We use the 1D stellar evolution code MESA to run select models at one solar mass at near zero metallicity to examine the effect of a lack of catalysts for CNO burning on the evolution of these models. We find that for metallicities below 10 −10 ##IMG## [http://ej.iop.org/images/2515-5172/4/9/172/rnaasabbc0eieqn1.gif] {${Z}_{\odot }$} a loop occurs on the HR diagram as the star evolves off the main sequence, corresponding to the onset of significant CNO burning in the core of the star. This feature is visible in the Kippenhahn diagram as a period where the core becomes convective while the burning takes place. During this loop, the degeneracy of the core is lifted as CNO burning produces around 3.7% of the total nuclear energy.

中文翻译：

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超低金属太阳质量恒星的CNO循环燃烧

我们使用一维恒星演化代码MESA在接近零金属度的一个太阳质量下运行精选模型，以研究缺乏CNO燃烧催化剂对这些模型演化的影响。我们发现对于低于10 -10的金属性## IMG ## [http://ej.iop.org/images/2515-5172/4/9/172/rnaasabbc0eieqn1.gif] {$ {Z} _ {\ odot } $}当恒星从主序列中脱离出来时，HR图上会出现一个循环，这对应于恒星核心中大量CNO燃烧的开始。此功能在Kippenhahn图表中可见，是燃烧发生时岩心对流的时期。在此循环中，随着CNO燃烧产生的核能约占总核能的3.7％，铁心的简并性得以提高。