We present a model atmosphere analysis of ten new DO white dwarfs and five new PG 1159 stars discovered in the Sloan Digital Sky Survey DR DR = Data Release 1 , DR2 and DR3 .
This is a significant increase in the number of known DOs and PG 1159 stars .
DO white dwarfs are situated on the white dwarf cooling sequence from the upper hot end ( T _ { eff } \approx 120 000 K ) down to the DB gap ( T _ { eff } \approx 45 000 K ) .
PG 1159 stars on the other hand feature effective temperatures which exceed T _ { eff } = 65 000 K with an upper limit of T _ { eff } = 200 000 K and are the proposed precursors of DO white dwarfs .
Improved statistics are necessary to investigate the evolutionary link between these two types of stars .
From optical SDSS spectra effective temperatures , surface gravities and element abundances are determined by means of non-LTE model atmospheres .