Grains in ionized nebulae: Spectral line diagnostics
Grains in ionized nebulae: Spectral line diagnostics
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电离星云中的颗粒：谱线诊断
DOI：
10.1086/175217
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
W. Feibelman
中科院分区：
文献类型：
--
作者：
J. Kingdon;G. Ferland;W. Feibelman
在气态星云中，可凝聚元素的耗尽可以提供证据，证明尘埃与电离气体混合良好。Al和CA是一般星际介质中最贫化的两种元素，因此测量它们在星云电离区的丰度是很重要的。我们计算一个大的网格的光电离模型和确定组的线比是相对不敏感的恒星和星云的参数，因此是很好的诊断确定相对丰度。基于（（Ca II）λ λ 291，7324的双重和检测的Al II）λ λ 2660，2669在紫外线的情况下，我们确定的范围内的铝和钙耗尽到NGC 7027和猎户座星云的颗粒。我们的研究结果表明，约0.3 dex的Al耗尽，但超过两个半数量级的Ca耗尽。基于Mg II lambda 2798的类似计算产生大约0.8dex的Mg损耗。这再次证实了从高和低电离Mg线确定的耗尽之间的差异。我们还发现了NGC 7027中Ca的“耗尽梯度”的证据，因为我们使用（Ca II）推断的外部中性区域的钙耗尽略高于使用（Ca V）推断的内部高电离区域。这种梯度可以测试当前的热电离气体中粒子存活的模型。
The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the ((Ca II) lambda lambda 291, 7324 doublet and the detection of Al II) lambda lambda 2660, 2669 in the ultraviolet, we determine the extent of aluminum and calcium depletion onto grains in NGC 7027 and the Orion Nebula. Our results show a approximately 0.3 dex depletion for Al, but a depletion of more than two and a half orders of magnitude for Ca. A similar calculation based on Mg II lambda 2798 yields roughly a 0.8 dex depletion for Mg. This reaffirms the discrepancy between depletion determined from high and low ionization Mg lines. We also find evidence for a 'depletion gradient' in Ca in NGC 7027, since the calcium depletion we infer for the outer, more neutral regions using (Ca II) is somewhat higher than that inferred for the inner high-ionization region, using (Ca v). This gradient can test current models of the survival of grains within hot ionized gas.