On the binary helium star DY Centauri: Chemical composition and evolutionary state

Abstract

DY Cen has shown a steady fading of its visual light by about 1 magnitude in the last 40 years suggesting a secular increase in its effective temperature. We have conducted non-LTE and LTE abundance analyses to determine the star's effective temperature, surface gravity, and chemical composition using high-resolution spectra obtained over two decades. The derived stellar parameters for three epochs suggest that DY Cen has evolved at a constant luminosity and has become hotter by about 5000 K in 23 years. We show that the derived abundances remain unchanged for the three epochs. The derived abundances of the key elements, including F and Ne, are as observed for the extreme helium stars resulting from a merger of an He white dwarf with a C-O white dwarf. Thus, DY Cen by chemical composition appears to be also a product of a merger of two white dwarfs. This appearance seems to be at odds with the recent suggestion that DY Cen is a single-lined spectroscopic binary.

Accepted to ApJ with 8 Figures and 5 Tables

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• SALT revisits DY Cen: a rapidly-evolving strontium-rich single helium star
• Non-Local Thermodynamic Equilibrium abundance analyses of the extreme helium stars: V652 Her and HD 144941
• Detection of fluorine in hot Extreme Helium Stars
• Revised surface abundances of R Coronae Borealis stars
• Detection of Enhanced Germanium in a New Cool Extreme Helium Star A 980: Insights and Implications