Predicted Space Motions for Hypervelocity and Runaway Stars: Proper Motions and Radial Velocities for the GAIA Era

TL;DR

This paper models the three-dimensional motions of hypervelocity and runaway stars in the Milky Way, predicting observable properties to distinguish them from halo stars and testing formation theories with upcoming GAIA data.

Contribution

It provides detailed predictions of stellar motions for HVSs and runaways in a realistic Galactic potential, aiding future observational tests.

Findings

Unbound HVSs are more common at 20-100 kpc than runaways.

Radial velocities effectively distinguish HVSs and runaways from halo stars at large distances.

Models align with observations for B-type HVSs and runaways, but not for solar-type candidates.

Abstract

We predict the distinctive three dimensional space motions of hypervelocity stars (HVSs) and runaway stars moving in a realistic Galactic potential. For nearby stars with distances less than 10~kpc, unbound stars are rare; proper motions alone rarely isolate bound HVSs and runaways from indigenous halo stars. At large distances of 20-100 kpc, unbound HVSs are much more common than runaways; radial velocities easily distinguish both from indigenous halo stars. Comparisons of the predictions with existing observations are encouraging. Although the models fail to match observations of solar-type HVS candidates from SEGUE, they agree well with data for B-type HVS and runaways from other surveys. Complete samples of g <= 20 stars with GAIA should provide clear tests of formation models for HVSs and runaways and will enable accurate probes of the shape of the Galactic potential.