Illustrative summary of the model advanced in this work. (a) DAHe white dwarf created by a stellar merger, such as between a carbon–oxygen and helium-core white dwarf (as shown by, e.g. Clayton et al. 2007; Menon et al. 2013) or subgiant. (b) Resulting ²²Ne-rich remnant cools until the onset of carbon–oxygen crystallization and ²²Ne distillation, which halt the cooling near T_eff ≈ 7500 K. (c) Distillation also provides sufficient energy to sustain a strong magnetic dynamo that powers the characteristic chromospheric emission through Ohmic heating. Superscript numbers indicate observed properties of DAHe stars: ¹typical masses M ≃ 0.8 M_⊙, ²rapid rotation, ³similar T_eff ≈ 7500 K near that of carbon–oxygen crystallization, ⁴magnetic fields B ≳ 5 MG, ⁵Balmer lines in emission, ⁶rotational light curve modulation, and ⁷lack of coronal emission in the prototype.