On internal wave breaking and tidal dissipation near the centre of a solar-type star
On internal wave breaking and tidal dissipation near the centre of a solar-type star
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太阳型恒星中心附近的内波破碎和潮汐耗散
DOI：
10.1111/j.1365-2966.2010.16400.x
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发表时间：
2010
影响因子：
4.8
通讯作者：
Barker A
中科院分区：
文献类型：
--
作者：
Barker A
我们研究的命运内部重力波接近中心的最初非旋转的太阳型星星，主要是使用二维数值模拟的基础上的圆柱模型。在这种星星的对流区和辐射区之间的界面上，潮汐力会激发出一系列内部重力波。我们推导了一个星星中心区域的Boussinesq型模型，并找到了一个非线性波解，该解在以潮汐力的角模式速度旋转的坐标系中是稳定的。然后，我们使用谱方法积分方程数值，目的是研究在什么幅度的波是受不稳定性。这些不稳定性被发现，导致波破碎时，振幅超过一个临界值。低于这个临界值，波从星星的中心完全反射。波破碎导致平均流加速，这对应于自旋的中心区域的星星，和形成一个临界层，它作为一个吸收障碍，为随后的传入波。当这些波在临界层附近继续被吸收时，星星从内到外旋转起来。我们的结果指出了一个重要的振幅依赖性的（修改）潮汐质量因子Q '，因为非线性效应是负责在星星的中心耗散。如果潮汐强迫的振幅超过了发生波浪破碎的临界振幅，那么这种机制就会在连续的潮汐频率范围内产生有效的耗散。这就要求，对于一颗质量为mp、轨道周期为P的行星，忽略恒星自转。然而，这一标准强烈地依赖于星星中心稳定分层的强度，因此它依赖于恒星质量和主序星年龄。如果破裂发生，我们发现，对于现在的太阳。对于固定的轨道参数，在质量在0.5到1.1 M <$m之间的太阳型恒星范围内，这一变化不超过5倍。因此，这个Q ′的估计是相当稳健的，并且可以合理地被认为适用于所有太阳型主序星，如果这个机制起作用的话。由此产生的耗散的强烈频率依赖性意味着这种效应在决定G和K恒星附近的巨行星的命运方面可能非常重要。我们预测更少的巨行星的轨道周期小于约2天围绕这样的恒星，如果他们造成打破在中心，由于这一过程的效率。即使波的振幅太低而不能引发破裂，辐射阻尼原则上也会导致恒星中心逐渐自旋并形成临界层。这一过程可以在受到质量较小的伴星扰动的太阳型恒星中提供有效的潮汐消散，但可能会被抵抗差自转发展的效应所阻止。然而，这些机制在具有对流核心的恒星中是无效的，例如WASP-18，WASP-12和OGLE-TR-56，也许部分解释了它们的亲密行星同伴的生存。
We study the fate of internal gravity waves approaching the centre of an initially non-rotating solar-type star, primarily using two-dimensional numerical simulations based on a cylindrical model. A train of internal gravity waves is excited by tidal forcing at the interface between the convection and radiation zones of such a star. We derive a Boussinesq-type model of the central region of a star and find a non-linear wave solution that is steady in the frame rotating with the angular pattern speed of the tidal forcing. We then use spectral methods to integrate the equations numerically, with the aim of studying at what amplitude the wave is subject to instabilities. These instabilities are found to lead to wave breaking whenever the amplitude exceeds a critical value. Below this critical value, the wave reflects perfectly from the centre of the star. Wave breaking leads to mean flow acceleration, which corresponds to a spin-up of the central region of the star, and the formation of a critical layer, which acts as an absorbing barrier for subsequent ingoing waves. As these waves continue to be absorbed near the critical layer, the star is spun up from the inside out. Our results point to an important amplitude dependence of the (modified) tidal quality factor Q′, since non-linear effects are responsible for dissipation at the centre of the star. If the amplitude of the tidal forcing exceeds the critical amplitude for wave breaking to occur, then this mechanism produces efficient dissipation over a continuous range of tidal frequencies. This requires, for a planet of mass mp in an orbit of period P around the current Sun, neglecting stellar rotation. However, this criterion depends strongly on the strength of the stable stratification at the centre of the star, and so it depends on stellar mass and main-sequence age. If breaking occurs, we find, for the current Sun. This varies by no more than a factor of 5 throughout the range of solar-type stars with masses between 0.5 and 1.1 M⊙, for fixed orbital parameters. This estimate of Q′ is therefore quite robust and can be reasonably considered to apply to all solar-type main-sequence stars, if this mechanism operates. The strong frequency dependence of the resulting dissipation means that this effect could be very important in determining the fate of close-in giant planets around G and K stars. We predict fewer giant planets with orbital periods of less than about 2 d around such stars if they cause breaking at the centre, due to the efficiency of this process. Even if the waves are of too low amplitude to initiate breaking, radiative damping could, in principle, lead to a gradual spin-up of the stellar centre and to the formation of a critical layer. This process could provide efficient tidal dissipation in solar-type stars perturbed by less massive companions, but it may be prevented by effects that resist the development of differential rotation. These mechanisms would, however, be ineffective in stars with a convective core, such as WASP-18, WASP-12 and OGLE-TR-56, perhaps partly explaining the survival of their close planetary companions.
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DOI：
10.1111/j.1365-2966.2009.14694.x
发表时间：
2009
影响因子：
4.8
作者：
Barker A
通讯作者：
Barker A
WASP-19b：迄今为止发现的周期最短的凌日系外行星
DOI：
10.1088/0004-637x/708/1/224
发表时间：
2010
期刊：
The Astrophysical Journal
影响因子：
--
作者：
L. Hebb;A. Collier;A. Triaud;T. Lister;B. Smalley;P. Maxted;C. Hellier;D. Anderson;D. Pollacco;M. Gillon;M. Gillon;D. Queloz;R. West;S. Bentley;B. Enoch;C. Haswell;K. Horne;M. Mayor;F. Pepe;D. Ségransan;I. Skillen;S. Udry;P. Wheatley
通讯作者：
P. Wheatley
DOI：
--
发表时间：
1981
期刊：
影响因子：
--
作者：
W. Press
通讯作者：
W. Press
旋转体的振荡：应用于动态潮汐和潮汐捕获的自伴形式主义
DOI：
10.1111/j.1745-3933.2005.00107.x
发表时间：
2005
影响因子：
--
作者：
J. Papaloizou;P. Ivanov
通讯作者：
P. Ivanov
临界水平下粘度和热传导对内部重力波的影响
影响因子：
3.7
作者：
Philip Hazel
通讯作者：
Philip Hazel