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 star s of 19 planetary nebulae, (2) we discuss their distance and position on the T/L diagram. By comparison with the distances determined by ind ividual or statistical methods, we see that most of these ''ground'' d istances 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 HIP PARCOS distances to SwSt 1 and Hu 2-1 are unexpected and are not trust worthy. Peculiar motions are analyzed, in terms of astrophysical param eters of the binary system A 35, and in relation with asymmetric morph ology.