Stellar radius as a function of the effective temperature for He-core WD evolutionary sequences with stellar masses going from 0.317 to 0.393 M_⊙. The solid lines represent evolutionary models from Istrate et al. (2016) for metallicity of Z = 0.02, dotted lines are Istrate et al. (2016) models for metallicity Z = 0.001 and the dashed lines are models from Althaus et al. (2013) for metallicity Z = 0.001. Both stars of the eclipsing system J2102−4145, are shown in black circles, with their respective radius and T_eff values found in this work.