Gas capture by distant protoplanets and the formation of Jovian planets.

为了弄清木星行星的形成过程及其特征的起源，我们研究了(I)覆盖原行星的气体包层的静态结构和(Ii)不稳定气体包络的坍塌过程，并开发了描述(Iii)星云气体被原行星俘获的模拟程序。我们的主要结果总结如下：(I)覆盖原行星的气体包络的静态结构气体包络的结构主要由行星吸积在包络中释放的能量决定。考虑到动压对入射小行星的碎裂作用，我们估算了能流，得到了气体包层的静态解。结果表明，行星体的碎裂相当大地减少了能流和临界核质量，我们得到的临界质量变成了以前研究所得值的四分之一。(Ii)不稳定气体包层的塌陷过程。其次，我们模拟了不稳定气体包层的塌陷过程，考虑了星云气体的流入。此外，我们还分析了崩塌气体的动力学不稳定性。然后，我们证明了没有发生Wuchterl(1993)提出的振荡不稳定性和物质抛射。我们的结果支持京都模型中提出的形成过程。(Iii)星云气体被原行星捕获利用(I)和(Ii)中的结果，我们开始开发描述星云气体被原行星捕获的新的模拟程序。以前的研究有一个缺点，即气体捕获的方式强烈依赖于代码的算法。我们现在正在开发新的代码，可以克服这个缺点。

To clarigy the formation processes of Jovian planets and the origin of their characters, we investigated (i) the static structure of the gas envelope covering a protoplanet and (ii) the collapse process of the unstable gas envelope and developed the simulation code describing (iii) the capture of the nebular gas by a protoplanet.Our main results are summarized as follows.(i) Static structure of the gas envolope covering a protoplanetThe structure of the gas envelope is mainly governed by the energy released in the envelope due to the accretion of planetesimals. Taking into account fragmention of incident planetesimals due to the dynamical pressure, we estimated the energy flux and obtained the static solution of the gas envelope. As a result, we showed that fragmentation of planetesimals fairly reduces the energy flux and the critical core mass and that the critical mass we obtained becomes 1/4 of the value obtained by the previous studies.(ii) The collapse process of the unstable gas envelopeNext, we performed simulations of the collapse of the unstable gas envelope, taking into account the infall of the nebular gas. Futhermore, we analized the dynamical instability of the collapsing gas. Then we showed that the oscillational instability and the mass ejection suggested by Wuchterl (1993) do not occur. Our results support the formation process proposed in Kyoto model.(iii) Capture of the nebular gas by a protoplanetUsing the results in (i) and (ii), we started the development of the new simulation code describing the capture of the nebular gas by a protoplanet. The previous study had a demerit that the way of the gas capture strongly depends on the algorism of the code. We are now developing the new code which can overcome the demerit.