Absence of a Correlation between White Dwarf Planetary Accretion and Primordial Stellar Metallicity

TL;DR

This study investigates whether the metallicity of progenitor stars influences white dwarf pollution by exoplanetary material, finding no significant correlation and suggesting giant planets are not the main cause.

Contribution

It provides observational evidence that primordial stellar metallicity does not significantly affect white dwarf accretion, challenging the role of gas giants in pollution events.

Findings

Polluted and non-polluted systems have similar metallicity distributions.

No significant correlation between white dwarf accretion rates and metallicity.

Results are potentially biased by selection effects.

Abstract

Over a quarter of white dwarfs have photospheric metal pollution, which is evidence for recent accretion of exoplanetary material. While a wide range of mechanisms have been proposed to account for this pollution, there are currently few observational constraints to differentiate between them. To investigate the driving mechanism, we observe a sample of polluted and non-polluted white dwarfs in wide binary systems with main-sequence stars. Using the companion stars' metallicities as a proxy for the white dwarfs' primordial metallicities, we compare the metallicities of polluted and non-polluted systems. Because there is a well-known correlation between giant planet occurrence and higher metallicity (with a stronger correlation for close-in and eccentric planets), these metallicity distributions can be used to probe the role of gas giants in white dwarf accretion. We find that the metallicity distributions of polluted and non-polluted systems are consistent with the hypothesis that both samples have the same underlying metallicity distribution. However, we note that this result is likely biased by several selection effects. Additionally, we find no significant trend between white dwarf accretion rates and metallicity. These findings suggest that giant planets are not the dominant cause of white dwarf accretion events in binary systems.