Non-linear dynamical tides in white dwarf binaries
Non-linear dynamical tides in white dwarf binaries
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DOI：
10.1093/mnras/staa1858
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发表时间：
2020-05
影响因子：
4.8
通讯作者：
Hang Yu;N. Weinberg;J. Fuller
中科院分区：
文献类型：
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作者：
Hang Yu;N. Weinberg;J. Fuller
紧凑型白矮星（WD）双星是天基引力波（GW）天文台的重要来源，越来越多的白矮星正被极低质量（ELM）和兹威基瞬变设施（ZTF）等调查发现。我们研究了非线性动态潮汐在这类双星中的影响。我们重点研究了全局三模参量不稳定性，并表明它具有比先前研究的局部破波条件低得多的阈值能量。通过对耦合模式网络的积分，我们计算了潮汐耗散率作为轨道周期的函数。我们构建了与这些数值结果相匹配的现象学模型，并用它们来评估WD双星的自旋和光度演化。而在线性理论中，WD的自旋频率可以锁定到轨道频率，我们发现当考虑非线性效应时，这种锁定无法保持。相反，随着轨道的衰减，自旋和轨道会时而同步时而不同步。每次它们不同步时，潮汐加热速率就会出现短暂但显著的下降。虽然紧凑型双星中的大多数WDs的亮度应该与以前的行波估计相似，但有几个百分点的WDs的亮度应该是原来的10倍左右，因为它们位于升温速率下降的地方。这为J0651中CO WD的低光度提供了一个潜在的解释。最后，我们考虑了潮汐对GW信号的影响，并表明激光干涉仪空间天线（LISA）和TianGO可以在厘赫兹系统中约束WD的惯性矩，使其优于$1{{\ \rm / \ %}}$。
Compact white dwarf (WD) binaries are important sources for space-based gravitational-wave (GW) observatories, and an increasing number of them are being identified by surveys like Extremely Low Mass (ELM) and Zwicky Transient Facility (ZTF). We study the effects of non-linear dynamical tides in such binaries. We focus on the global three-mode parametric instability and show that it has a much lower threshold energy than the local wave-breaking condition studied previously. By integrating networks of coupled modes, we calculate the tidal dissipation rate as a function of orbital period. We construct phenomenological models that match these numerical results and use them to evaluate the spin and luminosity evolution of a WD binary. While in linear theory the WD’s spin frequency can lock to the orbital frequency, we find that such a lock cannot be maintained when non-linear effects are taken into account. Instead, as the orbit decays, the spin and orbit go in and out of synchronization. Each time they go out of synchronization, there is a brief but significant dip in the tidal heating rate. While most WDs in compact binaries should have luminosities that are similar to previous traveling-wave estimates, a few per cent should be about 10 times dimmer because they reside in heating rate dips. This offers a potential explanation for the low luminosity of the CO WD in J0651. Lastly, we consider the impact of tides on the GW signal and show that the Laser Interferometer Space Antenna (LISA) and TianGO can constrain the WD’s moment of inertia to better than $1{{\ \rm per\ cent}}$ for centi-Hz systems.