Infrared Variability of Two Dusty White Dwarfs

TL;DR

This paper reports on observed infrared variability in two dusty white dwarfs, exploring potential causes and emphasizing the active evolution of circumstellar dust disks around white dwarfs.

Contribution

It presents the first detailed infrared variability study of two dusty white dwarfs, analyzing potential mechanisms behind their changing dust emission.

Findings

SDSS J1228+1040's IR flux decreased by 20% between 2007 and 2014.

G29-38's 10 μm silicate feature strengthened by 10% from 2004 to 2007.

Dust disks around white dwarfs are dynamically evolving over short timescales.

Abstract

The most heavily polluted white dwarfs often show excess infrared radiation from circumstellar dust disks, which are modeled as a result of tidal disruption of extrasolar minor planets. Interaction of dust, gas, and disintegrating objects can all contribute to the dynamical evolution of these dust disks. Here, we report on two infrared variable dusty white dwarfs, SDSS J1228+1040 and G29-38. For SDSS J1228+1040, compared to the first measurements in 2007, the IRAC [3.6] and [4.5] fluxes decreased by 20% by 2014 to a level also seen in the recent 2018 observations. For G29-38, the infrared flux of the 10 $\mu$m silicate emission feature became 10% stronger between 2004 and 2007, We explore several scenarios that could account for these changes, including tidal disruption events, perturbation from a companion, and runaway accretion. No satisfactory causes are found for the flux drop in SDSS J1228+1040 due to the limited time coverage. Continuous tidal disruption of small planetesimals could increase the mass of small grains and concurrently change the strength of the 10 $\mu$m feature of G29-38. Dust disks around white dwarfs are actively evolving and we speculate that there could be different mechanisms responsible for the temporal changes of these disks.