In the present work, we study the C8 flare that occurred on 2000 September 26 at 19:49?UT and observed by the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation spectrometer from the beginning of the impulsive phase to well beyond the disappearance in the X-rays. The emission first decayed progressively through equilibrium states until the plasma reached 2-3?MK. Then, a series of cooler lines, i.e., Ca X, Ca VII, Ne VI, O IV, and Si III (formed in the temperature range log T = 4.3-6.3 under equilibrium conditions), are emitted at the same time and all evolve in a similar way. Here, we show that the simultaneous emission of lines with such a different formation temperature is due to thermal instability occurring in the flaring plasma as soon as it has cooled below ~2?MK. We can qualitatively reproduce the relative start time of the light curves of each line in the correct order with a simple (and standard) model of a single flaring loop. The agreement with the observed light curves is greatly improved, and a slower evolution of the line emission is predicted, if we assume that the model loop consists of an ensemble of subloops or strands heated at slightly different times. Our analysis can be useful for flare observations with the Solar Dynamics Observatory/Extreme ultraviolet Variability Experiment.
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机译：在当前的工作中，我们研究了2000年9月26日UT发生的C8耀斑，该太阳耀斑是从脉冲阶段开始到消失之后，由太阳和日球天文台/太阳紫外线发射光谱仪观测到的在X光片上发射首先通过平衡态逐渐衰减，直到等离子体达到2-3？MK。然后，同时发出一系列较冷的管线，即Ca X，Ca VII，Ne VI，O IV和Si III（在平衡条件下在温度范围log T = 4.3-6.3下形成），所有以类似的方式发展。在这里，我们表明，具有如此不同的形成温度的线的同时发射是由于火焰等离子体一旦冷却到约2？MK以下就发生了热不稳定性。我们可以使用单个喇叭形环路的简单（和标准）模型，以正确的顺序定性地再现每条线的光曲线的相对开始时间。如果我们假设模型回路由一组在稍微不同的时间加热的子回路或线束组成，则与观察到的光曲线的一致性会大大改善，并且可以预测线发射的缓慢发展。我们的分析对于太阳动力学天文台/极端紫外线变异性实验的火光观测很有用。
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