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.
@article{arxiv.1407.2610,
title = {The Most Distant Stars in the Milky Way},
author = {John J. Bochanski and Beth Willman and Nelson Caldwell and Robyn Sanderson and Andrew A. West and Jay Strader and Warren Brown},
journal= {arXiv preprint arXiv:1407.2610},
year = {2014}
}
Comments
Accepted and in print by ApJL. Seven pages, 2 figures