单个K巨星猎户座V1192表面锂富集的反太阳差异旋转
Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis
摘要：
内容：在红巨星分支（RGB）中质量约为1 $-$ 2太阳的恒星代表了一个有趣的恒星演化时期，即对流包层与快速旋转的核心相互作用的时期。在这些混合事件中，新合成的锂可以与高角动量物质一起到达恒星表面。这种高角动量可能会改变表面旋转模式。目标：重新审视了单个快速旋转的K巨星V1192猎户座，以确定其表面的差异旋转，锂丰度和基本的恒星性质，如精确的旋转周期。其目的是独立地验证恒星的反太阳差异旋转，并可能找到与表面锂丰度的联系。方法：我们将时间序列多普勒成像应用于一个新的多历元数据集。总之，我们从2007- 2016年间STELLA机器人望远镜收集的光谱数据中重建了11幅多普勒图像。我们使用我们的反演代码iMap来重建所有恒星表面地图。我们从这些图像中提取的差分旋转跟踪系统点迁移作为恒星纬度的函数，从连续的图像互相关。结果如下：猎户座V1192在赫罗图中的位置表明，它正处于氦核心燃烧阶段，刚刚离开RGB凸起。我们测量了$A({\rm Li})_{\rm NLTE}=1.27$，即接近预期的从锂正常到富锂巨星的过渡值1.5的值。多普勒图像揭示了沿着赤道带准均匀排列的扩展黑暗区域。在研究时期内没有发现冷极点。斑点位移清楚地表明反日表面的差异旋转与$α=-0.11\pm0.02$剪切系数。结论：表面锂富集和特殊的表面旋转模式可能表明一个共同的起源。
英文摘要：
Context: Stars with about 1$-$2 solar masses at the red giant branch (RGB) represent an intriguing period of stellar evolution, i.e. when the convective envelope interacts with the fast-rotating core. During these mixing episodes freshly synthesized lithium can come up to the stellar surface along with high angular momentum material. This high angular momentum may alter the surface rotation pattern. Aims: The single rapidly rotating K-giant V1192 Ori is revisited to determine its surface differential rotation, lithium abundance, and basic stellar properties such as a precise rotation period. The aim is to independently verify the antisolar differential rotation of the star and possibly find a connection to the surface lithium abundance. Methods: We applied time-series Doppler imaging to a new multi-epoch data set. Altogether we reconstructed 11 Doppler images from spectroscopic data collected with the STELLA robotic telescope between 2007--2016. We used our inversion code iMap to reconstruct all stellar surface maps. We extracted the differential rotation from these images by tracing systematic spot migration as a function of stellar latitude from consecutive image cross-correlations. Results: The position of V1192 Ori in the Hertzsprung-Russell diagram suggests that the star is in the helium core-burning phase just leaving the RGB bump. We measure $A({\rm Li})_{\rm NLTE}=1.27$, i.e. a value close to the anticipated transition value of 1.5 from Li-normal to Li-rich giants. Doppler images reveal extended dark areas arranged quasi-evenly along an equatorial belt. No cool polar spot is found during the investigated epoch. Spot displacements clearly suggest antisolar surface differential rotation with $α=-0.11\pm0.02$ shear coefficient. Conclusions: The surface Li enrichment and the peculiar surface rotation pattern may indicate a common origin.
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