US 708 โ an unbound hyper-velocity subluminous O star
US 708 โ an unbound hyper-velocity subluminous O star
We report the discovery of an unbound hyper-velocity star, US 708, in the Milky Way halo, with a heliocentric radial velocity of . A quantitative NLTE model atmosphere analysis of optical spectra obtained with LRIS at the Keck I telescope shows that US 708 is an extremely helium-rich (NHe/) subluminous โฆ