Turbulent Convection and Pulsational Stability of Variable Stars. I. Oscillations of Long-Period Variables
Turbulent Convection and Pulsational Stability of Variable Stars. I. Oscillations of Long-Period Variables
复制标题
DOI：
10.1086/305601
复制
发表时间：
1997-10
期刊：
影响因子：
--
通讯作者：
D. Xiong;L. Deng;Q. L. C. P. M. Observatory;B. Observatory;Chinese Academy of Sciences
中科院分区：
文献类型：
--
作者：
D. Xiong;L. Deng;Q. L. C. P. M. Observatory;B. Observatory;Chinese Academy of Sciences
我们对 M = 1.0 M☉、L = 3000-8000 L☉、(X, Z) = (0.700, 0.020)、(0.735, 0.005) 的 6 个系列长周期变量模型进行了线性脉动稳定性调查。通过使用非局域和时间相关对流的统计理论来处理对流和振荡之间的动态和热力学耦合。结果表明，当忽略对流和振荡之间的耦合时，低温模型的基频和所有低频泛音始终是脉动不稳定的。当考虑耦合时，赫罗图上造父变星不稳定带外确实存在一个“米拉”脉动不稳定区。 Hayashi 赛道附近最酷的模型是脉动稳定的。对于高温，基模首先变得不稳定，然后第一泛音变得不稳定。对于较热的型号，第二至第四泛音中的某些泛音可能会变得不稳定。所有高于第四阶 (n > 4) 的模态都是脉动稳定的。赫罗图上这种不稳定区域的位置和宽度主要取决于恒星的质量、光度和金属丰度。相关性的总体性质如下：（1）对于相同的质量和光度，随着金属丰度的增加，不稳定区域变得稍宽，并移动到较低的有效温度。 (2) 对于给定的化学丰度，随着其光度的增加或质量的减少，不稳定区域变得更宽并移动到更低的有效温度。对于位于不稳定带外部的发光红色变量，对流和振荡之间的动态耦合平衡甚至可能超过热力学耦合。对于低温红变量的脉动不稳定性，不能再忽视湍流粘度。对于更高模态，湍流粘性的影响变得越来越重要，并最终可能成为脉动的主要阻尼机制。
We have performed a linear pulsational stability survey of six series of long-period variable models with M = 1.0 M☉, L = 3000-8000 L☉, and (X, Z) = (0.700, 0.020), (0.735, 0.005). The dynamic and thermodynamic couplings between convection and oscillations are treated by using a statistical theory of nonlocal and time-dependent convection. The results show that the fundamental and all the low overtones are always pulsationally unstable for the low-temperature models when the coupling between convection and oscillations is ignored. When the coupling is considered, there is indeed a "Mira" pulsational instability region outside of the Cepheid instability strip on the H-R diagram. The coolest models near the Hayashi track are pulsationally stable. Toward high temperature, the fundamental mode becomes unstable first and then the first overtone. Some one of the second to fourth overtones may become unstable for the hotter models. All the modes higher than the fourth (n > 4) are pulsationally stable. The position and the width of such an instability region on the H-R diagram critically depends on the mass, luminosity, and metal abundance of the star. The overall properties of the dependence are the following: (1) For the same mass and luminosity, the instability region becomes slightly wider and moves to lower effective temperatures as the metal abundance increases. (2) For a given chemical abundance, the instability region becomes wider and moves to the lower effective temperature as its luminosity increases or its mass decreases. For the luminous red variables seated outside the instability strip the dynamic coupling between convection and oscillations balances or may even overtake the thermodynamic coupling. Turbulent viscosity can no longer be ignored for the pulsational instability of the low-temperature red variables. The effect of turbulent viscosity becomes more and more important for higher modes, and may finally become the main damping mechanism of the pulsation.