Physical parameters of helium-rich subdwarf B stars from medium resolution optical spectroscopy

Most subdwarf B (sdB) stars have spectra that show helium (He) abundances depleted to a lesser or greater extent. This has been attributed to diffusion and gravitational settling. However a small but significant number of stars with similar temperatures and gravities show relatively strong helium spectra. The question is how these helium-rich sdB (He-sdB) stars are related to their He-deficient counterparts. We present physical parameters for sample of He-sdB stars using line-blanketed LTE models. From the analysis we show that the He-sdB stars are quite distinct from the He-poor sdB. We also explore the idea of a possible link between some extreme helium (EHe) stars and He-rich subdwarf O (He-sdO) stars.