Each curve depicts the evolution of the temperature-density profile of the accreting white dwarf at various times, as indicated in the legend, for a system that undergoes double detonation supernova (left panel) and a He nova (right panel). The black star indicates the C/O-He boundary, that moves to higher density as the WD accretes and contracts. In the left panel, the WD accretes at the rate of ∼10⁻⁸ M_⊙ yr⁻¹, igniting the high density regions of the He shell (> 10⁶ g cm⁻³), and so we classify the outcome as a double detonation supernova. In the right panel, the accretor’s evolution is initially dominated by the cooling of the WD. After the accretion starts, the WD accretes at ∼10⁻⁷ M_⊙ yr⁻¹. The WD experiences compressional heating, causing the low-density (< 10⁶ g cm⁻³) layers to ignite explosively. We then classify this system as a He nova.