Planetary engulfment as a trigger for white dwarf pollution

Abstract

The presence of a planetary system can shield a planetesimal disk from the secular gravitational perturbations due to distant outer massive objects (planets or stellar companions). As the host star evolves off the main sequence to become a white dwarf, these planets can be engulfed, triggering secular instabilities and leading to the tidal disruptions of small rocky bodies. These disrupted bodies can feed the white dwarfs with rocky material and possibly explain the high-metallicity material in their atmospheres. We illustrate how this mechanism can operate when the gravitational perturbations are due to the Kozai-Lidov mechanism from a stellar binary companion. We show that this mechanism can explain the observed levels of accretion if: (1) the planetary engulfment happens fast compared to the secular timescale, which is generally the case for wide binaries ($>100$ AU) and planetary engulfment during the Asymptotic Giant Branch; (2) the planetesimal disk has a total mass of $\sim 10^{-4}-10^{-2}{M}_{\oplus }$. We show that this new mechanism can provide a steady supply of material throughout the entire life of the white dwarfs for all cooling ages and can account for a large fraction (up to nearly half) of the observed polluted WDs.

14 pages, 4 figures. Revised version after referee's comments. Major changes include a new Figure 1 and section 4.4

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• Post main sequence evolution of icy minor planets II: water retention and white dwarf pollution around massive progenitor stars
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• The critical binary star separation for a planetary system origin of white dwarf pollution
• The unstable fate of the planet orbiting the A-star in the HD 131399 triple stellar system