N-BODY SIMULATIONS OF PLANETARY ACCRETION AROUND M DWARF STARS
N-BODY SIMULATIONS OF PLANETARY ACCRETION AROUND M DWARF STARS
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DOI：
10.1088/0004-637x/699/1/824
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发表时间：
2009-04
期刊：
影响因子：
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通讯作者：
M. Ogihara;S. Ida
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文献类型：
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作者：
M. Ogihara;S. Ida
我们已经调查了行星吸积的星子在类地行星区域内的冰线周围M矮星通过N体模拟，包括潮汐与磁盘气体的相互作用。由于M矮星的低光度，可居住带（HZ）位于内部区域（Au）。在近区，由于小轨道半径处的盘气体密度较高，I型迁移和偏心阻尼引起的轨道衰减是有效的。由于轨道衰变在盘的内缘附近终止，而盘的内缘又靠近HZ，所以在盘的内缘附近聚集的原行星会影响HZ行星的形成。冰线也在相对较内的区域，在0.03 Au。由于轨道半径较小，冰质原行星会快速地吸积，并在盘耗尽之前经历I型迁移。在M矮星周围的类地行星区，行星吸积的特征是轨道衰减快，靠近盘的内缘，以及大量的冰质原行星流入。在线性理论预测的I型迁移完全有效的情况下，我们发现迁移到主星星附近的原行星经历了紧密的散射和碰撞，最终有4到6颗行星保持在相互的平均运动共振中，它们的轨道具有小的偏心率（φ 0.01），并且它们在盘气体衰变前后都是稳定的。在缓慢迁移的情况下，共振捕获是如此有效，以至于密集的1040颗小原行星保持在相互的平均运动共振中。在这种情况下，他们开始轨道交叉后，磁盘气体衰减和偏心阻尼由于潮汐与气体的相互作用是没有更有效的。通过原行星的合并，形成了几颗行星，它们在相距很远的非共振轨道上，具有相对较大的偏心率（φ 0.05）。因此，最终的轨道配置（分离，共振或非共振，偏心率和分布）的类地行星周围的M矮星敏感地依赖于强度的I型迁移。我们还发现，大量的水冰是由I型迁移从外部区域和最终的行星附近的内盘边缘周围的M矮星通常是丰富的水冰，除了最里面的一个是由外行星屏蔽，除非I型迁移速度降低了100倍以上的线性理论预测。
We have investigated planetary accretion from planetesimals in terrestrial planet regions inside the ice line around M dwarf stars through N-body simulations including tidal interactions with disk gas. Because of low luminosity of M dwarfs, habitable zones (HZs) are located in inner regions (∼0.1 AU). In the close-in HZ, type-I migration and the orbital decay induced by eccentricity damping are efficient according to the high disk gas density in the small orbital radii. Since the orbital decay is terminated around the disk inner edge and the disk edge is close to the HZ, the protoplanets accumulated near the disk edge affect formation of planets in the HZ. Ice lines are also in relatively inner regions at ∼0.3 AU. Due to the small orbital radii, icy protoplanets accrete rapidly and undergo type-I migration before disk depletion. The rapid orbital decay, the proximity of the disk inner edge, and large amount of inflow of icy protoplanets are characteristic in planetary accretion in terrestrial planet regions around M dwarfs. In the case of full efficiency of type-I migration predicted by the linear theory, we found that protoplanets that migrate to the vicinity of the host star undergo close scatterings and collisions, and four to six planets eventually remain in mutual mean-motion resonances and their orbits have small eccentricities (≲0.01) and they are stable both before and after disk gas decays. In the case of slow migration, the resonant capture is so efficient that densely packed ∼40 small protoplanets remain in mutual mean-motion resonances. In this case, they start orbit crossing, after the disk gas decays and eccentricity damping due to tidal interaction with gas is no more effective. Through merging of the protoplanets, several planets in widely separated non-resonant orbits with relatively large eccentricities (∼0.05) are formed. Thus, the final orbital configurations (separations, resonant or non-resonant, eccentricity, and distribution) of the terrestrial planets around M dwarfs sensitively depend on strength of type-I migration. We also found that large amount of water–ice is delivered by type-I migration from outer regions and final planets near the inner disk edge around M dwarfs are generally abundant in water–ice except for the innermost one that is shielded by the outer planets, unless type-I migration speed is reduced by a factor of more than 100 from that predicted by the linear theory.