Quantifying the Evolution of Molecular Production Rates of Comet 21P/Giacobini–Zinner with iSHELL/NASA-IRTF
Quantifying the Evolution of Molecular Production Rates of Comet 21P/Giacobini–Zinner with iSHELL/NASA-IRTF
复制标题
使用 iSHELL/NASA-IRTF 量化彗星 21P/Giacobini-Zinner 分子生产率的演变
作者：
S. Faggi;M. Mumma;G. Villanueva;L. Paganini;M. Lippi
本文介绍了我们对21 P/Giacobini-Zinner彗星在2018年出现期间的分子表征结果。我们在四次观测中跟踪了彗星，总共八个晚上。使用NASA/IRTF（Maunakea，夏威夷）上的iSHEL-近红外高分辨率浸没式阶梯光栅光谱仪获得了21 P的高分辨率光谱。我们在（2.9-5.2）μm范围内的四个定制的iSHELL设置中检测到许多彗星发射线。在观测活动期间，CO相对于水的丰度显示出相对恒定的行为，表明水和CO的释气之间可能存在相关性。虽然21 P中的CO混合比与木星家族彗星（JFC）的参考中值一致，但乙烷相对于JFC的参考中值是耗尽的，除了一次观测运行（8月8日和9日），乙烷似乎过多。我们认为有几种可能的原因：乙烷爆发，减少水的释气，或由于核旋转的季节性影响。在近日点运行前，甲醇是过剩的参考中值相比，JFC，但它稳步下降到耗尽值在21 P的后近日点阶段，这表明可能的季节性影响。我们报告了乙炔、甲醛、氨和甲烷的3σ上限。我们测得的乙炔3σ上限和氰化氢检测值的比值与在光学波长下观察到的21 P中C2相对于CN的贫化一致。这一结果证实，21 P在负责C2生产的碳链主要挥发物中耗尽。
This paper presents results from our molecular characterization of comet 21P/Giacobini–Zinner during its 2018 apparition. We followed the comet during four observing runs, for a total of eight nights. The high-resolution spectra of 21P were acquired using iSHELL—the near-infrared high-resolution immersion echelle spectrograph on NASA/IRTF (Maunakea, Hawaii). We detected many cometary emission lines across four customized iSHELL settings in the (2.9–5.2) μm range. CO abundances relative to water displayed a relatively constant behavior during the observing campaign, suggesting a possible correlation between the outgassing of water and CO. While CO mixing ratios in 21P are consistent with the reference median value for Jupiter family comets (JFCs), ethane was depleted relative to the reference median value for JFCs, except for one observing run (August 8 and 9) in which ethane appeared overabundant. We consider several possible causes: an ethane outburst, decreasing outgassing of water, or a seasonal effect owing to nucleus rotation. In the pre-perihelion runs, methanol was overabundant compared with the reference median value for JFCs, however it decreased steadily to a depleted value during 21P’s post-perihelion phase, suggesting a possible seasonal effect. We report 3σ upper limits for acetylene, formaldehyde, ammonia, and methane. The ratios of our measured 3σ upper limits for acetylene and detections of hydrogen cyanide are consistent with the depletion of C2 relative to CN in 21P observed at optical wavelengths. This result confirms that 21P is depleted in the carbon-chain primary volatile responsible for C2 production.