Na-O anticorrelation and HB^⋆

IX. Kinematics of the program clusters A link between systemic rotation and HB morphology?

¹ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: michele.bellazzini@oabo.inaf.it
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ INAF – Osservatorio Astronomico di Catania, via S.Sofia 78, 95123 Catania, Italy
⁴ Dipartimento di Fisica e Astronomia, Universit di Catania, via S.Sofia 78, 95123 Catania, Italy

Received: 9 September 2011
Accepted: 4 November 2011

Abstract

We use accurate radial velocities for 1981 member stars in 20 Galactic globular clusters, collected within our large survey aimed at analyzing the Na-O anti-correlation, to study the internal kinematics of the clusters. We performed the first systematic exploration of the possible connections between cluster kinematics and the multiple populations phenomenon in GCs. We did not find any significant correlation between Na abundance and either velocity dispersion or systemic rotation. We searched for systemic rotation in the eight clusters of our sample that lack this analysis from previous works in the literature (NGC 2808, NGC 5904, NGC 6171, NGC 6254, NGC 6397, NGC 6388, NGC 6441, and NGC 6838). These clusters are found to span a wide range of rotational amplitudes from  ~0.0 km s^-1 (NGC 6397) to  ~13.0 km s^-1 (NGC 6441). We found a significant correlation between the ratio of rotational velocity to central velocity dispersion (V_rot/σ₀) and the horizontal branch morphology parameter (B − R)/(B + R + V). The ratio V_rot/σ₀ is found to correlate also with metallicity, possibly hinting at a significant role for dissipation in the process of formation of globular clusters; V_rot is found to correlate well with (B − R)/(B + R + V), M_V, σ₀, and [Fe/H]. All these correlations strongly suggest that systemic rotation may be intimately linked with the processes that led to the formation of globular clusters and the stellar populations they host.