[论文解读] Modelling circumbinary protoplanetary disks II. Gas disk feedback on planetesimal dynamical and collisional evolution in the circumbinary systems Kepler-16 and 34

Stefan Lines, Z. M. Leinhardt+3 more|Bristol Research (University of Bristol)|Apr 6, 2016

Astrophysics and Star Formation Studies参考文献 23被引用 7

一句话总结

本研究通过将三维N体模拟与流体动力学气体盘模型相结合，考察了开普勒-16和开普勒-34双星周围的原行星盘中星子的生长过程，发现非对称、进动的气体盘会引发高偏心率轨道和轨道倾角，导致侵蚀性碰撞，从而抑制星子的原位吸积。研究结果排除了开普勒-16b和开普勒-34b在原位形成的可能性，支持其在更大半径处形成后向内迁移的形成机制。

ABSTRACT

Aims. We investigate the feasibility of planetesimal growth in circumbinary protoplanetary disks around the observed systems Kepler- 16 and Kepler-34 under the gravitational influence of a precessing eccentric gas disk. Methods. We embed the results of our previous hydrodynamical simulations of protoplanetary disks around binaries into an N-body code to perform 3D, high-resolution, inter-particle gravity-enabled simulations of planetesimal growth and dynamics that include the gravitational force imparted by the gas. Results. Including the full, precessing asymmetric gas disk generates high eccentricity orbits for planetesimals orbiting at the edge of the circumbinary cavity, where the gas surface density and eccentricity have their largest values. The gas disk is able to efficiently align planetesimal pericenters in some regions leading to phased, non-interacting orbits. Outside of these areas eccentric planetesimal orbits become misaligned and overlap leading to crossing orbits and high relative velocities during planetesimal collisions. This can lead to an increase in the number of erosive collisions that far outweighs the number of collisions that result in growth. Gravitational focusing from the static axisymmetric gas disk is weak and does not significantly alter collision outcomes from the gas free case. Conclusions. Due to asymmetries in the gas disk, planetesimals are strongly perturbed onto highly eccentric orbits. Where planetesimals orbits are not well aligned, orbit crossings lead to an increase in the number of erosive collisions. This makes it difficult for sustained planetesimal accretion to occur at the location of Kepler-16b and Kepler-34b and we therefore rule out in-situ growth. This adds further support to our initial suggestions that most circumbinary planets should form further out in the disk and migrate inwards.

研究动机与目标

• 评估在开普勒-16和开普勒-34双星周围的真实气体盘条件下，原位星子吸积的可行性。
• 研究进动、偏心的气体盘所产生的引力反馈如何影响星子的轨道动力学及碰撞结果。
• 确定气体盘的非轴对称性与引力作用是否能够促进或阻碍星子的持续生长。
• 评估自引力、气体阻力与盘结构在恶劣双星环境中的星子演化过程中的作用。

提出的方法

• 结合论文I（FARGO-ADSG）的二维流体动力学结果与三维高分辨率N体模拟，包含星子间的相互引力。
• 将随时间变化的非轴对称气体盘引力势引入N体框架，以模拟进动、偏心的盘体作用力。
• 采用EDACM碰撞模型模拟星子碰撞结果，区分吸积与侵蚀过程。
• 引入星子间的自引力，以评估其在偏心率演化与环状结构形成中的作用。
• 通过解析公式实现轴对称气体阻力，以评估其相对于引力的影响程度。
• 系统性地改变盘参数（对称与非对称、单峰与混合尺寸分布），共进行12组模拟（A-L）。

实验结果

研究问题

• RQ1 在进动、非对称气体盘的影响下，开普勒-16双星周围的原行星盘中，星子能否实现原位生长？
• RQ2 非轴对称气体盘的引力势如何影响星子的偏心率与轨道对齐状态？
• RQ3 由于轨道倾角导致的轨道交叉与高速碰撞，在多大程度上导致侵蚀性结果而非吸积？
• RQ4 与无气体盘情况相比，气体盘的引力聚焦作用是增强还是抑制星子生长？
• RQ5 在非对称气体力作用下，星子间的自引力在稳定或破坏星子轨道方面起到何种作用？

主要发现

• 非对称、进动的气体盘在空腔边缘区域引发星子的高偏心率轨道，该区域气体面密度与偏心率均达到峰值。
• 在气体非对称性较高的区域，星子近日点趋于对齐，形成相位一致、互不干扰的轨道，从而降低碰撞频率。
• 在对齐区域之外，轨道倾角导致显著的轨道交叉与高相对速度，使侵蚀性碰撞数量远超吸积性碰撞。
• 静态、轴对称气体盘的引力聚焦作用微弱，与无气体盘情况相比，对碰撞结果无显著影响。
• 星子间的自引力在塑造偏心率分布方面起关键作用，尤其在轴对称气体盘条件下形成的密集环状结构中。
• 即使初始星子尺寸较大（R > 100 km），非对称气体盘仍会形成恶劣环境，阻止开普勒-16b与开普勒-34b轨道半径处的持续吸积。