  Context: The Sloan Digital Sky Survey Data Release 4 has provided spectra of
several new PG 1159 stars and DO white dwarfs. This increase in known hot
H-deficient compact objects significantly improves the statistics and helps to
investigate late stages of stellar evolution. Aims: From the optical SDSS
spectra, effective temperatures and surface gravities are derived in order to
place the observed objects in an evolutionary context. Especially the
connection between PG 1159 stars and DO white dwarfs shall be investigated.
Method: Using our non-LTE model atmospheres and applying chi^2-fitting
techniques, we determine stellar parameters and their errors. We derive total
stellar masses for the DO white dwarfs using model evolutionary tracks.
Results: We confirm three PG 1159 stars, with one showing ultra-high excitation
ion features, and one sdO which we originally classified as a PG 1159 star.
Additionally, we re-analysed the known PG 1159 star, PG 1424+535, with our new
models. Furthermore, we present the first spectral analyses of thirteen DO
white dwarfs, three of which show M-star features in their spectra, while two
display ultra-high excitation ion features.
