用于星族合成计算和星团模拟的大质量恒星极端贫金属环境演化轨道拟合公式
Fitting formulae for evolution tracks of massive stars under extreme metal poor environments for population synthesis calculations and star cluster simulations
摘要：
我们设计了极端贫金属环境下大质量恒星演化轨道的拟合公式，其中$M_\odot$和$Z_\odot$分别为太阳质量和金属丰度。我们的拟合公式是基于参考恒星模型，我们已经通过模拟EMP星的时间演化新获得的。我们的拟合公式考虑了以蓝超巨星（BSG）结束的恒星，以及跳过赫兹弹簧间隙（HG）相位和蓝环的恒星，这是大质量EMP星的特征。在我们的拟合公式中，当恒星完成其核心氦燃烧（CHeB）阶段时，它们可能仍然是BSG星。我们的拟合公式与我们的恒星演化模型符合得很好。我们可以使用这些拟合公式的SSE，BSE，NBODY4和NBODY6代码，这是广泛用于人口合成计算和星团模拟。这些拟合公式对于制作EMP环境下形成的二元黑洞的理论模板是有用的。
英文摘要：
We have devised fitting formulae for evolution tracks of massive stars with $8 \lesssim M/M_\odot \lesssim 160$ under extreme metal poor (EMP) environments for $\log (Z/Z_\odot) = -2, -4, -5, -6$, and $-8$, where $M_\odot$ and $Z_\odot$ are the solar mass and metallicity, respectively. Our fitting formulae are based on reference stellar models which we have newly obtained by simulating the time evolutions of EMP stars. Our fitting formulae take into account stars ending with blue supergiant (BSG) stars, and stars skipping Hertzsprung gap (HG) phases and blue loops, which are characteristics of massive EMP stars. In our fitting formulae, stars may remain BSG stars when they finish their core Helium burning (CHeB) phases. Our fitting formulae are in good agreement with our stellar evolution models. We can use these fitting formulae on the SSE, BSE, NBODY4, and NBODY6 codes, which are widely used for population synthesis calculations and star cluster simulations. These fitting formulae should be useful to make theoretical templates of binary black holes formed under EMP environments.
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