标题： 光谱学搜寻大麦哲伦云中的后红超巨星 II：大麦哲伦云黄色超巨星光谱中的湍流线宽 显示英文标题

标题： A Spectroscopic Hunt for Post-Red Supergiants in the Large Magellanic Cloud II: Turbulent Line Broadening in the Spectra of LMC Yellow Supergiants

摘要： 大质量恒星在赫茨普龙间隙是一个由短暂演化阶段的物体组成的混合种群：正在向红超巨星（RSG）阶段演化的黄色超巨星（YSGs）、部分剥离的后RSG，以及恒星演化中其他较少见的结果。对这些物体足够大的样本进行研究可以限制大质量恒星在这些尚不明确的阶段的结构和演化。作为我们持续寻找后RSG项目的一部分，我们使用在拉斯坎帕纳斯天文台的麦哲伦2/克莱德望远镜上获得的MIKE光谱仪的高分辨率光谱，对大麦哲伦云中的32个YSG进行了光谱线轮廓的特征分析。我们发现线轮廓因湍流光球运动而显著展宽。在拟合轮廓以测量微观湍流和宏观湍流速度后，我们在样本中识别出两个组，这两个组由两种速度尺度的比值分开。在这两个组中，宏观湍流速度与有效温度等恒星特性有关。此外，我们发现宏观湍流速度与其他可能探测大尺度光球运动的指标之间存在统计显著的相关性：光谱线轮廓的不对称性，以及从{\it 天体探测卫星}光变曲线中测得的随机低频变化的振幅和品质因数。这些相关性在两个YSG组之间有所不同。最后，我们构建了YSG在前RSG和后RSG阶段的一维演化模型，并发现这些模型中的对流速度与我们测量的微观湍流速度有合理的吻合。然而，模型中的宏观湍流速度远高于对流速度。 显示英文摘要

摘要： Massive stars in the Hertzsprung gap are a mixed population of objects in short-lived evolutionary phases: yellow supergiants (YSGs) evolving towards the red supergiant (RSG) phase, partially-stripped post-RSGs, and other, rarer outcomes of stellar evolution. Studies of sufficiently large samples of these objects can constrain massive star structure and evolution during these poorly-understood phases. As part of our ongoing program searching for post-RSGs, we characterized the spectral line profiles of 32 YSGs in the Large Magellanic Cloud using high-resolution spectra obtained with the MIKE spectrograph on the Magellan 2/Clay telescope at Las Campanas Observatory. We find that the line profiles are strongly broadened by turbulent photospheric motion. After fitting the profiles to measure microturbulent and macroturbulent velocities, we identify two groups within our sample that are separated by the ratio of the two velocity scales. In both groups, the macroturbulent velocity scales with stellar properties such as effective temperature. Additionally, we find statistically-significant correlations between the macroturbulent velocity and other possible probes of large-scale photospheric motions: line profile asymmetry, as well as the amplitude and quality factor of the stochastic low frequency variability measured from {\it Transiting Exoplanet Survey Satellite} lightcurves. These correlations differ between the two groups of YSGs. Finally, we construct 1D evolutionary models of YSGs in both pre- and post-RSG phases, and find reasonable agreement between the convective velocities in these models and our measured microturbulent velocities. However, the macroturbulent velocities are much higher than the convective velocities in the models.