AU Mic b的变化面：由CHEOPS和TESS看到的恒星斑点、自旋-轨道可分辨性和Transit定时变化
The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and Transit Timing Variations as seen by CHEOPS and TESS
摘要：
AU Mic是一个年轻的行星系，有一个清晰的碎片盘，显示出行星形成的迹象，还有两个在平均运动共振附近过境的温暖海王星。在这里，我们分析了三个过渡的AU Mic b观察到的特征ExOPlanet卫星（CHEOPS），补充部门1和27过境系外行星调查卫星（TESS）测光，和全天空自动调查（ASAS）从地面。Mic b的精确轨道周期为8.462995 \pm 0.000003 d，而恒星自转周期为P_{rot} =4.8367 \pm 0.0006 d。这两个周期表示7：4的自旋-轨道可互换性，精度为0.1%。因此，所有的凌日都是在四个可能的恒星中央星团之一的前面观测到的。这得到了强烈的支持，在第二次和第三次CHEOPS访问中看到了相同的复杂的星斑图案，它们被四个轨道（和七个恒星旋转）分开。使用自举分析，我们发现，耀斑和星斑的过境参数的精度降低了10%的行星与恒星的半径比和过境时间的精度3-4分钟。然而，被遮蔽的恒星黑子特征独立地证实了凌日时间变化（TTV）的存在，其幅度至少为4分钟。我们发现外伴星AU Mic c可能是引起观测到的TTV的原因。
英文摘要：
AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey (ASAS) from the ground. The refined orbital period of AU Mic b is 8.462995 \pm 0.000003 d, whereas the stellar rotational period is P_{rot}=4.8367 \pm 0.0006 d. The two periods indicate a 7:4 spin--orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 minutes. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 minutes. We find that the outer companion, AU Mic c may cause the observed TTVs.
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