We used the Javalambre Photometric Local Universe Survey (J-PLUS) second data release (DR2) photometry in 12 optical bands over 2176deg^2^ to estimate the fraction of white dwarfs with the presence of Ca II H+K absorption along the cooling sequence. We compared the J-PLUS photometry against metal-free theoretical models to estimate the equivalent width in the J0395 passband of 10nm centered at 395nm (EWJ0395), a proxy to detect calcium absorption. A total of 4399 white dwarfs with effective temperatures within 30000>Teff>5500K and masses of M>0.45M_{sun}_ were analyzed. Their EWJ0395 distribution was modeled using two populations, corresponding to polluted and non-polluted systems, to estimate the fraction of calcium white dwarfs (fCa) as a function of Teff. The probability of each individual white dwarf presenting calcium absorption, pca, was also computed. The comparison of EWJ0395 with both the measured Ca/He abundance and the identification of metal pollution from spectroscopy shows that EWJ0395 correlates with the presence of Ca II H+K absorption. The fraction of calcium white dwarfs changes along the cooling sequence, increasing from fCa~0 at Teff=13500K to fCa~0.15 at Teff=5500K. This trend reflects the selection function of calcium white dwarfs in the optical. We compare our results with the fractions derived from the 40pc spectroscopic sample and from Sloan Digital Sky Survey (SDSS) spectra. The trend found in J-PLUS observations is also present in the 40pc sample; however, SDSS shows a deficit of metal-polluted objects at Teff0.99. Twenty of them have spectra presented in previous studies, whereas we obtained follow-up spectroscopic observations for six additional targets. These 26 objects were all confirmed as metal-polluted systems.The J-PLUS optical data provide a robust statistical measurement for the presence of Ca II H+K absorption in white dwarfs. We find a 15+/-3% increase in the fraction of calcium white dwarfs from Teff=13500K to 5500K, which reflects their selection function in the optical from the total population of metal-polluted systems.

Cone search capability for table J/A+A/691/A211/wdpca (Atmospheric parameters and calcium absorption for J-PLUS DR2 white dwarfs)