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arXiv 2202.05342astro-ph.EP
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迁移陷阱是开普勒二分法的根本原因

Migration traps as the root cause of the Kepler dichotomy

Brianna Zawadzki, Daniel Carrera, Eric B. Ford

备注：
21 pages, 10 figures. Accepted for publication in The Astrophysical Journal
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摘要：

人们通常认为，“开普勒二分法”-在开普勒星表中有一颗凌日行星的行星系明显过多-反映了行星轨道相互倾斜的内在双峰性。在对行星形成进行了600次模拟之后，接着进行了模拟的开普勒观测，我们提出，这种明显的二分法反映了迁移量的差异和行星半长轴分离成不同的“集群”。我们发现，我们模拟的大质量系统迁移迅速，使更多的行星进入不到200天的轨道周期。外行星经常陷入迁移陷阱-一系列行星质量和位置，其中占主导地位的共同旋转扭矩阻止向内迁移-将系统分为两个集群。如果星系团足够分离，内部的星系团在动力学上会保持冷态，导致相互倾斜度较低，探测到多颗凌日行星的可能性较高。相反，我们模拟的低质量系统通常在200天内带来更少的行星，形成一个快速变得动态不稳定的单一集群，导致碰撞和高相互倾斜。我们提出了一种替代解释明显的开普勒二分法，在形成过程中的迁移陷阱导致开普勒探测窗口内的行星较少，相互倾斜只起次要作用。如果我们的假设是正确的，那么开普勒的STIP（具有紧密堆积的内部行星的系统）是逃脱了共同旋转陷阱捕获的行星样本，它们的大小可能是对原行星盘结构的有价值的探索。

英文摘要：

It is often assumed that the "Kepler dichotomy" -- the apparent excess of planetary systems with a single detected transiting planet in the Kepler catalog -- reflects an intrinsic bimodality in the mutual inclinations of planetary orbits. After conducting 600 simulations of planet formation followed by simulated Kepler observations, we instead propose that the apparent dichotomy reflects a divergence in the amount of migration and the separation of planetary semimajor axes into distinct "clusters". We find that our simulated high-mass systems migrate rapidly, bringing more planets into orbital periods of less than 200 days. The outer planets are often caught in a migration trap -- a range of planet masses and locations in which a dominant co-rotation torque prevents inward migration -- which splits the system into two clusters. If clusters are sufficiently separated, the inner cluster remains dynamically cold, leading to low mutual inclinations and a higher probability of detecting multiple transiting planets. Conversely, our simulated low-mass systems typically bring fewer planets inside 200 days, forming a single cluster that quickly becomes dynamically unstable, leading to collisions and high mutual inclinations. We propose an alternative explanation for the apparent Kepler dichotomy in which migration traps during formation lead to fewer planets inside the Kepler detection window, and where mutual inclinations play only a secondary role. If our scenario is correct, then Kepler's STIPs (Systems with Tightly-packed Inner Planets) are a sample of planets that escaped capture by co-rotation traps, and their sizes may be a valuable probe into the structure of protoplanetary discs.

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