SIMBAD references

We have constituted a sample of about 80 PN with defined morphologies and well observed basic parameters (fluxes, angular radii, expansion velocities and magnitudes of the central stars). For these PN, we have derived the central star masses by comparing the observed set of parameters with those predicted by a simple evolutionary model of a PN, expanding at the same velocity as the observed one. We have then examined the relations between the PN morphological types and other properties, linked to the central star mass. Bipolar PN are shown to have a wider distribution of central star masses than the rest of PN, and shifted towards higher values. They lie closer to the Galactic plane and tend to have larger N/O ratios. Point symmetric PN, which have not been much studied so far, are found to constitute an outstanding class. They show an almost perfect M_*-v_exp correlation. They correspond to a rather short evolutionary stage of PN. They lie, on average, further from the Galactic plane than bipolar PN and tend to have lower N/O. Globally, PN with higher central star masses are found closer to the Galactic plane, and the observed relation between N/O and M_* is roughly consistent with the predictions from evolutionary models for AGB stars.