Kapteyn选定区域71中的恒星运动学：麒麟座和人马座潮汐流取样
Kinematics of Stars in Kapteyn Selected Area 71: Sampling the Monoceros and Sagittarius Tidal Streams
摘要：
我们提出了位于Kapteyn选定区域71（l = 167.1，b = -34.7）的恒星的三维运动学分析，以前在那里发现了恒星过剩（Dinescu et al. 2002，Newberg et al. 2002）。先前的研究结果表明，恒星过剩具有从自行推断的冷运动学特征，并且最初与人马座矮星系（Sgr）的碎片有关-即南部拖尾。我们已经获得了径向速度使用水螅多目标光谱仪的WIYN 3.5米望远镜。对183颗自行选择的恒星的研究结果表明，在这个恒星过剩中占主导地位的人口不是Sgr的碎片，而是一个运动学上属于环状流的人口，现在被称为麒麟座流。为这一种群确定的轨道与Penarrubia等人（2005年）对独角兽流的预测非常吻合。这个星群的径向速度色散在20到30公里/秒之间，低于银河系的速度色散。此外，径向速度分布的形状在一侧显示出尖锐的截止，这更符合卫星破裂的模型预测，而不是银河场的分布。尽管我们现在相信恒星过剩区的大多数恒星都是麒麟座的一部分，但在这个恒星过剩区中，大约有10颗恒星具有非常负的径向速度，这清楚地表明它们属于Sgr尾随潮汐尾。
英文摘要：
We present a 3D kinematical analysis of stars located in Kapteyn Selected Area 71 (l = 167.1, b = -34.7), where previously a stellar excess was found (Dinescu et al. 2002, Newberg et al. 2002). Previous findings indicated that the stellar excess has a cold kinematical signature as inferred from proper motions, and was initially associated with debris from the Sagittarius dwarf galaxy (Sgr) -- namely the southern trailing tail. We have obtained radial velocities using the Hydra multiobject spectrograph on the WIYN 3.5 m telescope. Results for 183 proper-motion selected stars indicate that the dominant population in this stellar excess is not debris from Sgr, but rather a population that kinematically belongs to the ring-like stream that is now known as the Monoceros stream. The orbit determined for this population agrees very well with the predictions for the Monoceros stream from Penarrubia et al. (2005). The radial-velocity dispersion of this population is between 20 and 30 km/s, lower than that of the Galactic field. Also, the shape of the radial-velocity distribution shows a sharp cut-off on one side, which is more in line with model predictions of the disruption of a satellite rather than with the distribution of the Galactic field. Despite the fact that we now believe most of the stars in the stellar excess to be part of Monoceros, about ten stars in this stellar excess have highly negative radial velocities, which is a clear indication of their membership to the Sgr trailing tidal tail.
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