The frequency of transiting planetary systems around polluted white dwarfs

This paper investigates the frequency of transiting planetary systems around metal-polluted white dwarfs using high-cadence photometry from ULTRACAM and ULTRASPEC on the ground and space-based observations with TESS . Within a sample of 313 metal-polluted white dwarfs with available TESS light curves, two systems known to have irregular transits are blindly reco v ered by box-least-squares and Lomb–Scargle analyses, with no new detections, yielding a transit fraction of 0 . 8 + 0 . 6 −0 . 4 per cent. Planet detection sensitivities are determined using simulated transit injection and reco v ery for all light curves, producing upper limit occurrences o v er radii from dwarf to Kronian planets, with periods from 1 h to 27 d. The dearth of short-period, transiting planets orbiting polluted white dwarfs is consistent with engulfment during the giant phases of stellar evolution, and modestly constrains dynamical re-injection of planets to the shortest orbital periods. Based on simple predictions of transit probability, where ( R ∗ + R p ) /a 0 . 01, the findings here are nominally consistent with a model where 100 per cent of polluted white dwarfs have circumstellar debris near the Roche limit; ho we ver, the small sample size precludes statistical confidence in this result. Single transits are also ruled out in all light curves using a search for correlated outliers, providing weak constraints on the role of Oort-like comet clouds in white dwarf pollution.