The Giant Branch of ω Centauri: The Dependence of Kinematics on Abundance

For a sample of some 400 red giants in the chemically inhomogeneous globular cluster ω Centauri, we report correlations between the radial velocities of Mayor et al., which are accurate to ≲1 km s^-1, and the calcium abundances of Norris et al., which have internal accuracy of 0.06 dex. We find that the 20% metal-rich tail of the [Ca/H] distribution, as well as being more centrally concentrated, is kinematically cooler than the 80% metal-poorer component. At first glance one might interpret this as evidence consistent with a dissipative enrichment scenario of cluster formation. It obtains, however, that while the metal-poorer component exhibits well-defined systemic rotation, the metal-richer one shows no evidence of it, in contradistinction to the simple dissipative picture. A more natural explanation of the observed rotation and other chemical abundance data is provided by the globular cluster binary merger calculations of Makino et al., in the context of merging within the fragments first postulated by Searle.