Dusty White Dwarfs

Alongside my thesis advisor, Dr. Mukremin Kilic, I am studying remnant exoplanetary systems orbiting white dwarfs. Post-main sequence stellar mass loss can initiate resonances between planetary bodies, which throws some planetesimals out of the system and sends others in toward the compact stellar remnant. When a planetesimal approaches the white dwarf to within its tidal radius, it is ripped apart. The resultant debris eventually embodies a disk geometry, the re-radiated light from which we detect as excess radiation in the infrared.

If this circumstellar disk formation scenario is correct, debris disks at white dwarfs serve as tracers for remnant planetary systems. This opens up a new avenue for detection of exoplanetary systems. White dwarfs enable us to study planetary systems around stars in the mass regime (M > 3 Msol)  that currently eludes conventional exoplanet detection techniques.

In 2012 we conducted a near- and mid-infrared survey of a sample of 117 DA white dwarfs from the Palomar-Green survey. The white dwarfs in this sample are descendent from 1-7 Msol stars; this survey constrained the frequency of planetary systems in the elusive intermediate-mass regime. We found that at least 4.3% of 1-7 Msol stars host planetary systems (Barber et al. 2012) and added one new dusty white dwarf (PG 1541+651) to the literature (Kilic et al. 2012).

However, the mass distribution of this sample is strongly biased toward lower mass white dwarfs, descendants of main-sequence stars with  M < 3 Msol. To constrain the frequency of dusty disks around massive white dwarfs for the first time we recently proposed, and were awarded, Cycle 9 and Cycle 10 time on the Spitzer Space Telescope (prop ID: 90212 and 10062). With this data we will be able to say something about the presence of planets in the massive stellar regime that has thus far not been probed.

We also recently looked at 16 of the 52 WD+disk candidate systems identified by Debes et al. 2011 and determined that three quarters of these candidates have excesses not due to the presence of circumstellar dust, but a nearby background source contaminating the WISE photometry. The remaining four candidates we observed appear to be bonafide dusty WD systems. A paper presenting this work has recently been accepted for publication (Barber et al. 2014).

Below is a table of all currently known WD+disk systems.