Hypervolatiles in a Jupiter-family Comet: Observations of 45P/Honda–Mrkos–Pajdušáková Using iSHELL at the NASA-IRTF
Hypervolatiles in a Jupiter-family Comet: Observations of 45P/Honda–Mrkos–Pajdušáková Using iSHELL at the NASA-IRTF
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木星族彗星中的高挥发物：NASA-IRTF 使用 iSHELL 对 45P/Honda–Mrkos–Pajdušáková 进行观测
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发表时间：
2017
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通讯作者：
H. Weaver
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作者：
M. DiSanti;B. Bonev;N. Russo;R. Vervack;E. Gibb;N. Roth;A. McKay;H. Kawakita;L. Feaga;H. Weaver
我们在HI莫纳凯亚的美国宇航局红外望远镜设备上使用了新的高光谱分辨率交叉分散设施光谱仪ISHELL，观察了木星家族彗星(JFC)45P/本田-马尔科斯-帕杜šáková。我们报告了8个痕量母体分子(天然冰)的产水率以及产水率和相对于H2O的丰度比，这些分子是CO、CH4、H2CO、CH3OH、HCN、NH3、C2H2和C2H6，时间跨度为2017年1月6日和7日，也就是近日点后不久。与H2O和/或OH即时排放同时测量了痕量物种，这是H2O生产的替代指标，从而为确定45P的原生冰成分提供了可靠和一致的手段。其良好的地心径向速度(约−35公里S−1)允许敏感地测量“高挥发分”CO和CH4，这两种物质在JFC中的特征明显不足。我们的结果代表了迄今为止在JFC中对CO和CH4进行的最精确的地面测量，为建立关于其丰度的有意义的统计数据提供了基础。在奥尔特云彗星中，45P中CH4的丰度比(相对于H2O的0.79%±0.06%)与其测量的中值一致，而CO(0.60%±0.04%)被强烈亏损。与所有测量的彗星相比，HCN(0.049%±0.012%)被强烈亏损，CH3OH(3.6%±0.3%)被浓集，其余物种与其各自的中位数丰度一致。测得的45P的挥发性成分可能表明，冰在进入其核心之前就已经进行了处理。排放的空间分析表明，更多的挥发性物质被更多的挥发性物质释放到面向太阳的彗星半球。
We used the new high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASA Infrared Telescope Facility on Maunakea, HI, to observe Jupiter-family comet (JFC) 45P/Honda–Mrkos–Pajdušáková. We report water production rates, as well as production rates and abundance ratios relative to H2O, for eight trace parent molecules (native ices), CO, CH4, H2CO, CH3OH, HCN, NH3, C2H2, and C2H6, on 2 days spanning UT 2017 January 6/7 and 7/8, shortly following perihelion. Trace species were measured simultaneously with H2O and/or OH prompt emission, a proxy for H2O production, thereby providing a robust and consistent means of establishing the native ice composition of 45P. Its favorable geocentric radial velocity (approximately −35 km s−1) permitted sensitive measures of the “hypervolatiles” CO and CH4, which are substantially undercharacterized in JFCs. Our results represent the most precise ground-based measures of CO and CH4 to date in a JFC, providing a foundation for building meaningful statistics regarding their abundances. The abundance ratio for CH4 in 45P (0.79% ± 0.06% relative to H2O) was consistent with its median value as measured among Oort Cloud comets, whereas CO (0.60% ± 0.04%) was strongly depleted. Compared with all measured comets, HCN (0.049% ± 0.012%) was strongly depleted, CH3OH (3.6% ± 0.3%) was enriched, and the remaining species were consistent with their respective median abundances. The volatile composition measured for 45P could indicate processing of ices prior to their incorporation into its nucleus. Spatial analysis of emissions suggests enhanced release of more volatile species into the sunward-facing hemisphere of the coma.