The Thermal Phase Curve Offset on Tidally and Nontidally Locked Exoplanets: A Shallow Water Model
The Thermal Phase Curve Offset on Tidally and Nontidally Locked Exoplanets: A Shallow Water Model
复制标题
潮汐和非潮汐锁定系外行星的热相位曲线偏移：浅水模型
DOI：
10.3847/1538-4357/aa756e
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
G. Vallis
中科院分区：
文献类型：
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作者：
J. Penn;G. Vallis
利用含时变强迫的浅水模式，我们证明了行星自转时系外行星热位相曲线的峰值一般偏离次日食。也就是说，行星热点偏离最大加热点(恒星下点)，并可能领先或滞后于强迫；偏移的程度和符号是行星自转速度和轨道周期的函数。我们还发现，在移动作用力的坐标系下，系统达到了一个稳定状态。该模型是研究得很好的Matsuno-Gill模型的扩展，它是一个完整的球面几何结构，具有行星尺度的平移作用力，表示从主恒星接收到的太阳系外行星上的太阳辐射。模型中重力波的速度是评价相曲线偏移量的关键指标。如果恒星下点(相对于行星表面)的速度超过重力波的速度，那么热点将滞后于恒星下点，正如重力波动力学所预期的那样。然而，当星下点的移动速度低于系统的内波速度时，最热的点可能会引导强迫通过。我们通过考虑Rossby和Kelvin波动力学，以及在非常慢旋转的情况下的一维模型来解释这一结果，并给出了解析解。最后，我们考虑了由观测到的相位曲线来约束行星自转速度的反问题。
Using a shallow water model with time-dependent forcing, we show that the peak of an exoplanet thermal phase curve is, in general, offset from the secondary eclipse when the planet is rotating. That is, the planetary hot spot is offset from the point of maximal heating (the substellar point) and may lead or lag the forcing; the extent and sign of the offset are functions of both the rotation rate and orbital period of the planet. We also find that the system reaches a steady state in the reference frame of the moving forcing. The model is an extension of the well-studied Matsuno–Gill model into a full spherical geometry and with a planetary-scale translating forcing representing the insolation received on an exoplanet from a host star. The speed of the gravity waves in the model is shown to be a key metric in evaluating the phase curve offset. If the velocity of the substellar point (relative to the planet’s surface) exceeds that of the gravity waves, then the hot spot will lag the substellar point, as might be expected by consideration of forced gravity wave dynamics. However, when the substellar point is moving slower than the internal wave speed of the system, the hottest point may lead the passage of the forcing. We provide an interpretation of this result by consideration of the Rossby and Kelvin wave dynamics, as well as, in the very slowly rotating case, a one-dimensional model that yields an analytic solution. Finally, we consider the inverse problem of constraining planetary rotation rate from an observed phase curve.