The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters: The Internal Kinematics of the Multiple Stellar Populations in NGC 2808

Bellini, A.; Vesperini, E.; Piotto, G.; Milone, A. P.; Hong, J.; Anderson, J.; van der Marel, R. P.; Bedin, L. R.; Cassisi, S.; D’Antona, F.; Marino, A. F.; Renzini, A.
Referencia bibliográfica

The Astrophysical Journal Letters, Volume 810, Issue 1, article id. L13, 6 pp. (2015).

Fecha de publicación:
9
2015
Número de autores
12
Número de autores del IAC
1
Número de citas
81
Número de citas referidas
68
Descripción
Numerous observational studies have revealed the ubiquitous presence of multiple stellar populations in globular clusters and cast many difficult challenges for the study of the formation and dynamical history of these stellar systems. In this Letter we present the results of a study of the kinematic properties of multiple populations in NGC 2808 based on high-precision Hubble Space Telescope proper-motion measurements. In a recent study, Milone et al. identified five distinct populations (A–E) in NGC 2808. Populations D and E coincide with the helium-enhanced populations in the middle and the blue main sequences (mMS and bMS) previously discovered by Piotto et al.; populations A–C correspond to the redder main sequence that, in Piotto et al., was associated with the primordial stellar population. Our analysis shows that, in the outermost regions probed (between about 1.5 and 2 times the cluster half-light radius), the velocity distribution of populations D and E is radially anisotropic (the deviation from an isotropic distribution is significant at the ∼3.5σ level). Stars of populations D and E have a smaller tangential velocity dispersion than those of populations A–C, while no significant differences are found in the radial velocity dispersion. We present the results of a numerical simulation showing that the observed differences between the kinematics of these stellar populations are consistent with the expected kinematic fingerprint of the diffusion toward the cluster outer regions of stellar populations initially more centrally concentrated. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.