Bibcode
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 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.