Compositionally-driven convection in CO white dwarfs interiors during crystallization

Matias Castro Tapia ( Université McGill )

Once white dwarfs (WDs) form, they begin to cool on Gyr scales. At some point, the plasma in their core is dense and cool enough that the Coulomb forces dominate, and a solid lattice starts to grow outwards. The species in the interior redistribute depending on their phase diagram leading to gravitational sedimentation or unstable composition gradients that drive convection. However, such effects are not usually included in WD models; we use the MESA stellar evolution code to study the heat transport and convective velocities resulting from compositionally-driven convection in carbon-oxygen (CO) WDs, and also to calculate the impact on their cooling curve. Our initial results suggest that the efficient thermal diffusion in the WD interior should stabilize the inward convective heat flux, and then the process occurs in the thermohaline convection regime. Additionally, the convective velocities that we estimate are much smaller than what is obtained in recent studies challenging the idea of a crystallization-driven dynamo inducing strong magnetic fields in cool WDs.