The ensemble properties of comets: Results from narrowband photometry of 85 comets, 1976-1992
The ensemble properties of comets: Results from narrowband photometry of 85 comets, 1976-1992
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DOI：
10.1006/icar.1995.1190
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发表时间：
1995-12-01
期刊：
影响因子：
3.2
通讯作者：
Birch, PV
中科院分区：
文献类型：
--
作者：
AHearn, MF;Millis, RL;Birch, PV
本文介绍了17年来观测的85颗彗星的窄带测光结果。这些数据已被均匀地减少到分子生产率和粉尘生产率的代理。我们确认以前的调查，无论是我们自己的和其他人的，表明有没有分化与深度的彗星核，大多数彗星是非常相似的化学成分，彼此之间的尘埃-气体比不随彗星的动力学年龄。相对丰度与日心距离的变化不大，这意味着我们观察到的物种的密度依赖过程中的昏迷的作用是小的。对于大多数短周期彗星来说，从一次出现到下一次出现的变化也很小。然而，我们发现，彗星的组成有很大的分组，显然与形成的地点有关。特别是，大多数起源于柯伊伯带的彗星似乎在导致观察到的C-2和C-3的碳链分子中显着耗尽。柯伊伯带彗星也表现出较小的活动区域，陡峭的斜坡，以及比其他彗星更大的近日点不对称性，这意味着较小的活动部分。我们认为，至少成分的影响是原始的，而不是进化。我们还显示了一些属性，特别是尘埃与气体的比例，与近日点距离的显着，但无法解释的相关性。我们提供了强有力的证据表明，大多数CN，一些C-2，几乎没有NH产生的谷物在昏迷，而不是从核冰。有证据表明，水和其他冰之间的混合发生在颗粒水平，而不是在分子水平。我们还表明，必须有大量的彗星具有非常低的活动。这些数据似乎需要将具有不同组成的彗星混合成单个核，其中一些核包含在合奏中看到的几乎全部组合物，而另一些核包含的组合物范围要小得多。(C)出版社：Academic Press
We present the results of narrowband photometry of 85 comets observed over a period of 17 years. The data have been reduced homogeneously to molecular production rates and a proxy for the dust production rate. We confirm previous investigations, both our own and those of others, showing that there is no differentiation with depth in the cometary nucleus, that most comets are very similar to each other in chemical composition, and that the dust-to-gas ratio does not vary with the dynamical age of the comet. There is little variation of relative abundances with heliocentric distance, implying that for the species we observe the role of density-dependent processes in the coma is small. There is also little variation from one apparition to the next for most short-period comets.We show, however, that there are significant compositional groupings of comets, apparently related to place of formation. Specifically, the majority of comets originating in the Kuiper belt appear to be significantly depleted in the carbon-chain molecules that lead to the observed C-2 and C-3. Kuiper belt comets also exhibit smaller active areas, steeper slopes, and greater asymmetries about perihelion than do other comets, implying smaller active fractions. We argue that at least the compositional effect is primordial rather than evolutionary.We also show a significant but unexplained correlation of some properties, notably the dust-to-gas ratio, with perihelion distance. We provide strong evidence that most CN, some C-2, and virtually no NH are produced from grains in the coma rather than from nuclear ices. Evidence suggests that the mixing between water and other ices occurs at the level of grains rather than at the molecular level. We also show that there must be a large population of comets having very low activity. The data appear to require mixing of cometesimals with different compositions into individual nuclei, with some nuclei containing nearly the full range of compositions seen in the ensemble while others contain a much smaller range of compositions. (C) 1995 Academic Press, Inc.