The Rotation of Subpopulations in ? Centauri

We present the first result of the Ital-FLAMES survey of red giant branch (RGB) stars in ? Cen. Radial velocities with a precision of ~0.5 km s-1 are presented for 650 members of ? Cen observed with FLAMES-GIRAFFE at the Very Large Telescope. We found that stars belonging to the metal-poor (RGB-MP), metal-intermediate (RGB-MInt), and metal-rich (RGB-a) subpopulations of ? Cen are all compatible with having the same rotational pattern. Our results appear to contradict past findings by Norris et al., who could not detect any rotational signature for metal-rich stars. The slightly higher precision of the present measurements and the much larger sample size, especially for the stars richer in metals, appear as the most likely explanations for this discrepancy. The result presented here weakens the body of evidence in favor of a merger event in the past history of ? Cen.