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arXiv 1801.00892astro-ph.SRastro-ph.GA
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沃尔夫-拉叶行星状星云PB 8的双丰度电离结构

Bi-abundance ionization structure of the Wolf-Rayet planetary nebula PB 8

Ashkbiz Danehkar

备注：
18 pages, 6 figures, 10 tables, Publications of the Astronomical Society of Australia (PASA), Volume 35, id.e005
发表信息：
Publ.Astron.Soc.Austral.35:e005,2018
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摘要：

围绕[WN/WC]-混合中心星的行星状星云（PN）PB 8是具有中等丰度差异因子（ADF ~ 2-3）的行星状星云之一，这可能表明星云中嵌入了少量富含金属的包裹体（双丰度）。在这项工作中，我们已经建立了光电离模型，再现的光学和红外观测的PN PB 8使用非LTE恒星模型大气电离源。最初使用的化学均匀模型不能预测光学复合线（ORL）。然而，双丰度模型提供了一个更好的适合大多数观察到的ORL从N和O离子。在双丰度模型中，富含金属的包裹体占星云总体积的5.6%，并且比周围星云的平均值大约冷1.7倍。富金属包裹体的N/H和O/H丰度比分别比弥漫暖星云大1.0和1.7倍。为了重现PB 8的斯皮策光谱能量分布，还包括了尘气比为0.01（按质量计）的尘埃颗粒。据发现，富含金属的夹杂物的存在下，可以解释重元素ORL，而不同的颗粒种类和离散的晶粒尺寸的双灰尘化学可能产生的红外连续的PN。本研究表明，在少数丰度差异较大（ADF> 10）的PNe中检验的双丰度假说也适用于丰度差异中等的典型PNe。

英文摘要：

The planetary nebula (PN) PB 8 around a [WN/WC]-hybrid central star is one of PNe with moderate abundance discrepancy factors (ADFs ~ 2-3), which could be an indication of a tiny fraction of metal-rich inclusions embedded in the nebula (bi-abundance). In this work, we have constructed photoionization models to reproduce the optical and infrared observations of the PN PB 8 using a non-LTE stellar model atmosphere ionizing source. A chemically homogeneous model initially used cannot predict the optical recombination lines (ORLs). However, a bi-abundance model provides a better fit to most of the observed ORLs from N and O ions. The metal-rich inclusions in the bi-abundance model occupy 5.6 percent of the total volume of the nebula, and are roughly 1.7 times cooler and denser than the mean values of the surrounding nebula. The N/H and O/H abundance ratios in the metal-rich inclusions are ~ 1.0 and 1.7 dex larger than the diffuse warm nebula, respectively. To reproduce the Spitzer spectral energy distribution of PB 8, dust grains with a dust-to-gas ratio of 0.01 (by mass) were also included. It is found that the presence of metal-rich inclusions can explain the heavy element ORLs, while a dual-dust chemistry with different grain species and discrete grain sizes likely produces the infrared continuum of this PN. This study demonstrates that the bi-abundance hypothesis, which was examined in a few PNe with large abundance discrepancies (ADFs > 10), could also be applied to those typical PNe with moderate abundance discrepancies.

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