The Most Distant Stars in the Milky Way

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 74 kpc and ULAS J074417. 48+253233. 0 at 238 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 10 km s^-1 and 24 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.