Spitzer Observations of White Dwarfs: the Missing Planetary Debris Around DZ Stars

TL;DR

This study uses Spitzer observations to identify infrared excesses around white dwarfs, revealing a higher occurrence of dust disks in hotter stars and suggesting Poynting-Robertson drag influences material accretion.

Contribution

It extends previous research by detecting new dust disks around white dwarfs and analyzing their correlation with stellar temperature and material volatility.

Findings

Infrared excesses found around two white dwarfs, including the hottest known with a dust disk.

The fraction of white dwarfs with dust disks increases with stellar temperature.

Poynting-Robertson drag may significantly transfer material from dust disks into white dwarf atmospheres.

Abstract

We report a Spitzer/IRAC search for infrared excesses around white dwarfs, including 14 newly-observed targets and 16 unpublished archived stars. We find a substantial infrared excess around two warm white dwarfs --- J220934.84+122336.5 and WD 0843+516, the latter apparently being the hottest white dwarf known to display a close-in dust disk. Extending previous studies, we find that the fraction of white dwarfs with dust disks increases as the star's temperature increases; for stars cooler than 10,000 K, even the most heavily polluted ones do not have ~1000 K dust. There is tentative evidence that the dust disk occurrence is correlated with the volatility of the accreted material. In the Appendix, we modify a previous analysis to show that Poynting-Robertson drag might play an important role in transferring materials from a dust disk into a white dwarf's atmosphere.