Dynamical evolution and spectral characteristics of the stellar group Mamajek 2

The dynamical evolution of the recently detected stellar group Mamajek 2 is studied by means of its past 3D orbit. The past orbits of the open clusters NGC 2516 and $\alpha$ 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 $\pm$ 5 Myr. This dynamical age confirms the individual ages of 140 Myr for NGC 2516 and 120 $\pm$ 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.