THE KINEMATICS AND CHEMISTRY OF RED HORIZONTAL BRANCH STARS IN THE SAGITTARIUS STREAMS
THE KINEMATICS AND CHEMISTRY OF RED HORIZONTAL BRANCH STARS IN THE SAGITTARIUS STREAMS
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DOI：
10.1088/0004-637x/751/2/130
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发表时间：
2012-04
期刊：
影响因子：
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通讯作者：
W. Shi;Y. Chen;K. Carrell;G. Zhao
中科院分区：
文献类型：
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作者：
W. Shi;Y. Chen;K. Carrell;G. Zhao
我们使用理论模型从斯隆数字巡天DR7光谱数据中选择了沿着人马座（Sgr）矮星系流的556颗红色水平分支恒星。研究了Sgr流中恒星和相同位置的银河系恒星的金属丰度和α-元素分布。我们发现人马座恒星的金属丰度分布有两个峰，而银河系恒星的金属丰度分布有一个更明显的贫金属峰。同时，人马座恒星的[α/Fe]比值低于银河系恒星。在人马座恒星中，我们发现在人马座潮尾的前臂和后臂之间的金属丰度分布是不同的。领头臂的金属丰度和[α/Fe]分布与银河系相似。后臂主要由富金属组成，[α/Fe]明显低于银河系恒星。金属丰度梯度在后臂第一缠绕处为−（1.8±0.3）× 10−3度，在前臂第一缠绕处为−（1.5±0.4）× 10−3度。在前臂或后臂的第二缠绕处不存在明显的梯度。看来，由于银河系的潮汐力，人马座矮星系最初在第二个包层（较老）臂中失去了金属贫乏的成分，然后在第一个包层（较年轻）臂中富含金属的成分被破坏。最后，我们发现后臂在88°< Λ☉< 112°范围内的速度色散为σ = 9.808±1.0 km s−1，这与之前的文献一致。
We have selected 556 red horizontal branch stars along the streams of the Sagittarius (Sgr) dwarf galaxy from Sloan Digital Sky Survey DR7 spectroscopic data using a theoretical model. The metallicity and α-element distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [α/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distribution between the leading and trailing arms of the Sgr tidal tails. The metallicity and [α/Fe] distribution of the leading arm is similar to that of the Galaxy. The trailing arm is composed mainly of a metal-rich component and [α/Fe] is obviously lower than that of the Galactic stars. The metallicity gradient is −(1.8 ± 0.3)× 10−3 dex deg−1 in the first wrap of the trailing arm and −(1.5 ± 0.4)× 10−3 dex deg−1 in the first wrap of the leading arm. No significant gradient exists along the second wraps of the leading or trailing arms. It seems that the Sgr dwarf galaxy initially lost the metal-poor component in the second wrap (older) arms due to the tidal force of our Galaxy and then the metal-rich component is disrupted in the first wrap (younger) arms. Finally, we found that the velocity dispersion of the trailing arm from 88° < Λ☉ < 112° is σ = 9.808 ± 1.0 km s−1, which is consistent with previous work in the literature.