Planetesimals at DZ stars – I. Chondritic compositions and a massive accretion event

Abstract

There is a wealth of evidence to suggest that planetary systems can survive beyond the main sequence. Most commonly, white dwarfs are found to be accreting material from tidally disrupted asteroids, whose bulk compositions are reflected by the metals polluting the stellar photospheres. While many examples are known, most lack the deep, high-resolution data required to detect multiple elements, and thus characterise the planetesimals that orbit them. Here, spectra of seven DZ white dwarfs observed with Keck HIRES are analysed, where up to nine metals are measured per star. Their compositions are compared against those of solar system objects, working in a Bayesian framework to infer or marginalise over the accretion history. All of the stars have been accreting primitive material, similar to chondrites, with hints of a Mercury-like composition at one star. The most polluted star is observed several Myr after its last major accretion episode, in which a Moon-sized object met its demise.

Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf

“…The above analysis is self-consistent and agrees with prior work on polluted white dwarfs in the decreasing abundance phase of accretion (e.g., Swan et al 2023). On their own, these calculations argue that the magnetic field of WD 0816-310 has no significant impact on the relative sinking timescales for multiple heavy elements.…”