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arXiv 2103.03672astro-ph.SR
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旋转大质量恒星的对流核尺寸：I。来自太阳金属丰度OB场星的约束

Convective core sizes in rotating massive stars: I. Constraints from solar metallicity OB field stars

S. Martinet, G. Meynet, S. Ekström, S. Simón-Díaz, G. Holgado, N. Castro, C. Georgy, P. Eggenberger, G. Buldgen, S. Salmon, R. Hirschi, J. Groh, E. Farrell, L. Murphy

备注：
13 pages, 8 figures
发表信息：
A&A 648, A126 (2021)
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摘要：

对银河系O型和B型恒星的光谱研究表明，在HR图中观测到许多质量超过8 M $_{\odot}$的恒星，这些恒星刚好超出恒星模型预测的主序星（MS）带，这些恒星的计算具有适度的过冲。这可能是一个迹象表明，对流核心的大小在恒星的HR图的上部比这些模型预测的大。结合恒星演化模型和银河系O星和B星的大样本光谱参数，包括全新的信息，他们的投影旋转速度，我们重新审视MS大质量恒星的对流核心大小的问题。我们确认，恒星质量大于约8 M $_{\odot}$，对流核心的大小在MS阶段结束时增加更迅速的质量比在模型中计算的恒定步骤过冲选择重现在低质量范围（约2 M $_{\odot}$）的主序星宽度。这一结论对非旋转模型和旋转模型都是有效的，无论是中等角动量输运还是强角动量输运。然而，从TAMS位置获得的对流核心质量与质量的增加大于从表面速度下降推导出的质量大于约15 M $_{\odot}$。虽然目前的观测结果还不能决定TAMS给出的核心尺寸和速度下降之间的最佳选择，但我们讨论了不同的方法来摆脱这种困境。目前，与食双星的比较似乎更倾向于速度下降的解决方案。虽然我们确认需要更大的对流核心在更高的质量，我们发现之间的紧张局势，不同的方法，恒星质量超过15 M $_{\odot}$。使用单一年龄的恒星星族（非相互作用的双星或星团）将是解决这种紧张关系的一个巨大资产。

英文摘要：

Spectroscopic studies of Galactic O and B stars show that many stars with masses above 8 M$_{\odot}$ are observed in the HR diagram just beyond the Main-Sequence (MS) band predicted by stellar models computed with a moderate overshooting. This may be an indication that the convective core sizes in stars in the upper part of the HR diagram are larger than predicted by these models. Combining stellar evolution models and spectroscopic parameters derived for a large sample of Galactic O and B stars, including brand new information about their projected rotational velocities, we reexamine the question of the convective core size in MS massive stars. We confirm that for stars more massive than about 8 M$_{\odot}$, the convective core size at the end of the MS phase increases more rapidly with the mass than in models computed with a constant step overshoot chosen to reproduce the main sequence width in the low mass range (around 2 M$_{\odot}$). This conclusion is valid for both the cases of non-rotating models and rotating models either with a moderate or a strong angular momentum transport. The increase of the convective core mass with the mass obtained from the TAMS position is, however, larger than the one deduced from the surface velocity drop for masses above about 15 M$_{\odot}$. Although observations available at the moment cannot decide what is the best choice between the core sizes given by the TAMS and the velocity drop, we discuss different methods to get out of this dilemma. At the moment, comparisons with eclipsing binaries seem to favor the solution given by the velocity drop. While we confirm the need for larger convective cores at higher masses, we find tensions in-between different methods for stars more massive than 15 M$_{\odot}$. The use of single-aged stellar populations (non-interacting binaries or stellar clusters) would be a great asset to resolve this tension.

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