Using the multi-instrument observations, we make the first simultaneous imaging and spectral study on the null point of a fan-spine magnetic topology during a solar flare. When magnetic reconnection occurs at the null point, the fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the H$\alpha$ images, the fan-spine structure is partly filled and outlined by the bi-directional material flows ejected from the reconnection site. The extrapolated coronal magnetic field confirms the existence of the fan-spine topology. Before and after the flare peak, the total velocity of the outflows is estimated to be about 60 km s$^{-1}$. During the flare, the Si IV line profile at the reconnection region is enhanced both in the blue-wing and red-wing. At the flare peak time, the total velocity of the outflows is found to be 144 km s$^{-1}$. Superposed on the Si IV profile, there are several deep absorption lines with the blueshift of several tens of km s$^{-1}$. The reason is inferred to be that the bright reconnection region observed in Si IV channel is located under the cooler material appearing as dark features in the H$\alpha$ line. The blueshifted absorption lines indicate the movement of the cooler material toward the observer. The depth of the absorption lines also depends on the amount of cooler material. These results imply that this kind of spectral profiles can be used as a tool to diagnose the properties of cooler material above reconnection site.

中文翻译：

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太阳耀斑期间扇脊结构零点的成像和光谱研究

使用多仪器观测，我们对太阳耀斑期间扇脊磁拓扑的零点进行了第一次同步成像和光谱研究。当磁重联发生在零点时，扇脊结构在（极）紫外线通道中变亮。在 H$\alpha$ 图像中，扇脊结构被从重联点喷射的双向物质流部分填充和勾勒出来。外推的日冕磁场证实了扇脊拓扑的存在。在耀斑峰前后，外流的总速度估计约为 60 km s$^{-1}$。在耀斑期间，重联区的 Si IV 线轮廓在蓝翼和红翼中均得到增强。在耀斑高峰时间，流出的总速度为 144 km s$^{-1}$。叠加在Si IV剖面上，有几条深吸收线，蓝移几十公里s$^{-1}$。推断原因是在 Si IV 通道中观察到的明亮重联区位于较冷材料下方，在 H$\alpha$ 线中表现为暗特征。蓝移的吸收线表示较冷的材料向观察者移动。吸收线的深度还取决于冷却器材料的数量。这些结果意味着这种光谱剖面可以用作诊断重联点上方较冷材料特性的工具。推断原因是在 Si IV 通道中观察到的明亮重联区位于较冷材料下方，在 H$\alpha$ 线中表现为暗特征。蓝移的吸收线表示较冷的材料向观察者移动。吸收线的深度还取决于冷却器材料的数量。这些结果意味着这种光谱剖面可以用作诊断重联点上方较冷材料特性的工具。推断原因是在 Si IV 通道中观察到的明亮重联区位于较冷材料下方，在 H$\alpha$ 线中表现为暗特征。蓝移的吸收线表示较冷的材料向观察者移动。吸收线的深度还取决于冷却器材料的数量。这些结果意味着这种光谱剖面可以用作诊断重联点上方较冷材料特性的工具。