧-氖-镁（O-Ne-Mg）核心（质量为1.38 M）。与质量更大的恒星的铁核相比，它的引力势更小，而且在核反弹时处于核统计平衡的核也更小，这可能使星星以流体动力学的方式爆炸，而不是通过延迟中微子加热。用一维牛顿流体动力学代码进行堆芯坍塌模拟。我们得到一个非常弱的提示爆炸，其中没有r-处理发生。我们进一步模拟高能瞬发爆炸的冲击加热能量的增强，以调查在这样的事件中的r-过程核的生产所需的条件。r-过程核合成的计算使用核反应网络代码，包括相关的丰中子同位素与它们之间的反应。高度中子化的喷出物（Ye = 0.14-0.20）导致r过程核的产生，它们的相对丰度与太阳r过程模式非常一致。我们的研究结果表明，具有O-Ne-Mg核的8-10 M恒星的瞬发爆炸可能是一个有希望的r过程核的位置。每个事件的r-过程材料的质量比银河系化学演化研究预期的大大约2个数量级。因此，我们建议，只有一小部分的r-过程的材料是通过“混合回落”机制的核心物质，其中大部分的r-过程的材料福尔斯回落到原中子星星。宇宙年龄的下限是通过应用铀-钍（U-Th）精密时计对，并与在高度r-过程增强的、极贫金属的星星CS 31082-001中观测到的这些物质的比率进行比较而得出的。推断的年龄为14.1 ± 2.4 Gyr--与先前基于中微子风方案用相同的核质量公式获得的年龄相同。这表明，使用U-Th对获得的测时估计与所考虑的天体物理条件无关。
While the origin of r-process nuclei remains a long-standing mystery, recent spectroscopic studies of extremely metal poor stars in the Galactic halo strongly suggest that it is associated with core-collapse supernovae. In this study we examine r-process nucleosynthesis in a "prompt supernova explosion" from an 8-10 M☉ progenitor star as an alternative scenario to the "neutrino wind" mechanism, which has also been considered a promising site of the r-process. In the present model, the progenitor star has formed an oxygen-neon-magnesium (O-Ne-Mg) core (of mass 1.38 M☉) at its center. Its smaller gravitational potential, as well as the smaller core that is in nuclear statistical equilibrium at the time of core bounce, as compared with the iron cores in more massive stars, may allow the star to explode hydrodynamically rather than by delayed neutrino heating. The core-collapse simulations are performed with a one-dimensional, Newtonian hydrodynamic code. We obtain a very weak prompt explosion in which no r-processing occurs. We further simulate energetic prompt explosions by enhancement of the shock-heating energy in order to investigate conditions necessary for the production of r-process nuclei in such events. The r-process nucleosynthesis is calculated using a nuclear reaction network code including relevant neutron-rich isotopes with reactions among them. The highly neutronized ejecta (Ye ≈ 0.14-0.20) lead to robust production of r-process nuclei; their relative abundances are in excellent agreement with the solar r-process pattern. Our results suggest that prompt explosions of 8-10 M☉ stars with O-Ne-Mg cores can be a promising site of r-process nuclei. The mass of the r-process material per event is about 2 orders of magnitude larger than that expected from Galactic chemical evolution studies. We propose, therefore, that only a small fraction of r-process material is ejected via "mixing-fallback" mechanism of the core matter, wherein most of the r-process material falls back onto the proto-neutron star. A lower limit on the age of the universe is derived by application of the uranium-thorium (U-Th) chronometer pair by comparison with the observed ratio of these species in the highly r-process-enhanced, extremely metal poor star CS 31082-001. The inferred age is 14.1 ± 2.4 Gyr—the same as that obtained previously based on the neutrino wind scenario with the same nuclear mass formula. This suggests that chronometric estimates obtained using the U-Th pair are independent of the astrophysical conditions considered.