On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges
On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges
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DOI：
10.3847/1538-4357/aab9b9
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发表时间：
2018-03
期刊：
影响因子：
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通讯作者：
D. N'obrega-Siverio;F. Moreno-Insertis;J. Mart'inez-Sykora
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作者：
D. N'obrega-Siverio;F. Moreno-Insertis;J. Mart'inez-Sykora
浪涌是太阳大气中普遍存在的冷喷射，通常与紫外线爆发或日冕喷流等瞬态现象有关。最近的观测结果表明，从界面区域成像光谱仪浪涌，虽然传统上与色球线，可以表现出增强的发射Si IV与明亮的光谱轮廓比平均过渡区（TR）。在本文中，我们解释了为什么浪涌是自然的网站，以显示增强发射率在TR线。我们进行了2.5维辐射磁流体数值实验，包括硅和氧的非平衡（NEQ）电离的Bifrost代码。一个浪涌获得作为一个副产品的磁通量出现; TR包围出现的域强烈影响NEQ效应：假设统计平衡将产生一个没有Si IV和O IV离子在大部分区域。研究了Si iv λ1402.77和O iv λ1401.16谱线的浪涌等离子体发射特性，发现：（a）光学薄损耗和热传导的时间尺度很短，导致偏离统计平衡;（B）浪涌在Si iv谱线上发射较多，Si iv与O iv的发射率比大于标准TR。使用合成光谱，我们得出结论的视线效应的重要性：考虑到所涉及的几何形状的浪涌，视线可以削减发射层在小角度和/或交叉多次，造成突出的，空间上间歇性的增亮Si IV和O IV。
Surges are ubiquitous cool ejections in the solar atmosphere that often appear associated with transient phenomena like UV bursts or coronal jets. Recent observations from the Interface Region Imaging Spectrograph show that surges, although traditionally related to chromospheric lines, can exhibit enhanced emission in Si iv with brighter spectral profiles than for the average transition region (TR). In this paper, we explain why surges are natural sites to show enhanced emissivity in TR lines. We performed 2.5D radiative-MHD numerical experiments using the Bifrost code including the nonequilibrium (NEQ) ionization of silicon and oxygen. A surge is obtained as a by-product of magnetic flux emergence; the TR enveloping the emerged domain is strongly affected by NEQ effects: assuming statistical equilibrium would produce an absence of Si iv and O iv ions in most of the region. Studying the properties of the surge plasma emitting in the Si iv λ1402.77 and O iv λ1401.16 lines, we find that (a) the timescales for the optically thin losses and heat conduction are very short, leading to departures from statistical equilibrium, and (b) the surge emits in Si iv more and has an emissivity ratio of Si iv to O iv larger than a standard TR. Using synthetic spectra, we conclude the importance of line-of-sight effects: given the involved geometry of the surge, the line of sight can cut the emitting layer at small angles and/or cross it multiple times, causing prominent, spatially intermittent brightenings in both Si iv and O iv.