引力暗化引起的双行星系统KOI-89的自旋轨道失调
Spin-Orbit Misalignment of Two-Planet-System KOI-89 Via Gravity Darkening
摘要：
我们通过数值拟合两个由凌日行星KOI-89.01和KOI-89.02产生的\emph{Kepler}光度光变曲线来约束KOI-89系统的真实自旋-轨道对准。这两颗行星的周期分别为84.69天和207.58天。我们发现这两个天体都是低密度的巨行星，半径分别为$0.45 \pm 0.03~\mathrm{R_{jup}}$和$0.43 \pm 0.05~\mathrm{R_{jup}}$，自旋轨道不重合度分别为$72^{\circ} \pm 3^\circ$和$73^{\circ+11}_{-5}$。通过动态稳定性测试，我们证明了更高的系统稳定性与两个行星接近相互对齐的一般趋势，并估计他们的共对准角$20^\circ \pm 20^\circ$ -即行星与恒星不对齐，但可能彼此对齐。从这些结果中，我们限制KOI-89的错位机制，恒星盘二进制相互作用，通过行星盘相互作用，行星-行星散射，Kozai共振，或内部重力波磁盘翘曲。
英文摘要：
We constrain the true spin-orbit alignment of the KOI-89 system by numerically fitting the two \emph{Kepler} photometric lightcurves produced by transiting planets KOI-89.01 and KOI-89.02. The two planets have periods of 84.69 days and 207.58 days, respectively. We find that the two bodies are low-density giant planets with radii $0.45 \pm 0.03~\mathrm{R_{jup}}$ and $0.43 \pm 0.05~\mathrm{R_{jup}}$ and spin-orbit misalignments $72^{\circ} \pm 3^\circ$ and $73^{\circ+11}_{-5}$, respectively. Via dynamic stability tests we demonstrate the general trend of higher system stability with the two planets close to mutual alignment and estimate their coalignment angle to $20^\circ \pm 20^\circ$ -- i.e. the planets are misaligned with the star but may be aligned with each other. From these results, we limit KOI-89's misalignment mechanisms to star-disk-binary interactions, disk warping via planet-disk interactions, planet-planet scattering, Kozai resonance, or internal gravity waves.
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