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arXiv 1408.6993astro-ph.EP
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在热演化粘滞盘中通过寡头生长形成行星系

On the formation of planetary systems via oligarchic growth in thermally evolving viscous discs

Gavin A. L. Coleman, Richard P. Nelson

摘要:

我们提出了N体模拟的行星系形成的热演化,粘性盘模型。模拟包括I型迁移(包括共转力矩及其饱和度),间隙形成,II型迁移,气体吸积到行星核心,通过光蒸发和气体盘分散。其目的是检查是否寡头增长的情况下,结合自洽的磁盘模型和最新的处方光盘驱动的迁移,可以产生类似的行星系已被观察到的。结果与初始椎间盘质量相关。低质量盘形成了地球质量行星和超级地球的紧密系统。更高质量的盘形成了多代行星,质量范围为10 < mp <45 M_Earth。这些行星通常会迁移到内盘的I型,因为共旋力矩饱和,在那里它们会打开缺口,而II型则会迁移到中央恒星。偶尔,最后一代的低到中等质量的行星形成并由于气盘分散而存活下来。在我们的模拟中没有幸存的气体巨星形成。分析表明,这些行星只有在II型迁移开始之前,在轨道半径r > 10 au处形成核心并经历失控的气体吸积,才能在迁移中幸存下来。我们的结论是,在气体盘的生命周期中,质量mp > 10M_Earth以上的行星生长导致了同旋扭矩饱和和快速向内迁移,阻止了气体巨星的形成和生存。这一结果与一些人口合成模型显示的形成气体巨行星的成功相反。这种差异的出现,部分原因是,在人口合成模型中采用的II型移民处方导致太大的减少时,在行星占主导地位的制度的移民速度。

英文摘要:

We present N-body simulations of planetary system formation in thermally-evolving, viscous disc models. The simulations incorporate type I migration (including corotation torques and their saturation), gap formation, type II migration, gas accretion onto planetary cores, and gas disc dispersal through photoevaporation. The aim is to examine whether or not the oligarchic growth scenario, when combined with self-consistent disc models and up-to-date prescriptions for disc-driven migration, can produce planetary systems similar to those that have been observed. The results correlate with the initial disc mass. Low mass discs form close-packed systems of terrestrial-mass planets and super-Earths. Higher mass discs form multiple generations of planets, with masses in the range 10 < mp < 45M_Earth. These planets generally type I migrate into the inner disc, because of corotation torque saturation, where they open gaps and type II migrate into the central star. Occasionally, a final generation of low-to-intermediate mass planets forms and survives due to gas disc dispersal. No surviving gas giants were formed in our simulations. Analysis shows that these planets can only survive migration if a core forms and experiences runaway gas accretion at orbital radii r > 10 au prior to the onset of type II migration. We conclude that planet growth above masses mp > 10M_Earth during the gas disc life time leads to corotation torque saturation and rapid inward migration, preventing the formation and survival of gas giants. This result is in contrast to the success in forming gas giant planets displayed by some population synthesis models. This discrepancy arises, in part, because the type II migration prescription adopted in the population synthesis models causes too large a reduction in the migration speed when in the planet dominated regime.

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