The mass of RE J 0317-853 versus absolute V magnitudes for an ONe white dwarf. The different curves correspond to the effective temperatures 30 000–50 000 K. Above 1.28 M_⊙, we have to perform an extrapolation for T_eff > 30000 K. Since we cannot strictly estimate the extrapolation error, we visually added some uncertainty to the extrapolated values, which was subsequently used to estimate the errors in Table 6. The horizontal red line denotes the “observed” M_V.