论文标题
太阳型星岩心的潮汐激发重力波:共鸣和临界层形成
Tidally excited gravity waves in the cores of solar-type stars: resonances and critical-layer formation
论文作者
论文摘要
我们模拟了太阳型恒星核心中潮汐诱导的非线性重力波的传播和耗散。我们使用光谱元素代码对先前开发的BousSinesQ模型进行流体动力学模拟,以研究恒星核作为波腔,该波腔被定期用给定的方位角波数和可调节频率在外部边界处强迫。对于低振幅强迫,该系统在特定频率下具有站立G-Modes的共振,与潮汐扭矩高度依赖的情况相对应。对于高振幅强迫,激发的波迅速在中心附近断裂并向上旋转,以使随后的波被以扩展的临界层吸收,如先前的工作所发现,从而导致具有光滑频率依赖性的潮汐扭矩。对于中等振幅强迫,我们发现波浪的线性阻尼逐渐旋转到核心上,从而可以大大改变共振条件。系统可以根据强迫频率和最接近特征频率之间的差异向G模式共振发展。最终,临界层形成并吸收传入波,导致与高幅度迅速破裂的高振幅情况相似的情况。我们研究该过程对强迫幅度和频率以及扩散系数的依赖性。我们强调,由于波浪的非线性反馈,太阳能恒星中心的小prandtl数促进了差异旋转的核心的发展。我们的模拟和分析表明,这种重要的机制可能会大大改变重力波的相位,因此需要修改太阳能恒星中共振锁定的经典图片。
We simulate the propagation and dissipation of tidally induced nonlinear gravity waves in the cores of solar-type stars. We perform hydrodynamical simulations of a previously developed Boussinesq model using a spectral-element code to study the stellar core as a wave cavity that is periodically forced at the outer boundary with a given azimuthal wavenumber and an adjustable frequency. For low-amplitude forcing, the system exhibits resonances with standing g-modes at particular frequencies, corresponding to a situation in which the tidal torque is highly frequency-dependent. For high-amplitude forcing, the excited waves break promptly near the centre and spin up the core so that subsequent waves are absorbed in an expanding critical layer, as found in previous work, leading to a tidal torque with a smooth frequency-dependence. For intermediate-amplitude forcing, we find that linear damping of the waves gradually spins up the core such that the resonance condition can be altered drastically. The system can evolve towards or away from g-mode resonances, depending on the difference between the forcing frequency and the closest eigenfrequency. Eventually, a critical layer forms and absorbs the incoming waves, leading to a situation similar to the high-amplitude case in which the waves break promptly. We study the dependence of this process on the forcing amplitude and frequency, as well as on the diffusion coefficients. We emphasize that the small Prandtl number in the centre of solar-like stars facilitates the development of a differentially rotating core owing to the nonlinear feedback of waves. Our simulations and analysis reveal that this important mechanism may drastically change the phase of gravity waves and thus the classical picture of resonance locking in solar-type stars needs to be revised.