We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1-35 \mu m. The spectral model for G29-38 dust combines a wide range of materials based on spectral studies of comets and debris disks .
In order of their contribution to the mid-infrared emission , the most abundant minerals around G29-38 are amorphous carbon ( \lambda < 8 \mu m ) , amorphous and crystalline silicates ( 5–40 \mu m ) , water ice ( 10–15 and 23–35 \mu m ) , and metal sulfides ( 18–28 \mu m ) .
The amorphous C can be equivalently replaced by other materials ( like metallic Fe ) with featureless infrared spectra .
The best-fitting crystalline silicate is Fe-rich pyroxene .
In order to absorb enough starlight to power the observed emission , the disk must either be much thinner than the stellar radius ( so that it can be heated from above and below ) or it must have an opening angle wider than 2 ^ { \circ } .
A ‘ moderately optically thick ’ torus model fits well if the dust extends inward to 50 times the white dwarf radius , all grains hotter than 1100 K are vaporized , the optical depth from the star through the disk is \tau _ { \parallel } = 5 , and the radial density profile \propto r ^ { -2.7 } ; the total mass of this model disk is 2 \times 10 ^ { 19 } g. A physically thin ( less than the white dwarf radius ) and optically thick disk can contribute to the near-infrared continuum only ; such a disk can not explain the longer-wavelength continuum or strong emission features .
The combination of a physically thin , optically-thick inner disk and an outer , physically thick and moderately optically thin cloud or disk produces a reasonably good fit to the spectrum and requires only silicates in the outer cloud .
We discuss the mineralogical results in comparison to planetary materials .
The silicate composition contains minerals found from cometary spectra and meteorites , but Fe-rich pyroxene is more abundant than enstatite ( Mg-rich pyroxene ) or forsterite ( Mg-rich olivine ) in G29-38 dust , in contrast to what is found in most comet or meteorite mineralogies .
Enstatite meteorites may be the most similar solar system materials to the G29-38 dust .
Finally , we suggest the surviving core of a ‘ hot jupiter ’ as an alternative ( neither cometary nor asteroidal ) origin for the debris , though further theoretical work is needed to determine if this hypothesis is viable .