Planetesimal Accretion in Binary Systems: The Effects of Gas Dissipation
Planetesimal Accretion in Binary Systems: The Effects of Gas Dissipation
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DOI：
10.1086/591309
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发表时间：
2008-06
期刊：
影响因子：
--
通讯作者：
Jiwei Xie;Ji-lin Zhou
中科院分区：
文献类型：
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作者：
Jiwei Xie;Ji-lin Zhou
目前，在近双星系统中行星形成的一个主要理论问题是伴星的强烈扰动是否会增加主星周围的行星体的相对速度(ΔV)，从而阻碍它们的生长。根据以前的研究，虽然气体阻力可以通过迫使行星上的轨道对齐来降低相同大小的天体之间的ΔV，但它会增加不同大小的天体之间的ΔV。在本文中，我们针对γCephei双星系统，提出了一种可以克服这一困难的机制。结果表明，在耗散气盘中(典型的耗散时间尺度为~105-106年)，无论大小如何，所有的行星体最终都会聚到相同的受迫轨道，从而导致较低的撞击速度。这种减小ΔV的过程逐渐增加了净质量吸积，甚至可能引发大型天体(半径超过15公里)的失控增长。讨论了行星体大小分布的影响，发现它是决定碰撞演化结果的主要因素之一。无论如何，可以得出的结论是，通过在圆盘演化的早期阶段包括气体耗散，行星小吸积的条件变得更好，从小行星到行星胚胎的过程可以在像γCEP这样的紧密双星系统中完成。
Currently, one of the major theoretical problems concerning planet formation in close binary systems is whether the strong perturbation from the companion star can increase the relative velocities (ΔV) of planetesimals around the primary and thus hinder their growth. According to previous studies, while gas drag can reduce the ΔV between bodies of the same size by forcing orbital alignment on planetesimals, it increases the ΔV among bodies of different sizes. In this paper, focusing on the γ Cephei binary system, we propose a mechanism that can overcome this difficulty. We show that in a dissipating gas disk (with a typical dissipation timescale of ~105-106 yr), all the planetesimals eventually converge toward the same forced orbits regardless of their size, leading to much lower impact velocities. This process of decreasing ΔV progressively increases net mass accretion and can even trigger runaway growth for large bodies (radius above 15 km). The effect of the size distribution of planetesimals is discussed and is found to be one of the dominant factors determining the outcome of collisional evolution. In any case, it can be concluded that by including gas dissipation in the early stages of disk evolution, the conditions for planetesimal accretion become much better, and the progression from planetesimals to planet embryos can be accomplished in close binary systems such as γ Cep.