arXiv 1105.34532011-05-17astro-ph.GA

重元素X射线电离在原行星盘中的应用

X-ray Ionization of Heavy Elements Applied to Protoplanetary Disks

Máté Ádámkovics, Alfred E. Glassgold, Rowin Meijerink

备注：: Accepted for publication in ApJ
DOI：: 10.1088/0004-637X/736/2/143

摘要：

本文分析了在keV X射线辐照下，相对冷的气体中俄歇效应对重元素离子布居的影响，并对年轻恒星的吸积盘进行了讨论。高度带电的离子在中性气体中迅速还原为双电荷态，因此这里的目的是导出这些单电荷和双电荷离子的产生速率，并通过复合、电荷转移和分子反应来指定它们的转化。该理论是说明了在一个典型的金牛座T恒星盘模型中的11个宇宙中最丰富的重元素的丰度计算。气体的物理性质是确定与X射线辐照的热化学模型，这表明磁盘的气氛由一个热的气氛覆盖的主要是冷体的磁盘。有一个温暖的过渡层，氢，碳和氧从原子转变为分子物种，电离下降了几个数量级。然后，带双电荷的离子大部分被限制在盘的热外层。过渡区以下的主导离子的性质敏感地取决于重元素的丰度约束差。简要讨论了观测结果和磁旋转不稳定性与活动层的联系。

英文摘要：

The consequences of the Auger effect on the population of heavy element ions are analyzed for the case of relatively cool gas irradiated by keV X-rays, with intended applications to the accretion disks of young stellar ob jects. Highly charged ions are rapidly reduced to the doubly-charged state in neutral gas, so the aim here is to derive the production rates for these singly- and doubly-charged ions and to specify their transformation by recombination, charge transfer, and molecular reactions. The theory is illustrated by calculations of the abundances of eleven of the most cosmically abundant heavy elements in a model of a typical T Tauri star disk. The physical properties of the gas are determined with an X-ray irradiated thermal-chemical model, which shows that the disk atmosphere consists of a hot atmosphere overlaying the mainly cool body of the disk. There is a warm transition layer where hydrogen, carbon and oxygen are transformed from atomic to molecular species and the ionization drops by several orders of magnitude. The doubly charged ions are then largely confined to the hot outer layers of the disk. The nature of the dominant ions below the transition depends sensitively on the poorly constrained abundances of the heavy elements. Observational consequences and connections with the active layers of the magneto-rotational instability are briefly discussed.

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