快速旋转星的新印记：极端贫金属晕星中的低12 C/13 C比率
A new imprint of fast rotators: low 12C/13C ratios in extremely metal-poor halo stars
摘要：
快速恒星自转是目前最有希望在贫金属大质量恒星中产生原生氮的机制。在金属丰度$Z=10^{-8}$的快速旋转模型的产量计算的化学演化模型可以解释在正常的贫金属晕星中观察到的高N/O丰度。如果像人们所相信的那样，中等质量恒星没有足够的时间在如此低的金属丰度下对星际介质的富集做出贡献，那么上述结果就构成了在原始宇宙中存在快速旋转体的一个强有力的例子。快速旋转恒星模型的一个重要结果是产生了大量的原生13 C。因此，我们的目标是研究低金属丰度下快速自转对星际介质中12 C/13 C比值演化的影响。我们预测，如果快速旋转的大质量恒星是早期宇宙中的常见现象，那么具有与我们的星系晕相似的恒星形成历史的星系的原始星际介质的12 C/13 C比值应该在30-300之间。在没有快速旋转子的情况下，预测的12 C/13 C比率在[Fe/H]=-3.5时将为$\sim$ 4500，在[Fe/H]=-5.0左右时增加到$\sim$ 31000。目前关于星系晕中非常贫金属的巨大正常星的数据与包括快速旋转子在内的化学演化模型更吻合。为了验证我们的预测，需要对更多极端贫金属巨星和关闭恒星的12 C/13 C进行具有挑战性的测量。
英文摘要：
(abridged) Fast stellar rotation is currently the most promising mechanism for producing primary nitrogen in metal-poor massive stars. Chemical evolution models computed with the inclusion of the yields of fast rotating models at a metallicity $Z=10^{-8}$ can account for the high N/O abundances observed in normal metal-poor halo stars. If, as believed, intermediate mass stars did not have enough time to contribute to the interstellar medium enrichment at such low metallicities, the above result constitutes a strong case for the existence of fast rotators in the primordial Universe. An important result of stellar models of fast rotators is that large quantities of primary 13C are produced. Hence, our goal is to investigate the consequence of fast rotation on the evolution of the 12C/13C ratio in the interstellar medium at low metallicity. We predict that, if fast rotating massive stars were common phenomena in the early Universe, the primordial interstellar medium of galaxies with a star formation history similar to the one inferred for our galactic halo should have 12C/13C ratios between 30-300. Without fast rotators, the predicted 12C/13C ratios would be $\sim$ 4500 at [Fe/H]=-3.5, increasing to $\sim$ 31000 at around [Fe/H]=-5.0. Current data on very metal-poor giant normal stars in the galactic halo agree better with chemical evolution models including fast rotators. To test our predictions, challenging measurements of the 12C/13C in more extremely metal-poor giants and turnoff stars are required.
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