Description
White dwarfs which are “polluted” with metals can be used to gain unique insights into the geology of exoplanetary material. These objects provide evidence that iron core formation and incomplete condensation, the key geological processes defining Earth’s first order structure and composition, also operate in exoplanetary systems. However, analysis of polluted white dwarfs is complicated by the effect of “differential sinking”: different metals sink through the white dwarf’s atmosphere on different timescales. Metals which sink faster become artificially depleted, distorting the apparent composition of accreted material. This effect could potentially change the geological interpretation, so it is crucial to correct for it. However, the required correction depends on the treatment of the white dwarf's atmospheric physics. The extent of convective overshoot is of particular importance, as is the presence or absence of thermohaline mixing. These effects change the predicted (relative) sinking timescales of different metals. We compile grids of metal sinking timescales calculated using different treatments of these effects, among others. We present a range of case studies showing how the geological interpretation of white dwarf pollution can be affected by the use of these different grids. We also illustrate a generalised analytic framework to predict which white dwarfs are most likely to be affected as a function of their atmospheric type, surface gravity and effective temperature.
