The effects of dynamical interactions on planets in young substructured star clusters
The effects of dynamical interactions on planets in young substructured star clusters
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DOI：
10.1111/j.1365-2966.2011.19911.x
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发表时间：
2011-09
影响因子：
4.8
通讯作者：
R. Parker;S. Quanz
中科院分区：
文献类型：
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作者：
R. Parker;S. Quanz
我们提出了N体模拟年轻的子结构星星集群经历各种动态演化的情况下，研究在集群中的相互作用对行星系统的直接影响。我们的模型集群最初在冷塌缩，维里平衡和扩大，并放置在5或30 Au从他们的宿主恒星，零离心率的1千万亿质量的行星。我们发现，在1000万年后，10%的行星最初以30 Au的轨道运行，已经从它们的母星星中解放出来，形成了一个自由漂浮的行星群。这些行星中有一小部分被其他恒星捕获。还有10%的卫星轨道偏心率（以及较少的半长轴）发生了显著变化。对于行星最初在5 Au的分数是一个因素2低。偏心率的变化往往伴随着轨道倾角的变化，这可能导致具有多个行星的行星系统的额外动力学扰动。解放和分裂的行星系统的比例是最高的亚维里集群，但维里和监督集群也动态处理行星系统，由于在子结构的相互作用。在自由漂浮的行星中，那些在观测上仍然与星团相关的行星（即在星团中心两个半质量半径内），无论它们是在5或30 Au轨道上，其速度分布都与整个星星团相似，平均速度通常为1.1 km s−1。相反地，那些不再与星团有关联的行星，如果它们原本的速度是5 Au（109 km s−1），则它们的速度与非关联恒星相似，而原本的速度是30 Au的行星的速度（3.8 km s−1）比非关联恒星的速度（10.8 km s−1）低得多。这些发现突出了得出以下结论的潜在陷阱：（a）与星团恒星具有相似速度的行星代表初始质量函数的非常低的质量端;（B）在星团外围具有非常不同的观测速度的行星通过不同的机制形成。
We present N-body simulations of young substructured star clusters undergoing various dynamical evolutionary scenarios and examine the direct effects of interactions in the cluster on planetary systems. We model clusters initially in cool collapse, in virial equilibrium and expanding, and place a 1-Jupiter-mass planet at either 5 or 30 au from their host stars, with zero eccentricity. We find that after 10 Myr ∼10 per cent of planets initially orbiting at 30 au have been liberated from their parent star and form a population of free-floating planets. A small number of these planets are captured by other stars. A further ∼10 per cent have their orbital eccentricity (and less often their semimajor axis) significantly altered. For planets originally at 5 au the fractions are a factor of 2 lower. The change in eccentricity is often accompanied by a change in orbital inclination which may lead to additional dynamical perturbations in planetary systems with multiple planets. The fraction of liberated and disrupted planetary systems is highest for subvirial clusters, but virial and supervirial clusters also dynamically process planetary systems, due to interactions in the substructure. Of the planets that become free-floating, those that remain observationally associated with the cluster (i.e. within two half-mass radii of the cluster centre) have a similar velocity distribution to the entire star cluster, irrespective of whether they were on a 5 or 30 au orbit, with median velocities typically ∼1 km s−1. Conversely, those planets that are no longer associated with the cluster have similar velocities to the non-associated stars if they were originally at 5 au (∼9 km s−1), whereas the planets originally at 30 au have much lower velocities (3.8 km s−1) than the non-associated stars (10.8 km s−1). These findings highlight potential pitfalls of concluding that (a) planets with similar velocities to the cluster stars represent the very low mass end of the initial mass function and (b) planets on the periphery of a cluster with very different observed velocities form through different mechanisms.