论文标题
彗星67p/churyumov-gerasimenko的昏迷中的水矫形比率
Water Ortho-to-Para ratio in the coma of comet 67P/Churyumov-Gerasimenko
论文作者
论文摘要
H $ _2 $ O和NH $ _3 $的核旋转异构体的丰度比已在大约两打彗星中测量，平均值对应于$ \ sim $ 30 k的核旋转温度。然而，通常也观察到平衡的水矫正比（OPR）为3。 Rosetta上的Virtis（Virtis-H）的H频道提供了高分辨率2.5--2.9 $ $ m $ m的光谱H $ _2 $ o _2 $ o Vapor coma coma coma coma coma 67p/churyumov-gerasimenko（67p），适用于确定此comet水中水的OPR。分析了以肢体的观看几何形状获得的大型Virtis-H光谱数据集，涵盖了从1.24到2.73 AU的HeliePentric距离，从几百米到$ 100公里。 OPR与H $ _2 $ O旋转温度和色谱柱密度一起得出了每个光谱。 $ν_1$，$ν_1+ν_3-ν_1$和$ν_2+ν_2+ν_3-ν_2$在2.774--2.910 $ $ m范围内用于计算强度的$ν_3$在2.67 $ m $ m $ m $ m $ m $ m $ m $ m $ m $μm中的效果，该效果是在optical dectial tater fressiation farsifation tater tater效果，该效果是多么的效果。 $ f _ {\ rm atten} $。大多数OPR的确定受不透明效应的强烈影响，如OPR和柱密度之间观察到的抗相关性所证明，OPR与衰减因子$ f _ {\ rm atten} $之间的相关性。基于在低公开条件下获得的辐射传输计算和OPR值，我们的OPR为2.94 $ \ pm $ $ 0.06 $ 0.06。在67p的昏迷中测得的水OPR与实验室实验一致，表明从水冰中热解剖的水蒸气的统计值为3，而不论过去的水冰的过去构成过程如何。
Abundance ratios of the nuclear-spin isomers of H$_2$O and NH$_3$ have been measured in about two dozen comets, with a mean value corresponding to a nuclear-spin temperature of $\sim$ 30 K. The real meaning of these unequilibrated nuclear-spin abundance ratios is still debated. However, an equilibrated water ortho-to-para ratio (OPR) of 3 is also commonly observed. The H channel of VIRTIS (VIRTIS-H) on board Rosetta provided high-resolution 2.5--2.9 $μ$m spectra of H$_2$O vapour in the coma of comet 67P/Churyumov-Gerasimenko (67P), which are suitable for the determination of the OPR of water in this comet. A large dataset of VIRTIS-H spectra obtained in limb-sounding viewing geometry was analysed, covering heliocentric distances from 1.24 to 2.73 au and altitudes from a few hundred metres to $>$ 100 km. The OPR, together with the H$_2$O rotational temperature and column density, were derived for each spectra. The weak lines of the $ν_1$, $ν_1+ν_3-ν_1$ and $ν_2+ν_3-ν_2$ bands in the 2.774--2.910 $μ$m range were used to calculate by how much the strong $ν_3$ band centred at 2.67 $μ$m is attenuated due to optical depth effects, expressed by the attenuation factor $f_{\rm atten}$. Most OPR determinations are strongly affected by opacity effects, as demonstrated by the observed anti-correlation between the OPR and the column density, and the correlation between the OPR and attenuation factor $f_{\rm atten}$. Based on both radiative transfer calculations and OPR values obtained in low-opacity conditions, we derive an OPR of 2.94 $\pm$ 0.06 for comet 67P. The water OPR measured in the coma of 67P is consistent with laboratory experiments showing that water vapour that has thermally desorbed from water ice has a statistical value of 3, regardless of the past formation process of water ice.
