论文标题
重新访问KOI-89系统的体系结构
Revisiting the Architecture of the KOI-89 System
论文作者
论文摘要
尽管在超球星系中观察到的高恒星倾斜可能归因于倾斜行星轨道的过程，但它们也可能反映了原行星磁盘和恒星旋转之间的未对准。后一个假设预测了与中心恒星未对准的共平面多计划系统的存在。在这里，我们重新评估了KOI-89系统所声称的这种建筑的证据。 KOI-89 is an early-type star with one validated transiting planet KOI-89.01/Kepler-462b (period 84.7 days, radius $3.0\,R_\oplus$) and one transiting planet candidate KOI-89.02 (period 207.6 days, radius $4.0\,R_\oplus$), where the latter exhibits transit timing variations （TTV）。先前对过境光曲线中恒星重力 - 变形效应的建模推断出$ \ of 70^\ circ $的高恒星倾斜。我们对开普勒传输光曲线进行光动力学建模，并在轨道配置和过境时间上使用所得约束来更新重力变暗的过境模型。结果，我们没有发现过境形状中重力变暗作用的牢固证据，并得出结论，恒星倾斜不受数据的约束。从动态分析中，给出了低轨道偏心率的证据，因此系统体系结构可以与许多其他与恒星自旋对齐的扁平，近圆形轨道的多传输系统一致。我们发现授予其邻居的TTV暗示KOI-89.01具有质量$ \ gtrsim20 \，m_ \ oplus $。这将渲染它是已知的最密集的子核之一，主要由固体芯组成。如果TTV是由于看不见的第三行星，那么质量是可能的。
While high stellar obliquities observed in exoplanetary systems may be attributed to processes that tilt the planetary orbits, it is also possible that they reflect misalignments between protoplanetary disks and stellar spins. This latter hypothesis predicts the presence of co-planar multi-planetary systems misaligned with their central stars. Here we re-evaluate the evidence of such an architecture that has been claimed for the KOI-89 system. KOI-89 is an early-type star with one validated transiting planet KOI-89.01/Kepler-462b (period 84.7 days, radius $3.0\,R_\oplus$) and one transiting planet candidate KOI-89.02 (period 207.6 days, radius $4.0\,R_\oplus$), where the latter exhibits transit timing variations (TTVs). A previous modeling of the stellar gravity-darkening effect in the transit light curves inferred a high stellar obliquity of $\approx70^\circ$. We perform a photodynamical modeling of the Kepler transit light curves, and use the resulting constraints on the orbital configuration and transit times to update the gravity-darkened transit model. As a result, we find no firm evidence for gravity darkening effect in the transit shapes and conclude that stellar obliquity is not constrained by the data. Given evidence for low orbital eccentricities from the dynamical analysis, the system architecture can thus be consistent with many other multi-transiting systems with flat, near-circular orbits aligned with the stellar spin. We find that the TTVs imparted on its neighbor imply that KOI-89.01 has a mass $\gtrsim20\,M_\oplus$. This would render it one of the densest known sub-Neptunes, mostly composed of a solid core. Lower masses are possible if the TTVs are instead due to an unseen third planet.
