论文标题
揭示1D等温C-shock的一流体非理想MHD模拟中的阻力不稳定性
Revealing the drag instability in one-fluid nonideal MHD simulations of a 1D isothermal C-shock
论文作者
论文摘要
由于双极扩散,C型冲击被认为在湍流分子云中无处不在。我们研究了从GU&Chen局部线性理论中推断的1D等温C震中的阻力不稳定性是否可以出现在非理想的磁流失动力学模拟中。两种C-shock模型(具有狭窄和宽阔的稳态冲击宽度)被认为代表了恒星形成云的典型环境。单流体方法采用了电离 - 重组平衡。在1D模拟中,流入气体被正弦密度波动不断扰动,并以恒定的频率扰动。进入C-shock区域后,扰动显然会增长,直到它们在过渡到后冲击区域的过渡开始。我们表明,从模拟的生长扰动中局部提取的主要傅立叶模式的曲线与从线性分析得出的生长模式相匹配。此外,从主要模式得出的局部增长率和波频通常与线性理论中的局部增长率和波浪频率一致。因此,我们证实了模拟的1D等温C-shocks中阻力不稳定性的存在。我们还通过对模拟施加更大的振动扰动来探索不稳定性的非线性行为。我们发现阻力不稳定性可能会导致波浪陡峭,从而导致饱和扰动的生长。讨论了有关局部分析,非线性效应,一流体方法和天体物理应用的问题。
C-type shocks are believed to be ubiquitous in turbulent molecular clouds thanks to ambipolar diffusion. We investigate whether the drag instability in 1D isothermal C-shocks, inferred from the local linear theory of Gu & Chen, can appear in non-ideal magnetohydrodynamic simulations. Two C-shock models (with narrow and broad steady-state shock widths) are considered to represent the typical environment of star-forming clouds. The ionization-recombination equilibrium is adopted for the one-fluid approach. In the 1D simulation, the inflow gas is continuously perturbed by a sinusoidal density fluctuation with a constant frequency. The perturbations clearly grow after entering the C-shock region until they start being damped at the transition to the postshock region. We show that the profiles of a predominant Fourier mode extracted locally from the simulated growing perturbation match those of the growing mode derived from the linear analysis. Moreover, the local growth rate and wave frequency derived from the predominant mode generally agree with those from the linear theory. Therefore, we confirm the presence of the drag instability in simulated 1D isothermal C-shocks. We also explore the nonlinear behavior of the instability by imposing larger-amplitude perturbations to the simulation. We find that the drag instability is subject to wave steepening, leading to saturated perturbation growth. Issues concerning local analysis, nonlinear effects, one-fluid approach, and astrophysical applications are discussed.