Nucleosynthesis during the Merger of White Dwarfs and the Origin of R Coronae Borealis Stars

Understand

Many hydrogen deficient stars are characterised by surface abundance patterns that are hard to reconcile with conventional stellar evolution.

• Instead, it has been suggested that they may represent the result of a merger episode between a helium and a carbon-oxygen white dwarf.
• In this Letter, we present a nucleosynthesis study of the merger of a 0.4 M_sol helium white dwarf with a 0.8 M_sol carbon-oxygen white dwarf, by coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code.
• The resulting chemical abundance pattern, particularly for oxygen and fluorine, is in qualitative agreement with the observed abundances in R Coronae Borealis stars.