蟹状星云细丝中稀有气体氢和羟基阳离子鉴别的可能性
Exploring the Possibility of Identifying Hydride and Hydroxyl Cations of Noble Gas Species in the Crab Nebula Filament
摘要：
第一次在蟹状星云超新星遗迹中发现氩离子（ArH+）是由赫歇尔在亚毫米和远红外领域宣布的。最近，利用SOFIA在行星状星云（NGC 7027）中发现了氢氦阳离子（HeH+）。氖的元素丰度比氩高得多。然而，在太空中是否存在氘离子（NeH+）还有待证实。尽管羟基自由基（OH）以中性或阳离子形式非常丰富，但这种稀有气体的羟基阳离子（即，ArOH+，NeOH+和HeOH+）尚未在太空中被识别。在这里，我们采用光谱合成代码来检查的氢化物和羟基阳离子的各种同位素的Ar，Ne，和He在蟹状星云灯丝的化学演化，并计算其线发射率和内在的线表面亮度。我们成功地解释了所观察到的ArH+（617和1234 GHz），OH+（971 GHz）和H2（2.12微米）的一个过渡过渡的两个过渡的表面亮度。我们还解释了所观察到的各种分子和原子的跃迁之间的表面亮度比。我们发现，当氢数密度为~10^4-10^6 cm^-3，每H2的宇宙射线电离率为~10^-11-10^-10 s^-1时，我们的模型再现了观测到的总体特征。我们讨论了检测一些氢化物和羟基阳离子在螃蟹和弥漫的云环境的可能性。这些分子的一些过渡突出未来的天文探测。
英文摘要：
The first identification of the argonium ion (ArH+) towards the Crab Nebula supernova remnant was proclaimed by the Herschel in the sub-millimeter and far-infrared domain. Very recently the discovery of the hydro-helium cation (HeH+) in the planetary nebula (NGC 7027) has been reported by using the SOFIA. The elemental abundance of neon is much higher than that of the argon. However, the presence of neonium ions (NeH+) is yet to be confirmed in space. Though the hydroxyl radicals (OH) are very abundant either in neutral or in the cationic form, hydroxyl cations of such noble gases (i.e., ArOH+, NeOH+, and HeOH+) are yet to be identified in space. Here, we employ a spectral synthesis code to examine the chemical evolution of the hydride and hydroxyl cations of the various isotopes of Ar, Ne, and He in the Crab Nebula filament and calculate their line emissivity and intrinsic line surface brightness. We successfully explain the observed surface brightness of two transitions of ArH+ (617 and 1234 GHz), one transition of OH+ (971 GHz), and one transition of H2 (2.12 micrometer). We also explain the observed surface brightness ratios between various molecular and atomic transitions. We find that our model reproduces the overall observed features when a hydrogen number density of ~10^4-10^6 cm^-3 and a cosmic-ray ionization rate per H2 of ~10^-11-10^-10 s^-1 are chosen. We discuss the possibility of detecting some hydride and hydroxyl cations in the Crab and diffuse cloud environment. Some transitions of these molecules are highlighted for future astronomical detection.
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