The exceptionally favorable close approach of Jupiter-family comet 46P/Wirtanen in 2018 December enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, HI. We sampled emissions from H₂O, HCN, C₂H₂, NH₃, C₂H₆, and CH₃OH on UT 2018 December 21 using two instrumental settings that spanned the 2.9–3.6 μm spectral region. We also obtained a sensitive 3σ upper limit for H₂CO and for the rarely studied molecule HC₃N. We report rotational temperatures, production rates, and mixing ratios (relative to H₂O as well as to C₂H₆). We place our results in context by comparing them with other comets observed at near-IR wavelengths. We also compare our results with those obtained using the NIRSPEC-2 spectrograph on Keck II on UT December 17 and 18 and with results obtained from iSHELL on other dates during the same apparition. Within 1–2σ uncertainty, production rates obtained for all molecules in this work were consistent with those obtained using NIRSPEC-2 except H₂O, indicating low-level variability on a timescale of days. Mixing ratios with respect to H₂O in 46P/Wirtanen were consistent with corresponding values from NIRSPEC-2 within the uncertainty with the exception of CH₃OH, which yielded a higher ratio on December 21. Our measurements afforded a high temporal resolution that spanned ∼2/3 of the rotational period of 46P/Wirtanen, enabling us to test short-term variability in the production rates of H₂O and HCN due to rotational effects. Both H₂O and HCN production rates showed similar temporal variability, resulting in nearly constant HCN/H₂O.

木星族彗星46P / Wirtanen的非常有利贴近于2018年十二月启用其主要挥发性成分的特性与极高的空间分辨率，并使用在上Maunakea，H美国宇航局红外望远镜的光谱仪ISHELL敏感性我。我们采样选自H排放₂ O，HCN，C ₂ ħ ₂，NH ₃，C ₂ H ^ ₆和CH ₃使用所跨越的2.9-3.6 2个仪器设置在UT 2018年12月21 OH μ中号的光谱区域。我们还获得了H ₂ CO和很少研究的分子HC的敏感的3σ上限₃ N.我们报告旋转的温度下，生产速率，和混合比（相对于成H ₂ O作为以及至C ₂ ħ ₆）。通过将它们与在近红外波长观察到的其他彗星进行比较，我们将其结果置于上下文中。我们还将我们的结果与使用12月17日和18日在UT的Keck II上使用NIRSPEC-2光谱仪获得的结果，以及在同一次幻影中在其他日期从iSHELL获得的结果进行了比较。在1-2个σ的不确定性，对于这项工作的所有分子得到的生产速率分别为与获得的那些使用NIRSPEC-2除H外一致₂ O，指示天的时间尺度低级别的可变性。相对于H _2的混合比在46P / Wirtanen中的O与不确定性范围内NIRSPEC-2的相应值一致，但CH ₃ OH除外，该值在12月21日产生了更高的比率。我们的测量提供了一个高的时间分辨率，跨越了旋转的2/3左右。周期为46P / Wirtanen，这使我们能够测试由于旋转效应而产生的H ₂ O和HCN生产率的短期变化。H ₂ O和HCN的生产率均显示出类似的时间变异性，导致HCN / H ₂ O几乎恒定。