Can R Coronae Borealis stars form from the merger of two helium white dwarfs

摘要: Due to orbital decay by gravitational wave radiation, some close binary helium white dwarfs are expected merge within a Hubble time. The immediate merger products believed be He-rich subdwarf O (sdO) stars, essentially main-sequence stars. We present new evolution calculations for these post-merger stars beyond the core He-burning phase. most massive sdO develop strong shell and evolve become giants. include nucleosynthesis following of 0.4 M⊙ He dwarf pairs with metallicities Z= 0.0001, 0.004, 0.008 0.02. surface chemistries resulting giants in partial agreement observed abundances R Coronae Borealis (R CrB) extreme Such might represent third, albeit rare, channel latter, addition CO+He very late thermal pulse channels proposed previously. confirm recent suggestion that Li seen R CrB could form naturally during hot phase presence 3He from donor dwarf.