Indications for common origin and gravitational interaction in three binary LMC clusters.

Abstract

Three close pair clusters of the LMC, NGC 2006/SL 538, NGC 2011a/b and NGC 2042a/b, have been studied in order to establish their binarity. The stellar content in the outer region of each cluster has been investigated by means of low resolution objective UK Schmidt prism spectra, the cores of the clusters have been examined using low resolution integrated IUE spectra, whereas their density profiles and their observed dynamical parameters have been derived by means of star counts. The integrated spectra of their cores and the stellar content of their outer cluster regions have shown a common origin and a very young age (< 2 10^7^ yr) for each member of the pairs whereas their dynamical study has shown that they are gravitationally interacting. Comparing the age of their stellar content with their dynamical and relaxation times it has been found that these clusters are physically associated and had no time to relax by stellar encounters, no time to merge and no time to be destroyed by dynamical friction.