Predicting the COSIE-C Signal from the Outer Corona up to 3 Solar Radii
Predicting the COSIE-C Signal from the Outer Corona up to 3 Solar Radii
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DOI：
10.3847/1538-4357/aadcf1
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发表时间：
2018-08
期刊：
影响因子：
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通讯作者：
G. del Zanna;J. Raymond;V. Andretta;D. Telloni;L. Golub
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文献类型：
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作者：
G. del Zanna;J. Raymond;V. Andretta;D. Telloni;L. Golub
我们提出了在太阳静止状态下预期的信号估计，这将是用EUV日冕谱成像仪在其日冕模式下（COSIE-C）获得的。COSIE-C被提议定期观测相对未被探索的外日冕，在那里我们知道许多影响下日冕和太阳风的基本过程正在发生。COSIE-C光谱带，186-205 Å，是用Hinode EIS观测到的。我们在2007年获得了1.5 R⊙的Hinode EIS观测结果，表明该光谱带在静态流光中主要由Fe xii和Fe xi组成，并且电离温度几乎是恒定的。为了估计1.5-3.1 R⊙区域的COSIE-C信号，我们使用了一个基于CHIANTI原子数据和SoHO UVCS观测的模型，该模型在两个静止的1996年流星雨的Si xii和Mg x日冕线上进行观测。我们用一个简单的密度模型、光球丰度和1.4 MK的恒定温度再现了观测到的EUV辐射。我们表明，其他理论或半经验模型无法再现观测结果。我们发现在3r⊙下的日冕COSIE-C信号应该是每3次约5次。″静态流光中的1个像素。这是前所未有的，开辟了一个重要的发现空间。我们还简要讨论了杂散光和其他太阳特征的可见性。特别地，我们提出了对活跃区域流的UVCS观测，表明与安静的太阳情况相比，信号增加。
We present estimates of the signal to be expected in quiescent solar conditions, as would be obtained with the COronal Spectrographic Imager in the EUV in its coronagraphic mode (COSIE-C). COSIE-C has been proposed to routinely observe the relatively unexplored outer corona, where we know that many fundamental processes affecting both the lower corona and the solar wind are taking place. The COSIE-C spectral band, 186–205 Å, is well-known as it has been observed with Hinode EIS. We present Hinode EIS observations that we obtained in 2007 out to 1.5 R⊙, to show that this spectral band in quiescent streamers is dominated by Fe xii and Fe xi and that the ionization temperature is nearly constant. To estimate the COSIE-C signal in the 1.5–3.1 R⊙ region we use a model based on CHIANTI atomic data and SoHO UVCS observations in the Si xii and Mg x coronal lines of two quiescent 1996 streamers. We reproduce the observed EUV radiances with a simple density model, photospheric abundances, and a constant temperature of 1.4 MK. We show that other theoretical or semi-empirical models fail to reproduce the observations. We find that the coronal COSIE-C signal at 3 R⊙ should be about 5 counts/s per 3.″1 pixel in quiescent streamers. This is unprecedented and opens up a significant discovery space. We also briefly discuss stray light and the visibility of other solar features. In particular, we present UVCS observations of an active region streamer, indicating increased signal compared to the quiet Sun cases.