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arXiv 1506.07348astro-ph.EP
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恒星辐照3D盘中行星的向外迁移

Outwards migration for planets in stellar irradiated 3D discs

E. Lega, A. Morbidelli, B. Bitsch, A. Crida, J. Szulagyi

摘要:

我们第一次提出了嵌入恒星辐射盘的行星的3D模拟。众所周知,热效应可能会将行星迁移的方向从内向外逆转,从而有可能挽救原行星盘内部光学厚度较厚部分的行星。当考虑恒星辐射,除了作为热源的粘性摩擦,外盘的变化从阴影到耀斑结构。使用一个合适的分析公式,它已经表明,在张开的部分光盘的迁移是向内的;行星可以向外迁移,只有在光盘的阴影区,{因为熵的径向梯度更强}。为了证实这一结果的数值,我们已经计算了总扭矩作用于行星上的固定轨道嵌入恒星辐照的3D光盘使用流体动力学代码FARGOCA。我们发现定性良好的数值模拟得到的总扭矩和预测的解析公式之间的协议。对于大质量(>20个地球质量),我们发现定量的协议,我们获得向外迁移区域的行星高达60个地球质量的早期阶段的吸积盘。然而,我们发现,与解析公式的协议是相当偶然的,因为该公式低估了马蹄形区域的大小,这个错误是由其他条款,最有可能的冷却速率和饱和度的不完善的估计补偿。

英文摘要:

For the very first time we present 3D simulations of planets embedded in stellar irradiated discs. It is well known that thermal effects could reverse the direction of planetary migration from inwards to outwards, potentially saving planets in the inner, optically thick parts of the protoplanetary disc. When considering stellar irradiation in addition to viscous friction as a source of heating, the outer disc changes from a shadowed to a flared structure. Using a suited analytical formula it has been shown that in the flared part of the disc the migration is inwards; planets can migrate outwards only in shadowed regions of the disc, { because the radial gradient of entropy is stronger there}. In order to confirm this result numerically, we have computed the total torque acting on planets held on fixed orbits embedded in stellar irradiated 3D discs using the hydrodynamical code FARGOCA. We find qualitatively good agreement between the total torque obtained with numerical simulations and the one predicted by the analytical formula. For large masses (>20 Earth masses) we find quantitative agreement, and we obtain outwards migration regions for planets up to 60 Earth masses in the early stages of accretional discs. We find nevertheless that the agreement with the analytic formula is quite fortuitous because the formula underestimates the size of the horseshoe region; this error is compensated by imperfect estimates of other terms, most likely the cooling rate and saturation.

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