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>A Self-Consistent Optical, Ultraviolet, and Extreme-Ultraviolet Model for the Spectrum of the Hot White Dwarf G191-B2B
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A Self-Consistent Optical, Ultraviolet, and Extreme-Ultraviolet Model for the Spectrum of the Hot White Dwarf G191-B2B
The star G191-B2B is one of a number of hot DA white dwarfs whose atmospheres have been found to contain significant quantities of heavy elements, including C, N, O, Si, Fe, and Ni. Several earlier studies have measured their abundances using IUE echelle data in conjunction with synthetic spectra derived from theoretical model atmosphere calculations of varying degrees of sophistication. However, predictions of the EUV spectrum based on these observations failed completely to match either its shape or absolute flux level. We present here the results of new non-LTE model calculations including the effects of line blanketing from more than 9 million (mainly Fe and Ni) transitions. For the first time, we are able to find an effective temperature and composition that can consistently match the optical, FUV and EUV data. However, to maintain this agreement below the He ii Λ228 Lyman limit, it is necessary to incorporate additional He ii opacity in the form of photospheric, circumstellar or interstellar material.
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机译：G191-B2B星是许多热的DA白矮星之一，发现其大气中含有大量的重元素，包括C，N，O，Si，Fe和Ni。几项较早的研究已经使用IUE echelle数据和从理论程度不同的复杂程度的理论模型大气计算得出的合成光谱测量了其丰度。但是，基于这些观察结果的EUV光谱预测完全无法匹配其形状或绝对通量水平。我们在这里介绍了新的非LTE模型计算的结果，包括来自超过900万（主要是铁和镍）转变的线路覆盖效应。我们首次能够找到可以与光学，FUV和EUV数据一致的有效温度和成分。但是，为了使该协议保持在He ii 228 Lyman限制以下，有必要以光球，星际或星际物质的形式合并其他He ii不透明性。
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