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arXiv 1201.4668astro-ph.SR
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冷日珥等离子体热模的稳定性

Stability of thermal modes in cool prominence plasmas

Roberto Soler, Jose Luis Ballester, Susanna Parenti

摘要:

背景:磁流体动力学热模可能在太阳辐射的形成、等离子体凝聚和演化中起着重要作用。由于辐射损失和加热之间的不平衡而导致的不稳定的热模式可以导致快速的等离子体冷却和冷凝。因此,辐射损失函数的准确描述对于这一过程至关重要。目的:研究具有类似于太阳能等离子体性质的无界均匀等离子体中热模的稳定性。考虑了部分电离的影响。三种不同的参数化的辐射损失函数。方法:通过简正模分析,我们研究了叠加在平衡态上的线性非绝热微扰。我们找到了一个近似的热模不稳定性判据,而精确的线性增长率通过数值求解一般色散关系得到。热扰动的稳定性进行了比较,考虑三种不同的损失函数。结果如下:使用来自CHIANTI原子数据库的辐射损失的最新计算,我们发现,热模式可能是不稳定的,在较低的温度比先前存在的损失函数预测的双折射。热不稳定性可在低至约15,000 K的温度下发生。线性增长率表明,这种不稳定性可能对冷日珥凝聚的动力学和演化有重要影响。

英文摘要:

Context: Magnetohydrodynamic thermal modes may play an important role in the formation, plasma condensation, and evolution of solar prominences. Unstable thermal modes due to unbalance between radiative losses and heating can lead to rapid plasma cooling and condensation. An accurate description of the radiative loss function is therefore crucial for this process. Aims: We study the stability of thermal modes in unbounded and uniform plasmas with properties akin to those in solar prominences. Effects due to partial ionization are taken into account. Three different parametrizations of the radiative loss function are used. Methods: By means of a normal mode analysis, we investigate linear nonadiabatic perturbations superimposed on the equilibrium state. We find an approximate instability criterion for thermal modes, while the exact linear growth rate is obtained by numerically solving the general dispersion relation. The stability of thermal disturbances is compared for the three different loss functions considered. Results: Using up-to-date computations of radiative losses derived from the CHIANTI atomic database, we find that thermal modes may be unstable in prominences for lower temperatures than those predicted with previously existing loss functions. Thermal instability can take place for temperatures as low as 15,000 K, approximately. The obtained linear growth rates indicate that this instability might have an important impact on the dynamics and evolution of cool prominence condensations.

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