标题： 彗星中的CO 显示英文标题

标题： CO in distantly active comets

摘要： 大多数接近太阳的彗星的活动由冻结水的升华主导，水是彗星中最丰富的冰。 然而，一些彗星在距离太阳约3天文单位的水冰升华极限之外仍然活跃。 在遥远活跃彗星的观测记录和建模工作中，有三个天体占主导地位：长周期彗星C/1995 O1海尔-波普以及短周期彗星（具有半人马轨道）29P/施瓦斯曼-瓦赫曼1号和2060希伦。 我们总结了这三种天体已知的情况，强调它们的气体彗发。 我们从文献中计算了它们的CN/CO和CO2/CO生成率比值，并进行了讨论。 利用我们自己的数据，我们得出了这三个天体的CO生成率，以检查气体生成与不同轨道历史和/或大小之间的相关性。 我们发现轨道历史似乎在解释29P的CO生成率方面并不起重要作用。 即使29P经历了更多的太阳加热，它在相同日心距离下产生的CO比海尔-波普更多。 对这类天体的先前建模工作预测，29P应该已经去挥发化，而像海尔-波普这样的新鲜彗星则没有。 这可能表明29P的轨道历史与当前模型预测的不同，其当前轨道可能是最近才获得的。 另一方面，希伦的CO测量结果与其原始状态相比显著贫化是一致的，这可能是由于其体积更大带来的放射性加热增加，或者由于轨道历史导致的更高处理程度。 观测到的光谱线轮廓表明，在29P和海尔-波普大约5-6天文单位处发生了冰粒的发展和升华，这可能是在遥远活跃彗星中的一个共同特征，并且是所有在5天文单位以内的彗星的重要挥发物来源。 相比之下，狭窄的CO线轮廓表明CO在超过约4天文单位处起源于核，而不是扩展区域。 显示英文摘要

摘要： Activity of most comets near the Sun is dominated by sublimation of frozen water, the most abundant ice in comets. Some comets, however, are active well beyond the water-ice sublimation limit of ~3 AU. Three bodies dominate the observational record and modeling efforts for distantly active comets: the long-period comet C/1995 O1 Hale-Bopp and the short-period comets (with Centaur orbits) 29P/Schwassmann Wachmann 1 and 2060 Chiron. We summarize what is known about these three objects emphasizing their gaseous comae. We calculate their CN/CO and CO2/CO production rate ratios from the literature and discuss implications. Using our own data we derive CO production rates for all three objects, in order to examine a correlation between gas production and different orbital histories and/or size. We find that orbital history does not appear to play a significant role in explaining 29P's CO production rates. 29P outproduces Hale-Bopp at the same heliocentric distance, even though it has been subjected to much more solar heating. Previous modeling work on such objects predicts that 29P should have been de-volatilized over a fresher comet like Hale-Bopp. This may point to 29P having a different orbital history than current models predict, with its current orbit acquired more recently. On the other hand, Chiron's CO measurements are consistent with it being significantly depleted over its original state, perhaps due to increased radiogenic heating made possible by its much larger size or its higher processing due to orbital history. Observed spectral line profiles are consistent with development and sublimation of icy grains at about 5-6 AU for 29P and Hale-Bopp, and this is probably a common feature in distantly active comets, and an important source of volatiles for all comets within 5 AU. In contrast, the narrow CO line profiles indicate a nuclear, and not extended, origin for CO beyond ~4 AU.