Published in

Oxford University Press, Monthly Notices of the Royal Astronomical Society, 1(516), p. 794-810, 2022

DOI: 10.1093/mnras/stac2305

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

Journal article published in 2022 by E. J. Snowdon ORCID, L. J. A. Scott ORCID, C. S. Jeffery ORCID, V. M. Woolf ORCID
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Data provided by SHERPA/RoMEO

Abstract

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 $T_{\rm eff} = 34\, 970 ± 370$ K, $\log g/{\rm cm\, s^{-2}} = 4.79 ± 0.17$, 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.