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arXiv 0903.1492astro-ph.SR
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MG I 457.1 NM线路的温度诊断特性

The Temperature Diagnostic Properties of the MG I 457.1 NM Line

Oystein Langangen, Mats Carlsson

摘要:

我们分析了Mg I 457.1 nm谱线的重要形成过程。这条线是一条内部耦合线,并且源函数接近于局部热力学平衡(LTE)值。强耦合到当地的温度和相对较高的人口较低的水平(基态的镁I),使这条线在较低的色球/温度最低区域的温度诊断的理想候选人。由于非LTE电离,将探测的温度与绝对物理高度联系起来并不简单。我们分析了非LTE效应,发现低能级的光电离和级联碰撞复合共同主导电离平衡。适当考虑紫外线的线覆盖效应是获得正确的光电离率的必要条件。识别线中的主要非LTE效应使我们能够构建一个典型的模型原子,非常适合计算要求高的任务,例如全3D和/或时间相关的辐射转移。此外,我们分析了诊断潜力,这条线在类太阳大气中的温度,通过合成线从一系列参数化的大气模式。这些模型都是用固定的有效温度,但在能量方程中加入一个可变的热量项,以获得不同高度的色球温升。我们的结论是,该线具有显着的潜力,在诊断较低的色球层温度结构,特别是对于较冷的大气,如太阳黑子。

英文摘要:

We analyze the important formation processes for the Mg I 457.1 nm line. This line is an intercom- bination line and the source function is close to the local thermodynamic equilibrium (LTE) value. The strong coupling to the local temperature and the relatively high population of the lower level (the ground state of Mg I) makes this line an ideal candidate for temperature diagnostics in the lower chromosphere/temperature minimum region. Linking the temperature probed to an absolute phys- ical height is non trivial because of Non-LTE ionization. We analyze the Non-LTE effects and find that photo-ionization from the lower energy levels together with cascading collisional recombination dominate the ionization balance. Taking properly into account the line-blanketing in the UV is essen- tial for obtaining the right photoionization rates. The identification of the main Non-LTE effects in the line allows us to construct a quintessential model atom, ideal for computationally demanding tasks, e.g. full 3D and/or time-dependent radiative transfer. Furthermore we analyze the diagnostic potential to temperature of this line in solar-like atmospheres, by synthesizing the line from a series of parametrized atmospheric models. These models have been constructed with fixed effective temper- ature, but with a variable heat term in the energy equation to obtain a chromospheric temperature rise at different heights. We conclude that the line has a significant potential in the diagnostics of the lower chromosphere temperature structure, especially for cooler atmospheres, such as sunspots.

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