A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey
A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey
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DOI：
10.1086/498131
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发表时间：
2005-09
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影响因子：
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通讯作者：
C. Allende Prieto;T. Beers;R. Wilhelm;H. Newberg;C. Rockosi;B. Yanny;Y. S. Lee
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文献类型：
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作者：
C. Allende Prieto;T. Beers;R. Wilhelm;H. Newberg;C. Rockosi;B. Yanny;Y. S. Lee
我们对斯隆数字巡天 (SDSS) 第三次数据发布 (DR3) 中包含的 22,770 颗恒星的光谱和光度进行了分析。我们得出大气参数和距离。我们的分析程序使用三个最近发布的附近恒星的光谱库和替代方法进行了彻底检查。 SDSS 样本覆盖的恒星亮度范围为 14 < V < 22，主要位于银河系中纬度，并包含大量来自厚盘和晕星群的 F 型和 G 型恒星，因此包括银河系中一些最古老的恒星。我们发现晕星表现出广泛的铁丰度范围，峰值位于 [Fe/H] ≃ -1.4。这个群体基本上没有表现出银河系旋转。距银道面距离在 1 < |z| 范围内的厚盘 G 矮星< 3 kpc 显示出更加紧凑的金属丰度分布，最大值为 [Fe/H] ≃ -0.7，银河系自转中值落后于当地静止标准 63 km s-1。颜色指数和金属丰度与等时线的比较表明，在过去约 11 Gyr 的光晕中没有发生明显的恒星形成，但存在至少年轻 2 Gyr 的厚盘恒星。我们发现厚盘恒星的金属丰度几乎与距银心 5 到 14 kpc 之间的银心距离无关，这与薄盘恒星文献中发现的明显梯度形成鲜明对比。对于厚圆盘，没有明显的垂直金属丰度梯度，但我们在距平面 1 和 3 kpc 之间检测到 -16 ± 4 km s-1 kpc-1 的旋转速度梯度。我们估计样本中的恒星中有超过 2000 颗的铁丰度 [Fe/H] < -2，超过 150 颗恒星的铁丰度 [Fe/H] < -3。
We perform an analysis of spectra and photometry for 22,770 stars included in the third data release (DR3) of the Sloan Digital Sky Survey (SDSS). We derive atmospheric parameters and distances. Our analysis procedures are throughly checked using three recently published spectroscopic libraries of nearby stars and alternative methods. The SDSS sample covers a range in stellar brightness of 14 < V < 22, primarily at intermediate Galactic latitudes, and comprises large numbers of F- and G-type stars from the thick-disk and halo populations, therefore including some of the oldest stars in the Milky Way. We find that halo stars exhibit a broad range of iron abundances, with a peak at [Fe/H] ≃ -1.4. This population exhibits essentially no Galactic rotation. Thick-disk G-dwarf stars at distances from the Galactic plane in the range 1 < |z| < 3 kpc show a much more compact metallicity distribution, with a maximum at [Fe/H] ≃ -0.7, and a median Galactic rotation lagging the local standard of rest by 63 km s-1. A comparison of color indices and metal abundances with isochrones indicates that no significant star formation has taken place in the halo in the last ~11 Gyr, but there are thick-disk stars that are at least 2 Gyr younger. We find the metallicities of thick-disk stars to be nearly independent of Galactocentric distance between 5 and 14 kpc from the Galactic center, in contrast with the marked gradients found in the literature for the thin disk. No vertical metallicity gradient is apparent for the thick disk, but we detect a gradient in its rotational velocity of -16 ± 4 km s-1 kpc-1 between 1 and 3 kpc from the plane. We estimate that among the stars in our sample there are over 2000 with an iron abundance [Fe/H] < -2, and over 150 stars with an iron abundance [Fe/H] < -3.