Signs of a faint disc population at polluted white dwarfs

TL;DR

This study uses Spitzer IRAC observations to detect and analyze faint dust discs around polluted white dwarfs, revealing their prevalence, longevity, and decline over time, which informs the understanding of planetary system evolution.

Contribution

It provides the first evidence of faint dust discs around white dwarfs and characterizes their occurrence, properties, and evolution over time.

Findings

Infrared excesses suggest warm dust around some white dwarfs.

Discs are common but often undetected, possibly as narrow rings.

Disc lifetimes are on the order of 10^6 years, decreasing with stellar age.

Abstract

Observations of atmospheric metals and dust discs around white dwarfs provide important clues to the fate of terrestrial planetary systems around intermediate mass stars. We present Spitzer IRAC observations of 15 metal polluted white dwarfs to investigate the occurrence and physical properties of circumstellar dust created by the disruption of planetary bodies. We find subtle infrared excess emission consistent with warm dust around KUV 15519+1730 and HS 2132+0941, and weaker excess around the DZ white dwarf G245-58, which, if real, makes it the coolest white dwarf known to exhibit a 3.6 micron excess and the first DZ star with a bright disc. All together our data corroborate a picture where 1) discs at metal-enriched white dwarfs are commonplace and most escape detection in the infrared (possibly as narrow rings), 2) the discs are long lived, having lifetimes on the order of 10^6 yr or longer, and 3) the frequency of bright, infrared detectable discs decreases with age, on a timescale of roughly 500 Myr, suggesting large planetesimal disruptions decline on this same timescale.