JEFFERY C.S., HAMILL P.J., HARRISON P.M. and JEFFERS S.V.
Abstract (from CDS):
We have carried out quantitative analyses of three very low surface gravity extreme helium stars with very similar spectra. Their effective temperatures of ∼16000K fill a gap in a nearly continuous sequence of extreme helium stars all having similar luminosity-to-mass ratios, but extending from effective temperatures around 12000K to more than 20000K. Because of the low surface gravities and extremely rich line spectra, the model atmosphere calculations have been reviewed, and large-scale spectral synthesis techniques have been introduced to the analyses for the first time. In addition to the high carbon and nitrogen abundances usually seen in extreme helium stars, two of the programme stars have extremely high oxygen abundances, comparable with or greater than their carbon abundances.