[论文解读] Disc-protoplanet interaction Influence of circumprimary radiative discs on self-gravitating protoplanetary bodies in binary star systems

Markus Gyergyovits, Siegfried Eggl+2 more|arXiv (Cornell University)|May 20, 2014

Astrophysics and Star Formation Studies参考文献 36被引用 4

一句话总结

本研究提出了一种基于GPU-CPU的2D流体动力学代码，模拟双星系统中数千个自引力原行星与黏性、辐射冷却的原恒星盘之间的相互作用。结果表明，盘体引力和气体阻力显著改变了原行星轨道，其中动态演化的盘体提高了撞击速度并抑制了行星形成，而辐射冷却则导致更平静的盘体条件，有利于吸积过程。

ABSTRACT

Context. More than 60 planets have been discovered so far in systems that harbour two stars, some of which have binary semi-major axes as small as 20 au. It is well known that the formation of planets in such systems is strongly influenced by the stellar components, since the protoplanetary disc and the particles within are exposed to the gravitational influence of the binary. However, the question on how self-gravitating protoplanetary bodies affect the evolution of a radiative, circumprimary disc is still open. Aims. We present our 2D hydrodynamical GPU-CPU code and study the interaction of several thousands of self-gravitating particles with a viscous and radiative circumprimary disc within a binary star system. To our knowledge this program is the only one at the moment that is capable to handle this many particles and to calculate their influence on each other and on the disc. Methods. We performed hydrodynamical simulations of a circumstellar disc assuming the binary system to be coplanar. Our gridbased staggered mesh code relies on ideas from ZEUS-2D, where we implemented the FARGO algorithm and an additional energy equation for the radiative cooling according to opacity tables. To treat particle motion we used a parallelised version of the precise Bulirsch - Stoer algorithm. Four models in total where computed taking into account (i) only N-body interaction, (ii) N-body and disc interaction, (iii) the influence of computational parameters (especially smoothing) on N-body interaction, and (iv) the influence of a quiet low-eccentricity disc while running model (ii). The impact velocities where measured at two different time intervals and were compared. Results. We show that the combination of disc- and N-body self-gravity can have a significant influence on the orbit evolution of roughly Moon sized protoplanets.

研究动机与目标

• 模拟双星系统中自引力原行星对辐射冷却、黏性原恒星盘的影响。
• 评估盘体引力与气体阻力共同作用对原行星轨道演化及撞击速度的影响。
• 评估盘体动力学状态（平静 vs. 动态演化）以及数值平滑参数对行星形成结果的影响。
• 通过先前研究的基准模型验证代码在模拟辐射冷却和扭矩力方面的准确性。

提出的方法

• 基于ZEUS-2D的结构化网格、交错网格流体动力学代码，采用FARGO算法以提高数值稳定性。
• 引入能量方程与灰度表以模拟辐射冷却，实现盘体中真实的热结构。
• 使用并行化的Bulirsch-Stoer积分器，精确计算数千个原行星之间的N体引力作用。
• 模拟四种不同模型：仅N体模型、N体+盘体相互作用模型、平滑参数敏感性分析、盘体动力学状态影响分析。
• 应用亚开普勒旋转剖面与阻尼区的反射边界条件，以最小化人工反射效应。
• 通过解析解和先前基准模型（如Kley & Crida 2008）验证代码，重点关注盘体温度、标高比和扭矩分布。

实验结果

研究问题

• RQ1 自引力原行星群体对双星系统中辐射冷却原恒星盘的演化有何影响？
• RQ2 盘体引力与气体阻力在多大程度上改变了类月原行星的轨道演化与撞击速度？
• RQ3 盘体的动力学状态（平静 vs. 动态演化）如何影响行星形成效率与相遇概率？
• RQ4 引力软化长度等数值参数如何影响N体与盘体相互作用模拟的准确性与结果？
• RQ5 辐射冷却在塑造盘体结构与作用于嵌入原行星的扭矩分布中起什么作用？

主要发现

• 盘体对原行星的引力影响显著，其轨道演化超出仅由气体阻力预测的范围。
• 具有辐射冷却的盘体表现出更低的偏心率和更平静的动力学行为，相较于局部等温模型更有利于吸积过程。
• 在完全辐射冷却情况下，20地球质量行星所受的特定扭矩略高于Kley & Crida (2008)的结果，其最大标高比为0.059，出现在0.77 au处（绝热情况下）。
• 在动态演化的盘体中，原行星之间的撞击速度显著增加，降低了吸积效率，可能中止行星形成。
• N体模拟中的软化长度强烈影响模拟结果，软化长度越小，相遇频率越高，引力扰动越强。
• 代码成功再现了解析的盘体温度与标高比分布，高温区域存在轻微偏差，归因于非理想灰度行为。