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arXiv 0901.2048astro-ph.EP
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坠落的凌日系外巨行星

Falling Transiting Extrasolar Giant Planets

B. Levrard, C. Winisdoerffer, G. Chabrier

摘要:

我们重新审视的潮汐稳定性的太阳系外系统窝藏过境行星,并证明,独立于任何潮汐模型,只有一个(HAT-P-2B)的这些行星有一个潮汐平衡态,这意味着最终碰撞的这些对象与他们的主恒星。因此,传统的循环和同步时标不能被定义,因为相应的状态不代表潮汐演化的终点。使用数值模拟的耦合潮汐方程的自旋和轨道参数的每个过境行星系,我们证实了这些预测,并表明,轨道偏心率和恒星的密度不遵循通常假设的指数松弛,而是显着减少,最终达到零值,只有在最后失控合并的行星与恒星。{ \it all}旋转和轨道参数的唯一特征演化时间尺度是系统的寿命,其关键取决于恒星内潮汐耗散的大小。这些结果意味着凌日行星的近圆形轨道和恒星自转轴与行星轨道的对齐不太可能是由于潮汐耗散。其他的耗散机制,例如与原行星盘的相互作用,必须被调用来解释这些属性。

英文摘要:

We revisit the tidal stability of extrasolar systems harboring a transiting planet and demonstrate that, independently of any tidal model, none but one (HAT-P-2b) of these planets has a tidal equilibrium state, which implies ultimately a collision of these objects with their host star. Consequently, conventional circularization and synchronization timescales cannot be defined because the corresponding states do not represent the endpoint of the tidal evolution. Using numerical simulations of the coupled tidal equations for the spin and orbital parameters of each transiting planetary system, we confirm these predictions and show that the orbital eccentricity and the stellar obliquity do not follow the usually assumed exponential relaxation but instead decrease significantly, reaching eventually a zero value, only during the final runaway merging of the planet with the star. The only characteristic evolution timescale of {\it all} rotational and orbital parameters is the lifetime of the system, which crucially depends on the magnitude of tidal dissipation within the star. These results imply that the nearly circular orbits of transiting planets and the alignment between the stellar spin axis and the planetary orbit are unlikely to be due to tidal dissipation. Other dissipative mechanisms, for instance interactions with the protoplanetary disk, must be invoked to explain these properties.

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