Precise Ages of Field Stars from White Dwarf Companions in Gaia DR2

We analyze 4050 wide binary star systems involving a white dwarf (WD) and usually a main-sequence (MS) star, drawn from the large sample assembled by Tian et al. Using the modeling code BASE-9, we determine the system’s ages, the WD progenitors’ zero-age MS masses, the extinction values ( A V ), and the distance moduli. Discarding the cases with poor age convergences, we obtain ages for 3551 WDs, with a median age precision of σ τ / τ = 20%, and system ages typically in the range of 1–6 Gyr. We validated these ages against the very few known clusters and through cross validation of 236 WD-WD binaries. Under the assumption that the components are coeval in a binary system, this provides precise age constraints on the usually low-mass MS companions, mostly inaccessible by any other means.