A Tidally Disrupted Asteroid around the White Dwarf G29-38

Abstract

The infrared excess around the white dwarf G29-38 can be explained by emission from an opaque flat ring of dust with an inner radius of 0.14 R ⊙ and an outer radius < 1R ⊙ . This ring lies within the Roche region of the white dwarf where an asteroid could have been tidally destroyed, producing a system reminiscent of Saturn's rings. Accretion onto the white dwarf from this circumstellar dust can explain the observed calcium abundance in the atmosphere of G29-38. Either as a bombardment by a series of asteroids or because of one large disruption, the total amount of matter accreted onto the white dwarf may have been ∼ 4 × 10 24 g, comparable to the total mass of asteroids in the Solar System, or, equivalently, about 1% of the mass in the asteroid belt around the main sequence star ζ Lep.

Circumstellar debris and pollution at white dwarf stars

“…In a short but seminal paper, Jura (2003) modeled the observed properties of G29-38 by invoking a tidally-destroyed minor planet (i.e. asteroid) that generates an opaque, flat disk of dust analogous to the rings of Saturn.…”

“…Zuckerman et al 2003), this would imply an influx of star-grazing planetesimals, sustained over long periods, and is therefore unrealistic (as for the cometary impact model). The tidallydisrupted asteroid model circumvents this problem by arranging the debris in a flat and (vertically) opaque configuration (Jura, 2003). In this geometry, the disk height to width ratio is negligible, and only a tiny fraction of particles are subject to the full stellar radiation and drag force.…”

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

“…To fit the SED of the dust disk, we use the opaque disk model described in Jura (2003) with three free parameters, the inner disk radius R in , outer disk radius R out , and disk inclination i. The inner and outer disk radii are most sensitive to ∼3 μm and 8 μm fluxes, respectively, while the disk inclination affects all the infrared flux.…”

“…However, it was not until much later that a now widely accepted model was proposed to explain the source of the dust-tidal disruption of planetesimals (Debes & Sigurdsson 2002;Jura 2003). Subsequent progress has been rapid, particularly after the discovery of an infrared excess around a second white dwarf GD 362 (Kilic et al 2005;Becklin et al 2005).…”

“…The spectral energy distributions (SEDs) can be fit with a geometrically thin, optically thick disk within the tidal radius of the white dwarf (Jura 2003). The typical disk lifetime is estimated to be 10 5 -10 6 yr (Jura 2008;Rafikov 2011aRafikov , 2011bGirven et al 2012).…”