The Treatment of Non-LTE Line Blanketing in Spherically Expanding Outflows
The Treatment of Non-LTE Line Blanketing in Spherically Expanding Outflows
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DOI：
10.1086/305350
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发表时间：
1998-03
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影响因子：
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通讯作者：
D. Hillier;Doug L. Miller
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作者：
D. Hillier;Doug L. Miller
为了改进恒星风的光谱分析，对 Hillier 的非 LTE 辐射传输代码进行了广泛的修改。代码的主要改进是由于数千条重叠行而包含了覆盖。为了实现这种效果，我们使用了安德森首先提出的超级水平的想法。在我们的方法中，具有相似激发能量和能级的能级被分组在一起。在该组内，我们假设偏离系数是相同的。为了完全指定超级级别内各级别的种群，只需要求解超级级别的种群（或等效地，偏离系数）。我们的方法是单级 LTE 假设的自然扩展，因此 LTE 可以在深度上精确恢复。除了行覆盖修改之外，代码在其他方面也得到了显着改进。特别是，新代码结合了水平溶解效应、光电离截面中共振的影响以及俄歇电离效应。可以考虑具有热重新分布的电子散射，尽管它通常在共动坐标系中被相干地处理（这仍然导致观察者坐标系中的重新分布）。描述了几个示例计算来证明谱线覆盖对光谱分析的重要性。我们发现，覆盖层的加入使沃尔夫-拉叶 (W-R) 恒星中一些光学 CNO 谱线的强度改变了 2-5 倍。特别是，WC分级线C III λ5696和C IV λ5805的强度均因铁覆盖而增加。这应该有助于缓解非覆盖模型中发现的问题，这些模型无法匹配这些产品线的优势。我们还发现，在紫外线 (1100-1800 Å) 中，Fe 的影响在发射和吸收方面都很明显。发射对铁丰度很敏感，并且应该能够首次推断出 W-R 恒星中的铁丰度。对我们代码的改进应该会极大地促进对恒星风的光谱分析。我们将能够确定线路覆盖的重要性和影响，以及新代码中包含的其他几种效果。它还将使我们能够更好地确定 W-R 恒星参数，例如光度、元素丰度、风速和质量损失率。随着未来对相关物体（例如新星和超新星）的应用，我们的新代码还应该提高我们对这些具有扩展外流大气的物体的理解。
Extensive modifications to the non-LTE radiative transfer code of Hillier have been made in order to improve the spectroscopic analysis of stars with stellar winds. The main improvement to the code is the inclusion of blanketing due to thousands of overlapping lines. To implement this effect, we have used the idea of super levels first pioneered by Anderson. In our approach, levels with similar excitation energies and levels are grouped together. Within this group, we assume that the departure coefficients are identical. Only the population (or equivalently, the departure coefficient) of the super level need be solved in order to fully specify the populations of the levels within a super level. Our approach is a natural extension of the single-level LTE assumption, and thus LTE is recovered exactly at depth. In addition to the line blanketing modifications, the code has been improved significantly in other regards. In particular, the new code incorporates the effect of level dissolution, the influence of resonances in the photoionization cross sections, and the effect of Auger ionization. Electron scattering with a thermal redistribution can be considered, although it is normally treated coherently in the comoving frame (which still leads to redistribution in the observer's frame). Several example calculations are described to demonstrate the importance of line blanketing on spectroscopic analysis. We find that the inclusion of blanketing modifies the strengths of some optical CNO lines in Wolf-Rayet (W-R) stars by factors of 2-5. In particular, the strengths of the WC classification lines C III λ5696 and C IV λ5805 are both increased because of iron blanketing. This should help alleviate problems found with nonblanketed models, which were incapable of matching the strengths of these lines. We also find that, in the UV (1100-1800 Å), the influence of Fe is readily seen in both emission and absorption. The emission is sensitive to the iron abundance and should allow, for the first time, Fe abundances to be deduced in W-R stars. The improvements made to our code should greatly facilitate the spectroscopic analysis of stars with stellar winds. We will be able to determine the importance and influence of line blanketing, as well as of several other effects that have been included in the new code. It will also allow us to better determine W-R star parameters, such as luminosity, elemental abundances, wind velocity, and mass-loss rate. With future application to related objects, such as novae and supernovae, our new code should also improve our understanding of these objects with extended outflowing atmospheres.