The Galactic potential and the asymmetric distribution of hypervelocity stars - AstrophysicsReport as inadecuate

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Abstract: In recent years several hypervelocity stars HVSs have been observed in thehalo of our Galaxy. Such HVSs have possibly been ejected from the Galacticcenter and then propagated in the Galactic potential up to their currentposition. The recent survey for candidate HVSs show an asymmetry in thekinematics of candidate HVSs position and velocity vectors, where moreoutgoing stars than ingoing stars i.e. positive Galactocentric velocities vs.negative ones are observed. We show that such kinematic asymmetry, which islikely due to the finite lifetime of the stars and Galactic potentialstructure, could be used in a novel method to probe and constrain the Galacticpotential, identify the stellar type of the stars in the survey and estimatethe number of HVSs. Kinematics-independent identification of the stellar typesof the stars in such surveys e.g. spectroscopic identification could furtherimprove these results. We find that the observed asymmetry between ingoing andoutgoing stars favors specific Galactic potential models. It also implies alower limit of ~54+-8 main sequence HVSs in the survey sample >=648+-96 in theGalaxy, assuming that all of the main sequence stars in the survey originatefrom the Galactic center. The other stars in the survey are likely to be hotblue horizontal branch stars born in the halo rather than stars ejected fromthe Galactic center.

Author: Hagai B. Perets, Xufen Wu, HongSheng Zhao, Benoit Famaey, Gianfranco Gentile, Tal Alexander


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