IFMR and the position of the Praesepe white dwarfs (circles, Casewell et al. 2009) and NGC 6819 white dwarfs (diamonds, Kalirai et al. 2008) are shown in this diagram. The solid line is the best fit of Casewell et al. (2009), and the dashed line is the best fit from Kalirai et al. (2008) which is sensitive to the low-mass end. Red circles denote the positions of the MWDs discussed in this paper, and WD 0836+197 is a known outlier. For the MWDs considered in this work, the bold (black) errors correspond to the estimations made with the standard procedure as explained in Sect. 3, whereas the thin (red) error bars correspond to the 3σ error estimations including an adopted T_eff error of 2000 K.