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arXiv 0807.0573astro-ph
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自转对原始恒星演化的影响

Effects of rotation on the evolution of primordial stars

S. Ekström, G. Meynet, C. Chiappini, R. Hirschi, A. Maeder

摘要:

旋转已被证明在非常低的金属丰度下起决定性作用,带来几乎没有预期的严重质量损失。当金属丰度严格等于零时,这仍然成立吗?我们研究的目的就是要找到这个问题的答案,并确定旋转如何改变原始恒星的演化和化学特征。我们已经计算了14个微分旋转和非旋转恒星模型在零金属丰度,质量在9和200 Msol之间。这种演化一直延续到超新星爆发前的阶段。我们发现Z=0模型以接近局部角动量守恒的内部轮廓Omega(r)旋转,因为核壳耦合非常弱。旋转混合驱动的H-壳层的提升,由于CNO循环突然开始在壳层。这种提升导致高的14 N产量。一般来说,旋转模型比非旋转模型产生更多的金属。质量损失非常低,即使对于在主序列期间达到临界速度的模型。由于低质量损失和弱耦合,核心在演化结束时保持较高的角动量。死亡时的高旋转速率可能导致比先前预期的更强烈的爆炸,改变了模型的命运。将我们的产率纳入星系晕的化学演化模型中,预测在log O/H +12 = 4.2时,N/O、C/O和12 C/13 C比值的log值分别为-2.2、-0.95和50。

英文摘要:

(Abridged) Rotation has been shown to play a determinant role at very low metallicity, bringing heavy mass loss where almost none was expected. Is this still true when the metallicity strictly equals zero? The aim of our study is to get an answer to this question, and to determine how rotation changes the evolution and the chemical signature of the primordial stars. We have calculated 14 differentially-rotating and non-rotating stellar models at zero metallicity, with masses between 9 and 200 Msol. The evolution has been followed up to the pre-supernova stage. We find that Z=0 models rotate with an internal profile Omega(r) close to local angular momentum conservation, because of a very weak core-envelope coupling. Rotational mixing drives a H-shell boost due to a sudden onset of CNO cycle in the shell. This boost leads to a high 14N production. Generally, the rotating models produce much more metals than their non-rotating counterparts. The mass loss is very low, even for the models that reach the critical velocity during the main sequence. Due to the low mass loss and the weak coupling, the core retains a high angular momentum at the end of the evolution. The high rotation rate at death probably leads to a much stronger explosion than previously expected, changing the fate of the models. The inclusion of our yields in a chemical evolution model of the Galactic halo predicts log values of N/O, C/O and 12C/13C ratios of -2.2, -0.95 and 50 respectively at log O/H +12 = 4.2.

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