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M. Elitzur, D. Vinkovic (Dept. Phy &i Ast, University of Kentucky), A.S. Miroshnichenko (Dept. Phy & Ast, University of Toledo), Z. Ivezic (Dept. Astrophy. Sci., Princeton University)
The flared disk geometry of Chiang & Goldreich (CG) (ApJ, 490, 368, 1997) is currently the most popular model for the circumstellar dust distribution around pre-main-sequence stars. However, imaging observations suggest that optically thin halos are present through most of the pre-main-sequence phase. The halo provides additional heating of the disk, changes its temperature profile, and dominates the IR excess. Ignoring the halo in the radiative transfer models leads to erroneous interpretation of the dust properties and evolution.
So far, the only support for the CG model comes from its successful fitting of spectral energy distributions (SED). However, we show that for every CG model there is a mathematically equivalent disk+halo model with identical SED, therefore it is impossible to distinguish these two geometries without imaging data. We show that in AB Aur, the best-studied Herbig Ae/Be star, the CG-model is inconsistent with imaging observations. In contrast, the theoretical images from a disk+halo model successfully explain the observed images which are large and circularly symmetric at scattering wavelengths but small and elliptical at millimeter wavelengths. We propose a simple test to derive directly from the observed images an objective level of confidence in the applicability of the flared disk hypothesis.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.