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 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 $T_{\rm eff} = 34\, 970 \pm 370$ K, $\log g/{\rm cm\, s^{-2}} = 4.79 \pm 0.17$, nH/nHe ≃ 0.007, nC/nHe ≃ 0.007, nN/nHe ≃ 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 3α 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2022
- DOI:
- 10.1093/mnras/stac2305
- arXiv:
- arXiv:2208.07720
- Bibcode:
- 2022MNRAS.516..794S
- Keywords:
-
- stars: abundances;
- stars: chemically peculiar;
- stars: early-type;
- stars: individual: BPS CS 22940-0009;
- subdwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 16 pages, 8 figures, to be published in Monthly Notices of the Royal Astronomical Society