Oxygen isotopic ratios in cool R Coronae Borealis stars

Abstract

We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from high-resolution (R=50,000) K-band spectra. Lower limits to the 16O/17O and 14N/15}N ratios as well as Na and S abundances (when possible) are also given. RCB stars in our sample generally display less 18O than HdC stars - the derived 16O/18O ratios range from 3 to 20. The only exception is the RCB star WX CrA, which seems to be a HdC-like star with 16O/18O=0.3. Our result of a higher 16O/18O ratio for the RCB stars must be accounted for by a theory of the formation and evolution of HdC and RCB stars. We speculate that a late dredge-up of products of He-burning, principally 12C and 16O, may convert a 18O-rich HdC star into a 18O-poor RCB star as the H-deficient star begins its final evolution from a cool supergiant to the top of the white dwarf cooling track.

Accepted for publication in the Astrophysical Journal; 21 pages, 3 Tables, 11 Figures

References in corpus (3)

• Very Large Excesses of 18O in Hydrogen-Deficient Carbon and R Coronae Borealis Stars: Evidence for White Dwarf Mergers
• High-resolution spectroscopy of the R Coronae Borealis Star V Coronae Australis
• CNO abundances of HdC and RCB stars: a view of the nucleosynthesis in a white dwarf merger

Cited by in corpus (32)

• Double white dwarf mergers and elemental surface abundances in extreme helium and R Coronae Borealis stars
• Rapid Rotation of Low-Mass Red Giants Using APOKASC: A Measure of Interaction Rates on the Post-main-sequence
• The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final Helium Shell Flash?
• Do R Coronae Borealis Stars Form from Double White Dwarf Mergers?
• The ongoing pursuit of R Coronae Borealis stars: ASAS-3 survey strikes again
• 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
• Tracking down R Coronae Borealis stars from their mid-infrared WISE colours
• The Dust Properties of Two Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: in Search of a Possible Link
• A plethora of new R Coronae Borealis stars discovered from a dedicated spectroscopic follow-up survey
• Oxygen isotopic ratios in intermediate-mass red giants
• Evolving R Coronae Borealis Stars with MESA
• Neon and CNO Abundances for Extreme Helium Stars -- A Non-LTE Analysis
• Dust around R Coronae Borealis stars: I. Spitzer/IRS observations
• The impact of the revised ${}^{17}$O$(p,\alpha {)}^{14}$N reaction rate on ${}^{17}$O stellar abundances and yields
• The Galactic R Coronae Borealis stars : the C2 Swan bands, the carbon problem, and the 12C/13C ratio
• R Coronae Borealis Stars are Viable Factories of Pre-solar Grains
• Dust around R Coronae Borealis stars: II. Infrared emission features in a H-poor environment
• Modeling R Coronae Borealis Stars: Effects of He-Burning Shell Temperature and Metallicity
• Census of R Coronae Borealis stars I: Infrared light curves from Palomar Gattini IR
• The role of dredge-up in double white dwarf mergers
• The Double Dust Envelopes of R Coronae Borealis Stars
• R Coronae Borealis and dustless Hydrogen-deficient Carbon stars have different oxygen isotope ratios
• An All-Sky Search For R Coronae Borealis Stars in ASAS-SN
• VLTI observations of the dust geometry around R Coronae Borealis stars
• Are DY\,Persei stars cooler cousins of R Coronae Borealis stars?
• Abundance analyses of the new R Coronae Borealis stars: ASAS-RCB-8 and ASAS-RCB-10
• The carbon star DY Persei may be a cool R Coronae Borealis variable
• The changing nebula around the hot R Coronae Borealis star DY Centauri
• R Coronae Borealis Stars in M31 from the Palomar Transient Factory
• The hot R Coronae Borealis star DY Centauri is a binary
• Oxygen Isotope Ratios in Hydrogen-Deficient Carbon Stars: A Correlation with Effective Temperature and Implications for White Dwarf Merger Outcomes
• Merged white dwarfs and nucleosynthesis