Abstract

If the mass loss rate, dot {M}, or the modified wind momentum, Pi , of central stars of planetary nebulae (CSPN) is strictly related to the luminosity, the study of their winds can be used to derive their distance as suggested in the literature. However, the mass loss rates and modified wind momenta of a sample of 13 CSPN published in the literature show a separation into two groups, which differ by a factor 10 to 10² in Pi . This is partly, but not completely, due to differences in the adopted methods for mass loss determinations, and partly due to differences in the adopted stellar parameters, mainly the effective temperature. We have adopted a homogeneous set of stellar parameters, based on the Zanstra method, the dynamical ages of the nebulae and on evolutionary tracks, and scaled the mass loss rates accordingly. The revised data show that there is a large jump in dot {M} and Pi near T_eff =~ 60 000 K, with dot {M} and Pi being larger by a factor 10 to 10² for the cooler group of CSPN of spectral type Of, than for the hotter group of type O. This discontinuity is most likely due to a bi-stability jump. The revised data do not show a clear relation between Pi and the luminosity. The consequences are discussed in terms of the post-AGB evolution theory and the radiation driven wind models.