Milky Way中最远的恒星
The Most Distant Stars in the Milky Way
摘要：
我们报告发现的最遥远的银河系（MW）恒星的日期：ULAS J001535.72 $+$ 015549.6和ULAS J074417.48 $+$ 253233.0。这些恒星被选为M巨星候选者是基于它们的红外和光学颜色以及缺乏自行。我们使用MMT/红通道摄谱仪光谱确认它们是外晕巨星。这两颗恒星的距离都很大，其中ULAS J001535.72 $+$ 015549.6的距离为$274 \pm 74$ kpc，而ULAS J074417.48 $+$ 253233.0的距离为238 $\pm$ 64 kpc，使它们成为第一颗发现的超过200 kpc的MW恒星。ULAS J001535.72 $+$ 015549.6和ULAS J074417.48 $+$ 253233.0都在以$52 \pm 10$ km s $^{-1}$和$24 \pm 10$ km s $^{-1}$的速度远离银河系中心。利用它们的距离和运动学，我们考虑了可能的起源，例如：从矮星系的潮汐剥离，从MW的磁盘喷射，或在一个未被发现的矮星系的成员。这些M巨星，以及在这次活动中也被证实的两个内晕巨星，是第一个绘制我们银河系外晕大部分未被探索的区域的地图。
英文摘要：
We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72$+$015549.6 at $274 \pm 74$ kpc and ULAS J074417.48$+$253233.0 at 238 $\pm$ 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0 are both moving away from the Galactic center at $52 \pm 10$ km s$^{-1}$ and $24 \pm 10$ km s$^{-1}$, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.
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