A Search for Variation in the H2O Ortho-Para Ratio and Rotational Temperature in the Inner Coma of Comet C/2004 Q2 (Machholz)
A Search for Variation in the H2O Ortho-Para Ratio and Rotational Temperature in the Inner Coma of Comet C/2004 Q2 (Machholz)
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寻找彗星 C/2004 Q2 (Machholz) 内彗发中 H2O 正对比和旋转温度的变化
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发表时间：
2007
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通讯作者：
N. Russo
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作者：
B. Bonev;M. Mumma;G. Villanueva;M. DiSanti;R. Ellis;K. Magee;N. Russo
我们展示了奥尔特云彗星C/2004 Q2 （Machholz）内彗发中H2O的旋转温度和正对位比的空间分辨测量结果。我们的结果是基于在2.9 μm附近通过“热带”荧光直接同时检测邻水和对水。我们发现随着原子核距离的增加（高达~1000 km），旋转温度有明显的下降。随着核距的增加，正对位比保持不变（在随机不确定性范围内），接近统计平衡值3.0（2.86±0.06[0.17]，分别包含随机[系统]不确定性），导致自旋温度Tspin≥34 K。我们将目前的结果与其他彗星的报道结果进行了比较，并讨论了解释由测量的正对位比推断出的自旋温度的困难。对核自旋转化的特殊条件的进一步了解，将检验得出的自旋温度在多大程度上反映了彗星冰的形成历史或加工记录。
We present spatially resolved measurements of the rotational temperature and ortho-para ratio for H2O in the inner coma of the Oort Cloud comet C/2004 Q2 (Machholz). Our results are based on direct simultaneous detections of ortho-H2O and para-H2O via "hot-band" fluorescence near 2.9 μm. We find a well-defined decline in rotational temperature with increasing nucleocentric distance (up to ~1000 km). The ortho-para ratio remains constant (within stochastic uncertainty) with increasing nucleocentric distance and is close to the statistical equilibrium value of 3.0 (2.86 ± 0.06 [0.17], including, respectively, stochastic [systematic] uncertainty), resulting in spin temperature Tspin ≥ 34 K. We compare the present results with those reported for other comets and discuss the difficulties in interpreting spin temperatures deduced from measured ortho-para ratios. Improved understanding of the special conditions that enable nuclear spin conversion would test the extent to which derived spin temperatures reflect the formative history or the processing record of cometary ices.