The behavior of the velocity projection factor was studied for three individual Lines, He I 4438 Å, Si III 4553 Å, and N II 4442 Å, and for the complete spectrum in the radially pulsating helium rich star V652 Her. It is shown that the projection factor is itself a function of expansion velocity.

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We present a statistical analysis of a complete sample (255) of northern planetary nebulae (PNe). Our analysis is based on morphology as a main parameter. The major morphological classes are: round (26&#37 of the sample), elliptical (61&#37), and bipolar (13&#37) PNe. About a half of the round and 30 &#37 of the elliptical PNe present multiple

Multiple shell planetary nebulae (MSPNe) are most likely a consequence of the modulation of the mass-loss rate during the thermal pulses on the AGB. By using numerical simulations of their formation, the models' predictions and the history of the winds can be investigated. As their halos have low densities and expansion velocities, MSPNe are

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