Comparison of abundances of WD and the MS star using optical data. Abundances are shown relative to Mg, and normalised to Solar composition on a log scale. The model with the highest Bayesian evidence, which includes heating, is shown in orange. This model also includes a feeding zone. The best model which does not include heating is shown in blue. This model cannot fit the data well, and so is heavily disfavoured. The small confidence interval for the non-heating model is due to its limited number of free parameters, mostly fixed or tightly constrained.