Using open clusters to study mixing in low- and intermediate-mass stars
  In many evolutionary stages, low- and intermediate-mass stars show signs of mixing of the surface material with material from the interior. To account for all the details revealed by the observations it is necessary to include non-standard physical processes in the models (e.g. atomic diffusion and rotation-induced mixing). The study of mixing in stars of different masses, ages, and chemical composition helps to identify and constrain these processes. In this sense, stars in open clusters are the ideal targets. All stars in one given cluster have the same age and chemical composition, and their masses can be well estimated. By studying many clusters, one can separate and trace the effects of these different parameters. 
Rodolfo Smiljanic (ESO)
astro-ph.SR