Tidal truncation of circumplanetary discs
Tidal truncation of circumplanetary discs
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环行星盘的潮汐截断
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
S. Lubow
中科院分区：
文献类型：
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作者：
R. Martin;S. Lubow
我们分析了环行星盘的一些特性。流经此类圆盘的流动可能为气态巨行星提供大部分质量，并且此类圆盘可能是形成常规卫星的场所。我们将这些盘建模为受中央恒星潮汐力影响的吸积盘。来自恒星的潮汐扭矩消除了盘外缘附近的盘角动量，并允许吸积盘气体以适合稳定吸积的速率失去角动量。环绕行星盘在周期性弹道轨道交叉的半径附近被截断，此处盘上的潮汐力很强。对于行星希尔半径 r H 来说，该半径出现在大约 0.4r H 处。在盘增生的 T Tauri 阶段，盘相当厚，长宽比 H/r ≳ 0.2，并且盘边缘在径向尺度 ∼ H ∼ 0.1r H 上逐渐变细。圆盘流体方程可以在希尔近似中重新调整为类似于质量比为 1 的双星系统中圆盘的流动方程的形式。对于圆形或稍微偏心轨道的行星，圆盘主体内不存在明显的共振。尽管如此，涉及共振的潮汐驱动波在截断圆盘方面发挥着重要作用，尤其是当圆盘相当厚时。我们使用一维时间相关模型和稳态模型以及二维平滑粒子流体动力学模拟对圆盘结构进行建模。环行星盘结构取决于盘湍流粘度随半径的变化，并且对吸积气体的角分布不敏感。死区可能出现在环行星盘内并导致密度结构。如果圆盘自始至终都是湍流，则预测的常规木星和土星卫星位置附近的圆盘结构是平滑的，没有明显的特征有利于在其当前位置形成。亚结构，例如由于圆盘湍流的变化，可能会导致迁移卫星的捕获。
We analyse some properties of circumplanetary discs. Flow through such discs may provide most of the mass to gas giant planets, and such discs are likely sites for the formation of regular satellites. We model these discs as accretion discs subject to the tidal forces of the central star. The tidal torques from the star remove the disc angular momentum near the disc outer edge and permit the accreting disc gas to lose angular momentum at the rate appropriate for steady accretion. Circumplanetary discs are truncated near the radius where periodic ballistic orbits cross, where tidal forces on the disc are strong. This radius occurs at approximately 0.4r H for the planet Hill radius r H . During the T Tauri stage of disc accretion, the disc is fairly thick with aspect ratio H/r ≳ 0.2 and the disc edge tapering occurs over a radial scale ∼ H ∼ 0.1r H . The disc fluid equations can be rescaled in the Hill approximation to a form similar to the flow equations for a disc in a binary star system with a mass ratio of unity. For a circular or slightly eccentric orbit planet, no significant resonances lie within the main body of the disc. Tidally driven waves involving resonances none the less play an important role in truncating the disc, especially when it is fairly thick. We model the disc structure using one-dimensional time-dependent and steady-state models and also two-dimensional smoothed particle hydrodynamics simulations. The circumplanetary disc structure depends on the variation of the disc turbulent viscosity with radius and is insensitive to the angular distribution of the accreting gas. Dead zones may occur within the circumplanetary disc and result in density structures. If the disc is turbulent throughout, the predicted disc structure near the location of the regular Jovian and Saturnian satellites is smooth with no obvious feature that would favour formation at their current locations. It may be possible that substructure, such as due to variations in the disc turbulence, could lead to the trapping of migrating satellites.