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 $T_{\mathrm{eff}}=34970\pm 370$ K, $\log g/\mathrm{cm}{\mathrm{s}}^{-2}=4.79\pm 0.17$, $n_{\mathrm{H}}/n_{\mathrm{He}}\simeq 0.007$, $n_{\mathrm{C}}/n_{\mathrm{He}}\simeq 0.007$, $n_{\mathrm{N}}/n_{\mathrm{He}}\simeq 0.002$, 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 toward the helium main sequence.

16 pages, 8 figures, to be published in Monthly Notices of the Royal Astronomical Society

References in corpus (10)

• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• SkyMapper Southern Survey: Second Data Release (DR2)
• Modeling He-rich subdwarfs through the hot-flasher Scenario
• Hydrogen and helium line formation in OB dwarfs and giants. A hybrid non-LTE approach
• Abundance analyses of helium-rich subluminous B stars
• The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis
• GALEX J184559.8-413827: a new extreme helium star identified using SALT
• A search for heavy-metal stars: abundance analyses of hot subdwarfs with Subaru

Cited by in corpus (1)

• The distribution, kinematics and luminosities of extreme helium stars as probes of their origin and evolution