Exomoons as sources of white dwarf pollution

Polluted white dwarf stars offer a unique way to study the bulk compositions of exoplanetary material. These stars show evidence of recent accretion of rocky bodies in the form of excess metal lines in their spectra. The spectra tell us about the relative elemental abundances of the accreted material. One of the challenges of this method is to determine the origins of the parent bodies for the pollution, be they asteroids, comets, or moons. Motivated by recent observations of excess beryllium in several polluted WDs attributable to accretion of icy moons, we set out to assess the prevalence of moons as white dwarf polluters through analyses of observed white dwarfs and n-body simulations.

By applying an analytical model for the duration of pollution events, we find that the extrapolated parent body masses resemble those of moons around giant planets in our Solar System more than they do asteroids. Using N-body simulations and numerical calculations of accumulated pollution, we characterize the fraction of polluted white dwarfs currently accreting moons as opposed to asteroids.