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The EUV spectrum of the Sun: SOHO, SEM, and CDS irradiances

机译：太阳的EUV光谱：SOHO，SEM和CDS辐照度

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We use calibrated extreme-UV (EUV) spectral irradiances obtained from observations with the Solar & Heliospheric Observatory (SOHO) Coronal Diagnostics Spectrometer Normal Incidence Spectrometer (NIS) to estimate the signal measured by the Solar EUV Monitor (SEM) first-order band, 260 to 340 ? (SEM 1). The NIS observes the resonance lines He?ii 304 ? and Si?xi 303 ? directly in second order. The irradiances of the other lines in the band are estimated with a differential emission measure (DEM) modelling, using updated atomic data. The observations analysed here were obtained during 1998–2011, which means that they span the maximum and minimum of Cycle 23. The current knowledge of the SEM 1 degradation is used to find effective areas during the dates of the NIS observations and to predict the SEM 1 count rates across the band. The total count rates, estimated by folding the NIS-based spectra with the SEM 1 effective areas, agree very well (within 10–20%) with the observed ones during solar minimum conditions, when the He?ii 304 ? is the dominant contribution to the band. Excellent agreement with the Solar Dynamics Observatory (SDO) Extreme ultraviolet Variability Experiment (EVE) observations is also found. On the other hand, the predicted SEM 1 count rates during the Cycle-23 maximum are significantly (by about 30%) lower than the observed ones. The solar spectrum in the SEM 1 band changes significantly during maximum conditions, with the He?ii 304 ? only contributing about 40%. A significant fraction of the observed count rates comes from coronal emission in an off-band spectral region that has recently been discovered. An explanation for the discrepancy needs further investigation.
机译：我们使用从太阳和日球天文台（SOHO）日冕诊断光谱仪法向入射光谱仪（NIS）观测获得的校准的极端UV（EUV）光谱辐照度来估算由太阳EUV监视器（SEM）一阶波段测量的信号， 260至340吗？ （SEM 1）。 NIS观察到共振线He？ii 304？和Si？xi 303吗？直接以第二顺序。使用更新的原子数据，通过差分发射测量（DEM）建模来估算该频带中其他线的辐照度。这里分析的观测值是在1998-2011年期间获得的，这意味着它们跨越了第2​​3个周期的最大和最小值。当前对SEM 1降解的了解可用于在NIS观测期间查找有效区域并预测SEM。 1个计算整个频段的费率。通过将基于NIS的光谱与SEM 1有效面积折叠，可以估算出总计数率，在太阳最低条件下，当He？ii 304≤时，与观察到的计数率非常吻合（在10％到20％之内）。是乐队的主要贡献。还发现了与太阳动力学天文台（SDO）极好的紫外线变异性实验（EVE）观测值的一致性。另一方面，在最大Cycle-23周期内预测的SEM 1计数率显着低于观察值（约30％）。使用He？ii 304？在最大条件下，SEM 1波段的太阳光谱会发生显着变化。仅贡献了约40％。观察到的计数率的很大一部分来自最近发现的带外光谱区域中的日冕发射。有关差异的解释需要进一步调查。

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