The B-type giant HD 271791 in the Galactic halo. Linking run-away stars to hyper-velocity stars
Abstract
Context: Young, massive stars have been found in the distant Galactic halo. Dynamical ejection from the Galactic disc has been suggested as the origin of these “run-away stars”. The so-called hyper-velocity stars have been found to travel so fast that they are unbound to the Galaxy. Only a supermassive black hole (SMBH) appears to be able to accelerate the stars to such high velocities, which suggests that the Galactic centre is their place of origin.
Aims: We revisit the run-away B star HD 271791 to determine its nature and origin.
Methods: High-resolution optical echelle spectra are analysed using LTE model atmospheres. Based on proper-motion measurements, the 3D kinematic of the star is investigated by means of numerical experiments.
Results: HD 271791 is found to be a massive (11 M⊙), rapidly-rotating B-type star. Its chemical composition is found to be consistent with that of the sun. Its Galactic rest-frame velocity exceeds the Galactic escape velocity.
Conclusions: According to its space velocity, HD 271791 qualifies as a hyper-velocity star. Its kinematic constrains the place of birth to the outer Galactic disc and rules out the Galactic centre. HD 271791 is also too young (<30 Myr) to have originated in the Galactic centre. This challenges the SMBH paradigm for the origin of hyper-velocity stars.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 2008
- DOI:
- 10.1051/0004-6361:200809767
- Bibcode:
- 2008A&A...483L..21H
- Keywords:
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- stars: individual: HD 271791;
- stars: distances;
- stars: early-type;
- stars: atmospheres;
- Galaxy: center;
- Galaxy: halo