EBLM项目。VII。环联星宿主行星EBLM J0608-59 A/TOI-1338 A的自旋-轨道对准
The EBLM project. VII. Spin-orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A
摘要：
已知有十几个短周期的分离双星拥有凌日环双星行星。到目前为止，在所有的环双星系统中，行星和双星的轨道都在几度之内对齐。然而，作为其形成、演化和潮汐历史的重要示踪物的主星的双折射率，迄今为止只在一个环双星系统中测量过。EBLM J 0608 -59/TOI-1338是一个低质量食双星系统，最近发现了一颗由TESS确定的环双星行星。在这里，我们在主食期间进行高分辨率光谱学测量主要成分的投影恒星质量。主星的自转轨道角很低，因此主星与双星和行星轨道成一条直线，投影的自转轨道角为$β= 2.8 \pm 17.1$ deg。由我们对$v\sin{i_\star}$的测量得出的$18.1 \pm 1.6$日的自转周期表明，主星还没有与双星轨道伪同步，但与陀螺年代学和与双星伴星的弱潮汐相互作用是一致的。我们的结果，结合已知的共面性的双星和行星轨道，是暗示形成从一个单一的磁盘。最后，我们还考虑了微弱的二级恒星的光谱是否会影响我们的测量。我们通过模拟表明，我们的系统的效果是可以忽略不计的，但可以导致强烈的偏见，在$v\sin{i_\star}$和$β$较高的通量比。我们鼓励未来的研究在日食光谱测试通量比$\gtrsim 1$ ppt暗二次的假设。
英文摘要：
A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin-orbit angle $β= 2.8 \pm 17.1$ deg. The rotation period of $18.1 \pm 1.6$ days implied by our measurement of $v\sin{i_\star}$ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in $v\sin{i_\star}$ and $β$ for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios $\gtrsim 1$ ppt.
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