Hydrodynamic simulations of white dwarf-white dwarf mergers and the origin of R Coronae Borealis stars
Journal article, 2024
We study the properties of double white dwarf (DWD) mergers by performing hydrodynamic simulations using the new and improved adaptive mesh refinement code octo-tiger. We follow the orbital evolution of DWD systems of mass ratio $q=0.7$ for tens of orbits until and after the merger to investigate them as a possible origin for R Coronae Borealis (RCB) type stars. We reproduce previous results, finding that during the merger, the helium WD donor star is tidally disrupted within 20-80 min since the beginning of the simulation onto the accretor carbon-oxygen WD, creating a high temperature shell around the accretor. We investigate the possible helium burning in this shell and the merged object's general structure. Specifically, we are interested in the amount of oxygen-16 dredged-up from the accretor to the hot shell and the amount of oxygen-18 produced. This is critical as the discovery of very low oxygen-16 to oxygen-18 ratios in RCB stars pointed out the merger scenario as a favourable explanation for their origin. A small amount of hydrogen in the donor may help keep the oxygen-16 to oxygen-18 ratios within observational bounds, even if moderate dredge-up from the accretor occurs. In addition, we perform a resolution study to reconcile the difference found in the amount of oxygen-16 dredge-up between smoothed-particle hydrodynamics and grid-based simulations.
hydrodynamics
stars: carbon
stars: evolution
white dwarfs
methods: numerical
binaries: close
Author
Sagiv Shiber
Louisiana State University
Orsola De Marco
Macquarie University
Patrick M. Motl
Indiana University
Bradley Munson
McMaster University
Louisiana State University
Dominic C. Marcello
Louisiana State University
Juhan Frank
Louisiana State University
Patrick Diehl
Los Alamos National Laboratory
Louisiana State University
Geoffrey C. Clayton
Louisiana State University
Bennett N. Skinner
McMaster University
University of Arizona
Hartmut Kaiser
Louisiana State University
Gregor Daiss
Louisiana State University
University of Stuttgart
Dirk Pflueger
University of Stuttgart
Jan Staff
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 535 2 1914-1943Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1093/mnras/stae2343