arXiv 2005.140972020-05-28astro-ph.EP

晶粒长大对原行星盘热结构的影响

Influence of grain growth on the thermal structure of protoplanetary discs

Sofia Savvidou, Bertram Bitsch, Michiel Lambrechts

备注：: Accepted by A&A, 27 pages, 19 figures
发表信息：: A&A 640, A63 (2020)
DOI：: 10.1051/0004-6361/201936576

摘要：

原行星盘的热结构是由尘埃颗粒提供的不透明性来调节的。然而，以前的作品往往考虑简化处方的尘埃不透明度在流体动力学光盘模拟，例如，通过考虑只有一个单一的颗粒大小。在目前的工作中，我们进行2D流体动力学模拟的原行星盘的不透明度是自洽计算的尘埃人口，考虑到颗粒的大小，成分和丰度。我们首先比较模拟使用单晶粒尺寸的两个不同的多晶粒尺寸分布在不同水平的湍流强度，参数化通过$α$粘度，和不同的气体表面密度。假设一个单一的尘埃尺寸会导致不准确的计算光盘的热结构，因为晶粒尺寸主导的不透明度增加与轨道半径。总的来说，两个粒度分布，一个仅限于破碎，另一个确定从一个更完整的破碎-凝聚平衡，给出了类似的结果的热结构。我们发现，这两种粒度分布给不太陡峭的不透明度梯度，导致不太陡峭的纵横比梯度，相比，只有微米级的灰尘光盘。此外，在具有颗粒尺寸分布的盘中，最内侧的向外迁移区域被移除，并且嵌入在这样的盘中的行星经历较低的迁移速率。我们还调查了水的冰线位置上的α-粘度，在1 AU的初始气体表面密度和灰尘-气体比的依赖性，并找到独立的分布使用的$r_{ice} \propto α^{0.61} Σ_{g,0}^{0.8} f_{DG}^{0.37}$。在颗粒生长、不透明度和盘热力学之间的反馈回路的加入允许对吸积盘和行星形成进行更加自洽的模拟。

英文摘要：

The thermal structure of a protoplanetary disc is regulated by the opacity that dust grains provide. However, previous works have often considered simplified prescriptions for the dust opacity in hydrodynamical disc simulations, e.g. by considering only a single particle size. In the present work we perform 2D hydrodynamical simulations of protoplanetary discs where the opacity is self-consistently calculated for the dust population, taking into account the particle size, composition and abundance. We first compare simulations using single grain sizes to two different multi-grain size distributions at different levels of turbulence strengths, parameterized through the $α$-viscosity, and different gas surface densities. Assuming a single dust size leads to inaccurate calculations of the thermal structure of discs, because the grain size dominating the opacity increases with orbital radius. Overall the two grain size distributions, one limited by fragmentation only and the other determined from a more complete fragmentation-coagulation equilibrium, give similar results for the thermal structure. We find that both grain size distributions give less steep opacity gradients that result in less steep aspect ratio gradients, in comparison to discs with only micrometer sized dust. Moreover, in the discs with a grain size distribution, the innermost outward migration region is removed and planets embedded is such discs experience lower migration rates. We also investigate the dependency of the water iceline position on the alpha-viscosity, the initial gas surface density at 1 AU and the dust-to-gas ratio and find $r_{ice} \propto α^{0.61} Σ_{g,0}^{0.8} f_{DG}^{0.37}$ independently of the distribution used. The inclusion of the feedback loop between grain growth, opacities and disc thermodynamics allows for more self-consistent simulations of accretion discs and planet formation.

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