ASTROPHYSICS AND SPACE SCIENCE, cilt.329, sa.1-2, ss.119-125, 2010 (SCI-Expanded)
As part of an extended study of the surface abundances of extremely helium-rich hot subdwarfs, highresolution optical échelle spectra of the three helium-rich subdwarf B stars LB 1766, SB 21 and BPS 22940–0009 are presented. Opacity-sampled line-blanketed model atmospheres have been used to derive atmospheric properties and surface abundances. All three stars are moderately metal-poor compared with the Sun ([Fe/H] ≈ −0.4). The first two stars are nitrogen-rich He-sdBs, while the third is a carbon-rich He-sdB. The surface composition and locus of single N-rich He-sdBs are currently best explained by the merger of two helium white dwarfs. C-rich He-sdBs require further investigation.