The nitrogen and silicon abundance of sdO-stars.

Abundances of nitrogen and silicon were determined by means of multi-level calculations for three helium-rich subluminous O-stars, HD 49798, HD 127493 and BD+75 deg 325. Analysis of the line spectra of a III and Si IV yields three results: microturbulence is small, i.e., less than 10 km sec; the silicon abundance is solar, and nitrogen is strongly overabundant. Taking into account the carbon-deficiency of these stars and the fact that no lines of oxygen are seen in the spectra, it is concluded that CNO cycle-processed material is involved.