Coronal Diagnostics from Narrowband Images Around 30.4 nm
Coronal Diagnostics from Narrowband Images Around 30.4 nm
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DOI：
10.1007/s11207-012-9974-z
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发表时间：
2012-03
期刊：
影响因子：
2.8
通讯作者：
V. Andretta;D. Telloni;G. Del Zanna-G.-Del Zanna-146786635
中科院分区：
文献类型：
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作者：
V. Andretta;D. Telloni;G. Del Zanna-G.-Del Zanna-146786635
以30.4 nm为中心的波段拍摄的图像通常用于绘制太阳盘面上HeiLy α线的辐射。该谱线是在太阳光谱中观察到的极紫外线中最强的谱线之一，也是该波长范围内提供有关上色球层或下过渡区信息的少数谱线之一。然而，当观察离边日冕时，附近Sixi 30.3 nm线的贡献可能变得很大。在这项工作中，我们的目标是估计这两条线在太阳活动最小的太阳日冕的相对贡献。我们结合联合收割机的测量，从CDS采取在2008年8月的温度和密度分布从半经验模型的日冕计算辐射的两条线，和其他代表性的日冕线（如Mgx62.5 nm，Sixii52.1 nm）。考虑到两个诊断量从线比（温度和密度）和线辐射的绝对单位，我们得到一个很好的整体观测和模型之间的匹配。我们发现，Sixiline占主导地位的Heiiline从临边以上的高达302R的流光，而它的贡献在30.4 nm波段的窄带成像预计将变得更小，甚至可以忽略不计的日冕超过302R的日冕，精确的值是强烈依赖于日冕温度分布。
Images taken in the band centered at 30.4 nm are routinely used to map the radiance of the HeiiLy α line on the solar disk. That line is one of the strongest, if not the strongest, line in the EUV observed in the solar spectrum, and one of the few lines in that wavelength range providing information on the upper chromosphere or lower transition region. However, when observing the off-limb corona, the contribution from the nearby Sixi30.3 nm line can become significant. In this work we aim at estimating the relative contribution of those two lines in the solar corona around the minimum of solar activity. We combine measurements from CDS taken in August 2008 with temperature and density profiles from semiempirical models of the corona to compute the radiances of the two lines, and of other representative coronal lines (e.g.Mgx62.5 nm, Sixii52.1 nm). Considering both diagnosed quantities from line ratios (temperatures and densities) and line radiances in absolute units, we obtain a good overall match between observations and models. We find that the Sixiline dominates the Heiiline from just above the limb up to ≈ 2R⊙in streamers, while its contribution to narrowband imaging in the 30.4 nm band is expected to become smaller, even negligible in the corona beyond ≈ 2 – 3R⊙, the precise value being strongly dependent on the coronal temperature profile.