  We carried out a quantitative spectral analysis of 73 hot subluminous O-stars
selected from the SDSS spectral database. While the helium deficient sdOs are
scattered over a wide range of effective temperature and gravity, the helium
enriched sdO stars are concentrated in a small intervall of 40kK to 50kK and
log g = 5.5 ... 6.0. Comparing the distribution in the T_eff-log g-diagram with
evolutionary tracks, we find the helium deficient sdOs to be the progeny of the
sdB stars. The results for the helium enriched ones are less conclusive. Both
the merger of two white dwarfs and the delayed helium core flash scenarios are
viable options to be explored further.
