用EUVE恒星观测作为高密度太阳耀斑等离子体诊断的SDO/EVE数据中Fe XX-Fe XXII发射线的评估
An assessment of Fe XX - Fe XXII emission lines in SDO/EVE data as diagnostics for high density solar flare plasmas using EUVE stellar observations
摘要：
太阳动力学观测站的极紫外光变率实验（EVE）获得了太阳全圆盘的极紫外光（EUV）光谱，光谱分辨率为~1 A，节奏为10 s。这样的光谱分辨率通常被认为是太低的电子密度（N_e）敏感的发射线强度比的可靠测定，由于混合。然而，先前的工作已经表明，在EVE的90-60埃波长范围内，有限数量的Fe XXI特征在相对较低的耀斑密度（N_e ~ 10^11-10^12 cm^-3）下确实提供了有用的N_e诊断。在这里，我们调查，如果在EVE 90-160 A范围内的额外的高度电离的Fe线的比率可以可靠地采用作为N_e诊断。特别是，评估了这种诊断提供高N_e（~10^13 cm^-3）耀斑等离子体密度估计的潜力。我们的研究采用了X级耀斑的EVE光谱，结合极紫外探测器（EUVE）卫星对高度活跃的晚型恒星的观测，以及诊断良好的托卡马克等离子体的实验数据，两者在波长覆盖范围和光谱分辨率上都与EVE相似。在EVE数据中确定了几个电子密度值一致的比值，包括Fe XX 113.35/121.85和Fe XXII 114.41/135.79，它们作为EUVE和托卡马克结果提供的N_e诊断的可靠性是可信的。这些比值还可以用来测定太阳耀斑等离子体中高达~10^13 cm^-3的密度。
英文摘要：
The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disk Sun at a spectral resolution of ~1 A and cadence of 10 s. Such a spectral resolution would normally be considered to be too low for the reliable determination of electron density (N_e) sensitive emission line intensity ratios, due to blending. However, previous work has shown that a limited number of Fe XXI features in the 90-60 A wavelength region of EVE do provide useful N_e-diagnostics at relatively low flare densities (N_e ~ 10^11-10^12 cm^-3). Here we investigate if additional highly ionised Fe line ratios in the EVE 90-160 A range may be reliably employed as N_e-diagnostics. In particular, the potential for such diagnostics to provide density estimates for high N_e (~10^13 cm^-3) flare plasmas is assessed. Our study employs EVE spectra for X-class flares, combined with observations of highly active late-type stars from the Extreme Ultraviolet Explorer (EUVE) satellite plus experimental data for well-diagnosed tokamak plasmas, both of which are similar in wavelength coverage and spectral resolution to those from EVE. Several ratios are identified in EVE data which yield consistent values of electron density, including Fe XX 113.35/121.85 and Fe XXII 114.41/135.79, with confidence in their reliability as N_e-diagnostics provided by the EUVE and tokamak results. These ratios also allow the determination of density in solar flare plasmas up to values of ~10^13 cm^-3.
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