BOOTSTRAPPING DIELECTRONIC RECOMBINATION FROM SECOND-ROW ELEMENTS AND THE ORION NEBULA
BOOTSTRAPPING DIELECTRONIC RECOMBINATION FROM SECOND-ROW ELEMENTS AND THE ORION NEBULA
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DOI：
10.1088/0004-637x/804/2/100
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
N. Badnell;G. J. Ferland;G. J. Ferland;T. Gorczyca;D. Nikolić;G. Wagle
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文献类型：
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作者：
N. Badnell;G. J. Ferland;G. J. Ferland;T. Gorczyca;D. Nikolić;G. Wagle
双电子复合(DR)是光致电离云中大多数重元素的主要复合过程。当自电离态的位置已知时，可以准确地预测物种的DR率。不幸的是，这样的数据不适用于大多数第三行和更高行的元素。这带来了一种不确定性，对光电离云来说尤其严重，因为低温意味着DR通过非常低的自电离态发生。本文讨论了在星云中建立[S III]/[S II]比值的主要过程--S2+→？>；S+DR。我们使用一种新的方法推导出了第二行离子的经验速率系数，这些离子确实有准确的数据。光电离模型被用来再现猎户座星云中心区域的[O III]/[O II]/[O I]/[Ne III]强度比。O和Ne具有精确的原子数据，可以用来推导出→104K下的S2+∼？>；S+DR速率系数。我们对S2+→？>；S+的DR速率系数进行了新的计算，并量化了自电离能级位置的不确定性对其的影响。将经验和理论结果结合起来，我们得到了在所有温度下的结果速率系数的简单拟合，以并入到光谱合成代码中。这种方法可以用来计算其他离子的经验DR率，前提是对O和Ne的几个电离阶段有很好的观测。
Dielectronic recombination (DR) is the dominant recombination process for most heavy elements in photoionized clouds. Accurate DR rates for a species can be predicted when the positions of autoionizing states are known. Unfortunately such data are not available for most third- and higher-row elements. This introduces an uncertainty that is especially acute for photoionized clouds, where the low temperatures mean that DR occurs energetically through very low-lying autoionizing states. This paper discusses S2+ → ?> S+ DR, the process that is largely responsible for establishing the [S iii]/[S ii] ratio in nebulae. We derive an empirical rate coefficient using a novel method for second-row ions, which do have accurate data. Photoionization models are used to reproduce the [O iii]/[O ii]/[O i]/[Ne iii] intensity ratios in central regions of the Orion Nebula. O and Ne have accurate atomic data and can be used to derive an empirical S2+ → ?> S+ DR rate coefficient at ∼104 K. We present new calculations of the DR rate coefficient for S2+ → ?> S+ and quantify how uncertainties in the autoionizing level positions affect it. The empirical and theoretical results are combined and we derive a simple fit to the resulting rate coefficient at all temperatures for incorporation into spectral synthesis codes. This method can be used to derive empirical DR rates for other ions, provided that good observations of several stages of ionization of O and Ne are available.