White dwarf pollution by planets in stellar binaries

Approximately 0.2 +/- 0.2 of white dwarfs (WDs) show signs of pollution by metals, which is likely due to the accretion of tidally disrupted planetary material. Models invoking planet-planet interactions after WD formation generally cannot explain pollution at cooling times of several Gyr. We consider a scenario in which a planet is perturbed by Lidov-Kozai oscillations induced by a binary companion and exacerbated by stellar mass-loss, explaining pollution at long cooling times. Our computed accretion rates are consistent with observations assuming planetary masses between similar to 0.01 and 1 M-Mars, although non-gravitational effects may already be important for masses less than or similar to 0.3 M-Mars. The fraction of polluted WDs in our simulations, similar to 0.05, is consistent with observations of WDs with intermediate cooling times between similar to 0.1 and 1 Gyr. For cooling times less than or similar to 0.1 Gyr and greater than or similar to 1 Gyr, our scenario cannot explain the high observed pollution fractions of up to 0.7. Nevertheless, our results motivate searches for companions around polluted WDs.