Fates of the sub-stellar objects (FOSSO) II. Evidence for Suppression of Metal Pollution in White Dwarfs by Close Substellar Companions

TL;DR

This study provides observational and simulation evidence that close substellar companions around white dwarfs significantly reduce metal pollution by clearing small bodies, indicating a protective effect on planetary debris accretion.

Contribution

It offers the first conclusive observational evidence that close substellar companions suppress metal pollution in white dwarfs, supported by dynamical simulations.

Findings

White dwarfs with close companions have a metal-pollution fraction of about 7.7%, much lower than single white dwarfs.

Wider companions do not significantly affect metal pollution, with fractions similar to single white dwarfs.

Dynamical simulations show close companions can clear 80-90% of small-body contaminants.

Abstract

Approximately 25--50\% of white dwarfs (WDs) exhibit metal absorption lines in their photospheres, interpreted as evidence of ongoing/recent accretion of planetary debris from remnant systems. Previous theoretical studies have suggested that massive, close-in substellar companion may prevent delivery of larger bodies via dynamical interactions, thereby reducing white-dwarf pollution. However, no conclusive observational evidence has yet been established to confirm such a protective effect. In this work, based on a sample of 17 white dwarf-substellar companion (1--75 $M_{\rm J}$) systems with reliable spectroscopic classifications, we find that white dwarfs hosting close substellar companions (orbital period $P < 5$ d) exhibit a metal-pollution fraction of $7.7^{+11.3}_{-4.0}\%$, which is suppressed by a factor of $5.75^{+3.24}_{-1.94}$ (corresponding to a protection efficiency of $87.2^{+3.4}_{-9.2}\%$) relative to single white dwarfs with a confidence level of 99.96\%. In contrast, white dwarfs with wider companions show a metal-pollution fraction of approximately $25.0^{+24.0}_{-12.8}\%$, comparable to that of single white dwarf systems. To interpret these results, we perform ensembles of N-body integrations and demonstrate that massive close-in substellar companions are capable of clearing 80\%--90\% of small-body contaminants. The good consistency between the observational statistics and dynamical simulations provides strong evidence for suppressed metal pollution in white dwarfs with close companions, and offers insights into the long-term dynamical evolution of WD remanent systems.