SIMBAD references

2016ApJ...821L..13N - Astrophys. J., 821, L13-L13 (2016/April-2)

An extremely fast halo hot subdwarf star in a wide binary system.


Abstract (from CDS):

New spectroscopic observations of the halo hyper-velocity star candidate SDSS J121150.27+143716.2 (V = 17.92 mag) revealed a cool companion to the hot subdwarf primary. The components have a very similar radial velocity and their absolute luminosities are consistent with the same distance, confirming the physical nature of the binary, which is the first double-lined hyper-velocity candidate. Our spectral decomposition of the Keck/ESI spectrum provided an sdB+K3V pair, analogous to many long-period subdwarf binaries observed in the Galactic disk. We found the subdwarf atmospheric parameters: {T}_{eff}=30 600±500 K, logg=5.57±0.06 cm s-2, and He abundance log(nHe/nH)=-3.0±0.2. Oxygen is the most abundant metal in the hot subdwarf atmosphere, and Mg and Na lines are the most prominent spectral features of the cool companion, consistent with a metallicity of [Fe/H]=-1.3. The non-detection of radial velocity variations suggest the orbital period to be a few hundred days, in agreement with similar binaries observed in the disk. Using the SDSS-III flux calibrated spectrum we measured the distance to the system d=5.5±0.5 kpc, which is consistent with ultraviolet, optical, and infrared photometric constraints derived from binary spectral energy distributions. Our kinematic study shows that the Galactic rest-frame velocity of the system is so high that an unbound orbit cannot be ruled out. On the other hand, a bound orbit requires a massive dark matter halo. We conclude that the binary either formed in the halo or was accreted from the tidal debris of a dwarf galaxy by the Milky Way.

Abstract Copyright: © 2016. The American Astronomical Society. All rights reserved.

Journal keyword(s): binaries: spectroscopic - Galaxy: halo - stars: atmospheres - stars: horizontal-branch - stars: kinematics and dynamics - subdwarfs

Simbad objects: 3

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