The Drop During Less Than 300 Days of a Dusty White Dwarf's Infrared Luminosity

Abstract

We report Spitzer/Infrared Array Camera photometry of WD J0959−0200, a white dwarf that displays excess infrared radiation from a disk, likely produced by a tidally disrupted planetesimal. We find that in 2010, the fluxes in both 3.6 μm and 4.5 μm decreased by ∼35% in less than 300 days. The drop in the infrared luminosity is likely due to an increase of the inner disk radius from one of two scenarios: (1) a recent planetesimal impact; (2) instability in the circumstellar disk. The current situation is tantalizing; high-sensitivity, high-cadence infrared studies will be a new tool to study the interplay between a disk and its host white dwarf star.

A search for variable white dwarfs in large-area time-domain surveys: a pilot study in SDSS Stripe 82

“…The presence of metals in the photosphere of SDSS J0121−0028 strongly supports the hypothesis that the observed infrared excess is due to a debris disc. There is growing evidence of variability in some white dwarf debris discs, including changes in the optical line profiles (Gänsicke et al 2008;Wilson et al 2015) and line fluxes (Wilson et al 2014) from gaseous discs, as well as changes in the infrared flux from the dust (Xu & Jura 2014). However, to date, optical variability in white dwarfs with debris discs has only been observed at amplitudes much lower than what we measured for SDSS J0121−0028.…”

Infrared observations of white dwarfs and the implications for the accretion of dusty planetary material

“…This model provides a good fit to the observations (e.g. Xu & Jura 2012;Jura 2003), however, Farihi et al (2009) note that the observations are, in general, consistent with a single temperature black-body, and some authors have modelled the emission as optically thin rings or halos (Reach et al 2005(Reach et al , 2009). Silicate emission features, that must result from optically thin emitting regions, were detected for all six white dwarfs searched for such features ).…”

“…Such dust, however, would produce a detectable infrared excess, as for optically thin discs, there is insufficient gas released for this mechanism to occur (Metzger et al 2012). Jura (2008) and Xu & Jura (2012) suggest that gas might be released following high velocity collisions between disrupted bodies or fragments, or sputtering of fragments incident onto a preexisting dust disc. This gas could enhance accretion rates in an undetected optically thin dust disc, or itself be accreted directly onto the star.…”

Detectable close-in planets around white dwarfs through late unpacking

“…High levels of variability in these discs (e.g. Gänsicke et al 2008;Wilson et al 2014;Xu & Jura 2014) on timescales of years highlight the current dynamical activity occuring in these systems.…”