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 Title: 

            Observations and Modeling of Dust Stratification in T Tauri Circumstellar Disks

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 Authors:

          Gaspard Duchene, Observatoire de Grenoble (France)

          Christophe Pinte, Observatoire de Grenoble (France)

          Caer McCabe, JPL

          Francois Menard, Observatoire de Grenoble (France)

          Andrea Ghez, UCLA

          Karl Stapelfeldt, JPL

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 Abstract:

          We have recently obtained deep high angular resolution scattered light images of circumstellar disks surrounding several T Tauri stars in the near-infrared (using Keck-LGSA Keck-LWS). In combination with HST-ACS, WFPC2 and NICMOS images of the same objects, we have created complete sets of images ranging from 0.6 to 4-12 microns for three disks (GG Tau, HK Tau B, HV Tau C). Using the wavelength dependence of scattering of photons off dust grains, these images suggest that dust grains are vertically segregated, with larger grains (several microns in diameter) located more deeply, closer to the disk midplane. This could result from dust settling and/or growth by coagulation in the disk's densest parts. We use a multiple scattering Monte Carlo code to simulate disk images in an attempt to constrain both the disk geometry (fixed at all wavelength) and the dust grain properties (derived from the wavelength coverage). We show that it is not possible to reproduce simultaneously all scattered light images of a given disks from the optical to the mid-infrared regime with a single disk model that does not include vertical segregation of the dust population. We have also implemented in our code a physical treatment of dust segregation in disks. With this addition, we are able to reproduce simultaneously all images of the GG Tau and HK Tau B disks over a decade in wavelength, confirming that dust segregation has possibly occured in these disks.

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