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arXiv 1507.03599astro-ph.SRastro-ph.EP
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行星质量伴星激发的螺旋激波结构

The Structure of Spiral Shocks Excited by Planetary-mass Companions

Zhaohuan Zhu, Ruobing Dong, James M. Stone, Roman R. Rafikov

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20 pages, 22 figures, ApJ In press
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摘要：

直接的影像观测揭示了原行星盘的螺旋结构。以前的研究表明，行星引起的螺旋臂不能解释这些螺旋图案中的一些，因为螺旋臂的大螺距角和高对比度。我们已经进行了三维（3-D）流体动力学模拟研究年轻行星激发的螺旋尾流/激波。我们发现，与线性理论相反，螺旋臂的螺距角确实依赖于行星的质量，这可以用非线性密度波理论来解释。第二（甚至第三）旋臂，特别是内旋臂，也会被大质量行星所激发。当行星质量较大时，被激发的旋臂会有较大的螺旋角，主旋臂和次旋臂在方位角方向上的间距也会较大。我们还发现，虽然在外盘的手臂没有表现出太多的垂直运动，内臂有显着的垂直运动，这增强了密度扰动的磁盘大气。结合流体动力学模型与蒙特卡罗辐射转移计算，我们发现，内螺旋臂是相当突出的合成近红外图像使用全三维流体动力学模型比图像的基础上2-D模型假设垂直流体静力学平衡，表明需要模型观测与全三维流体动力学。总的来说，伴星诱导的螺旋臂不仅可以精确定位伴星的位置，还可以提供三种独立的方式（俯仰角、两个臂之间的间隔和臂的对比度）来限制伴星的质量。

英文摘要：

Direct imaging observations have revealed spiral structures in protoplanetary disks. Previous studies have suggested that planet-induced spiral arms cannot explain some of these spiral patterns, due to the large pitch angle and high contrast of the spiral arms in observations. We have carried out three dimensional (3-D) hydrodynamical simulations to study spiral wakes/shocks excited by young planets. We find that, in contrast with linear theory, the pitch angle of spiral arms does depend on the planet mass, which can be explained by the non-linear density wave theory. A secondary (or even a tertiary) spiral arm, especially for inner arms, is also excited by a massive planet. With a more massive planet in the disk, the excited spiral arms have larger pitch angle and the separation between the primary and secondary arms in the azimuthal direction is also larger. We also find that although the arms in the outer disk do not exhibit much vertical motion, the inner arms have significant vertical motion, which boosts the density perturbation at the disk atmosphere. Combining hydrodynamical models with Monte-Carlo radiative transfer calculations, we find that the inner spiral arms are considerably more prominent in synthetic near-IR images using full 3-D hydrodynamical models than images based on 2-D models assuming vertical hydrostatic equilibrium, indicating the need to model observations with full 3-D hydrodynamics. Overall, companion-induced spiral arms not only pinpoint the companion's position but also provide three independent ways (pitch angle, separation between two arms, and contrast of arms) to constrain the companion's mass.

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