标题： WO型沃尔夫-拉耶星：大质量恒星演化的最后辉煌 显示英文标题

标题： WO-Type Wolf-Rayet Stars: the Last Hurrah of Massive Star Evolution

摘要： WO型沃尔夫-拉叶（WR）星是否是大质量恒星演化末期核心坍缩前的最后阶段？ 尽管WC型和WO型WR星的光谱非常相似，但WO型显示出更强的O VI $\lambda \lambda$3811,34发射线特征。 这通常被解释为WO型比WC型富含氧元素，因此演化得更进一步。 然而，先前的研究未能成功模拟这一谱线，导致相对丰度不确定，并且两者之间的关系仍未解决。 为了回答这个基本问题，我们使用UV、光学和NIR光谱以及辐射传输代码CMFGEN对LMC中的六个WC型和两个WO型WR星进行了建模，以确定它们的物理特性。 我们发现WO型并不比WC型富含氧；相反，O VI 特征对丰度不敏感。 但是，WO型的碳含量显著高于WC型，而氦含量则较低，因此WO型演化得更进一步。 将我们的结果与单星Geneva和双星BPASS演化模型进行比较表明，虽然许多性质相符，但WO型的碳含量更高，氧含量更低，超出了这两组演化模型的预测。 这种差异可能归因于$^{12}$C+$^4$He$\rightarrow^{16}$O 核反应速率的巨大不确定性；我们证明，如果Kunz等人提供的反应速率降低25-50%，那么观测结果将与理论预测很好地匹配。 这也将有助于解释LIGO/VIRGO探测到的质量处于理论上质量上限间隙内的黑洞。 显示英文摘要

摘要： Are WO-type Wolf Rayet (WR) stars in the final stage of massive star evolution before core-collapse? Although WC- and WO-type WRs have very similar spectra, WOs show a much stronger O VI $\lambda \lambda$3811,34 emission-line feature. This has usually been interpreted to mean that WOs are more oxygen rich than WCs, and thus further evolved. However, previous studies have failed to model this line, leaving the relative abundances uncertain, and the relationship between the two types unresolved. To answer this fundamental question, we modeled six WCs and two WOs in the LMC using UV, optical, and NIR spectra with the radiative transfer code CMFGEN in order to determine their physical properties. We find that WOs are not richer in oxygen; rather, the O VI feature is insensitive to the abundance. However, the WOs have a significantly higher carbon and lower helium content than the WCs, and hence are further evolved. A comparison of our results with single-star Geneva and binary BPASS evolutionary models show that while many properties match, there is more carbon and less oxygen in the WOs than either set of evolutionary model predicts. This discrepancy may be due to the large uncertainty in the $^{12}$C+$^4$He$\rightarrow^{16}$O nuclear reaction rate; we show that if the Kunz et al. rate is decreased by a factor of 25-50%, then there would be a good match with the observations. It would also help explain the LIGO/VIRGO detection of black holes whose masses are in the theoretical upper mass gap.