缺氢（前）白矮星中NeVIII线的鉴定：限制最热恒星温度的新工具
Identification of NeVIII lines in H-deficient (pre-) white dwarfs: a new tool to constrain the temperature of the hottest stars
摘要：
这是我们第一次在光谱类型为PG 1159的已知最热（Teff> 150，000 K）缺氢（前）白矮星的远紫外光谱中发现NeVIII吸收线。它们起源于光球，可以通过合成的非LTE线轮廓进行匹配。我们还表明，在这些恒星的紫外线和光学发射线的数量可以解释为光球NeVIII功能，而不是迄今为止怀疑，作为沿激波区在恒星风中创建的电离OVIII线。因此，我们认为，在热[WR]型中心恒星的相同的发射线的长期识别是由于超高电离物质（OVII-VIII，CV-VI）必须修改。这些线可以完全归因于热激发的物种（NeVII-VIII，NV，OVI）。在已知最热的富氦白矮星KPD 0005 +5106中也发现了光球NeVIII谱线，其中一些以前也被认为是OVIII谱线。这是一个惊喜，因为必须得出结论，KPD 0005 +5106比迄今为止假设的（Teff = 120，000 K）热得多（Teff = 200，000 K）。这是证实了一个重新评估的HeII线光谱。我们推测，温度高到足以解释神秘的，硬X射线发射（1千电子伏）作为光球起源。
英文摘要：
For the first time, we have identified NeVIII absorption lines in far-UV spectra of the hottest known (Teff>150,000 K) hydrogen-deficient (pre-) white dwarfs of spectral type PG1159. They are of photospheric origin and can be matched by synthetic non-LTE line profiles. We also show that a number of UV and optical emission lines in these stars can be explained as being photospheric NeVIII features and not, as hitherto suspected, as ultrahigh ionised OVIII lines created along shock-zones in the stellar wind. Consequently, we argue that the long-standing identification of the same emission lines in hot [WR]-type central stars as being due to ultrahigh-ionised species (OVII-VIII, CV-VI) must be revised. These lines can be entirely attributed to thermally excited species (NeVII-VIII, NV, OVI). Photospheric NeVIII lines are also identified in the hottest known He-rich white dwarf KPD0005+5106 some of which were also attributed to OVIII previously. This is a surprise because it must be concluded that KPD0005+5106 is much hotter (Teff=200,000 K) than hitherto assumed (Teff=120,000 K). This is confirmed by a re-assessment of the HeII line spectrum. We speculate that the temperature is high enough to explain the mysterious, hard X-ray emission (1 keV) as being of photospheric origin.
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