A MONTE-CARLO STUDY OF THE POPULATION OF PLANETARY-NEBULAE IN THE GALACTIC BULGE

A new method of analysis of the planetary nebula (PN) phenemenon is pr oposed, in which the observations of a complete sample of PN in the Ga lactic bulge (GBPN) are compared to simulated samples. Such an approac h will provide important tests for the theory of evolution of planetar y nebulae and their nuclei. In the framework of the presently adopted models for the PN evolution, we show how the average properties of the GBPN observed with the VLA are biased with respect to those of the pa rent PN populations compatible with the observational data. We find th at, assuming that the PN nuclei evolve according to the Schonberner tr acks, the central star mass distribution for the observable GBPN is na rrow (standard deviation of less than 0.05 M.) and centered on value e qual to 0.6 M. or less. We show that a campaign of systematic measurem ents of the GBPN expansion velocities will lead to useful constraints to the models. We also show how some of the widespread ideas on PN (e. g. the usual interpretation of the nebular mass-radius relation) break down with a more careful analysis taking explicitely into account the observational selection effects.