Modelling the warm H2 infrared emission of the Helix nebula cometary knots Modelling the H2 emission of cometary knots
Modelling the warm H2 infrared emission of the Helix nebula cometary knots Modelling the H2 emission of cometary knots
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模拟螺旋星云彗星结的暖 H2 红外发射 模拟彗星结的 H2 发射
DOI：
10.1111/j.1365-2966.2011.19094.x
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发表时间：
2011
影响因子：
4.8
通讯作者：
Aleman I
中科院分区：
文献类型：
--
作者：
Aleman I
在行星状星云中经常可以观察到氢分子的释放。在红外H2发射线中拍摄的图像显示，至少部分分子发射是在电离区域内产生的。在最好的研究案例中，H2的发射是在彗星结（CK）中产生的，彗星状的结构被认为是嵌入电离气体中的致密中性气体团。大部分的H2排放的CKs似乎是产生在电离的扩散气体和结的中性材料之间的薄层中，在一个迷你的光解区域（mini-PDR）。然而，PDR模型发表到目前为止，不能完全解释的所有特征的氢排放的CKs。在这项工作中，我们使用光电离程序Aangabato研究了CKs的H_2发射，特别是在结的H ~+/H_0界面上产生的H_2发射，那里似乎产生了H_21-O S（1）发射的很大一部分。我们的研究结果表明，在这样一个区域的分子氢的生产可以解释所观察到的发射，特别是H2红外线的高激发温度的几个特点。我们发现，来自H2观测的温度，即使是一个单一的结，将非常强烈地依赖于所观察到的过渡，与更高的温度来自激发能级。我们还提出，在CK图像中观察到的Hα和[Nii]峰发射之间的分离可能是结与星星的距离的影响，因为对于远离中心星星的结，[Nii]线比Hα更靠近CK的边界。
Molecular hydrogen emission is commonly observed in planetary nebulae. Images taken in infrared H2emission lines show that at least part of the molecular emission is produced inside the ionized region. In the best studied case, the Helix nebula, the H2emission is produced inside cometary knots (CKs), comet-shaped structures believed to be clumps of dense neutral gas embedded within the ionized gas. Most of the H2emission of the CKs seems to be produced in a thin layer between the ionized diffuse gas and the neutral material of the knot, in a mini-photodissociation region (mini-PDR). However, PDR models published so far cannot fully explain all the characteristics of the H2emission of the CKs. In this work, we use the photoionization code Aangabato study the H2emission of the CKs, particularly that produced in the interface H+/H0of the knot, where a significant fraction of the H21–0 S(1) emission seems to be produced. Our results show that the production of molecular hydrogen in such a region may explain several characteristics of the observed emission, particularly the high excitation temperature of the H2infrared lines. We find that the temperature derived from H2observations, even of a single knot, will depend very strongly on the observed transitions, with much higher temperatures derived from excited levels. We also proposed that the separation between the Hα and [Nii] peak emission observed in the images of CKs may be an effect of the distance of the knot from the star, since for knots farther from the central star the [Nii] line is produced closer to the border of the CK than Hα.