We use Modules for Experiments in Stellar Astrophysics ( MESA ) to construct stellar evolution models that reach a hydrogen-deficient , carbon-rich giant phase like the R Coronae Borealis ( R CrB ) stars .
These models use opacities from OPAL and ÆSOPUS that cover the conditions in the cool , H-deficient , CNO-enhanced envelopes of these stars .
We compare models that begin from homogeneous He stars with models constructed to reproduce the remnant structure shortly after the merger of a He and a CO white dwarf ( WD ) .
We emphasize that models originating from merger scenarios have a thermal reconfiguration phase that can last up to \approx 1 \mathrm { kyr } post merger , suggesting some galactic objects should be in this phase .
We illustrate the important role of mass loss in setting the lifetimes of the R CrB stars .
Using AGB-like mass loss prescriptions , models with CO WD primaries \lesssim 0.7 \mathrm { \mathrm { M } _ { \odot } } typically leave the R CrB phase with total masses \approx 0.6 - 0.7 \mathrm { \mathrm { M } _ { \odot } } , roughly independent of their total mass immediately post-merger .
This implies that the descendants of the R CrB stars may have a relatively narrow range in mass and luminosity as extreme He stars and a relatively narrow range in mass as single WDs .