The B-type giant HD 271791 in the Galactic halo. Linking run-away stars to hyper-velocity stars

Details The B-type giant HD 271791 in the Galactic halo. Linking run-away stars to hyper-velocity stars The B-type giant HD 271791 in the Galactic halo. Linking run-away stars to hyper-velocity stars

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008a%26a...483l..21h&link_type=abstract

Astronomy and Astrophysics, Volume 483, Issue 2, 2008, pp.L21-L24

Astronomy and Astrophysics

Astrophysics

32

Stars: Individual: Hd 271791, Stars: Distances, Stars: Early-Type, Stars: Atmospheres, Galaxy: Center, Galaxy: Halo

Scientific paper

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&sun;), 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.
Based on
observations collected at the European Southern Observatory at La Silla, Chile,
ESO proposal No. 073.D-0495(A).

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