Discs and haloes in pre-main-sequence stars |
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Authors: | Dejan Vinkovi eljko Ivezi Anatoly S Miroshnichenko Moshe Elitzur |
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Institution: | Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA;Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA;Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USA |
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Abstract: | We study the infrared (IR) emission from flared discs with and without additional optically thin haloes. Flux calculations of a flared disc in vacuum can be considered a special case of the more general family of models in which the disc is imbedded in an optically thin halo. In the absence of such a halo, flux measurements can never rule out its existence because the disc flaring surface defines a mathematically equivalent halo that produces the exact same flux at all IR wavelengths. When a flared disc with height H at its outer radius R is imbedded in a halo whose optical depth at visual wavelengths is τhalo , the system IR flux is dominated by the halo whenever τhalo > (1/4) H / R . Even when its optical depth is much smaller, the halo can still have a significant effect on the disc temperature profile. Imaging is the only way to rule out the existence of a potential halo, and we identify a decisive test that extracts a signature unique to flared discs from imaging observations. |
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Keywords: | radiative transfer circumstellar matter stars: formation stars: imaging stars: pre-main-sequence dust extinction |
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