Rotation of the Globular Cluster ω Centauri

Abstract

A LONG series of observations and measurements of photographic plates taken on the globular cluster ω Centauri has now been completed by members of the staff of the Royal Greenwich Observatory at Herstmonceux. The observational material was obtained at the Radcliffe Observatory in Pretoria and at the Royal Observatory at the Cape of Good Hope, with the co-operation of the Radcliffe Observer, Dr. A. D. Thackeray, and of H.M. Astronomer at the Cape, Dr. R. H. Stoy, respectively. Details will be published in the R.G.O. Annals and Bulletins shortly, but special attention is directed here to the fact that the cluster has been observed to be rotating, and that the rate of rotation agrees with a theoretical value deduced from the ellipticity of the cluster. The view is therefore supported that the structure of the cluster is given by an appropriate modification of the isothermal gas sphere, and, moreover, that the elliptical shape of the cluster is a consequence of a rotation considerably greater than galactic rotation. This latter result disposes of the view that the elliptical shape is a consequence of galactic tidal forces.