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Interactions between planets and debris disks

行星和碎片盘之间的相互作用

基本信息

批准号：
1786835
负责人：
金额：
--
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1786835
关键词：
Interactions between planets debris disks

项目摘要

The planetesimals which make up debris disks are dynamically perturbed by any planets that are present in the system; these perturbations influence the disk structure. By observing ~mm sized dust grains (which result from larger bodies colliding and grinding themselves down, and thus are expected to trace out the distribution of planetesimals) we can therefore make inferences about the planetary systems of stars with debris disks. For example, some of the best evidence for the history of our Solar System comes from studying the structure of the Sun's Asteroid and Edgeworth-Kuiper belts.In the first instance this project is focusing on HD107146, a ~100Myr old solar-type star which hosts a relatively wide debris disk, extending from ~30 to 150AU. Recent ALMA observations of the disk suggest that there is a depletion in the surface density of planetesimals at around 80AU. One possible explanation is that there is a planet of a few Earth masses on a circular orbit at ~80AU which is clearing the region immediately surrounding it of planetesimals. The exact shape of the depletion is not well-constrained, however: good fits to the observations are obtained from both a radial density profile that increases with distance but has a complete gap at ~80AU (as would be expected if there is a planet at the depletion), and a double-power-law profile that shows a partial depletion over a much broader range, which would require some other explanation.Another idea that has been proposed is that a planet was scattered out into the disk on an eccentric orbit, and the observed structure is a result of the way the planet's orbit was circularised as it interacted with the disk. However, in cases where planets at large separations are seen and the debris disk is detected, the planet appears to have depleted the disk almost completely, in contrast to the relatively small depletion seen for HD107146; other scenarios should therefore be considered.In this project we will consider how a multi-planet system would shape the disk; specifically, we will examine the effect of secular resonances. These occur where the precession rate of the planets equals that of the planetesimals in the disk, and act over long timescales to excite the eccentricities of these planetesimals. Objects on eccentric orbits will spend the majority of their time at distances not equal to their semi-major axis; this could therefore give rise to a depletion of the kind seen in the HD107146 system if there is a secular resonance at ~80AU. We will begin by proposing a two-planet system, and aim to constrain the parameter space (consisting of the planet masses and distances) to as great an extent as possible by considering the requirements imposed by the observed disk structure and the secular interaction timescale. N-body dynamical simulations will then be used to investigate the disk structures that would arise from various combinations of planets. The output from these simulations will also be post-processed to include the effect of disk depletion due to catastrophic collisions, which grind planetesimals into small particles which are blown out of the system by radiation pressure.Having examined the specific example of HD107146, we aim to extend this secular analysis to other debris disks which show depletions; in the longer term we will also be considering more generally the observable effects of other types of planet-disk interaction.

组成碎片盘的星子会受到系统中存在的任何行星的动态扰动；这些扰动会影响磁盘结构。通过观察~毫米大小的尘埃颗粒（由较大天体碰撞和磨碎而产生，因此有望追踪出星子的分布），我们可以对带有碎片盘的恒星的行星系统做出推断。例如，太阳系历史的一些最佳证据来自于对太阳小行星和埃奇沃斯-柯伊伯带结构的研究。首先，该项目的重点是 HD107146，这是一颗约 100Myr 的古老太阳型恒星，其拥有相对较宽的碎片盘，范围从约 30 天文单位到 150 个天文单位。最近 ALMA 对星盘的观测表明，星子的表面密度在 80AU 左右出现了损耗。一种可能的解释是，在大约 80 天文单位的圆形轨道上有一颗质量只有几个地球的行星，它正在清除其周围区域的星子。然而，耗尽的确切形状并没有得到很好的约束：从随距离增加但在~80AU处有完整间隙的径向密度剖面（如果有一颗行星处于耗尽状态，这将是预期的）和显示在更广泛范围内的部分耗尽的双幂律剖面中获得了与观测结果的良好拟合。提出的另一个想法是行星是沿着偏心轨道分散到圆盘中，观察到的结构是行星轨道在与圆盘相互作用时被圆形化的结果。然而，在看到距离较远的行星并检测到碎片盘的情况下，行星似乎几乎完全耗尽了盘，这与 HD107146 看到的相对较小的耗尽形成鲜明对比；因此，应该考虑其他情况。在这个项目中，我们将考虑多行星系统如何塑造圆盘；具体来说，我们将研究长期共振的影响。这些发生在行星的进动速率等于盘中微星子的进动速率的情况下，并且在很长的时间尺度上作用以激发这些微星子的偏心率。偏心轨道上的物体大部分时间都在不等于其半长轴的距离上；因此，如果在 ~80AU 处存在长期共振，这可能会导致 HD107146 系统中出现的那种损耗。我们将首先提出一个双行星系统，旨在通过考虑观测到的盘结构和长期相互作用时间尺度的要求，尽可能大地约束参数空间（由行星质量和距离组成）。然后，N 体动力学模拟将用于研究由各种行星组合产生的盘结构。这些模拟的输出也将进行后处理，以包括由于灾难性碰撞而导致的磁盘耗尽的影响，这些碰撞将星子磨成小颗粒，这些颗粒被辐射压力吹出系统。在检查了 HD107146 的具体示例后，我们的目标是将这种长期分析扩展到其他显示耗尽的碎片盘；从长远来看，我们还将更广泛地考虑其他类型的行星盘相互作用的可观察到的影响。