VERY METAL-POOR OUTER-HALO STARS WITH ROUND ORBITS
VERY METAL-POOR OUTER-HALO STARS WITH ROUND ORBITS
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DOI：
10.1088/2041-8205/763/1/l17
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发表时间：
2012-12
期刊：
影响因子：
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通讯作者：
Kohei Hattori;Y. Yoshii;T. Beers;D. Carollo;Y. S. Lee
中科院分区：
文献类型：
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作者：
Kohei Hattori;Y. Yoshii;T. Beers;D. Carollo;Y. S. Lee
银河系中晕星的轨道运动反映了它们形成的祖先系统的轨道运动，这使得追踪银河系的质量组装历史成为可能。根据精确的自行和视线速度直接测量三维速度，揭示了大多数内晕区的晕星在偏心轨道上运动。然而，由于缺乏这些恒星的精确自行，我们对遥远的、原位的晕星样本的运动的理解仍然有限。在这里，我们探讨了一个独立的模型分析的视线速度和空间分布的最近的样本1865年精心挑选的晕蓝水平分支（BHB）恒星在30千秒差距的银河系中心。我们发现贫金属（[Fe/H]-2.0）BHB星的平均自转速度。我们还发现，相对更多的金属丰富的BHB星占主导地位的恒星偏心轨道，如以前观察到的其他恒星样本的内晕区域。相比之下，贫金属的BHB恒星主要是由更圆、更低偏心率的轨道上的恒星组成。我们的研究结果表明，银河系的祖先系统的运动，有助于在30千秒差距内发现的恒星种群直接与他们的金属丰度，这可能是与他们的物理性质，如气体分数。这些结果是一致的存在一个内/外晕结构的晕系统，主张由Alberlo等人。
The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move in eccentric orbits. However, our understanding of the motions of distant, in situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] −2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stellar samples in the inner-halo region. By contrast, the very metal-poor BHB stars are dominated by stars on rounder, lower-eccentricity orbits. Our results indicate that the motion of the progenitor systems of the Milky Way that contributed to the stellar populations found within 30 kpc correlates directly with their metal abundance, which may be related to their physical properties such as gas fractions. These results are consistent with the existence of an inner/outer halo structure for the halo system, as advocated by Carollo et al.