Instituto de Astronomia , UNAM, Mexico
In this contribution I will present the results of measuring the bulk outflow shell velocities for a large number of planetary nebulae that span a wide range of evolutionary stages and different stellar populations. The data are based on the SPM Kinematic Catalogue of galactic planetary nebulae. These results reveal from a statistical perspective the kinematic evolution of the bulk outflow or expansion velocities of PNe and their relation to the changing characteristics of the central star, providing for the first time a solid benchmark from observations for models predictions.
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