C/2004 Q2（Machholz）彗星挥发物的亚毫米光谱观测
Submillimetric spectroscopic observations of volatiles in comet C/2004 Q2 (Machholz)
摘要：
我们的目标是确定生产率的几个父母和产品挥发物和12 C/13 C同位素碳比的长周期彗星C/2004 Q2（Machholz），这是可能来自奥尔特云。2005年1月，在日心距离为1.2天文单位处，利用亚毫米望远镜（SMT）进行高分辨率光谱观测，测量了彗发中几个分子的高信噪比谱线发射。我们已经得到了几种挥发物（CH_3OH，HCN，H_（13）CN，HNC，H_2CO，CO和CS）的生产率通过比较观察到的和模拟的线积分强度。此外，CH 3OH（7-6）系列的多线观测允许我们使用旋转图技术来估计旋转温度。我们发现，这些线采样的水平的CH 3 OH的人口分布可以描述的旋转温度为40 \pm 3 K。推导出的相对于氰化氢的混合比为CO/CH 3OH/H2 CO/CS/HNC/H13 CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1，假设由于观测时的不确定星历和望远镜指向误差，指向偏移为8”。在C/2004 Q2（Machholz）中测得的相对分子丰度介于奥尔特云彗星中获得的低到典型值之间，这表明它以前曾访问过内部太阳系并经历过热处理。HNC/HCN丰度比约为3.1%，与其他彗星相当，说明了对日心距离的依赖性，并且可能由低温大气中的离子分子化学过程来解释。根据试验性H13 CN检测，H12 CN/H13 CN同位素对的97 \pm 30的测量值与大地值一致。
英文摘要：
We aim to determine the production rates of several parent and product volatiles and the 12C/13C isotopic carbon ratio in the long-period comet C/2004 Q2 (Machholz), which is likely to originate from the Oort Cloud. The line emission from several molecules in the coma was measured with high signal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU by means of high-resolution spectroscopic observations using the Submillimeter Telescope (SMT). We have obtained production rates of several volatiles (CH3OH, HCN, H13CN, HNC, H2CO, CO and CS) by comparing the observed and simulated line-integrated intensities. Furthermore, multiline observations of the CH3OH (7-6) series allow us to estimate the rotational temperature using the rotation diagram technique. We find that the CH3OH population distribution of the levels sampled by these lines can be described by a rotational temperature of 40 \pm 3 K. Derived mixing ratios relative to hydrogen cyanide are CO/CH3OH/H2CO/CS/HNC/H13CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a pointing offset of 8" due to the uncertain ephemeris at the time of the observations and the telescope pointing error. The measured relative molecular abundances in C/2004 Q2 (Machholz) are between low- to typical values of those obtained in Oort Cloud comets, suggesting that it has visited the inner solar system previously and undergone thermal processing. The HNC/HCN abundance ratio of ~3.1% is comparable to that found in other comets, accounting for the dependence on the heliocentric distance, and could possibly be explained by ion-molecule chemical processes in the low-temperature atmosphere. From a tentative H13CN detection, the measured value of 97 \pm 30 for the H12CN/H13CN isotopologue pair is consistent with a telluric value.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
