The Omega Centauri globular cluster and the area surveyed

Image of the Omega Centauri globular cluster from the the Digital Sky Survey (left). The image covers a region of 2.1 x 1.1 degrees on the sky, illustrating the very large extent of this cluster of stars. The right image is the ACS exposure taken with the Hubble Space Telescope which the astronomers used to detect and study the two distinct populations of hydrogen core-burning stars. The position of the ACS field with respect to the full globular cluster is shown as the red box. This field was chosen to lie in the outskirts of the cluster in order to ensure that there won't be any "crowding" problems and that there would be only one star in each FLAMES/VLT fiber.