Density diagnostics derived from the O iv and S iv intercombination lines observed by IRIS
Density diagnostics derived from the O iv and S iv intercombination lines observed by IRIS
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DOI：
10.1051/0004-6361/201628965
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发表时间：
2016-07
影响因子：
6.5
通讯作者：
V. Polito;G. Zanna;J. Dud'ik;H. Mason;A. Giunta;K. Reeves
中科院分区：
文献类型：
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作者：
V. Polito;G. Zanna;J. Dud'ik;H. Mason;A. Giunta;K. Reeves
利用界面区成像光谱仪（IRIS）观测到的1400 A附近Oiv 2s 22 p2P-2s 2 p24 P和Siv 3s 23 p2P-3s 3 p24 P互组合谱线的强度，为诊断太阳过渡区等离子体中的电子数密度（Ne）提供了有用的工具。我们测量了IRIS观测到的各种太阳特征中的电子数密度，包括活动区（AR）环，plage和增亮，以及2015年6月22日M 6.5级耀斑的带状物。利用Oiv线和Siv线的发射率比，我们发现我们的观测结果与AR环中发射等离子体接近等温（log T [K]= 5）和等密度（Ne = 1010.6cm-3）相一致。此外，利用Siv线比，在耀斑的脉冲阶段获得了高的电子数密度（Ne = 1013 cm-3）.我们注意到，S iv线提供了比O iv线更高的密度灵敏度范围。最后，我们研究了高密度（Ne = 1011 cm-3）对电离平衡的影响。特别是，分数离子丰度被发现向更低的温度为高密度相比，低密度的情况下。我们还探讨了非麦克斯韦电子分布对我们的诊断方法的影响。
The intensity of the O iv 2s 2 2p 2 P–2s2p 2 4 P and S iv 3 s 2 3p 2 P–3s 3p 2 4 P intercombination lines around 1400 A observed with the Interface Region Imaging Spectrograph (IRIS) provide a useful tool to diagnose the electron number density ( N e ) in the solar transition region plasma. We measure the electron number density in a variety of solar features observed by IRIS, including an active region (AR) loop, plage and brightening, and the ribbon of the 22-June-2015 M 6.5 class flare. By using the emissivity ratios of O iv and S iv lines, we find that our observations are consistent with the emitting plasma being near isothermal (log T [K] ≈ 5) and iso-density ( N e ≈ 10 10.6 cm -3 ) in the AR loop. Moreover, high electron number densities ( N e ≈ 10 13 cm -3 ) are obtained during the impulsive phase of the flare by using the S iv line ratio. We note that the S iv lines provide a higher range of density sensitivity than the O iv lines. Finally, we investigate the effects of high densities ( N e ≳ 10 11 cm -3 ) on the ionization balance. In particular, the fractional ion abundances are found to be shifted towards lower temperatures for high densities compared to the low density case. We also explored the effects of a non-Maxwellian electron distribution on our diagnostic method.