The entry geometry and velocity of planetary debris into the Roche sphere of a white dwarf

Dimitri Veras,Alexander J Mustill,Nikolaos Georgakarakos,Tim Cunningham,Ian Dobbs-Dixon,Uri Malamud

doi:10.1093/mnras/stab1667

Abstract

ABSTRACT Our knowledge of white dwarf planetary systems predominately arises from the region within a few Solar radii of the white dwarfs, where minor planets breakup, form rings and discs, and accrete on to the star. The entry location, angle, and speed into this Roche sphere has rarely been explored but crucially determines the initial geometry of the debris, accretion rates on to the photosphere, and ultimately the composition of the minor planet. Here, we evolve a total of over 105 asteroids with single-planet N-body simulations across the giant branch and white dwarf stellar evolution phases to quantify the geometry of asteroid injection into the white dwarf Roche sphere as a function of planetary mass and eccentricity. We find that lower planetary masses increase the extent of anisotropic injection and decrease the probability of head-on (normal to the Roche sphere) encounters. Our results suggest that one can use dynamical activity within the Roche sphere to make inferences about the hidden architectures of these planetary systems.

Highlights

A near-ubiquitous feature of white dwarf planetary systems is planetary debris near or in the star’s photosphere
The focus of this work is on the geometry of asteroid encounters with the white dwarf Roche sphere, our high-resolution simulations yield multiple dynamical results of potential interest
Circular planetary orbits fail to perturb asteroids into the white dwarf Roche sphere, a result known from both numerics (Frewen & Hansen 2014) and analytics (Antoniadou & Veras 2016, 2019)

Summary

Introduction

A near-ubiquitous feature of white dwarf planetary systems is planetary debris near or in the star’s photosphere. Detections of terrestrial or giant planets orbiting white dwarfs have been less frequent, and currently include a handful of only giant planets (Thorsett et al 1993; Sigurdsson et al 2003; Luhman et al 2011; Gansicke et al 2019; Vanderburg et al 2020). This disparity in the abundances of different observational signatures motivates theoretical investigations which attempt to link planetary system architectures with the debris and accretion onto white dwarfs. A goal is to uncover the hidden architectures through our observations of debris and accretion

Objectives

Results

Conclusion