Planetesimals at DZ stars I: chondritic compositions and a massive accretion event

TL;DR

This study analyzes high-resolution spectra of seven DZ white dwarfs to determine their accreted planetesimal compositions, revealing mostly primitive, chondritic material and evidence of a recent large-scale accretion event.

Contribution

It provides detailed compositional analysis of planetesimals accreted onto white dwarfs using high-resolution spectra and Bayesian inference, highlighting primitive and diverse compositions.

Findings

All stars accreted primitive, chondritic material.

One star shows Mercury-like composition.

Evidence of a recent large accretion event in one star.

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.