The r-process in Magnetorotational Supernovae
The r-process in Magnetorotational Supernovae
复制标题
磁旋转超新星中的 r 过程
DOI：
10.1088/2041-8205/811/1/l10
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Nobuya
中科院分区：
文献类型：
--
作者：
Tsujimoto;Takuji; Nishimura;Nobuya
早期宇宙中的快速富集是r过程元素化学演化中最热门的开放性问题之一。银河晕中金属含量极低的恒星的丰度表明，r过程元素的化学富集有明确的证据。然而，考虑到产生重r过程元素的生产事件的潜在稀有性，小质量星系是研究r过程富集演化特征的理想试验台。它们的出现是可以计数的，因此在恒星丰度中可以找到每个事件的富集路径。研究了天龙座（Draco）和雕刻家（Sculptor）矮球星系（dSph） [Fe/H] >−2早期阶段Eu丰度的化学特征。因此，我们限制了早期dsph中Eu生产的性质。我们发现天龙座dSph经历了一些Eu的产生事件，而由于其更大的恒星质量，雕刻家dSph中Eu的富集更加持续。据估计，每100−200颗核心坍缩超新星产生Eu的事件率约为1颗，通过将这一频率与观测到的[Fe/H]约为[Eu/H] ~−1.3的平台值相关联，可以推断出Eu质量为每单个事件约（1-2）× 10−5 M⊙。观察到的平台表明早期Eu富集在[Fe/H]≈−2处停止。这种选择性操作只在低金属丰度的恒星上支持磁旋超新星，这需要非常快的旋转，作为早期Eu生产的地点。我们表明，从化学进化中推断出的Eu产率与相应超新星模型的核合成结果吻合得很好。
One of the hottest open issues involving the chemical evolution of r-process elements is fast enrichment in the early universe. Clear evidence for the chemical enrichement of r-process elements is seen in the stellar abundances of extremely metal poor stars in the Galactic halo. However, small-mass galaxies are the ideal testbed for studying the evolutionary features of r-process enrichment given the potential rarity of production events yielding heavy r-process elements. Their occurrences become countable and thus an enrichment path due to each event can be found in the stellar abundances. We examine the chemical feature of Eu abundance at an early stage of [Fe/H]≲− 2 in the Draco and Sculptor dwarf spheroidal (dSph) galaxies. Accordingly, we constrain the properties of Eu production in the early dSphs. We find that the Draco dSph experienced a few Eu production events, whereas Eu enrichment took place more continuously in the Sculptor dSph due to its larger stellar mass. The event rate of Eu production is estimated to be about one per 100− 200 core-collapse supernovae, and a Eu mass of∼(1–2)× 10− 5 M⊙ per single event is deduced by associating this frequency with the observed plateau value of [Eu/H]∼− 1.3 for [Fe/H]≳− 2. The observed plateau implies that early Eu enrichment ceases at [Fe/H]≈− 2. Such a selective operation only in low-metallicity stars supports magnetorotational supernovae, which require very fast rotation, as the site of early Eu production. We show that the Eu yields deduced from chemical evolution agree well with the nucleosynthesis results from corresponding supernovae models.