Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-09-12
Astrophys.J.697:2096-2101,2009
Astronomy and Astrophysics
Astrophysics
7 pages, 3 figures. Added an appendix. Accepted to ApJ
Scientific paper
10.1088/0004-637X/697/2/2096
In recent years several hypervelocity stars (HVSs) have been observed in the halo of our Galaxy. Such HVSs have possibly been ejected from the Galactic center and then propagated in the Galactic potential up to their current position. The recent survey for candidate HVSs show an asymmetry in the kinematics of candidate HVSs (position and velocity vectors), where more outgoing stars than ingoing stars (i.e. positive Galactocentric velocities vs. negative ones) are observed. We show that such kinematic asymmetry, which is likely due to the finite lifetime of the stars and Galactic potential structure, could be used in a novel method to probe and constrain the Galactic potential, identify the stellar type of the stars in the survey and estimate the number of HVSs. Kinematics-independent identification of the stellar types of the stars in such surveys (e.g. spectroscopic identification) could further improve these results. We find that the observed asymmetry between ingoing and outgoing stars favors specific Galactic potential models. It also implies a lower limit of ~54+-8 main sequence HVSs in the survey sample (>=648+-96 in the Galaxy), assuming that all of the main sequence stars in the survey originate from the Galactic center. The other stars in the survey are likely to be hot blue horizontal branch stars born in the halo rather than stars ejected from the Galactic center.
Alexander Tal
Famaey Benoit
Gentile Gianfranco
Perets Hagai B.
Wu Xufen
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