2009ApJ...691..212J

The dynamical evolution of the recently detected stellar group Mamajek 2 is studied by means of its past three-dimensional orbit. The past orbits of the open clusters NGC 2516 and α Persei, belonging to the so-called "Local Association," were also computed in order to check for a possible common past dynamical evolution of these systems. To complete the data of the Mamajek 2 small group, we have obtained high-resolution FEROS spectra to measure the radial and also the projected rotational velocities of its members; an estimate of its metallicity was obtained as well. Two exceptionally low-rotating A-type stars turned out to be a strong magnetic Ap star in one case, and a normal A0 star with near-solar metallicity in the other. The dynamical results showed that NGC 2516 and Mamajek 2 may have had a common origin at the age of 135±5 Myr. This dynamical age confirms the individual ages of 140 Myr for NGC 2516 and 120±25 Myr for Mamajek 2 obtained independently by photometric methods. Both these groups appear to have the same solar metallicity giving support to a common birth scenario. The dynamical approach is showing that some bound open clusters can form in a coeval fashion with unbound stellar groups or with associations.