A Survey of Proper Motion Stars. XVII. A Deficiency of Binary Stars on Retrograde Galactic Orbits and the Possibility that omega Centauri is Related to the Effect

Abstract

We find a deficiency of binary stars moving on strongly retrograde Galactic orbits. No binary deficiencies are seen for U or W velocities, however. From theoretical analyses, we rule out preferential disruption of pre-existing binary stars due to encounters with massive perturbers. We also rule out globular clusters as the source of the effect since prograde motions are more likely to create such an effect. We search for star streams and find one possible candidate, but it is not on a retrograde orbit and probably represents the remains of a cluster that has passed too near the Galactic center. Based on a very small number of stars, we find that about the right fraction of stars on retrograde Galactic orbits share some chemical similarities to the cluster omega Cen, suggesting that its parent galaxy could be the explanation.