The Link Between Planetary Systems, Dusty White Dwarfs, and Metal-Polluted White Dwarfs

Abstract

It has long been suspected that metal polluted white dwarfs (types DAZ, DBZ, and DZ) and white dwarfs with dusty disks possess planetary systems, but a specific physical mechanism by which planetesimals are perturbed close to a white dwarf has not yet been fully posited. In this paper we demonstrate that mass loss from a central star during post main sequence evolution can sweep planetesimals into interior mean motion resonances with a single giant planet. These planetesimals are slowly removed through chaotic excursions of eccentricity that in time create radial orbits capable of tidally disrupting the planetesimal. Numerical N-body simulations of the Solar System show that a sufficient number of planetesimals are perturbed to explain white dwarfs with both dust and metal pollution, provided other white dwarfs have more massive relic asteroid belts. Our scenario requires only one Jupiter-sized planet and a sufficient number of asteroids near its 2:1 interior mean motion resonance. Finally, we show that once a planetesimal is perturbed into a tidal crossing orbit, it will become disrupted after the first pass of the white dwarf, where a highly eccentric stream of debris forms the main reservoir for dust producing collisions. These simulations, in concert with observations of white dwarfs, place interesting limits on the frequency of planetary systems around main sequence stars, the frequency of planetesimal belts, and the probability that dust may obscure future terrestrial planet finding missions.

The frequency of planetary debris around young white dwarfs

“…Even in the case where 100% of stars form planetary systems, this alone is insufficient to deliver Si to the surfaces of all their white dwarf remnants within the appropriate timescale. Successful models that deliver debris to the surfaces of white dwarfs indicate that a combined planet-planetesimal belt is necessary Debes et al 2012) and it seems plausible that this architecture may be common but not universal. Closer inspection of the atmospheric parameters reveals a significant difference between the stars where no metals are detected, and those where metals are observed at abundances compatible with radiative levitation (Table 3), which is illustrated in Fig.…”

Circumstellar debris and pollution at white dwarf stars

“…From energetic considerations about half the mass of the fragments will become unbound (Lacy et al, 1982;Rees, 1988), an important outcome that has been overlooked when inferring parent body masses based on the observed photospheric metals. Bound material remains on highly eccentric orbits, at least initially (Evans & Kochanek, 1989); rubble pile simulations with only gravitational forces show that bound pieces will continue along their original orbits via increasingly filled rings, and that some particle clusters require multiple passes to be disrupted (Debes et al, 2012b;Veras et al, 2014a).…”

Drifting asteroid fragments around WD 1145+017

“…Additionally, dusty debris disks have been found around many of these polluted white dwarfs (Zuckerman et al 1987), linking the presence of elements in the photosphere to circumstellar material near the star's tidal disruption radius for rocky material (Kilic et al 2006;Farihi et al 2009;Barber et al 2012;Rocchetto 2015). The accepted explanation for these observations is that after the white dwarf's progenitor leaves the main sequence and undergoes mass loss, the progenitor's planetary system destabilizes, perturbing planetary orbits close enough to the white dwarf for tidal disruption (Debes & Sigurdsson 2002;Debes et al 2012;Mustill et al 2014;Veras et al 2014;.…”