Extended Data Fig. 3: Modelled surface luminosity for different scenarios.

The surface luminosity is shown as a function of cooling age for 1.05, 1.15 and 1.25 M_☉ C–O white dwarf models. The dotted lines correspond to the nominal case considered in Fig. 4a. The solid lines represent cooling sequences in which a standard composition⁷ is used instead of a post-merger profile (a), in which distillation is only partially completed (b) and in which X(²²Ne) = 0.06 and distillation is turned off (c). Post-merger chemical profiles are assumed in panels b and c.