超亮LMC超巨星HDE 269896光谱的一个新特征
A New Feature in the Spectrum of the Superluminous LMC Supergiant HDE 269896
摘要：
我们在LMC超巨星HDE 269896，ON 9.7 Ia $^+$的光谱中发现了N Ⅱ 5000 A复合体的强选择性发射。由于该天体的光谱类型也有非常强的He II $λ$ 4686发射，因此在其扩展的大气中存在异常广泛的电离范围。该光谱的公布模型没有重现这些排放特征，但我们表明，增加氮和氦丰度，以及其他模型参数的微小变化，可以做到这一点。HDE 269896的形态和可能的进化关系，照亮了新的光谱特征，OB动物园的其他居民进行了讨论。这个天体可能处于一个立即的预WNVL（非常晚WN）状态，这又是至少一些发光蓝色变星的静止状态。更一般地说，HDE 269896中的N II光谱提供了O型光谱中两种明显不同类型的线行为发生的惊人证明：正常吸收线，在高风密度下形成天鹅座P剖面，而来自相同离子的选择性发射线则没有。对这些特征的进一步分析将促进对原子物理学和极端恒星大气的理解。
英文摘要：
We have found strong selective emission of the N II 5000A complex in the spectrum of the LMC hypergiant HDE 269896, ON9.7 Ia$^+$. Since this object also has anomalously strong He II $λ$4686 emission for its spectral type, an unusually wide range of ionization in its extended atmosphere is indicated. The published model of this spectrum does not reproduce these emission features, but we show that increased nitrogen and helium abundances, together with small changes in other model parameters, can do so. The morphological and possible evolutionary relationships of HDE 269896, as illuminated by the new spectral features, to other denizens of the OB Zoo are discussed. This object may be in an immediate pre-WNVL (Very Late WN) state, which is in turn the quiescent state of at least some Luminous Blue Variables. More generally, the N II spectrum in HDE 269896 provides a striking demonstration of the occurrence of two distinctly different kinds of line behavior in O-type spectra: normal absorption lines that develop P Cygni profiles at high wind densities, and selective emission lines from the same ions that do not. Further analysis of these features will advance understanding of both atomic physics and extreme stellar atmospheres.
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