论文标题
恒星中有近距离行星的恒星自动振荡的潮气激发
Tidal excitation of autoresonant oscillations in stars with close-by planets
论文作者
论文摘要
近距离行星可能会通过其随时间变化的潮汐潜力来激发其宿主恒星中的各种振荡。最近已经提出了比恒星旋转频率小得多的磁性振荡，以说明在几个行星托管恒星中观察到的自旋轨道可分辨性。原则上，它们可以通过与宿主旋转的参考框架中的频率变化的潮汐电势的傅立叶分量在孤立的细长磁通管中共鸣。但是，由于这种高阶潮汐成分的弱点，需要一种机制，需要长时间锁定振荡（$ 10^{3} -10^{7} $年），以使振动幅度振幅生长。我们建议锁定机制是振荡频率对其振幅的非线性依赖性产生的自动兑换。我们建议，进入自动耐药性的宿主中，角动量损失率大大降低，这有助于长期以来将这些系统保持在该状态。我们将模型应用于10个显示旋转轨道可分性的系统的样本，并估计相关潮汐电势频率的最大漂移，使它们能够进入自动顾问。由于行星轨道的潮汐演化以及磁化风的恒星角动量损失，因此将这种漂移与预期的漂移进行了比较，发现自动耐药性是八个系统中的可行机制，至少在我们理想化的模型中。自动替代状态的持续时间和相关的自旋轨道可分解性可能与宿主星的主要序列寿命相媲美，这表明旋律学可能不适用于这些宿主。
Close-by planets may excite various kinds of oscillations in their host stars through their time-varying tidal potential. Magnetostrophic oscillations with a frequency much smaller than the stellar rotation frequency have recently been proposed to account for the spin-orbit commensurability observed in several planet-hosting stars. In principle, they can be resonantly excited in an isolated slender magnetic flux tube by a Fourier component of the time-varying tidal potential with a very low frequency in the reference frame rotating with the host. However, due to the weakness of such high-order tidal components, a mechanism is required to lock the oscillations in phase with the forcing for long time intervals ($10^{3}-10^{7}$ years) in order to allow the oscillation amplitude to grow. We propose that the locking mechanism is an autoresonance produced by the non-linear dependence of the oscillation frequency on its amplitude. We suggest that the angular momentum loss rate is remarkably reduced in hosts entering autoresonance that contributes to maintain those systems in that regime for a long time. We apply our model to a sample of ten systems showing spin-orbit commensurability and estimate the maximum drifts of the relevant tidal potential frequencies that allow them to enter the autoresonant regime. Such drifts are compared with the expected drifts owing to the tidal evolution of the planetary orbits and the stellar angular momentum loss in the magnetized winds finding that autoresonance is a viable mechanism in eight systems, at least in our idealized model. The duration of the autoresonant regime and the associated spin-orbit commensurability may be comparable with the main-sequence lifetimes of the host stars, indicating that gyrochronology may not be applicable to those hosts.
