White dwarf planetary debris dependence on physical structure distributions within asteroid belts

Abstract

White dwarfs which exhibit transit signatures of planetary debris and accreted planetary material provide exceptional opportunities to probe the material composition and dynamical structure of planetary systems. Although previous theoretical work investigating the role of minor body disruption around white dwarfs has focussed on spherical bodies, Solar System asteroids can be more accurately modelled as triaxial ellipsoids. Here we present an analytical framework to identify the type of disruption (tidal fragmentation, total sublimation or direct impact) experienced by triaxial asteroids approaching white dwarfs on extremely eccentric (e ∼ 1) orbits. This framework is then used to identify the outcomes for simplified Main belt analogues of 100 bodies across five different white dwarf temperatures. We also present an empirical relationship between cooling age and effective temperature for both DA and DB white dwarfs to identify the age of the white dwarfs considered here. We find that using a purely spherical shape model can underestimate the physical size and radial distance at which an asteroid is subjected to complete sublimation, and these differences increase with greater elongation of the body. Contrastingly, fragmentation always occurs in the largest semi-axis of a body and so can be modelled by a sphere of that radius. Both fragmentation and sublimation are greatly affected by the body’s material composition, and hence by the composition of their progenitor asteroid belts. The white dwarf temperature, and hence cooling age, can affect the expected debris distribution: higher temperatures sublimate large elongated asteroids, and cooler temperatures accommodate more direct impacts.

Metal pollution of the solar white dwarf by solar system small bodies

“…For the TNOs, the clones are not shown. The top horizontal axis shows the WD's effective temperature as converted from t cool using equation (9) ofMcDonald & Veras (2021) which was a fit of the model ofFontaine et al (2001).…”

Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments

“…1). The implicit assumption in the current analyses of polluted white dwarfs -that accretion proceeds both synchronously and symmetricallyis clearly valid when a solid body directly strikes the white dwarf's surface (Brown et al 2017;McDonald & Veras 2021) but such instances are predicted to be exceedingly rare (Veras et al 2021). Instead, the accretion process is thought to begin with a tidal disruption and the formation of an eccentric tidal disc (Debes et al 2012;Veras et al 2014;Nixon et al 2020;Malamud & Perets 2020a,b), whose fragments can subsequently accrete via a range of processes (e.g., Veras et al 2015a,b;Malamud et al 2021;Li et al 2021;Brouwers et al 2022b).…”