First Comet Observations with NIRSPEC-2 at Keck: Outgassing Sources of Parent Volatiles and Abundances Based on Alternative Taxonomic Compositional Baselines in 46P/Wirtanen
First Comet Observations with NIRSPEC-2 at Keck: Outgassing Sources of Parent Volatiles and Abundances Based on Alternative Taxonomic Compositional Baselines in 46P/Wirtanen
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DOI：
10.3847/psj/abd03c
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发表时间：
2021-04
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通讯作者：
B. Bonev;N. Dello Russo;M. DiSanti;E. Martin;G. Doppmann;R. Vervack;G. Villanueva;H. Kawakita;E. Gibb;M. Combi;N. Roth;M. Saki;A. McKay;M. Cordiner;D. Bodewits;J. Crovisier;N. Biver;A. Cochran;Y. Shou;Y. Khan;K. Venkataramani
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作者：
B. Bonev;N. Dello Russo;M. DiSanti;E. Martin;G. Doppmann;R. Vervack;G. Villanueva;H. Kawakita;E. Gibb;M. Combi;N. Roth;M. Saki;A. McKay;M. Cordiner;D. Bodewits;J. Crovisier;N. Biver;A. Cochran;Y. Shou;Y. Khan;K. Venkataramani
对Keck II望远镜的NIRSpec仪器进行了重大升级，及时完成了对2018年12月飞临地球的46P/Wirtanen彗星的近红外光谱观测。这些研究确定了几种挥发物的丰度，包括C2H2、C2H6、CH3OH、NH3、HCN、H2CO和H2O。气体旋转温度和柱密度的长缝空间分布可以诊断彗发中冰粒的存在，并了解不同的挥发物是否与共同或不同的放气源有关。这些空间分布表明，C2H2、C2H6和HCN有共同的放气源，而H2O和CH3OH有额外的、更广泛的源。这些发现与空间飞行任务(Rosetta和EPOXI)的观测相结合，促使继续进行研究，以解决在更大的彗星样本中C2H6、C2H2和HCN是否有共同的释放来源(似乎与二氧化碳有关)，以及与H2O和CH3OH相比，这些物种的释放是否存在系统性差异。挥发物的丰度是相对于H2O和C2H6报告的，这是传统的做法。选择C2H6虽然不是独一无二的，但表明了将彗星中母体挥发分的化学分类扩展到额外的成分“基线”的价值，而且重要的是，彗发丰度与空间分布揭示的潜在挥发关联之间的更紧密结合。我们关于成分和出气来源的调查结果包括与46P/Wirtanen作为未来航天器目标的未来评估有关的信息。
A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H2O and CH3OH. Abundances of volatiles are reported relative to H2O, as traditionally done, as well as C2H6. While not unique, the choice of C2H6 demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional “baselines” and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target.