Preliminary and revised position of J1604+1000 (light red and dark red 1σ error bars) in the Kiel diagram. The black lines are evolutionary tracks for stripped helium cores from Driebe et al. (1998) labeled with their respective masses (stars evolve from top to bottom). For reference, the locus of the zero-age horizontal branch (ZAHB) for [Fe/H]= − 1.48 (Dorman et al. 1993) is shown as a dashed gray line. The meaning of the (light) blue data points is the same as in Fig. 6. The six proto-He WDs that are mentioned in the text – PSR J1816+4510, EVR-CB-001, GALEX 1717+6757, HD 188112, EL CVn, and WASP 0247−25 B – are presented in black.