A new model for the ν1 vibrational band of HCN in cometary comae, with application to three comets
A new model for the ν1 vibrational band of HCN in cometary comae, with application to three comets
复制标题
彗星彗发中 HCN ν1 振动带的新模型，适用于三颗彗星
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
D. Prialnik
中科院分区：
文献类型：
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作者：
M. Lippi;G. Villanueva;M. DiSanti;H. Böhnhardt;M. Mumma;B. Bonev;D. Prialnik
目标。氰化氢（HCN）在彗星大气中有效地辐射红外波长，需要一个新的量子带模型来正确解释高分辨率光谱。8 P/Tuttle彗星、C/2007 W1（Boattini）和C/2008 Q3（Garradd）的HCN光谱已经被我们的团队在甚大望远镜（VLT）上使用高分辨率的CRIRES（CRyogenic CRyogenic cryogenic red Echelle Spectometer）记录下来，最终为我们新开发的模型提供了一个很好的测试。方法.我们利用最新的光谱参数建立了HCN的ν1基函数的量子带模型，并用它反演了上述三颗彗星中的HCN。对于每颗彗星，我们在3 μm附近的光谱区域采集了几条HCN谱线，并检索了分子产生速率，混合比和旋转温度。结果与其他彗星相比，8 P/Tuttle的HCN含量相对较低，而C/2007 W1（Boattini）似乎较丰富，C/2008 Q3（Garradd）则正常。在8 P/Tuttle中观察到的HCN的空间分布是对称的，与核的各向同性释气一致，而在彗星C/2007 W1中，我们观察到反太阳方向的HCN不对称过量。我们研究了HCN-CN的父母通过比较我们的生产率比（HCN/H2O）与那些CN/OH在光学波长。在彗星C/2007 W1中，这两个混合比是相当的，而在8 P/Tuttle中，我们推导出的HCN丰度太低，不能支持HCN分子作为CN自由基的唯一母体。
Aims. Hydrogen cyanide (HCN) radiates effectively at infrared wavelengths in cometary atmospheres, and a new quantum-band model is needed to properly interpret high-resolution spectra. HCN spectra of comets 8P/Tuttle, C/2007 W1 (Boattini), and C/2008 Q3 (Garradd) have been recorded by our team using the high-resolution CRyogenic InfraRed Echelle Spectometer (CRIRES) at the Very Large Telescope (VLT), ultimately posing an excellent test for our newly developed model. Methods. We developed a quantum-band model for the ν1 fundamental of HCN using the latest spectroscopic parameters available and with it retrieved HCN in the above mentioned three comets. For each comet, we sampled several lines of HCN in the spectral region near 3 μm, and retrieved molecular production rates, mixing ratios, and rotational temperatures. Results. When compared to other comets, 8P/Tuttle is relatively depleted in HCN, while C/2007 W1 (Boattini) appears to be enriched and C/2008 Q3 (Garradd) normal. The spatial profile of HCN observed in 8P/Tuttle is symmetric, consistent with isotropic outgassing from the nucleus, while in comet C/2007 W1 we observed an asymmetric excess of HCN in the anti-solar direction. We investigated the HCN-CN parentage by comparing our production rate ratios (HCN/H2O) with those of CN/OH derived at optical wavelengths. In comet C/2007 W1 the two mixing ratios are comparable, while in 8P/Tuttle our derived HCN abundance is too low to support the HCN molecule as the only parent of the CN radical.