Spectroscopic analysis of BPS CS 22940−0009: connecting evolved helium stars

ABSTRACT BPS CS 22940−0009 is a helium-rich B-star that shares characteristics with both B subdwarfs and extreme helium stars. The optical spectrum of has been analysed from SALT observations. atmospheric parameters were found to be $T_{\rm eff} = 34\, 970 \pm 370$ K, $\log g/{\rm cm\, s^{-2}} 4.79 0.17$, nH/nHe ≃ 0.007, nC/nHe nN/nHe 0.002, although further improvement the line fits would desirable. This places star as link between He-sdB EHe populations in g-T space. abundance profile shows enrichment N CNO-processing, C 3α burning. Depletion Al, Si, S low upper limit for Fe show intrinsically metal-poor. results are consistent having formed merger two white dwarfs currently evolving towards main sequence.