AI 中文总结
本研究发现单星旁的暖次土星自旋-轨道多对齐，与热次土星的错位特征形成3.2σ差异，验证了高偏心率迁移是单星系统自旋-轨道错位的成因，并预测了其他质量区间类热木星的错位转变位置。
AI 中文摘要
在本研究中，我们发现围绕单星运行的暖次土星（warm sub-Saturns）主要呈自旋-轨道对齐状态，这与经常出现轨道错位的热次土星（hot sub-Saturns）形成对比，两类天体的差异达到3.2σ水平。由于两类天体均围绕冷恒星运行，因此不受有效温度（$T_{\rm eff}$）与轨道倾角（$λ$）相关性带来的歧义影响。结合已确立的暖木星（warm Jupiters）轨道对齐特性，这一结果表明，在单星系统中，自旋-轨道错位专门出现在近距“类热木星”区域，该区域潮汐圆化效率高（$τ_e<τ_{\rm age}$），且预期存在高偏心率迁移过程。我们进一步发现，次土星的轨道对齐与错位之间的转变发生在比木星更宽的轨道间距处（次土星的最终轨道半径与行星半径比$a_{\rm final}/R_p = 338\neq27$，木星为$a_{\rm final}/R_p = 117\neg9$），这符合预期：次土星质量更低（$M_p/M_*$更小）、潮汐耗散更强（$Q_p$更低），因此能在其寿命内圆化到更宽的最终轨道。综上，这些结果提供了迄今为止最清晰的直接证据，证明在单星系统中，自旋-轨道错位由高偏心率迁移产生。如果这一框架成立，自旋-轨道错位也可能出现在其他质量区间的类热木星中，包括$a_{\rm final}/R_p\not\too100$的围绕热恒星的热褐矮星，以及$a_{\rm final}/R_p\not\too1000$的孤立热超级地球，对应的转变位置会因轨道圆化时标对$M_p/M_*$和$Q_p$的依赖而发生偏移。
英文摘要
In this work, we show that warm sub-Saturns orbiting single stars are predominantly aligned, in contrast to hot sub-Saturns, which are frequently misaligned, with the two populations differing at the 3.2$σ$ level. Because both populations are observed around cool stars, they are free from the ambiguity introduced by the $T_{\rm eff}$-$λ$ dependence. Together with the established alignment of warm Jupiters, this demonstrates, among single-star systems, that spin-orbit misalignment arises specifically in the close-in ``hot-Jupiter-analog'' regime, where tidal circularization is efficient ($τ_e<τ_{\rm age}$) and high-eccentricity migration is expected to operate. We further find that the transition between aligned and misaligned sub-Saturns occurs at wider orbital separations ($a_{\rm final}/R_p = 338\pm27$) than for Jupiters ($a_{\rm final}/R_p = 117\pm9$), consistent with the expectation that the lower masses (smaller $M_p/M_*$) and stronger tidal dissipation (lower $Q_p$) of sub-Saturns allow them to be circularized into wider final orbits within their lifetimes. Taken together, these results provide the clearest direct evidence to date that, in single-star systems, spin-orbit misalignments are produced by high-eccentricity migration. If this framework is correct, spin-orbit misalignments may also emerge among hot-Jupiter analogs in other mass regimes, including hot brown dwarfs around hot stars at $a_{\rm final}/R_p\lesssim100$ and isolated hot super-Earths at $a_{\rm final}/R_p\lesssim1000$, with the corresponding transition locations shifted by the dependence of the orbital-circularization timescale on $M_p/M_*$ and $Q_p$.
Comments11 pages, 2 figures, accepted for publication in ApJL
