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arXiv 1504.01733astro-ph.SR
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IRIS诊断的形成。IV。Mg II三重线作为低色球加热的新诊断

The Formation of IRIS diagnostics. IV. The Mg II triplet lines as a new diagnostic for lower chromospheric heating

Tiago M. D. Pereira, Mats Carlsson, Bart De Pontieu, Viggo Hansteen

摘要:

在h&k线周围的区域存在Mg II的三条次级线。在太阳光谱中,这些谱线主要出现在吸收谱线中,但在某些情况下也会变成发射谱线。这项工作的目的是研究这种三联体的形成,并调查它们可能带来的任何诊断价值。使用3D辐射磁流体动力学模拟安静的太阳和耀斑通量出现,我们合成光谱,并调查光谱特征如何响应底层大气。我们发现,发射线是罕见的,通常是由较低的色球(1500 K以上,电子密度高于10 $^{18}$ m $^{-3}$)的温度急剧上升。在这两种模拟中,谱线对柱质量>= 5 e-4 g cm $^{-2}$时发生的温度升高敏感。另外的信息也可以从峰翼比和谱线轮廓的形状中推断出来。使用NASA的界面区域成像光谱仪的观测结果,我们发现吸收和发射线轮廓与合成光谱具有相似的形状,这表明这些线代表了一个有用的诊断,补充了MgII h&k线。

英文摘要:

A triplet of subordinate lines of Mg II exists in the region around the h&k lines. In solar spectra these lines are seen mostly in absorption, but in some cases can become emission lines. The aim of this work is to study the formation of this triplet, and investigate any diagnostic value they can bring. Using 3D radiative magnetohydrodynamic simulations of quiet Sun and flaring flux emergence, we synthesize spectra and investigate how spectral features respond to the underlying atmosphere. We find that emission in the lines is rare and is typically caused by a steep temperature increase in the lower chromosphere (above 1500 K, with electron densities above 10$^{18}$ m$^{-3}$). In both simulations the lines are sensitive to temperature increases taking place at column masses >= 5e-4 g cm$^{-2}$. Additional information can also be inferred from the peak-to-wing ratio and shape of the line profiles. Using observations from NASA's Interface Region Imaging Spectrograph we find both absorption and emission line profiles with similar shapes to the synthetic spectra, which suggests that these lines represent a useful diagnostic that complements the MgII h&k lines.

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