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The Dust Cloud around the White Dwarf G 29-38. II. Spectrum from 5 to 40 μm and Mid-Infrared Photometric Variability

Reach, William T. and Lisse, Carey and von-Hippel, Ted and Mullally, Fergal (2009) The Dust Cloud around the White Dwarf G 29-38. II. Spectrum from 5 to 40 μm and Mid-Infrared Photometric Variability. Astrophysical Journal, 693 (1). pp. 697-712. ISSN 0004-637X.

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We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1 to 35 μm. 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 (λ < 8 μm), amorphous and crystalline silicates (5-40 μm), water ice (10-15 and 23-35 μm), and metal sulfides (18-28 μm). 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°. 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 τ║ = 5, and the radial density profile α r ^(–2.7); the total mass of this model disk is 2 × 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 cannot 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 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.

Item Type:Article
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Reach, William T.0000-0001-8362-4094
Lisse, Carey0000-0002-9548-1526
Additional Information:© 2009 The American Astronomical Society. Received 2008 August 12; accepted 2008 August 21; published 2009 March 3. W.T.R. gratefully acknowledges discussions on radiative transfer in disks with Moshe Elitzur in 2007 May. W.T.R. gratefully acknowledges discussions on extrasolar giant planets with Adam Burrows in 2007 June. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.
Funding AgencyGrant Number
Subject Keywords:infrared: stars; stars: individual (G29-38, WD 2326+049); white dwarfs
Issue or Number:1
Record Number:CaltechAUTHORS:20090929-145312600
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Official Citation:The Dust Cloud around the White Dwarf G 29-38. II. Spectrum from 5 to 40 μm and Mid-Infrared Photometric Variability William T. Reach, Carey Lisse, Ted von Hippel, and Fergal Mullally 2009 ApJ 693 697-712 doi: 10.1088/0004-637X/693/1/697
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16120
Deposited By: Ruth Sustaita
Deposited On:02 Oct 2009 22:01
Last Modified:30 Oct 2019 22:00

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