On masses and ejection of planetary nebulae around PG 1159 stars

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The H-deficient PG 1159 stars are rosetta stones for the understanding of post-AGB evolution. At their hottest stage of evolution, they display the formation of white dwarfs: the nuclear burning is close to its end and gravitational effects will further dominate their evolution. Two facts make them ideal to check against evolutionary theory: firstly, 7 out of 27 known PG 1159 stars are pulsators; secondly, about every other PG 1159 star has an associated planetary nebula. We propose a detailed examination of these by imaging and spectroscopy in order to investigate a possible relation between the masses of central stars and their surrounding nebula, the ionization structure of the nebulae which displays the time-dependence of their ejection, and the chemical composition of the nebulae.