X-Shooting ULLYSES：大规模恒星在低金属含量下的第十四部分。SMC晚期O和B超巨星的性质揭示了在大魔方云中的风的金属含量依赖性
X-Shooting ULLYSES: Massive stars at low metallicity XIV. Properties of SMC late-O and B supergiants reveal the metallicity dependence of winds in the Magellanic Clouds
AI总结：
研究SMC晚期O和B超巨星的风特性，揭示金属含量对风动量的影响，发现质量损失率是关键因素，并指出需亮蓝变量喷发或双星相互作用解释WR星形成。
摘要：
考虑辐射驱动风的物理特性，风的性质应取决于恒星大气的金属含量。因此，研究不同金属含量的恒星风可以对广泛用于演化的计算中使用的预设进行验证。我们通过定量结合紫外和光学光谱分析，使用CMFGEN获得了20颗SMC中的晚期O和B超巨星的恒星和风性质。通过将这些性质与大魔方云对应研究进行比较，该研究具有相似的样本和数据，并且采用了与本研究相同建模技术，我们推导出一个与金属含量相关的风动量配方，适用于$5.4 \leq \log{L_{\rm bol}/L_{\odot}} \leq6.1$和$14 \leq T_{\rm eff}/{\rm kK} \leq 32$。我们发现风动量对金属含量有显著依赖性，这主要归因于质量损失率。我们没有发现25到21kK之间质量损失率或终端风速与逃逸速度比的不连续性证据，这可能归因于双稳态跃迁。恒星参数在不同方法和辐射传输代码之间保持一致，而质量损失率差异显著，我们的值通常较低。我们发现40%的样本中进化质量和光谱质量之间存在差异，其中进化质量通常系统性地更高。蓝超巨星的质量损失率远低于剥离恒星包层和后续形成经典沃尔夫-雷杰特（WR）星的水平，导致结论认为亮蓝变量喷发或双星相互作用是解释SMC中WR星群特征的必要因素。
英文摘要：
Considering the physics of radiation-driven winds of massive stars, the wind properties should depend on the metal content of the stellar atmosphere. Therefore, studying the winds of massive stars in different metallicities provides a sanity check on prescriptions that are widely used in evolutionary calculations. We obtained the stellar and wind properties of a sample of 20 late-O and B supergiants in the Small Magellanic Cloud (SMC) from a quantitative combined UV and optical spectroscopic analysis using CMFGEN. By comparing these properties with those of a Large Magellanic Cloud counterpart study, which has a similar sample and data, and employed the same modelling techniques used in this study, We derived a metallicity-dependent recipe for wind momentum, which is applicable for $5.4 \leq \log{L_{\rm bol}/L_{\odot}} \leq6.1$ and $14 \leq T_{\rm eff}/{\rm kK} \leq 32$. We find a significant dependence of the wind momentum on the metallicity, which is largely due to the mass-loss rates. We do not find any evidence of a discontinuity in either the mass-loss rate or the ratio of the terminal wind velocity to the escape velocity between $25$ and $21$~kK, which could be attributed to the bi-stability jump. Stellar parameters are consistent across different methods and radiative transfer codes, whereas mass-loss rates differ significantly, with our values being generally lower. We find a discrepancy between the evolutionary and spectroscopic masses in $40\%$ of our sample, with the evolutionary mass usually being systematically higher. The mass-loss rates of blue supergiants are far too low to strip the stellar envelope and the subsequent formation of classical Wolf-Rayet (WR) stars, leading to the conclusion that luminous blue variable eruptions or binary interactions are necessary to explain the characteristics of the WR population in the SMC.
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