Missing Planets Around Massive White Dwarfs

We know of as few as two dozen confirmed exoplanets with host stars with masses greater than 3.5 M_⊙, as these stars are not conducive to conventional detection methods such as radial velocities or transits. All stars less than at least 7 M_⊙ will eventually evolve into white dwarfs, which can thus provide a unique way to constrain planetary occurrence around intermediate-mass stars on the main sequence. Metal lines in white dwarf spectra act as signposts for remnant planetary systems. Ultraviolet spectra collected by the Hubble Space Telescope over 7 cycles in the past 11 years suggest that 40% of 262 bright, hot white dwarfs are metal polluted. Yet, the fraction of white dwarfs showing metal pollution significantly decreases as the mass of the white dwarf increases: fewer than 10% of massive white dwarfs (descendants of stars with masses greater than 3.5 M_⊙ on the main sequence) are metal polluted. We discuss possible observational biases affecting metal diffusion timescales, such as radiative levitation. Ultimately we aim to assess what the missing planets around massive white dwarfs shed light on, and how these occurrence rates can connect to the formation and survival of planets around intermediate-mass stars.