论文标题
高金属性和低金属性汉弗莱斯戴维森极限的理论研究
A theoretical investigation of the Humphreys-Davidson limit at high and low metallicity
论文作者
论文摘要
当前的巨大恒星进化网格无法同时再现红色超级巨人（Humphrey-Davidson（HD）极限的经验上的亮度极限，在高和低金属性下。在这项研究中，我们可以更好地了解将大量恒星进化为蓝色和红色超级巨头阶段的原因，其最终目的是在不同的金属度（Z）下重现HD极限。对于太阳能，LMC和SMC Z，我们为20-60m的质量范围开发了八个网格，以探测半传染和过度冲洗的效果。我们将旋转和非旋转模型与有效（Alpha_semi = 100）和低效率的半传染（Alpha_semi = 0.1）进行比较，具有高和低核心过冲（0.1或0.5）。通过比较在每个阶段花费的核心燃烧寿命的比例，研究了红色和蓝色的超级进化阶段。我们发现，通过超过alpha_ov = 0.5来扩展对流核心对后MS进化有影响，这可能会禁用半传输导致更多的RSG，但缺乏BSG。因此，我们实施Alpha_ov = 0.1，该= 0.1，该= 0.1，尽管对于标准的alpha_semi = 1，但在半传染的混合上切换将导致高清限制高于低z处的高清极限。 L〜5.8自然。由于强大的质量损失使包膜结构耗尽，因此在高Z上的效果在高Z上不活跃，因此不能形成半主流区域。 Z依赖性的质量损失在设置HD极限作为Z的函数方面起间接但具有决定性的作用。有效的半传输和低量和依赖标准Z依赖性的质量损失的组合，我们在所有金属度上都发现了自然的HD极限。
Current massive star evolution grids are not able to simultaneously reproduce the empirical upper luminosity limit of red supergiants, the Humphrey-Davidson (HD) limit at high and low metallicity. In this study, we provide a better understanding of what drives massive star evolution to blue and red supergiant phases, with the ultimate aim of reproducing the HD limit at varied metallicities (Z). For solar, LMC, and SMC Z, we develop eight grids of MESA models for the mass range 20-60M to probe the effect of semiconvection and overshooting. We compare rotating and non-rotating models with efficient (alpha_semi = 100) and inefficient semi-convection (alpha_semi = 0.1), with high and low core overshooting (alpha_ov of 0.1 or 0.5). The red and blue supergiant evolutionary phases are investigated by comparing the fraction of core He-burning lifetimes spent in each phase. We find that the extension of the convective core by overshooting alpha_ov = 0.5 has an effect on the post-MS evolution which can disable semiconvection leading to more RSGs, but a lack of BSGs. We therefore implement alpha_ov = 0.1 which switches on semiconvective mixing, though for standard alpha_semi = 1, would result in an HD limit which is higher than observed at low Z. Therefore, we need to implement very efficient semiconvection of alpha_semi = 100 which reproduces the HD limit at log L ~ 5.5 for the Magellanic Clouds while simultaneously reproducing the Galactic HD limit of log L ~ 5.8 naturally. The effect of semiconvection is not active at high Z due to the depletion of the envelope structure by strong mass loss such that semiconvective regions could not form. Z-dependent mass loss plays an indirect, yet decisive role in setting the HD limit as a function of Z. For a combination of efficient semiconvection and low overshooting with standard Z-dependent mass loss, we find a natural HD limit at all metallicities.
