Non-Lte Model Atmospheres. VII. The Hydrogen and Helium Spectra of the O Stars

An extensive series of non-LTE calculations of the H, He I, and He II spectra of 0 stars has been carried out by using relatively complete atomic models, allowing for several levels and lines simultaneously. Results are presented for continuum fluxes and for equivalent widths and profiles of the lines. Detailed comparisons are made with the spectra of eleven 0 and B0 stars. It is found that major departures from LTE play a dominant role in the formation of the H and He spectra of these stars. With the non-LTE models we are able to obtain for the first time a consistent explanation of the observations of both lines and continua. The present results show that an assumed helium/hydrogen ratio of 0.10 reproduces the observations; thus present estimates of abundances in 0 stars helium are consistent with those derived by other methods.