Proper motions and trajectories for 16 extreme runaway and hypervelocity stars

Warren R. Brown, Jay Anderson, Oleg Y. Gnedin, Howard E. Bond, Margaret J. Geller, Scott J. Kenyon

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


We measure proper motions with the Hubble Space Telescope for 16 extreme radial velocity stars, mostly unbound B stars in the Milky Way halo. Twelve of these stars have proper motions statistically consistent with zero, and thus have radial trajectories statistically consistent with a Galactic center "hypervelocity star" origin. The trajectory of HE 0437-5439 is consistent with both Milky Way and Large Magellanic Cloud origins. A Galactic center origin is excluded at 3σ confidence for two of the lowest radial velocity stars in our sample, however. These two stars are probable disk runaways and provide evidence for ∼500 km s-1 ejections from the disk. We also measure a significant proper motion for the unbound sdO star US 708. Its 1000 km s-1 motion is in some tension with proposed supernova ejection models, but can be explained if US 708 was ejected from the stellar halo. In the future, we expect Gaia will better constrain the origin of these remarkable unbound stars.

Original languageEnglish (US)
Article number49
JournalAstrophysical Journal
Issue number1
StatePublished - May 1 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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