Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs

TL;DR

This study uses Spitzer IRAC photometry to search for mid-infrared excesses around five white dwarfs, aiming to detect planetary debris or companions, but finds no significant excesses, constraining possible planetary system remnants.

Contribution

First mid-infrared photometry of these specific white dwarfs with detailed companion and disk search, providing new constraints on planetary debris presence post stellar evolution.

Findings

No excesses due to companions >20 M_J observed.

No circumstellar dust disks detected around the targets.

Limits placed on the types and sizes of potential disks.

Abstract

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently unknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC photometry accurate to $\sim$3% for four DAZs and one DA with circumstellar absorption lines in the UV. We search for excesses due to unseen companions or circumstellar dust disks. We use {\em Hubble Space Telescope} NICMOS imaging of these white dwarfs to gauge the level of background contamination to our targets as well as rule out common proper motion companions to WD 1620-391. All of our targets show no excesses due to companions $>$20 M$_{J}$, ruling out all but very low mass companions to these white dwarfs at all separations. No excesses due to circumstellar disks are observed, and we place limits on what types of disks may still be present.