IRIS Mg ii Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole
IRIS Mg ii Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole
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DOI：
10.3847/1538-4357/ab5db1
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
Akiko Tei;S. Gunár;P. Heinzel;T. Okamoto;J. Štěpán;S. Jejčič;K. Shibata
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作者：
Akiko Tei;S. Gunár;P. Heinzel;T. Okamoto;J. Štěpán;S. Jejčič;K. Shibata
我们研究了在太阳极冕洞中用IRIS观测到的Mg ii h和k线的离边针状体。我们分析了获得的光谱的大数据集，以提取有关线强度、位移和宽度的定量信息。观测到的Mg ii谱线在低海拔处宽而双峰，在中海拔处宽而平顶，在高海拔处窄而单峰，多普勒频移最大。我们使用一维非LTE垂直板模型（即，考虑偏离局部热力学平衡的模型），以解释观测结果并研究针状物沿着视线（LOS）的叠加如何影响合成Mg ii线轮廓。所使用的多板模型是静态的，即，没有任何LOS速度，或者假设随机分配的各个板的LOS速度，表示针状物动态。我们进行了这样的单板坯和多板坯建模的一组广泛的模型输入参数，并显示了依赖于这些参数的Mg II线轮廓。我们表明，所观察到的线宽的h和k线的配置文件的强烈影响的存在下，多个针状沿着LOS。我们后来表明，在更高的海拔地区获得的配置文件可以复制的单板模型代表个别骨针。我们发现，具有随机分布的LOS速度范围为-25到25 km s-1的多板模型可以很好地再现在中等高度观测到的Mg ii剖面的宽度和形状。
We investigated the off-limb spicules observed in the Mg ii h and k lines by IRIS in a solar polar coronal hole. We analyzed the large data set of obtained spectra to extract quantitative information about the line intensities, shifts, and widths. The observed Mg ii line profiles are broad and double peaked at lower altitudes, broad but flat topped at middle altitudes, and narrow and single peaked with the largest Doppler shifts at higher altitudes. We use one-dimensional non-LTE vertical slab models (i.e., models that consider departures from local thermodynamic equilibrium) in single-slab and multi-slab configurations to interpret the observations and to investigate how a superposition of spicules along the line of sight (LOS) affects the synthetic Mg ii line profiles. The used multi-slab models either are static, i.e., without any LOS velocities, or assume randomly assigned LOS velocities of individual slabs, representing the spicule dynamics. We conducted such single-slab and multi-slab modeling for a broad set of model input parameters and showed the dependence of the Mg ii line profiles on these parameters. We demonstrated that the observed line widths of the h and k line profiles are strongly affected by the presence of multiple spicules along the LOS. We later showed that the profiles obtained at higher altitudes can be reproduced by single-slab models representing individual spicules. We found that the multi-slab model with a random distribution of the LOS velocities ranging from −25 to 25 km s−1 can well reproduce the width and the shape of Mg ii profiles observed at middle altitudes.