Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
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DOI：
10.1086/300824
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发表时间：
1999-05
期刊：
影响因子：
--
通讯作者：
R. Wilhelm;T. Beers;R. Gray
中科院分区：
文献类型：
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作者：
R. Wilhelm;T. Beers;R. Gray
我们讨论了一种光谱和光度技术，使现场水平分支（FHB）和其他A型恒星的识别和分类，即使从相对较低的信噪比中等分辨率的光谱。该技术利用从模型大气计算预测的宽带UBV颜色和从合成光谱确定的巴耳末线轮廓和Ca II K等效宽度来估计有效温度范围为6000- 10，000 K的恒星的物理参数Teff、log g和[Fe/H]。与标准星的高信噪比谱比较表明，我们的方法在σ（Teff）= ±250 K，σ（log g）= ±0.14 dex，σ（[Fe/H]）= ±0.12 dex的参数上存在分散性。这种精度允许分离低表面重力的FHB和其他表面重力通常较高的A型（以及稍晚的）恒星。我们还发展了一种合成模板比较技术，它在金属线星和特殊A型星的识别中是非常有效的。对光谱中的噪声对物理参数测定的影响的详细研究表明，对于信噪比在10 < S/N < 20范围内的光谱，估计的表面重力的散射σ（log g）= ±0.25 dex足够小，可以使我们考虑的热星的噪声诱导的错误分类率小于10%。有效温度精度σ（Teff）= ±225 K，金属丰度精度σ（[Fe/H]）= ± 0.3dex。
We discuss a spectroscopic and photometric technique that enables the identification and classification of field horizontal-branch (FHB) and other A-type stars, even from relatively low signal-to-noise ratio medium-resolution spectra. This technique makes use of broadband UBV colors predicted from model atmosphere calculations and Balmer line profiles and Ca II K equivalent widths determined from synthetic spectra to estimate the physical parameters Teff, log g, and [Fe/H] for stars in the effective temperature range 6000–10,000 K. A comparison of our method with high signal-to-noise ratio spectra of standard stars indicates a scatter in the derived parameters of σ(Teff) = ±250 K, σ(log g) = ±0.14 dex, and σ([Fe/H]) = ±0.12 dex. This precision allows for a separation of low surface gravity FHB and other, generally higher surface gravity, A-type (and somewhat later) stars. We also develop a synthetic-template comparison technique, which is very effective in the identification of metallic-line and peculiar A-type stars. A detailed investigation of the influence of noise in the spectra on the determination of physical parameters shows that, for spectra with signal-to-noise ratios in the range 10 < S/N < 20, the scatter in estimated surface gravity, σ(log g) = ±0.25 dex, is sufficiently small to keep the noise-induced misclassification rate for the hot stars we consider to less than 10%. Effective temperatures of precision σ(Teff) = ±225 K and metallicities of precision σ([Fe/H]) = ±0.3 dex can be obtained.