BD-22 3467，一颗DAO型恒星，激发了Abell 35星云
BD-22 3467, a DAO-type star exciting the nebula Abell 35
摘要：
光谱分析的热，致密的恒星与NLTE（非本地热平衡）模型大气技术可以精确测定光球参数。由此导出的光球金属丰度是恒星演化理论的关键约束。先前对星云A 35的激发星BD-22 3467的光谱分析仅基于He+C+N+O+Si+Fe模型。对于我们的分析，我们使用最先进的全金属线覆盖的NLTE模型大气，考虑从氢到镍的23种元素的不透明度。为了分析高分辨率和高信噪比FUV（远紫外，FUSE）和UV（HST/STIS）观测，我们结合了恒星大气模型和星际线吸收模型，以完全再现整个观测到的紫外光谱。在Teff = 80 +/- 10 kK和log g =7.2 +/- 0.3时，与BD-22 3467的UV观察结果最一致。虽然验证了先前分析的Teff，但log g显著较低。我们重新分析了硅和铁的谱线（分别为太阳丰度的1/100和大约1/100），并首次在这颗恒星中确定了氩、铬、锰、钴和镍，并确定了丰度分别为太阳的12、70、35、150和5倍。我们的结果与DA型白矮星扩散模型的预言部分一致。光球和星际线吸收模型的组合再现了90%以上的观测到的吸收功能。恒星质量为M ~ 0.48 Msun。BD-22 3467的质量可能不足以上升到渐近巨星分支，并且可能直接从延伸的水平分支进化到了白矮星状态。这就可以解释为什么它周围没有行星状星云。然而，恒星电离周围的星际物质，模仿行星状星云。
英文摘要：
Spectral analyses of hot, compact stars with NLTE (non-local thermodynamical equilibrium) model-atmosphere techniques allow the precise determination of photospheric parameters. The derived photospheric metal abundances are crucial constraints for stellar evolutionary theory. Previous spectral analyses of the exciting star of the nebula A 35, BD-22 3467, were based on He+C+N+O+Si+Fe models only. For our analysis, we use state-of-the-art fully metal-line blanketed NLTE model atmospheres that consider opacities of 23 elements from hydrogen to nickel. For the analysis of high-resolution and high-S/N (signal-to-noise) FUV (far ultraviolet, FUSE) and UV (HST/STIS) observations, we combined stellar-atmosphere models and interstellar line-absorption models to fully reproduce the entire observed UV spectrum. The best agreement with the UV observation of BD-22 3467 is achieved at Teff = 80 +/- 10 kK and log g =7.2 +/- 0.3. While Teff of previous analyses is verified, log g is significantly lower. We re-analyzed lines of silicon and iron (1/100 and about solar abundances, respectively) and for the first time in this star identified argon, chromium, manganese, cobalt, and nickel and determined abundances of 12, 70, 35, 150, and 5 times solar, respectively. Our results partially agree with predictions of diffusion models for DA-type white dwarfs. A combination of photospheric and interstellar line-absorption models reproduces more than 90 % of the observed absorption features. The stellar mass is M ~ 0.48 Msun. BD-22 3467 may not have been massive enough to ascend the asymptotic giant branch and may have evolved directly from the extended horizontal branch to the white dwarf state. This would explain why it is not surrounded by a planetary nebula. However, the star, ionizes the ambient interstellar matter, mimicking a planetary nebula.
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