On the dynamics and collisional growth of planetesimals in misaligned binary systems
On the dynamics and collisional growth of planetesimals in misaligned binary systems
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DOI：
10.1051/0004-6361/201015378
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发表时间：
2011-04
影响因子：
6.5
通讯作者：
M. Fragner;R. Nelson;W. Kley
中科院分区：
文献类型：
--
作者：
M. Fragner;R. Nelson;W. Kley
上下文很大一部分恒星，包括年轻的金牛座T星，被观测到是双星或多星系统的成员。在演化的早期阶段，当双星被气体和尘埃盘包围时，双星轨道平面和盘中平面可能相互倾斜。对于与金牛T星相关的相对较厚的原恒星盘，预计在这种情况下，盘将变得轻微弯曲，并围绕双星系统的角动量矢量进行固体进动。目前还不清楚嵌入这样一个圆盘中的固体（如星子）将如何动态演化并影响行星的形成。目标。我们研究了嵌入在气态原行星盘模型中的微行星的动力学，该模型被一个在圆形倾斜轨道上的双星伴星扰动。这项工作的主要重点是检查的碰撞速度的星子，以确定的条件下，通过吸积的星子增长可能会发生，而不是侵蚀或灾难性的破坏。我们考虑的参数是双星倾角γF、双星间距D、盘质量Md和小行星半径si。我们的标准模型D = 60 Au，γF = 45 μ m，盘质量相当于最小质量太阳星云模型。方法.我们使用三维流体动力学代码来模拟光盘的演变。微行星被视为非相互作用的测试粒子，其演化是由于气体阻力、圆盘的引力和由于伴星星星的引力摄动。我们检测到的时刻，当两个微行星轨道交叉的另一个，并使用这些轨道交叉事件来估计的碰撞速度的微行星。结果对于具有适度倾角的双星系统（γF = 25 π），我们发现盘引力阻止了微行星轨道经历强的微分节进动（在没有盘的情况下，微行星轨道会发生这种情况），并迫使微行星平均与盘一起进动。然而，对于不同大小的微行星，轨道平面相对于彼此变得适度倾斜，导致碰撞速度明显抑制微行星的生长。对于较大的双星倾角（γF = 45 °），Kozai效应被发现打开，导致非常大的相对速度的增长，其数量级为每秒几公里。结论.我们的结论是，行星形成通过相互吸积的星子是很难实现的倾斜的二元系统与本文所考虑的参数类似，虽然更遥远的恒星同伴比我们所研究的应该不会出现这样的问题。对于高倾斜系统，Kozai效应开启，形成行星的前景似乎确实非常遥远。
Context. A large fraction of stars, including young T Tauri stars, are observed to be members of binary or multiple systems. During the early stages of evolution when the individual binary stars are surrounded by a gaseous and dusty disc, the binary orbit plane and disc midplane may be mutually inclined. For the relatively thick protostellar discs associated with T Tauri stars, it is expected that in this scenario the disc will become mildly warped and undergo solid body precession around the angular momentum vector of the binary system. At the present time it is unclear how solid bodies such as planetesimals embedded in such a disc will evolve dynamically and affect the formation of planets. Aims. We investigate the dynamics of planetesimals embedded in gaseous protoplanetary disc models which are perturbed by a binary companion on a circular, inclined orbit. The main focus of this work is to examine the collisional velocities of the planetesimals in order to determine the conditions under which planetesimal growth through accretion is likely to occur, rather than erosion or catastrophic disruption. The parameters we consider are the binary inclination, γF, the binary separation, D, the disc mass, Md ,a nd planetesimal radius si. Our standard model has D = 60 AU, γF = 45 ◦ , and a disc mass equivalent to that of the minimum mass solar nebula model. Methods. We use a 3-dimensional hydrodynamics code to model the evolution of the disc. The planetesimals are treated as noninteracting test particles which evolve because of gas drag, the gravitational force of the disc, and the gravitational perturbation due to the companion star. We detect the moment when two planetesimal orbits cross one another, and use these orbit crossing events to estimate the collisional velocities of the planetesimals. Results. For binary systems with modest inclination (γF = 25 ◦ ), we find that the disc gravity prevents the planetesimal orbits from undergoing strong differential nodal precession (which they would do in the absence of the disc), and forces the planetesimals to precess with the disc on average. For planetesimals of different size, however, the orbit planes become modestly inclined with respect to one another, leading to collisional velocities that would clearly inhibit planetesimal growth. For larger binary inclinations (γF = 45 ◦ ), the Kozai effect is found to switch on, causing the growth of very large relative velocities which are on the order of a few kilometres per second. Conclusions. We conclude that planet formation via the mutual accretion of planetesimals is difficult to achieve in an inclined binary system with parameters similar to those considered in this paper, although more distant stellar companions than those we have studied should not present such a problem. For highly inclined systems in which the Kozai effect switches on, the prospects for forming planets would appear to be very remote indeed.