| Summary: | We enhance the treatment of crystallization for models of white dwarfs (WDs) in the stellar evolution software Modules for Experiments in Stellar Astrophysics (MESA) by implementing carbon–oxygen (C/O) phase separation. The phase separation process during crystallization leads to transport of oxygen toward the centers of WDs, resulting in a more compact structure that liberates gravitational energy as additional heating that modestly slows WD cooling timescales. We quantify this cooling delay in MESA C/O WD models over the mass range 0.5–1.0 M _⊙ , finding delays of 0.5–0.8 Gyr for typical C/O interior profiles. MESA WD cooling timescales including this effect are generally comparable to other WD evolution models that make similar assumptions about input physics. When considering phase separation alongside ^22 Ne sedimentation, however, we find that both MESA and BaSTI WD cooling models predict a more modest sedimentation delay than the latest LPCODE models, and this may therefore require a reevaluation of previously proposed solutions to some WD cooling anomalies that were based on LPCODE models of ^22 Ne sedimentation. Our implementation of C/O phase separation in the open-source stellar evolution software MESA provides an important tool for building realistic grids of WD cooling models, as well as a framework for expanding on our implementation to explore additional physical processes related to phase transitions and associated fluid motions in WD interiors.
|
|---|