Emission from very small grains and PAH molecules in Monte Carlo radiation transfer codes: Application to the edge-on disk of Gomez's Hamburger

Kenneth Wood, Barbara A. Whitney, Thomas Robitaille, Bruce T. Draine

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We have modeled optical to far-infrared images, photometry, and spectroscopy of the object known as Gomez's Hamburger. We reproduce the images and spectrum with an edge-on disk of mass 0.3 M and radius 1600AU, surrounding an A0 III star at a distance of 280 pc. Our mass estimate is in excellent agreement with recent CO observations. However, our distance determination is more than an order of magnitude smaller than previous analyses, which inaccurately interpreted the optical spectrum. To accurately model the infrared spectrum we have extended our Monte Carlo radiation transfer codes to include emission from polycyclic aromatic hydrocarbon (PAH) molecules and very small grains (VSG). We do this using precomputed PAH/ VSG emissivity files for a wide range of values of the mean intensity of the exciting radiation field. When Monte Carlo energy packets are absorbed by PAHs/VSGs, we reprocess them to other wavelengths by sampling from the emissivity files, thus simulating the absorption and reemission process without reproducing lengthy computations of statistical equilibrium, excitation, and de-excitation in the complex many-level molecules. Using emissivity lookup tables in our Monte Carlo codes gives us the flexibility to use the latest grain physics calculations of PAH /VSG emissivity and opacity that are being continually updated in the light of higher resolution infrared spectra. We find our approach gives a good representation of the observed PAH spectrum from the disk of Gomez's Hamburger. Our models also indicate that the PAHs/VSGs in the disk have a larger scale height than larger radiative equilibrium grains, providing evidence for dust coagulation and settling to the midplane.

Original languageEnglish (US)
Pages (from-to)1118-1123
Number of pages6
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 1 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Accretion, accretion disks
  • Circumstellar matter
  • Dust, extinction
  • Radiative transfer


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