Evolving R Coronae Borealis stars with mesa

Journal Article · 27 June 2019 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stz1732 · OSTI ID:1532815

Lauer, Amber ^[1]; Chatzopoulos, Emmanouil ^[2]; Clayton, Geoffrey C.  ^[2]; Frank, Juhan ^[2]; Marcello, Dominic C. ^[2]

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1. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA, Triangle Universities Nuclear Lab, Duke University, Durham, NC 27710, USA
2. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA

ABSTRACT The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich supergiants. They undergo extreme, irregular declines in brightness of many magnitudes due to the formation of thick clouds of carbon dust. It is thought that RCB stars result from the mergers of CO/He white dwarf (WD) binaries. We constructed post-merger spherically symmetric models computed with the mesa code, and then followed the evolution into the region of the Hertzsprung-Russell (H−R) diagram where the RCB stars are located. We also investigated nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed. We have also discovered that the N abundance depends sensitively on the peak temperature in the He-burning shell. Our mesa modelling consists of engineering the star by adding He-WD material to an initial CO-WD model, and then following the post-merger evolution using a nuclear-reaction network to match the observed RCB abundances as it expands and cools to become an RCB star. These new models are more physical because they include rotation, mixing, mass-loss, and nucleosynthesis within mesa. We follow the later evolution beyond the RCB phase to determine the stars’ likely lifetimes. The relative numbers of known RCB and extreme helium stars correspond well to the lifetimes predicted from the mesa models. In addition, most of computed abundances agree very well with the observed range of abundances for the RCB class.

• Sponsoring Organization: USDOE
• Grant/Contract Number: DE–SC0014231
• OSTI ID: 1532815
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Vol. 488 Journal Issue: 1; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English