A comparison of Hipparcos parallaxes with planetary nebulae spectroscopic distances

The Hipparcos satellite has measured the parallax of a small sample of planetary nebulae. In this paper we consider the results for 3 planetary nebulae (PN) for which spectroscopic distances have also been determined from stellar gravities. These gravities in turn have been derived from profile fitting of selected hydrogen and helium lines (Mendez et al., 1988 a, b, 1992). A comparison of these distances shows that the Hipparcos distances are all considerably smaller. This same effect has been found in two other PN central stars, whose distance has been determined from the VLA measured nebular expansion. The question of the mass of the central star of PHL 932 is also discussed.