A sample of planetary nebulae observed by HIPPARCOS

By using HIPPARCOS data (magnitudes, parallaxes, proper motions), (1) we determine new values of the apparent luminosity of the central stars of 19 planetary nebulae, (2) we discuss their distance and position on the T/L diagram. By comparison with the distances determined by individual or statistical methods, we see that most of these "ground" distances look overestimated when we trust the HIPPARCOS trigonometric parallaxes. It seems that for compact nebulae, the nebula itself could influence the parallax measurement. In particular, the very small HIPPARCOS distances to SwSt 1 and Hu 2-1 are unexpected and are not trustworthy. Peculiar motions are analyzed, in terms of astrophysical parameters of the binary system A 35, and in relation with asymmetric morphology.