来自17 P/Holmes彗星的氰化氢和氰中大量过量的重氮
Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes
摘要：
2007年10月24日彗星17 P/Holmes爆发后不久，我们对它进行了毫米波和光学观测，得出HCN的14 N/15 N = 139 +/- 26，CN的14 N/15 N = 165 +/- 40，确定HCN与CN具有相同的非地球同位素组成。在重新分析以前发表的测量结果后，对长周期彗星C/1995 O 1（海尔-波普）也得到了同样的结论。这些结果与HCN是彗星大气中CN的主要母体这一点是一致的。相对于地球大气的15 N过量值表明，在太阳系形成的某个阶段，太阳星云中的含N挥发物经历了重要的N同位素分馏。HCN分子在被并入奥尔特云和柯伊伯带彗星之前，从未与太阳星云中的主要氮库达到同位素平衡。HCN和CN中的12 C/13 C比值测量结果与地面值一致。
英文摘要：
From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of October 24, 2007, we derive 14 N/15N = 139 +/- 26 in HCN, and 14N/15N = 165 +/- 40 in CN, establishing that HCN has the same non-terrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp) after a reanalysis of previously published measurements. These results are compatible with HCN being the prime parent of CN in cometary atmospheres. The 15N excess relative to the Earth atmospheric value indicates that N-bearing volatiles in the solar nebula underwent important N isotopic fractionation at some stage of Solar System formation. HCN molecules never isotopically equilibrated with the main nitrogen reservoir in the solar nebula before being incorporated in Oort-cloud and Kuiper-belt comets. The 12C/13C ratios in HCN and CN are measured to be consistent with the terrestrial value.
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