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

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

Automated summary

BPS CS 22940-0009 is a helium-rich B-type star that shares characteristics with both helium-rich B subdwarfs and extreme helium stars. The analysis of its optical spectrum reveals atmospheric parameters and abundance profile consistent with known helium star populations, suggesting that BPS CS 22940-0009 may have formed from the merger of two helium white dwarfs and is currently evolving towards the helium main sequence.