行星状星云NGC 7027中氦氢化物离子（HeH $^+$）振动辐射的探测
Detection of vibrational emissions from the helium hydride ion (HeH$^+$) in the planetary nebula NGC 7027
摘要：
本文报道了在行星状星云NGC 7027中探测到氦氢化物阳离子（HeH+）的v=1-0 P（1）（3.51629微米）和P（2）（3.60776微米）振转谱线的发射。这些探测是由美国宇航局在莫纳克亚的红外望远镜设施（IRTF）上的iSHELL光谱仪获得的。这证实了Guesten等人最近报告的HeH+的发现。（2019），他们使用SOFIA空中天文台的GREAT仪器在149.137微米处观察到其纯旋转J=1-0跃迁。测量的HeH+ v=1-0 P（1）线的通量与我们对NGC 7027中HeH+的形成、破坏和激发的模型符合得很好。然而，J=1-0纯旋转线的测量强度明显超过模型预测，v=1-0 P（2）线的测量强度也是如此，分别超过2.9和2.3倍。这些差异的可能原因进行了讨论。我们对NGC 7027的观测，覆盖了3.26 - 3.93微米的光谱区域，导致检测到60多条谱线，包括9条来自CH+的振转辐射。后者是第一次在天文源中检测到。
英文摘要：
We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) rovibrational lines of the helium hydride cation (HeH+) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J=1-0 transition at 149.137 micron. The flux measured for the HeH+ v=1-0 P(1) line is in good agreement with our model for the formation, destruction and excitation of HeH+ in NGC 7027. The measured strength of the J=1-0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v=1-0 P(2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26 - 3.93 micron spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH+. The latter are detected for the first time in an astronomical source.
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