The critical binary star separation for a planetary system origin of white dwarf pollution

TL;DR

This paper investigates the conditions under which white dwarf pollution originates from planetary debris versus binary companion winds, deriving critical binary separation thresholds and providing practical functions for predicting pollution sources.

Contribution

It introduces a method to determine the binary separation beyond which white dwarf pollution is likely from planetary systems, incorporating various stellar and accretion parameters.

Findings

Pollution in most white dwarfs in binaries likely originates from planetary material.

Derived functions relate binary separation to stellar properties and accretion rates.

Identified a critical binary separation threshold for planetary system pollution.

Abstract

The atmospheres of between one quarter and one half of observed single white dwarfs in the Milky Way contain heavy element pollution from planetary debris. The pollution observed in white dwarfs in binary star systems is, however, less clear, because companion star winds can generate a stream of matter which is accreted by the white dwarf. Here we (i) discuss the necessity or lack thereof of a major planet in order to pollute a white dwarf with orbiting minor planets in both single and binary systems, and (ii) determine the critical binary separation beyond which the accretion source is from a planetary system. We hence obtain user-friendly functions relating this distance to the masses and radii of both stars, the companion wind, and the accretion rate onto the white dwarf, for a wide variety of published accretion prescriptions. We find that for the majority of white dwarfs in known binaries, if pollution is detected, then that pollution should originate from planetary material.