Sunday, October 9, 2016

White Dwarfs in Binary Systems Often Show Pullition by Metals, Probably From Impacting Exoplanets


Hamers et al


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 ∼0.01 and 1MMars, although nongravitational effects may already be important for masses ≲0.3MMars. The fraction of polluted WDs in our simulations, ∼0.05, is consistent with observations of WDs with intermediate cooling times between ∼0.1 and 1 Gyr. For cooling times ≲0.1 Gyr and ≳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.

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