Limits on Mode Coherence in Pulsating DA White Dwarfs Due to a Nonstatic Convection Zone
Limits on Mode Coherence in Pulsating DA White Dwarfs Due to a Nonstatic Convection Zone
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DOI：
10.3847/1538-4357/ab6a0e
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发表时间：
2020-01
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影响因子：
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通讯作者：
M. Montgomery;J. Hermes;D. Winget;B. Dunlap;K. Bell
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作者：
M. Montgomery;J. Hermes;D. Winget;B. Dunlap;K. Bell
脉动的标准理论处理恒星模型中无穷小扰动的频率和增长率。被计算为线性驱动的模式应随时间按指数增加其振幅;通常观察到的振幅几乎恒定的事实证明，非线性机制抑制了有限振幅脉动的增长。模型预测脉动氢大气（DAV）白色矮星中对流区的质量对温度非常敏感（即，），导致即使是低振幅的放大器也可能经历显著的非线性效应。特别是，有限振幅g模式脉动的外转折点可以随局部表面温度而变化，产生与驻波所需的相位不同的反射波。这可能导致模式的相干性的缺乏以及其全局幅度的减小。在本文中，我们表明：（1）是否计算出一个模式传播到对流区的底部是它在傅里叶谱中的宽度的准确预测，（2）由外部转折点反射产生的相移足够大，以产生显着的阻尼，（3）振幅和周期预计从蓝边增加到中间的不稳定带，并且随后随着接近红色边缘而减小。这种振幅的减小与观测数据一致，而周期的减小还没有得到系统的研究。
The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes that are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly constant amplitudes are usually observed is evidence that nonlinear mechanisms inhibit the growth of finite-amplitude pulsations. Models predict that the mass of convection zones in pulsating hydrogen-atmosphere (DAV) white dwarfs is very sensitive to temperature (i.e., ), leading to the possibility that even low-amplitude pulsators may experience significant nonlinear effects. In particular, the outer turning point of finite-amplitude g-mode pulsations can vary with the local surface temperature, producing a reflected wave that is out of phase with what is required for a standing wave. This can lead to a lack of coherence of the mode and a reduction in its global amplitude. In this paper we show that (1) whether a mode is calculated to propagate to the base of the convection zone is an accurate predictor of its width in the Fourier spectrum, (2) the phase shifts produced by reflection from the outer turning point are large enough to produce significant damping, and (3) amplitudes and periods are predicted to increase from the blue edge to the middle of the instability strip, and subsequently decrease as the red edge is approached. This amplitude decrease is in agreement with the observational data while the period decrease has not yet been systematically studied.