Calcium relative abundance, log Ca/Не, as a function of effective temperature, $T_{\text{eff}}^{\text{C}19}$, from Coutu et al. (2019) for the 47 white dwarfs in common with the J-PLUS + Gaia sample (circles). The solid line in both panels shows the expected detection limit for EW_Jo395 = 13.5 Å derived from theoretical models with log g = 8. Left panel: the color scale represents EW_J0395, with white symbols having EW_J0395 < 0 A. Right panel: the color scale represents S/N in the J0395 EW with two discrete possibilities, being larger or lower than 5/N_EW = 2.3. This value corresponds to a 99% detection or EW_J0395 ≈ 13.5 A given the uncertainties in the measurements.