Detection of fluorine in hot Extreme Helium Stars

Abstract

The main objective of this paper is to explore abundances of fluorine in hot Extreme Helium Stars (EHes). Overabundance of fluorine is a characteristic feature for cool EHes and R Coronae Borealis (RCB) stars and further enforces their close connection. For hot EHes this relationship with the cooler EHes, based on their fluorine abundance is unexplored. We present in this paper the first abundance estimates of fluorine determined from singly ionised fluorine lines (F\,{\sc ii}) for 10 hot EHe stars from optical spectra. Fluorine abundances were determined using the F\,{\sc ii} lines in two windows centered at 3505 Å\ and 3850 Å. Six of the 10 stars show significant enhancement of fluorine similar to the cool EHes. Two carbon-poor hot EHes show no signature of fluorine and have a significant low upper limit for the F abundance. These fluorine abundances are compared with the other elemental abundances observed in these stars which provide an idea about the formation and evolution of these stars. The trends of fluorine with C, O, and Ne show that significant helium burning after a CO-He white dwarf merger can account for a majority of the observed abundances. Predictions from simulations of white dwarf mergers are discussed in light of the observed abundances.

arXiv comment41 pages, 18 figures, 5 tables, Accepted for publication in ApJ

References in corpus (25)

• Abundances of the elements in the solar system
• Very Large Excesses of 18O in Hydrogen-Deficient Carbon and R Coronae Borealis Stars: Evidence for White Dwarf Mergers
• Internal mixing and surface abundance of [WC]-CSPN
• Post-merger evolution of carbon-oxygen + helium white dwarf binaries and the origin of R Coronae Borealis and extreme helium stars
• Fluorine in R Coronae Borealis Stars
• Nucleosynthesis during the Merger of White Dwarfs and the Origin of R Coronae Borealis Stars
• On the galactic chemical evolution of sulfur
• Abundance analyses of cool extreme helium stars
• An analysis of ultraviolet spectra of Extreme Helium Stars and new clues to their origins
• Reproducing the observed abundances in RCB and HdC stars with post-double degenerate merger models - constraints on merger and post-merger simulations and physics processes
• Can R CrB stars form from the merger of two helium white dwarfs?
• Fluorine in the Solar neighborhood: No evidence for the neutrino process
• A new solar fluorine abundance and a fluorine determination in the two open clusters M 67 and NGC 6404
• Fluorine in the solar neighborhood - is it all produced in AGB-stars?
• Evolving R Coronae Borealis Stars with MESA
• Neon and CNO Abundances for Extreme Helium Stars -- A Non-LTE Analysis
• Discovery of Fluorine in Cool Extreme Helium Stars
• Fluorine Abundances of Galactic Low-Metallicity Giants
• Isotope shifts in ${}^{20,22}$Ne -- Precision measurements and global analysis in the framework of intermediate coupling
• GALEX J184559.8-413827: a new extreme helium star identified using SALT
• Abundance analysis of cool extreme helium star: LSS 3378
• Fluorine Abundances in the Globular Cluster M 4
• Non-Local Thermodynamic Equilibrium abundance analyses of the extreme helium stars: V652 Her and HD 144941
• Abundance analyses of the new R Coronae Borealis stars: ASAS-RCB-8 and ASAS-RCB-10
• On the binary helium star DY Centauri: Chemical composition and evolutionary state

Cited by in corpus (7)

• Modeling R Coronae Borealis Stars: Effects of He-Burning Shell Temperature and Metallicity
• Fluorine Abundances in the Galactic Nuclear Star Cluster
• The first heavy-metal hot subdwarf composite binary SB 744
• Revised surface abundances of R Coronae Borealis stars
• Merged white dwarfs and nucleosynthesis
• Detection of Enhanced Germanium in a New Cool Extreme Helium Star A 980: Insights and Implications
• Method for tilt correction of calibration lines in high resolution spectra