tokens: best fit and subsequently adjusting the result. The best-fit is obtained for T eff = 10, 140 K, and log g = 8.10. Statistical uncertainties are negligible due to the high SNR of the optical spectrum. Subsequently, we performed a photometric fit of the available APASS and Gaia DR2 photometry (Table 2 ), in which we used the Gaia DR2 parallax and the white dwarf mass–radius relation (Fontaine, Brassard Bergeron 2001 ) as additional priors. We have not used VHS photometry to be sure that the IR excess has no effect in the fit. The photometric fit delivers a 0.1 dex-lower surface gravity. Hence, we iterated between spectroscopic (log g fixed) and photometric ( fixed) fits, until both methods converged to a final solution. The difference between the initial spectroscopic fit and the final result is adopted as the error estimate, resulting in T eff = 10, 090 ± 50 K and log g = 8.00 ± 0.13. The interstellar reddening obtained as a result of our fitting procedure is negligible, and of the order of 0.01 mag. We measured the radial velocities of the strongest metal lines via fitting Gaussian models and estimated the uncertainty as the scatter between the measurements of the different lines. For the 2011 spectrum, we obtained an average radial velocity of = 44 ± 5 km s −1 and for the 2019 spectrum, = 47 ± 8 km s −1 . The individual radial velocities for the different lines are presented in table 6. The atmospheric parameters of WDJ1814−7354 correspond to a white dwarf mass of M ⊙ and a cooling age of Gyr. Using the Cummings et al. ( 2018 ) initial-to-final-mass relation (IFMR), we infer a progenitor mass of M ⊙ . To estimate the progenitor age, we used the evolutionary tracks of Choi et al. ( 2016 ). For a progenitor mass of 1.3 M ⊙ (late F-type star), the progenitor age is τ MS = 5.2 Gyr, and the total age of the white dwarf would be τ MS + τ cool = 5.8 Gyr. The large systematic uncertainty implied by the empirical IFMR translates into a large uncertainty on the progenitor age. For the upper limit of the progenitor mass of 1.8 M ⊙ (a late A-type star), the progenitor age would be τ MS = 3.4 Gyr, so the lower limit on the total age of the white dwarf is 4 Gyr. The upper limit on the total age is unconstrained, because the lower limit of the progenitor mass is 0.9 M ⊙ (an early K dwarf star), whose lifetime could be comparable or longer than the age of the Universe. 4.2 Composition of the accreted material and diffusion time-scales The abundances of the three detected elements (Mg, Ca, and Fe) are given in Table 7 . The listed abundances and uncertainties are the averages and the standard deviations inferred from the modelling of the strongest lines for each detected element: lines at 3933.66, 3968.47, 8498.02, 8542.09, 8662.14 (Ca ii ), and 4226.73 Å (Ca i ) for Calcium; lines at 4481.13 (Mg ii ), 3838.29, 5167.32, 5172.68, and 5183.69 Å (Mg i ) for Magnesium; and lines at 3609, 3619, 3632, 3720, 3738, 3750, 3759, 3816, 3821, and 3826 Å for iron (Fe i ).
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